BLAKE ELECTRONIC COMMUNICATION SYSTEM
22. The hotter a component gets, the more noise it will generate. T
23. "Shot" noise creates a "noise current" in an electronic device such as a
transistor. T
Chapter 1: Introduction to Communication Systems
24. "Flicker" noise is worst at radio frequencies. F
TRUE/FALSE
25. Signal-to-noise ratio is more important than noise power. T
1. The first electronic communications device was the telephone. F
26. With cascaded stages in a communication system, the noise from the first stage
is the least important. F
2. Transatlantic radio communication started in 1901. T
3. A communication system may or may not include a channel. F
27. Due to the frequency, a radio signal requires a "real-time" analyzer to look at the
spectrum. F
4. "Baseband" refers to the basic carrier frequency band. F
MULTIPLE CHOICE
5. Putting an information signal onto a carrier is called "modulation". T
6. The carrier frequency is higher than the highest baseband frequency. T
1. The theory of radio waves was originated by:
a. Marconi
c. Maxwell
b. Bell
d .Hertz
7. A modulated carrier occupies a band of frequencies. T
8. "Detection" is another term for demodulation. T
9. The amount of information per second that can be sent is independent of
bandwidth. F
10. It is possible to combine FDM and TDM in the same system. T
11. For radio signals, longer wavelength means higher frequency. F
12. Noise is easily removed from an analog signal by using filters. F
13. As long as a one can be distinguished from a zero, a digital signal corrupted by
noise can be restored to its original form. T
14. Audio signals are in the time-domain, but radio signals are in the frequency
domain. F
15. Any periodic AC signal contains an infinite series of harmonic frequencies. T
16. Every term in a Fourier series must be used in calculations. F
17. All noise in a system can be eliminated by using good grounding and shielding. F
18. The sparking brushes of a DC motor can cause radio frequency noise. T
19. Signals with fast rise and fall times can cause radio frequency noise. T
20. Digital systems such as computers are not affected by noise. F
21. Every component in an electronic system generates noise. T
2. The person who sent the first radio signal across the Atlantic Ocean was:
a. Marconi
c. Maxwell
b. Bell
d. Hertz
3. The transmission of radio waves was first done by:
a. Marconi
c. Maxwell
b. Bell
d. Hertz
4. Radians per second is equal to:
a. 2π
π×f
c. the phase angle
b f ÷ 2π
d. none of the above
5. A complete communication system must include:
a. a transmitter and receiver
b. a transmitter, a receiver, and a channel
c. a transmitter, a receiver, and a spectrum analyzer
d. a multiplexer, a demultiplexer, and a channel
6. The bandwidth required for a modulated carrier depends on:
a. the carrier frequency
c. the signal-plus-noise to noise ratio
b. the signal-to-noise ratio
d. the baseband frequency range
7. When two or more signals share a common channel, it is called:
a. sub-channeling
c. SINAD
b. signal switching
d. multiplexing
8. TDM stands for:
a. Time-Division Multiplexing
b. Two-level Digital Modulation
c. Time Domain Measurement
d. none of the above
9. FDM stands for:
a. Fast Digital Modulation
b. Frequency Domain Measurement
c. Frequency-Division Multiplexing
d. none of the above
10. The wavelength of a radio signal is:
a. equal to f ÷ c
c. the distance a wave travels in one period
b. equal to c ÷ λ
d. how far the signal can travel without distortion
11. Distortion is caused by:
a. creation of harmonics of baseband frequencies
b. baseband frequencies "mixing" with each other
c. shift in phase relationships between baseband frequencies
d. all of the above
12. The collection of sinusoidal frequencies present in a modulated carrier is called
its:
a. frequency-domain representation
c. spectrum
b. Fourier series
d. all of the above
13. The baseband bandwidth for a voice-grade (telephone) signal is:
a. approximately 3 kHz
c. at least 5 kHz
b. 20 Hz to 15,000 Hz
d. none of the above
14. Noise in a communication system originates in:
a. the sender
c. the channel
b. the receiver
d. all of the above
15. "Man-made" noise can come from:
a. equipment that sparks
b. temperature
23. SINAD is calculated as:
a. signal voltage divided by noise voltage
b. signal power divided by noise power
c. first add the signal power to the noise power, then divide by noise
power
d. none of the above
24. Noise Figure is a measure of:
a. how much noise is in a communications system
b. how much noise is in the channel
c. how much noise an amplifier adds to a signal
d. signal-to-noise ratio in dB
25. The part, or parts, of a sinusoidal carrier that can be modulated are:
a. its amplitude
b. its amplitude and frequency
c. its amplitude, frequency, and direction
d. its amplitude, frequency, and phase angle
COMPLETION
c. static
d. all of the above
1. The telephone was invented in the year ______.
ANS:
16. Thermal noise is generated in:
a. transistors and diodes
b. resistors
c. copper wire
d. all of the above
17. Shot noise is generated in:
a. transistors and diodes
b. resistors
c. copper wire
d. none of the above
18. The power density of "flicker" noise is:
a. the same at all frequencies
b. greater at high frequencies
c. greater at low frequencies
d. the same as "white" noise
19. So called "1/f" noise is also called:
a. random noise
c. white noise
b. pink noise
d. partition noise
20. "Pink" noise has:
a. equal power per Hertz
b. equal power per octave
22. Signal-to-Noise ratio is calculated as:
a. signal voltage divided by noise voltage
b. signal power divided by noise power
c. first add the signal power to the noise power, then divide by noise
power
d. none of the above
c. constant power
d. none of the above
21. When two noise voltages, V1 and V2, are combined, the total voltage VT is:
a. VT = sqrt(V1 x V1 + V2 x V2)
c. VT = sqrt(V1 x V2)
b. VT = (V1 + V2)/2
d. VT = V1 + V2
1863
2. Radio signals first were sent across the Atlantic in the year _______.
ANS:
1901
3. The frequency band used to modulate the carrier is called the ______ band.
ANS:
base
4. The job of the carrier is to get the information through the _______.
ANS:
channel
5. The bandwidth of an unmodulated carrier is _______.
ANS:
zero
6. The 'B' in Hartley's Law stands for _______.
ANS:
bandwidth
7. In _______, you split the bandwidth of a channel into sub-channels to carry
multiple signals.
ANS:
FDM
8. In _______, multiple signal streams take turns using the channel.
ANS:
TDM
9. VHF stands for the _______ frequency band.
ANS:
very high
5. A microwave receiver has a noise temperature of 145 K. Find its noise figure.
ANS:
1.5
10. The more information per second you send, the ________ the bandwidth
required.
ANS:
greater, larger, wider
6. Suppose there is 30 µV from one noise source that is combined with 40 µV from
another noise source. Calculate the total noise voltage.
ANS:
50 µV
11. The VHF band starts at _______ MHz.
ANS: 30
7. If you have 100 mV of signal and 10 mV of noise, both across the same 100-ohm
load, what is the signal-to-noise ratio in dB?
ANS:
20 dB
12. The UHF band starts at ______ MHz.
ANS:
300
13. A radio signal's ________ is the distance it travels in one cycle of the carrier.
ANS:
wavelength
14. In free space, radio signals travel at approximately _________ meters per
second.
ANS:
300 million
15. The equipment used to show signals in the frequency domain is the ________.
ANS:
spectrum analyzer
16. Mathematically, a spectrum is represented by a _______ series.
ANS:
Fourier
17. Disabling a receiver during a burst of atmospheric noise is called ________.
ANS:
noise blanking or blanking
8. The input to an amplifier has a signal-to-noise ratio of 100 dB and an output
signal-to-noise ratio of 80 dB. Find NF, both in dB and as a ratio.
ANS:
20 dB, NF = 100
9. Two cascaded amplifiers each have a noise figure of 5 and a gain of 10. Find the
total NF for the pair.
ANS:
5.4
10. Explain why you could use a diode as a noise source with a spectrum close to
that of pure thermal noise. How would you control the amount of noise generated?
ANS:
When current flows through a diode, it generates shot noise that can be
represented as a current source, the output of which is a noise current.
The equation for the noise current is very similar to the equation for
thermal noise voltage. Since the power in the shot noise is proportional
to the diode current, controlling the diode current controls the noise
power.
18. For satellite communications, ________ noise can be a serious problem.
ANS:
solar
Chapter 2: Radio-Frequency Circuits
19. Thermal noise is caused by the random motions of ________ in a conductor.
ANS:
electrons
TRUE/FALSE
1. In general, components behave the same at 20 MHz as they do at 1 kHz. F
SHORT ANSWER
2. Stray capacitance is important in high-frequency amplifiers. T
1. Name the five elements in a block diagram of a communications system.
ANS:
Source, Transmitter, Channel, Receiver, Destination
2. Name five types of internal noise.
ANS:
Thermal, Shot, Partition, 1/f, transit-time
3. Microwave-frequency circuits look much different from circuits designed for 1
MHz. T
4. All electronic devices have both capacitive and inductive properties. T
3. Why is thermal noise called "white noise"?
ANS:
White light is composed of equal amounts of light at all visible
frequencies. Likewise, thermal noise has equal power density over a wide
range of frequencies.
5. As frequency increases, capacitive effects decrease. F
4. What is "pink noise"?
ANS:
Light is pink when it contains more red than it does other colors, and red
is at the low end of the visible spectrum. Likewise, pink noise has higher
power density at lower frequencies.
7. An "unstable" amplifier is one that oscillates, or is close to oscillating. T
6. At some frequency, a capacitor will self-resonate with the inductance of its leads.
T
8. Base-to-emitter capacitance can cause a common-emitter amplifier to oscillate. F
9. "Distributed Constants" refers to a mathematical operation to calculate gain. F
10. "Shielding" prevents RF signals from coupling between components in a system.
T
11. A "ground-plane" is a type of shielding. T
12. A "gimmick" is a type of shielding. F
13. Removing any RF signals off the Vcc lines is an example of "decoupling". T
14. Decoupling usually involves a "bypass" capacitor. T
15. Basically, radio-frequency amplifiers can not be distinguished from other
amplifiers. F
16. Resonant circuits are common in RF amplifiers. T
17. Increasing the load on a tuned amplifier increases its Q. F
18. In a common-emitter amplifier, the collector-base capacitance "looks" bigger
than it is. T
19. The Miller Effect only occurs in common-base amplifiers. F
4. A resonant circuit is:
a. a simple form of bandpass filter
b. used in narrowband RF amplifiers
c. both a and b
d. none of the above
5. Loading down a tuned-circuit amplifier will:
a. raise the Q of the tuned circuit
b. lower the Q of the tuned circuit
c. "multiply" the Q
d. have no effect on Q
6. The "Miller Effect" can:
a. cause an amplifier to oscillate
b. cause an amplifier to lose gain
c. reduce the bandwidth of an amplifier
d. all of the above
7. In a BJT, the Miller Effect is due to:
a. inductance of collector lead
b. collector-to-emitter capacitance
c. base-to-emitter capacitance
d. base-to-collector capacitance
8. The Miller Effect can be avoided by:
a. using a common-emitter amplifier
b. using a common-base amplifier
c. increasing the Q of the tuned circuit
d. it cannot be avoided
20. The Miller Effect can reduce the bandwidth of an amplifier. T
21. The Miller Effect can be reduced using neutralization. T
9. In RF amplifiers, impedance matching is usually done with:
a. RC coupling
c. direct coupling
b. transformer coupling
d. lumped reactance
22. A piezoelectric crystal behaves like a very low-Q tuned circuit. F
23. The frequency of a crystal oscillator is much more stable than an LC oscillator. T
24. Mixers must be nonlinear in order to work. T
10. Neutralization cancels unwanted feedback by:
a. adding feedback out of phase with the unwanted feedback
b. bypassing the feedback to the "neutral" or ground plane
c. decoupling it
d. none of the above
25. A mixer will produce "sum and difference" frequencies. T
MULTIPLE CHOICE
1. The time it takes a charge carrier to cross from the emitter to the collector is
called:
a. base time
c. charge time
b. transit time
d.Miller time
2. A real capacitor actually contains:
a. capacitance and resistance only
b. capacitance and inductance only
c. capacitance, inductance, and resistance
d. reactance only
3. Bypass capacitors are used to:
a. remove RF from non-RF circuits
b. couple RF around an amplifier
11. For a "frequency multiplier" to work, it requires:
a. a nonlinear circuit
b. a linear amplifier
c. a signal containing harmonics
d. an input signal that is an integer multiple of the desired frequency
12. A sinusoidal oscillation from an amplifier requires:
a. loop gain equal to unity
b. phase shift around loop equal to 0 degrees
c. both a and b, but at just one frequency
d. none of the above
13. The conditions for sinusoidal oscillation from an amplifier are called:
a. the loop-gain criteria
c. the Bode criteria
b. the Hartley criteria
d. the Barkhausen criteria
c. neutralize amplifiers
d. reduce the Miller effect
14. The Hartley oscillator uses:
a. a tapped inductor
b. a two-capacitor divider
c. an RC time constant
d. a piezoelectric crystal
15. The Colpitts VFO uses:
a. a tapped inductor
b. a two-capacitor divider
c. an RC time constant
d. a piezoelectric crystal
16. The Clapp oscillator is:
a. a modified Hartley oscillator
b. a modified Colpitts oscillator
c. a type of crystal-controlled oscillator
d. only built with FETs
17. A varactor is:
a. a voltage-controlled capacitor
b. a diode
c. used in tuner circuits
d. all of the above
18. Crystal-Controlled oscillators are:
a. used for a precise frequency
b. used for very low frequency drift (parts per million)
c. made by grinding quartz to exact dimensions
d. all of the above
19. If two signals, Va = sin(ωat) and Vb = sin(ωbt), are fed to a mixer, the output:
a. will contain ω1 = ωa + ωb and ω2 = ωa – ωb
b. will contain ω1 = ωa / ωb and ω2 = ωb / ωa
c. will contain ω = (ωa + ωb ) / 2
d. none of the above
20. In a balanced mixer, the output:
a. contains equal (balanced) amounts of all input frequencies
b. contains the input frequencies
c. does not contain the input frequencies
d. is a linear mixture of the input signals
21. "VFO" stands for:
a. Voltage-Fed Oscillator
b. Variable-Frequency Oscillator
4. Interactions between parts of an RF circuit can be reduced by using ________
between them.
ANS: shielding
5. A ________ circuit is used to remove RF from the DC voltage bus.
ANS:
decoupling
6. In high-frequency RF circuits, the placement of wires and _________ can be
critical.
ANS:
components
7. A ________ capacitor is used to short unwanted RF to ground.
ANS:
bypass
8. The bandwidth of a tuned-circuit amplifier depends on the ________ of the
tuned circuit.
ANS:
Q
9. A value of ________ or more for Q is required for the approximate tuned circuit
equations to be valid.
ANS:
10
10. In a class C RF amplifier, the ________ extracts one frequency from all the
harmonics contained in the device current (e.g. collector current).
ANS:
tuned circuit
11. Using additional feedback to compensate for "stray" feedback is called
__________.
ANS:
neutralization
12. A Colpitts oscillator uses a ________ voltage divider to provide feedback.
ANS:
capacitive
c. Varactor-Frequency Oscillator
d. Voltage-Feedback Oscillator
22. A "frequency synthesizer" is:
a. a VCO phase-locked to a reference frequency
b. a VFO with selectable crystals to change frequency
c. a fixed-frequency RF generator
d. same as a mixer
COMPLETION
13. Electrically, a piezoelectric crystal has both a _________ and a _______
resonant frequency.
ANS:
series, parallel
14. To produce sum and difference frequencies, a mixer must be a non-________
circuit.
ANS:
linear
15. At some bias point, a diode or a transistor can act as a _________-law mixer.
ANS:
square
1. Generally, conductor lengths in RF circuits should be ________.
ANS:
short
2. At UHF frequencies and above, elements must be considered as ________
instead of as being "lumped".
ANS:
distributed
3. When one side of a double-sided pc board is used for ground, it is called a
________.
ANS:
ground-plane
SHORT ANSWER
1. What inductance would you use with a 47-pF capacitor to make a tuned circuit
for 10 MHz?
ANS:
5.4 µH
2. What value of Q is required for a 10-MHz tuned circuit to have a bandwidth of
100 kHz?
ANS:
100
3. A tuned-circuit amplifier with a gain of 10 is being used to make an oscillator.
What should be the value of the feedback ratio to satisfy the Barkhausen criteria?
ANS:
0.1
4. What is the advantage of a Clapp oscillator compared to a Colpitts oscillator?
ANS:
It is more stable because it "swamps" the device capacitance with large
value capacitors in the feedback divider.
5. If a varactor has a capacitance of 90 pF at zero volts, what will be the capacitance
at 4 volts?
ANS:
30 pF
6. An oscillator has a frequency of 100 MHz at 20°C, and a tempco of +10 ppm per
degree Celsius. What will be the shift in frequency at 70°C? What percentage is
that?
ANS:
50 kHz, 0.05%
11. Overmodulation produces "splatter". T
12. Modulation index can be derived from a time-domain view of the AM signal. T
13. Modulation index can be derived from a frequency-domain view of the AM
signal. T
14. In AM, the lower baseband frequencies are in the LSB and the higher baseband
frequencies are in the USB. F
15. The upper sideband contains the same information as the lower sideband. T
16. In AM, most of the power is in the sidebands. F
17. In plain AM, the job of the carrier is to allow simple demodulation. T
18. The upper sideband has twice the power of the lower sideband. F
7. Two sinusoidal signals, V1 and V2, are fed into an ideal balanced mixer. V1 is a 20MHz signal; V2 is a 5-MHz signal. What frequencies would you expect at the output
of the mixer?
ANS:
15 MHz and 25 MHz
8. Suppose the phase-locked-loop frequency synthesizer of Figure 2.39 has a
reference frequency of 1 MHz and a fixed-modulus divider of 10. What should be
the value of the programmable divider to get an output frequency of 120 MHz?
ANS:
12
19. In AM, only one information signal can be sent on any given frequency. F
20. It is possible to transmit stereo audio signals using AM. T
21. SSBSC is derived from DSBSC. T
22. SSB AM requires twice the bandwidth of plain AM. F
23. SSB AM is much more efficient than plain AM. T
Chapter 3: Amplitude Modulation
24. To see an envelope in SSB AM, at least two modulating audio tones are
required. T
25. AM has inherently worse fidelity than FM. F
TRUE/FALSE
1. It is easy to modulate and demodulate a carrier using AM. T
MULTIPLE CHOICE
2. AM makes efficient use of transmitter power. F
1. AM stands for:
a. Audio Modulation
b. Amplitude Modulation
3. AM signals are affected by relatively low levels of electrical noise. T
4. The "envelope" of an AM signal resembles the modulating signal. T
5. AM works by varying the carrier power. F
6. Modulation is not a linear process. T
7. In AM, the amplitude of the carrier changes in step with the modulation. F
8. Mathematically, AM involves multiplication of the carrier by the information
signal. T
9. Sideband power is a linear function of the modulation index. F
10. The modulation index should be greater than 1 for best efficiency. F
c. Angle Modulation
d. Antenna Modulation
2. The "envelope" of an AM signal is due to:
a. the baseband signal
c. the amplitude signal
b. the carrier signal
d. none of the above
3. If the audio Va sin(ωat) modulates the carrier Vc sin(ωct), then the modulation
index, m, is:
a. m = ωa / ωc
c. m = (Va / Vc)2
b. m = Va / Vc
d. m = Va / ωa
4. The equation for full-carrier AM is:
a. v(t) = (Ec + Em) × sin(ωct)
b. v(t) = (Ec + Em) × sin(ωmt) + sin(ωct)
c. v(t) = (Ec × Em) × sin(ωmt) × sin(ωct)
d. v(t) = (Ec + Em sin(ω
ωmt)) × sin(ω
ωct)
5. Overmodulation causes:
a. distortion
b. splatter
c. both a and b
d. none of the above
6. The peak voltage of an AM signal goes from Emax to Emin. The modulation index,
m, is:
a. m = Emin / Emax
c. m = (Emax – Emin) / (Emax + Emin)
b. m = Emax / Emin
d. m = (Emax + Emin) / (Emax – Emin)
7. At 100% modulation, the total sideband power is:
a. equal to the carrier power
c. half the carrier power
b. twice the carrier power
d. 1.414 x carrier power
8. If Va sin(ωat)) amplitude modulates the carrier Vc sin(ωct), it will produce the
frequencies:
a. ωc + ωa and ωc – ωa
c. ωc + ωa and 2ωc + 2ωa
b. (ωc + ωa)/2 and (ωc – ωa)/2
d. none of the above
9. If a 5-kHz signal modulates a 1-MHz carrier, the bandwidth of the AM signal will
be:
a. 5 kHz
c. 1.005 MHz
b. 10 kHz
d. none of the above
10. The modulation index can be derived from:
a. the time-domain signal
b. the frequency-domain signal
c. both a and b
d. none of the above
11. If an AM radio station increases its modulation index, you would expect:
a. the audio to get louder at the receiver
b. the received RF signal to increase
c. the signal-to-noise ratio to increase
d. all of the above
12. The main problem in using quadrature AM would be:
a. requires too much bandwidth
b. requires too much power
c. incompatibility with ordinary AM radios
d. all of the above
13. As compared to plain AM, SSB AM:
a. is more efficient
b. requires a more complex demodulator circuit
c. requires less bandwidth
d. all of the above
16. If an SSB transmitter radiates 1000 watts at peak modulation, what will it
radiate with no modulation?
a. 1000 watts
c. 250 watts
b. 500 watts
d. 0 watts
17. Music on AM radio stations is "low-fidelity" because:
a. AM is susceptible to noise
b. commercial AM stations use low power
c. commercial AM stations have a narrow bandwidth
d. all of the above
18. The type of information that can be sent using AM is:
a. audio
b. video
c. digital data
d. all of the above
19. Two tones modulate an AM carrier. One tone causes a modulation index of m1
and the other tone causes a modulation index of m2. The total modulation index is:
a. m1 + m2
c. sqrt(m1 x m2 + m2 x m1)
b. (m1 + m2) / 2
d. sqrt(m1 x m1 + m2 x m2)
20. To demodulate a USB SSB signal, the receiver must:
a. be set to USB mode
c. both a and b
b. reinsert the carrier
d. none of the above
COMPLETION
1. An advantage of AM is that the receiver can be very ________.
ANS:
simple
2. A disadvantage of AM is its ________ use of power.
ANS:
inefficient
3. The ________ of an AM signal resembles the shape of the baseband signal.
ANS:
envelope
4. In AM, modulating with a single audio tone produces ________ sidebands.
ANS:
two
5. Compared to the USB, the information in the LSB is ________.
ANS:
the same
6. Compared to the USB, the power in the LSB is _________.
ANS:
the same
7. In AM, total sideband power is always ________ than the carrier power.
ANS:
less
14. The SC in SSB SC stands for:
a. single-carrier
b. suppressed-carrier
c. sideband-carrier
d. none of the above
15. PEP stands for:
a. Peak Envelope Power
b. Peak Efficiency Power
c. Peak Envelope Product
d. none of the above
8. In AM, as the modulation index increases, the carrier power _________.
ANS:
remains constant
9. The power in an AM signal is maximum when the modulation index is ________.
ANS:
one
10. In AM, a voice-band signal of 300 Hz to 3000 Hz will require a bandwidth of
_________.
ANS:
6000 Hz
7. A carrier can be frequency modulated with audio at the same time it is phase
modulated with data. F
8. Mathematically, an FM signal has an infinite number of sidebands. T
11. With a 1-MHz carrier, if the LSB extends down to 990 kHz, then the USB will
extend up to _________.
ANS:
1010 kHz
9. At certain modulation frequencies, the power in the carrier frequency of an FM
signal can go to zero. T
12. If an AM transmitter puts out 100 watts with no modulation, it will put out
_________ watts with 100% modulation.
ANS:
150
10. In FM, the modulation index depends on the frequency deviation. T
SHORT ANSWER
12. In FM, as in AM, the modulation index cannot exceed one. F
1. An AM transmitter generates 100 watts with 0% modulation. How much power
will it generate with 20% modulation?
ANS:
102 watts
13. In PM, the phase shift is proportional to the instantaneous amplitude of the
modulating signal. T
11. In FM, the modulation index depends on the frequency of the modulating
signal. T
14. A PM signal can be converted into an FM signal. T
2. If the carrier power is 1000 watts, what is the power in the USB at 70.7%
modulation?
ANS:
125 watts
15. Unlike AM, a single modulating tone can produce many sidebands. T
16. In FM, more sidebands means more power. F
3. A carrier is modulated by three audio tones. If the modulation indexes for the
tones are 0.3, 0.4, and 0.5, then what is the total modulation index?
ANS:
0.707
17. FM is sometimes called a constant-bandwidth communications mode. T
18. An FM signal is best looked at with a spectrum analyzer. T
4. You look at an AM signal with an oscilloscope and see that the maximum Vpp is
100 volts and the minimum Vpp is 25 volts. What is the modulation index?
ANS:
0.6
19. An oscilloscope display will reveal much detail about an FM signal. F
20. There is no such thing as narrowband FM. F
5. A SSB transmitter is connected to a 50-ohm antenna. If the peak output voltage
of the transmitter is 20 volts, what is the PEP?
ANS:
4 watts
21. In FM, the signal-to-noise ratio of a receiver's output can be better than that at
the receiver's input. T
Chapter 4: Angle Modulation
22. In the presence of noise, an FM system exhibits an abrupt transition called
"threshold effect". T
TRUE/FALSE
23. Stereo FM signals produce a better signal-to-noise ratio at the receiver than
mono does. F
1. PM is another term for FM. F
MULTIPLE CHOICE
2. In FM, the frequency of the modulated signal varies with the instantaneous
amplitude of the modulating signal. T
3. Unlike AM, the amplitude of an FM signal does not change with modulation. T
4. Similar to AM, the power of an FM signal changes with modulation. F
5. Class C amplifier stages can be used throughout an FM transmitter. T
6. PM is often used to send digital data. T
1. The FM modulation index:
a. increases with both deviation and modulation frequency
b. increases with deviation and decreases with modulation frequency
c. decreases with deviation and increases with modulation frequency
d. is equal to twice the deviation
2. An FM receiver switching suddenly between two stations on nearby frequencies
is called:
a. the capture effect
c. the "two-station" effect
b. the threshold effect
d. none of the above
3. The bandwidth of an FM signal is considered to be limited because:
a. there can only be a finite number of sidebands
b. it is equal to the frequency deviation
c. it is band-limited at the receiver
d. the power in the outer sidebands is negligible
COMPLETION
4. Mathematically, the calculation of FM bandwidth requires the use of:
a. ordinary trigonometry and algebra
c. Taylor series
b. Bessel functions
d. fractals
2. PM is extensively used in ________ communication.
ANS:
data
5. FM bandwidth can be approximated by:
a. Armstrong's Rule
c. Carson's Rule
b. Bessel's Rule
d. none of the above
6. NBFM stands for:
a. National Broadcast FM
b. Non-Broadcast FM
c. Near Band FM
d. Narrowband FM
7. When FM reception deteriorates abruptly due to noise, it is called:
a. the capture effect
c. the noise effect
b. the threshold effect
d. the limit effect
8. One way to derive FM from PM is:
a. integrate the modulating signal before applying to the PM oscillator
b. integrate the signal out of the PM oscillator
c. differentiate the modulating signal before applying to the PM oscillator
d. differentiate the signal out of the PM oscillator
9. Pre-emphasis is used to:
a. increase the signal to noise ratio for higher audio frequencies
b. increase the signal to noise ratio for lower audio frequencies
c. increase the signal to noise ratio for all audio frequencies
d. allow stereo audio to be carried by FM stations
10. FM stereo:
a. uses DSBSC AM modulation
b. is implemented using an SCA signal
c. has a higher S/N than mono FM
d. is not compatible with mono FM
11. A pre-emphasis of 75µs refers to:
a. the time it takes for the circuit to work
b. the "dead time" before de-emphasis occurs
c. the time delay between the L and R channels
d. the time-constant of the filter circuits used
12. An SCA signal:
a. can use amplitude modulation
b. can use FM modulation
c. is monaural
d. all of the above
13. The modulation index of an FM signal can be determined readily:
a. using measurements at points where J0 equals one
b. using measurements at points where J0 equals zero
c. using measurements at points where the deviation equals zero
d. only by using Bessel functions
1. FM and PM are two forms of ________ modulation.
ANS:
angle
3. Compared to AM, the signal-to-noise ratio of FM is usually _________.
ANS:
better
4. Compared to AM, the bandwidth of FM is usually ________.
ANS:
wider, greater
5. FM transmitters can use Class ________ amplifiers since amplitude linearity is
not important.
ANS:
C
6. Both the power and amplitude of an FM signal ________ as modulation is
applied.
ANS: stay constant
7. In FM, the frequency deviation is proportional to the instantaneous _________ of
the modulating signal.
ANS:
amplitude
8. The frequency deviation of an FM signal occurs at a rate equal to the _________
of the modulating signal.
ANS:
frequency
9. Mathematically, the number of sidebands in an FM signal is __________.
ANS:
infinite
10. As FM sidebands get farther from the center frequency, their power _________.
ANS:
decreases
11. Mathematically, the value of an FM modulation index can be as high as
________.
ANS:
any number
12. In FM, as the modulating frequency decreases, the modulation index
_________.
ANS:
increases
13. In FM, as the frequency deviation decreases, the modulation index _________.
ANS:
decreases
14. As the FM modulation index increases, the number of significant sidebands
_________.
ANS:
increases
15. The bandwidth of an FM signal can be approximated using _________ rule.
ANS:
Carson's
15. For certain values of mf, such as 2.4, the amplitude of the carrier frequency
___________.
ANS:
disappears, goes to zero
9. Using Carson's rule, what is the approximate bandwidth of an FM signal with a
modulation index of 2 being modulated by a 5-kHz signal?
ANS:
30 kHz
17. FM bandwidth can be calculated precisely using _________ functions.
ANS:
Bessel
10. Using the Bessel chart of Figure 4.1, what is the bandwidth of an FM signal with
a modulation index of 2 being modulated by a 5-kHz signal if we ignore sidebands
containing less than 1% of the total power?
ANS:
30 kHz
18. The ________ effect is characteristic of FM reception in a noisy environment.
ANS:
threshold
19. The _______ effect is seen when an FM receiver is exposed to two FM signals
that are close to each other in frequency.
ANS:
capture
20. Rest frequency is another name for an FM _________ frequency.
ANS:
carrier
Chapter 5: Transmitters
TRUE/FALSE
1. All transmitters produce spurious signals. T
SHORT ANSWER
2. Any amplifier will produce harmonic distortion. T
1. If a 2-volt instantaneous value of modulating signal amplitude causes a 10-kHz
deviation in carrier frequency, what is the deviation sensitivity of the modulator?
ANS:
5 kHz / volt
3. There is a simple correlation between supply power and output power for
transmitters. F
2. If a 2-kHz audio tone causes a frequency deviation of 4 kHz, what is the
modulation index?
ANS:
2
3. What will be the deviation caused by a 3-kHz tone if the modulation index is 3?
ANS:
9 kHz
4. If the deviation sensitivity of an FM modulator is 2 kHz /V, what will be the
modulation index caused by a 1-volt, 1-kHz audio signal?
ANS:
2
4. Transmitters designed for two-way voice communications must be rated for
continuous operation at full power. F
5. Baseband spectrum often must be restricted to keep transmitted bandwidth
within legal limits. T
6. Compression is used to restrict baseband spectrum. F
7. The opposite of compression is expansion. T
8. In a transmitter, the ALC circuit prevents overmodulation. T
5. At a modulation index of 2, how much power is in the carrier of a 1000-watt FM
transmitter?
ANS:
48.4 watts
9. In a transmitter, the ALC circuit causes compression. T
6. At a modulation index of 2, how much power is in the first pair of sidebands of a
1000-watt FM transmitter?
ANS:
673 watts
11. In full-carrier AM, modulation is typically done before the RF power amplifier. F
7. At a modulation index of 2, how much power is in the fifth pair of sidebands of a
1000-watt FM transmitter?
ANS:
200 mW (0.2 watt)
10. Compression is commonly used in commercial broadcast transmitters. T
12. If the RF stages are all Class C, then AM must be done with low-level
modulation. F
13. Commercial broadcast AM stations typically use high-level modulation. T
14. Low-level AM modulation requires linear RF amplifiers. T
8.How would you use the fact that J0 is zero for certain known values of mf (2.4,
5.5, etc) to measure the frequency deviation of an FM modulator?
ANS:
Use an audio frequency generator to modulate the FM carrier. Using a
spectrum analyzer, adjust the audio frequency until the carrier amplitude
vanishes. Record the audio frequency. Then do the calculation: δ = fm ×
mf where mf will have one of the known values. For example, if fm is
measured to be 2 kHz when mf is 5.5, then δ is 11 kHz.
15. For good frequency stability, a crystal oscillator is generally required. T
16. A variable-frequency oscillator cannot be crystal-controlled. F
17. Vacuum tubes are still used in high-power transmitters, even new ones. T
18. In a commercial broadcast AM transmitter, all the power in the sidebands came
from the audio amplifier. T
19. Typically, some kind of matching circuit is required between a transmitter's
output stage and the antenna. T
20. For testing purposes, the output of a transmitter should be disconnected from
the antenna and left with an open-circuit load. F
21. In a transceiver, the same audio circuits are used by both the transmitter and
the receiver. T
22. In solid-state transmitters, it is common to modulate both the driver and the
power RF stage. T
23. Mixing and amplitude modulation are essentially the same process. T
24. DSBSC is never done at low level. F
25. To generate SSB from DSBSC, a mechanical filter can be used. T
26. To generate SSB from DSBSC, a crystal filter can be used. T
27. It is possible that the LSB and the USB can become swapped during a mixing
process. T
28. The RF power amplifiers in a SSB transmitter are Class C for better efficiency. F
4. The difference between the DC power into a transmitter and the RF power
coming out:
a. is a measure of efficiency
c. may require water cooling
b. heats the transmitter
d. all of the above
5. Baseband compression produces:
a. a smaller range of frequencies from low to high
b. a smaller range of amplitude from soft to loud
c. a smaller number of signals
d. none of the above
6. With high-level AM:
a. all RF amplifiers can be nonlinear
b. minimum modulation power is required
c. minimum RF power is required
d. all of the above
7. With high-level AM:
a. the RF amplifiers are typically Class
b. the RF amplifiers are typically Class B
c. the RF amplifiers are typically Class C
d. the RF amplifiers are typically Class AB
8. With low-level AM:
a. the RF amplifiers must be Class A
b. the RF amplifiers must be Class B
c. the RF amplifiers must be linear
d. the RF amplifiers must be low-power
29. In FM, a frequency multiplier will also multiply the deviation. T
9. Power amplifiers must be linear for any signal that:
a. is complex
c. has variable frequency
b. has variable amplitude
d. all of the above
30. Frequency doublers are usually Class B. F
31. Mixing can lower a carrier frequency as well as raise it. T
32. Indirect FM uses a phase modulator. T
33. Even low-power transmitters can cause an RF burn to the skin. T
MULTIPLE CHOICE
1. The ability to change operating frequency rapidly without a lot of retuning is
called:
a. agility
c. VFO
b. expansion
d. spread-spectrum
2. ALC stands for:
a. Amplitude Level Control
b. Automatic Level Control
c. Accurate Level Control
d. none of the above
3. In an AM transmitter, ALC is used to:
a. keep the modulation close to 100%
b. keep the modulation below 100%
c. maximize transmitted power
d. all of the above
10. In high-level AM, "high-level" refers to:
a. the power level of the carrier
b. the power level of the modulation
c. the power level of the final RF amplifier
d. none of the above
11. In high-level AM, the power in the sidebands comes from:
a. the modulating amplifier
c. the driver stage
b. the RF amplifier
d. the carrier
12. In an AM transmitter with 100% modulation, the voltage of the final RF stage
will be:
a. approximately half the DC supply voltage
b. approximately twice the DC supply voltage
c. approximately four times the DC supply voltage
d. none of the above
13. Practical transmitters are usually designed to drive a load impedance of:
a. 50 ohms resistive
c. 300 ohms resistive
b. 75 ohms resistive
d. 600 ohms resistive
14. Which of the following can be used for impedance matching?
a. pi network
c. both a and b
b. T network
d. a bridge circuit
25. Frequency multipliers are:
a. essentially balanced modulators
b. essentially Class C amplifiers
15. When a transmitter is connected to a resistor instead of an antenna, the resistor
is called:
a. a heavy load
c. a temporary load
b. a dummy load
d. a test load
COMPLETION
16. When a transmitter is connected to a resistor instead of an antenna, the resistor
must be:
a. wire-wound
c. 1% tolerance or better
b. non-inductive
d. all of the above
17. A Class D amplifier is:
a. very efficient
b. essentially pulse-width modulation
c. essentially pulse-duration modulation
d. all of the above
c. essentially mixers
d. none of the above
1. The accuracy and stability of a transmitter frequency is fixed by the ________
oscillator.
ANS:
carrier
2. In the USA, the __________ sets requirements for accuracy and stability of a
transmitter's frequency.
ANS:
FCC
3. In Canada, _________ sets requirements for accuracy and stability of a
transmitter's frequency.
ANS:
Industry Canada
18. To generate a SSB signal:
a. start with full-carrier AM
b. start with DSBSC
c. start with a quadrature signal
d. all of the above
4. Frequency __________ is the ability of a transmitter to change frequency without
a lot of retuning.
ANS:
agility
19. The carrier is suppressed in:
a. a balanced modulator
b. a mixer
c. a frequency multiplier
d. none of the above
5. Power output of SSB transmitters is rated by _________.
ANS:
PEP
20. To remove one AM sideband and leave the other you could use:
a. a mechanical filter
c. both a and b
b. a crystal filter
d. none of the above
21. A direct FM modulator:
a. varies the frequency of the carrier oscillator
b. integrates the modulating signal
c. both a and b
d. none of the above
22. An indirect FM modulator:
a. requires a varactor in the carrier oscillator
b. varies the phase of the carrier oscillator
c. both a and b
d. none of the above
23. AFC stands for:
a. Amplitude to Frequency Conversion
b. Automatic Frequency Centering
c. Automatic Frequency Control
d. Audio Frequency Control
24. With mixing:
a. the carrier frequency can be raised
b. the carrier frequency can be lowered
c. the carrier frequency can be changed to any required value
d. the deviation is altered
6. Reducing the dynamic range of a modulating signal is called _________.
ANS:
compression
7. The opposite of compression is called _________.
ANS:
expansion
8. ALC is a form of ________.
ANS:
compression
9. High-level modulation allows the RF amplifiers to operate more _________.
ANS:
efficiently
10. Low-level modulation requires the RF amplifiers to be __________.
ANS:
linear
11. To isolate the oscillator from load changes, a ________ stage is used.
ANS:
buffer
12. The peak collector voltage in a Class C RF amplifier is ________ than the DC
supply voltage.
ANS:
higher
13. Most practical transmitters are designed to operate into a ____-ohm load.
ANS:
50
14. Transmitters built with transistor RF amplifiers often use a ________ network
for impedance matching.
ANS:
T
15. Matching networks also act as filters to help reduce ________ levels.
ANS:
harmonic
16. Severe impedance _________ can destroy a transmitter's output stage.
ANS:
mismatch
17. Transceivers combine a transmitter and a ________ into one "box".
ANS:
receiver
18. To allow a high modulation percentage, it is common to modulate the ________
as well as the power amplifier in transistor modulators.
ANS:
driver
19. Pulse-width modulation is the same as pulse-_________ modulation.
ANS:
duration
3. The power amplifier of an AM transmitter draws 100 watts from the power
supply with no modulation. Assuming high-level modulation, how much power does
the modulation amplifier deliver for 100% modulation?
ANS:
50 watts
4. If the final RF amplifier of an AM transmitter is powered by 100 volts DC, what is
the maximum collector voltage at 100% modulation?
ANS:
400 volts
5. Suppose the output of a balanced modulator has a center frequency of 10 MHz.
The audio modulation frequency range is 1 kHz to 10 kHz. To pass the USB, what
should be the center frequency of an ideal crystal filter?
ANS:
10.005 MHz
6. Suppose you have generated a USB SSB signal with a nominal carrier frequency of
10 MHz. What is the minimum frequency the SSB signal can be mixed with so that
the output signal has a nominal carrier frequency of 50 MHz?
ANS:
40 MHz
20. Switching amplifiers are sometimes called Class _________ amplifiers.
ANS:
D
7. Suppose you have an FM modulator that puts out 1 MHz carrier with a 100-hertz
deviation. If frequency multiplication is used to increase the deviation to 400 hertz,
what will be the new carrier frequency?
ANS:
4 MHz
21. Because the sideband filter in a SSB transmitter is fixed, ________ is used to
operate at more than one frequency.
ANS:
mixing
8. What is the efficiency of a 100-watt mobile transmitter if it draws 11 amps from a
12-volt car battery?
ANS:
75.8%
22. To generate a SSB signal, it is common to start with a _________ signal.
ANS:
DSBSC
Chapter 6: Receivers
23. Indirect FM is derived from ________ modulation.
ANS:
phase
TRUE/FALSE
24. Using a varactor to generate FM is an example of a ________ modulator.
ANS:
reactance
1. The first radio receiver was built in 1918. F
2. Almost all modern receivers use the superheterodyne design. T
25. The modern way to make a stable VFO is to make it part of a
____________________ loop.
ANS:
phase-locked
3. A tuned circuit at the input increases receiver sensitivity. F
SHORT ANSWER
4. Since both fo and Q increase with frequency, the bandwidth of a resonant LC
circuit remains constant as it is tuned to higher frequencies. F
1. If a 50-MHz oscillator is accurate to within 0.001%, what is the range of possible
frequencies?
ANS:
50 MHz ± 500 hertz
2 .Suppose you had an FM signal with a carrier of 10 MHz and a deviation of 10 kHz.
Explain how you could use it to get an FM signal at 100 MHz with a deviation of 20
kHz.
ANS:
First, put the signal through a frequency doubler to get a 20-MHz carrier
with a 20-kHz deviation. Then mix that signal with an 80-MHz carrier to
generate a 100-MHz carrier with 20-kHz deviation.
5. The resistance of a coil is a function of frequency. T
6. The superhet was invented by Heinrich Hertz. F
7. In a receiver, the first RF amplifier is largely responsible for overall noise
performance. T
8. In a superhet, the local oscillator must be set to the transmitter's carrier
frequency. F
9. In a superhet, the output of the mixer is the IF. T
10. In a superhet, most of the gain comes from the IF amplifiers. T
34. If the BFO in a SSB receiver is 100 hertz low, what comes out of the speaker may
sound like Donald Duck, but it will be understandable. T
11. In a superhet, most of the selectivity comes from the IF amplifiers. T
35. DSBSC transmitters often use a pilot carrier to allow coherent detection. T
12. All superhets use a separate local oscillator. F
36. FM receivers are similar to AM receivers in basic design. T
13. In high-side injection, the incoming RF is at a higher frequency than the local
oscillator. F
37. There is no way to demodulate an FM signal with an AM receiver. F
14. The mixer and the local oscillator can use the same transistor. T
38. Modern FM receivers commonly use Foster-Seeley discriminators. F
15. The IF frequency is constant as a receiver is tuned to various frequencies. T
39. Both PLLs and quadrature detectors can be used to demodulate FM. T
16. There can be only one mixer and one IF in a superhet receiver. F
40. Quadrature detectors are sensitive to variations in carrier amplitude. T
17. In AM receivers, the antenna and the inductor of the tuner circuit can be the
same thing. T
41. Squelch is the same as muting. T
42. A bipolar transistor can be used as a mixer, but a FET cannot. F
18. Bandwidth and signal-to-noise-ratio are not related in a superhet. F
19. Shape-factor is a measure of selectivity. T
MULTIPLE CHOICE
20. Phase distortion should be minimized for reliable voice communications. F
1. The two basic specifications for a receiver are:
a. the sensitivity and the selectivity
b. the number of converters and the number of IFs
c. the spurious response and the tracking
d. the signal and the noise
21. A receiver's response to weak signals is limited by the noise generated inside
the receiver. T
22. The AGC in a receiver can cause "blocking". T
23. Careful design can eliminate all spurious responses. F
2. The superheterodyne receiver was invented by:
a. Foster
c. Armstrong
b. Seeley
d. Hertz
24. Image frequencies are eliminated by the IF. F
25. "Software radios" use a DSP to replace all hardware up to and including the
detector. F
26. It is possible that a transmitter on one frequency can appear at two spots on a
receiver's dial. T
27. A detector is the same as a demodulator. T
3. Trimmers and padders are:
a. two types of adjusting tools
b. small adjustable resistors
c. small adjustable inductors
d. small adjustable capacitors
4. "Skin effect" refers to:
a. the way radio signals travel across a flat surface
b. the tissue-burning effect of a strong RF signal
c. the increase of wire resistance with frequency
d. none of the above
28. Envelope detectors are typically used in FM receivers. F
29. Envelope detectors are complicated, but extremely linear. F
5. The "front end" of a receiver can include:
a. the tuner
c. the mixer
b. the RF amplifier
d. all of the above
30. There is a way to use a diode to demodulate a SSB signal. T
31. A SSB signal requires a ratio detector. F
6. "IF" stands for:
a. intermediate frequency
b. intermodulation frequency
c. indeterminate frequency
d. image frequency
32. In a SSB receiver, the BFO injects the carrier into the detector. T
33. In a SSB receiver, it is relatively easy for the injected carrier to match the
frequency and phase of the transmitter's carrier. F
7. AGC stands for:
a. Audio Gain Control
b. Automatic Gain Control
c. Active Gain Control
d. Active Gain Conversion
8 . When comparing values for shape factor:
a. a value of 1.414 dB is ideal
b. a value of 0.707 is ideal
c. a value of 1.0 is ideal
d. there is no ideal value
9. The local oscillator and mixer are combined in one device because:
a. it gives a greater reduction of spurious responses
b. it increases sensitivity
c. it increases selectivity
d. it is cheaper
10. Basically, sensitivity measures:
a. the weakest signal that can be usefully received
b. the highest-frequency signal that can be usefully received
c. the dynamic range of the audio amplifier
d. none of the above
18. Image frequencies occur when two signals:
a. are transmitted on the same frequency
b. enter the mixer, with one being a reflected signal equal to the IF
frequency
c. enter the mixer, one below and one above the local oscillator by a
difference equal to IF
d. enter the mixer, and the difference between the two signals is equal to
twice the IF
19. Image frequency problems would be reduced by:
a. having an IF amplifier with the proper shape factor
b. having a wideband RF amplifier after the mixer
c. having a narrowband RF amplifier before the mixer
d. none of the above
20. A common AM detector is the:
a. PLL
c. ratio detector
b. envelope detector
d. all of the above
11. Basically, selectivity measures:
a. the range of frequencies that the receiver can select
b. with two signals close in frequency, the ability to receive one and
reject the other
c. how well adjacent frequencies are separated by the demodulator
d. how well the adjacent frequencies are separated in the mixer
21. An FM detector is the:
a. PLL
b. ratio detector
12. The frequency of the local oscillator:
a. is above the RF frequency
b. is below the RF frequency
c. can be either above of below the RF frequency
d. is fixed, typically at 455 kHz.
22. Germanium diodes are used in AM detectors because:
a. they are faster than silicon diodes
b. they are cheaper than silicon diodes
c. they minimize distortion from nonlinearity
d. all of the above
13. When comparing values for shape factor:
a. a value of 2 is better than a value of 4
b. a value of 4 is better than a value of 2
c. both values are basically equivalent
d. none of the above
23. A common SSB detector is:
a. a PLL
c. a BFO
b. a diode
d. a product detector
14. Distortion in a receiver can occur in:
a. the mixer
c. the IF amplifiers
b. the detector
d. all of the above
15. Phase distortion is important in:
a. voice communications systems c. monochrome video receivers
b. color video receivers
d. all of the above
16. The response of a receiver to weak signals is usually limited by:
a. the AGC
b. noise generated in the receiver
c. the dynamic range of the receiver
d. the type of detector circuit being used
17. An image must be rejected:
a. prior to mixing
b. prior to IF amplification
c. prior to detection
d. images cannot be rejected
c. quadrature detector
d. all of the above
24. BFO stands for:
a. Beat Frequency Oscillator
b. Barrier Frequency Oscillator
25. Which would be best for DSBSC:
a. carrier detection
b. coherent detection
c. Bipolar Frequency Oscillator
d. Bistable Frequency Oscillator
c. envelope detection
d. ratio detection
26. To demodulate both SSB and DSBSC, you need to:
a. use a Foster-Seeley discriminator
b. reinject the carrier
c. use double conversion
d. use one diode for SSB and two diodes for DSBSC
27. An FM detector that is not sensitive to amplitude variations is:
a. Foster-Seeley detector
c. a PLL detector
b. a quadrature detector
d. all of the above
28. The function of a limiter is:
a. to remove amplitude variations
b. to limit spurious responses
c. to limit dynamic range
d. to limit noise response
29. Suppressing the audio when no signal is present is called:
a. AGC
c. AFC
b. squelch
d. limiting
30. LNA stands for:
a. Limited-Noise Amplifier
b. Low-Noise Amplifier
c. Low-Noise Audio
d. Logarithmic Noise Amplification
5. The superhet was invented in the year ________.
ANS:
1918
32. The function of AFC is:
a. maintain a constant IF frequency
b. match the local oscillator to the received signal
c. lock the discriminator to the IF frequency
d. none of the above
c. Silicon-Activated Wafer
d. Software-Activated Wave
34. The important property of a SAW is:
a. it stabilizes the audio in a receiver
b. it allows software radios to be built
c. it is a stable bandpass filter
d. none of the above
35. The main function of the AGC is to:
a. keep the gain of the receiver constant
b. keep the gain of the IF amplifiers constant
c. keep the input to the detector at a constant amplitude
d. all of the above
36. DSP stands for:
a. Dynamic Signal Properties
b. Direct Signal Phase
c. Distorted Signal Packet
d. Digital Signal Processor
37. SINAD stands for:
a. Sinusoidal Amplitude Distortion
b. Signal and Noise Amplitude Distortion
c. Signal-plus-Noise-to-Noise Ratio
d. Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio
38. TRF stands for:
a. Tuned Radio Frequency
b. Tracking Radio Frequency
c. Transmitted Radio Frequency
d. Tuned Receiver Function
COMPLETION
1. Almost all modern receivers use the _________ principle.
ANS:
superheterodyne
3. When two tuned circuits __________ each other, it means that when the
frequency of one is adjusted, the other changes with it.
ANS:
track
4. The ________ effect causes the resistance of wire to increase with frequency.
ANS:
skin
31. AFC stands for:
a. Audio Frequency Compensator
b. Autodyne Frequency Compensation
c. Automatic Frequency Control
d. Autonomous Frequency Control
33. SAW stands for:
a. Symmetrical Audio Wave
b. Surface Acoustic Wave
2. The first radio receiver of any kind was built in the year _______.
ANS: 1887
6. In a receiver, the _________ refers to the input filter and RF stage.
ANS:
front end
7. In a superhet, the output of the ________ goes to the IF amplifiers.
ANS:
mixer
8. In a superhet, the _________ frequency is the difference between the local
oscillator frequency and the received signal frequency.
ANS:
intermediate, IF
9. The _________ circuit adjusts the gain of the IF amplifiers in response to signal
strength.
ANS:
AGC
10. An __________ converter uses the same transistor for both the local oscillator
and the mixer.
ANS:
autodyne
11. In low-side injection, the local oscillator is _________ than the received signal
frequency.
ANS:
lower
12. _________ is the ability of a receiver to separate two signals that are close to
each other in frequency.
ANS:
Selectivity
13. _________ is the ability of a receiver to receive and successfully demodulate a
very weak signal.
ANS: Sensitivity
14. A receiver with two different IF frequencies is called a double-_________
receiver.
ANS:
conversion
15. A multiple-conversion receiver will have better rejection of _________
frequencies.
ANS:
image
16. A demodulator is also called a _________.
ANS:
detector
17. An ________ detector uses a diode to half-wave rectify an AM signal.
ANS:
envelope
18. A _______ detector is used for SSB signals.
ANS:
product
19. A BFO produces a locally generated _________.
ANS:
carrier
20. A DSBSC signal requires a ________ detection circuit.
ANS:
coherent
33. An _____-meter is designed to indicate signal strength in many communications
receivers.
ANS: S
34. The effectiveness of FM _________ is measured by a receiver’s quieting
sensitivity.
ANS:
limiting
35. A ________ refers to any kind of FM or PM detector.
ANS:
discriminator
SHORT ANSWER
21. FM detectors have a characteristic _________-shaped curve.
ANS:
S
22. While still commonly found, the Foster-Seeley and ratio detectors are
__________.
ANS:
obsolescent
23. Unlike the PLL detector, the quadrature detector is sensitive to changes in
_________ of the input signal.
ANS:
amplitude
24. A dual-_________ MOSFET is useful for AGC.
ANS:
gate
25. Diode mixers are too _______ to be practical in most applications.
ANS:
noisy
26. The IF amplifiers in an AM receiver must be Class ______.
ANS:
A
27. A double-tuned IF transformer is usually _________ coupled for the response to
have a flat top and steep sides.
ANS:
over
28. Multiple IF stages can be _________-tuned to increase the bandwidth.
ANS:
stagger
28. Compared to tuned circuits, ceramic and crystal IF filters do not require
__________.
ANS:
adjustment
30. Up-conversion is when the output of the mixer is a ___________ frequency than
the incoming signal.
ANS:
1. Suppose the bandwidth of a tuned circuit is 10 kHz at 1 MHz. Approximately what
bandwidth would you expect it to have at 4 MHz?
ANS:
20 kHz
2. Using high-side injection for a 1-MHz IF, what is the frequency of the local
oscillator when the receiver is tuned to 5 MHz?
ANS:
6 MHz
3. An IF filter has a –60 dB bandwidth of 25 kHz and a –6 dB bandwidth of 20 kHz.
What is the shape factor value?
ANS:
1.25
4. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what
would be the image frequency if the receiver was tuned to 50 MHz?
ANS:
60 MHz
5. Suppose a SSB receiver requires an injected frequency of 1.5 MHz. What would
be the acceptable frequency range of the BFO if the maximum acceptable baseband
shift is 100 hertz?
ANS:
1.5 MHz ± 100 hertz
6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary
and secondary. What value of kc do you need to achieve optimal coupling?
ANS:
0.06
7. What value of transformer coupling would a double-tuned 10-MHz IF amplifier
with optimal coupling need to get a bandwidth of 100 kHz?
ANS:
0.01
Chapter 7: Digital Communications
higher
31. In a block converter, the frequency of the first local oscillator is __________.
ANS:
fixed, constant
32. Typically, AGC reduces the gain of the ________ amplifiers.
ANS:
IF
TRUE/FALSE
1. Analog signals cannot be sent using digital techniques. F
2. Digitizing a signal can reduce distortion. T
3. Digitizing a signal can improve the signal-to-noise ratio. T
28. Quantizing is converting a sample of an analog signal to a binary number. T
4. Morse code is an example of a binary digital transmission system. F
29. Quantizing always introduces some error. T
5. Digital signals can be modulated onto an analog carrier. T
30. Quantizing always introduces some "noise". T
6. Digitization removes noise and distortion from analog signals. F
31. The significance of quantizing noise increases as the number of bits per sample
increases. F
7. A digital signal can be changed from a 1 to a 0 by noise. T
8. A regenerative repeater converts a degraded pulse into a new pulse. T
9. TDM is easy to implement with digital signals. T
32. The dynamic range of a digital transmission system depends on the number of
bits per sample. T
33. The bandwidth required by a digital transmission system depends on the
number of bits per sample. T
10. Unlike analog, digital communications is not band-limited. F
34. Companding allows improved dynamic range for a given bandwidth. T
11. The amount of digital data that can be sent is limited by the channel capacity
(C). F
35. The companding system used in America is known as "A-Law" companding. F
12. The digital data rate is limited by the bandwidth of the channel. T
36. Companding is basically a linear process. F
13. The digital data rate is limited by the SNR of the channel. T
37. Companding can be done with analog circuitry. T
14. The digital data rate is limited by the number of levels transmitted. T
38. Digital companding is used by most modern telephone systems. T
15. The Shannon-Hartley theorem describes how to obtain the Shannon limit for
transmission. F
39. With delta modulation, only one bit is transmitted per cycle. T
40. Delta modulation is particularly well suited to rapidly changing analog signals. F
16. Digital data can be sent through a channel no matter how low the SNR is, as
long as it is not zero. T
41. Delta modulation is prone to "granular noise". T
17. Analog signals must be sampled before they can be sent in digital form. T
42. Adaptive delta modulation reduces the occurrence of "slope-overload". T
18. Mathematically, it is not possible to completely reconstruct a band-limited
signal from only samples of the signal. F
43. A disadvantage of adaptive delta modulation is that it requires a higher bit rate
than PCM. F
19. The Nyquist Rate is equal to half the highest frequency component of the analog
signal. F
44. Digital data is put onto a cable using a line code. T
45. Unipolar line coding requires DC continuity. T
20. Natural sampling is also called "flat-top" sampling. F
46. Bipolar RZ coding generates DC and low-frequency AC components. F
21. Flat-top sampling requires a sample-and-hold circuit. T
47. The Manchester line code provides strong timing information. T
22. Aliasing occurs when the sampling rate is too high. F
48. The basic DS-1 signal consists of 12 voice channels. F
23. Foldover distortion occurs when the sampling rate is too low. T
49. In DS-1, each analog voice channel is sampled 8000 times per second. T
24. Sampling is actually a form of modulation. T
50. In DS-1, the bit rate for each voice channel is 56 kbits per second. F
25. The output of a sampler is a PDM signal. F
51. A T-1 frame contains 193 bits. T
26. The most commonly used digital modulation scheme is PCM. T
52. T-1 uses AMI. T
27. In PCM, the number of levels is the same as the number of bits. F
53. A T-1 cable can be twisted-pair copper wires. T
54. A T-1 line runs at 1.544 Mbits per second. T
10. Foldover distortion is caused by:
a. noise
b. too many samples per second
c. too few samples per second
d. all of the above
55. In DS-1, bits are sometimes "stolen" from the voice channel to be used for
signaling. T
11. The immediate result of sampling is:
a. a sample alias
b. PAM
c. PCM
56. "Lossy" compression involves transmitting all the data in the original signal, but
with fewer bits. F
12. Which of these is not a pulse-modulation technique:
a. PDM
b. PWM
c. PPM
57. "Lossless" compression schemes look for redundancies in the data. T
13. Quantizing noise (quantization noise):
a. decreases as the sample rate increases
b. decreases as the sample rate decreases
c. decreases as the bits per sample increases
d. decreases as the bits per sample decreases
58. "Run-Length" encoding is a type of lossless compression. T
d. PDM
d. PPS
MULTIPLE CHOICE
1. The first digital code was the:
a. ASCII code
b. Baudot code
c. Morse code
d. none of the above
2. In digital transmission, signal degradation can be removed using:
a. an amplifier
c. a regenerative repeater
b. a filter
d. all of the above
3. TDM stands for:
a. Time-Division Multiplexing
b. Time-Domain Multiplexing
4. Hartley's Law is:
a. I = ktB
b. C = 2B log2M
c. Ten-Digital Manchester
d. Ten Dual-Manchester
c. C = B log2(1 + S/N)
d. SR = 2fmax
5. The Shannon-Hartley theorem is:
a. I = ktB
c. C = B log2(1 + S/N)
b. C = 2B log2M d. SR = 2fmax
6. The Shannon Limit is given by:
a. I = ktB
b. C = 2B log2M
c. C = B log2(1 + S/N)
d. SR = 2fmax
7. The Nyquist Rate can be expressed as:
a. I = ktB
c. C = B log2(1 + S/N)
b. C = 2B log2M
d. SR = 2fmax
8. Natural Sampling does not use:
a. a sample-and-hold circuit
b. true binary numbers
c. a fixed sample rate
d. an analog-to-digital converter9.
9. Which is true about aliasing and foldover distortion?
a. They are two types of sampling error.
b. You can have one or the other, but not both.
c. Aliasing is a technique to prevent foldover distortion.
d. They are the same thing.
14. The dynamic range of a system is the ratio of:
a. the strongest transmittable signal to the weakest discernible signal
b. the maximum rate of conversion to the minimum rate of conversion
c. the maximum bits per sample to the minimum bits per sample
d. none of the above
15. Companding is used to:
a. compress the range of base-band frequencies
b. reduce dynamic range at higher bit-rates
c. preserve dynamic range while keeping bit-rate low
d. maximize the useable bandwidth in digital transmission
16. In North America, companding uses:
a. the Logarithmic Law
b. the A Law
c. the α Law (alpha law)
d. the µ Law (mu law)
17. In Europe, companding uses:
a. the Logarithmic Law
b. the A Law
c. the α Law (alpha law)
d. the µ Law (mu law)
18. Codec stands for:
a. Coder-Decoder
b. Coded-Carrier
c. Code-Compression
d. none of the above
19. A typical codec in a telephone system sends and receives:
a. 4-bit numbers
c. 12-bit numbers
b. 8-bit numbers
d. 16-bit numbers
20. Compared to PCM, delta modulation:
a. transmits fewer bits per sample
b. requires a much higher sampling rate
c. can suffer slope overload
d. all of the above
21. In delta modulation, "granular noise" is produced when:
a. the signal changes too rapidly
c. the bit rate is too high
b. the signal does not change
d. the sample is too large
22. The number of framing bits in DS-1 is:
a. 1
b. 2
c. 4
d. 8
37. A vocoder implements compression by:
a. constructing a model of the transmission medium
b. constructing a model of the human vocal system
c. finding redundancies in the digitized data
d. using lossless techniques
23. Which coding scheme requires DC continuity:
a. AMI
c. unipolar NRZ
b. Manchester
d. bipolar RZ
24. Manchester coding:
a. is a biphase code
b. has a level transition in the middle of every bit period
c. provides strong timing information
d. all of the above
COMPLETION
1. Digitizing a signal often results in ________ transmission quality.
ANS:
improved, better
25. Compared to PCM, adaptive delta modulation can transmit voice:
a. with a lower bit rate but reduced quality
b. with a lower bit rate but the same quality
c. only over shorter distances
d. only if the voice is band-limited
2. To send it over an analog channel, a digital signal must be _________ onto a
carrier.
ANS:
modulated
26. Framing bits in DS-1 are used to:
a. detect errors
c. synchronize the transmitter and receiver
b. carry signaling
d. all of the above
27. So-called "stolen" bits in DS-1 are used to:
a. detect errors
c. synchronize the transmitter and receiver
b. carry signaling
d. all of the above
28.
The number of bits per sample in DS-1 is:
a. 1
b. 2
c. 4
29. The number of samples per second in DS-1 is:
a. 8 k
b. 56 k
c. 64 k
d. 8
d. 1.544 x 106
6. A ________ repeater is used to restore the shape of pulses on a digital cable.
ANS:
regenerative
c. 56 kb/s
d. 8 kb/s
31. In DS-1, bits are transmitted over a T-1 cable at:
a. 1.544 Mb/s
b. 64 kb/s
c. 56 kb/s
d. 8 kb/s
c. NRZ coding
d. pulse-width coding
33. The number of frames in a superframe is:
a. 6
b. 12
c. 24
4. In analog channels, the signal-to-noise ratio of an analog signal gradually
________ as the length of the channel increases.
ANS:
decreases, gets worse
5. The ________ value of a pulse is the only information it carries on a digital
channel.
ANS:
binary
30. The bit rate for each channel in DS-1 is:
a. 1.544 Mb/s
b. 64 kb/s
32. A T-1 cable uses:
a. Manchester coding
b. bipolar RZ AMI coding
3. To send it over a digital channel, an analog signal must first be ________.
ANS:
digitized
d. 48
7. There are techniques to detect and _________ some errors in digital
transmission.
ANS:
correct
8. Converting an analog signal to digital form is another source of _________ in
digital transmission systems.
ANS:
error, noise
9. ________-division multiplexing is easily done in digital transmission.
ANS:
Time
10. All practical communications channels are band-_________.
ANS:
limited
34. A typical T-1 line uses:
a. twisted-pair wire
b. coaxial cable
c. fiber-optic cable
d. microwave
11. ________ Law gives the relationship between time, information capacity, and
bandwidth.
ANS:
Hartley's
35. "Signaling" is used to indicate:
a. on-hook/off-hook condition
b. busy signal
c. ringing
d. all of the above
12. Ignoring noise, the _________ theorem gives the maximum rate of data
transmission for a given bandwidth.
ANS:
Shannon-Hartley
36. Compared to standard PCM systems, the quality of the output of a vocoder is:
a. much better
c. about the same
b. somewhat better
d. not as good
13. ________ sampling is done without a sample-and-hold circuit.
ANS:
Natural
14. The _________ limit gives the maximum rate of data transmission for a given
bandwidth and a given signal-to-noise ratio.
ANS:
Shannon
15. The ________ Rate is the minimum sampling rate for converting analog signals
to digital format.
ANS:
Nyquist
16. ________ distortion occurs when an analog signal is sampled at too slow a rate.
ANS:
Foldover
17. ________ means that higher frequency baseband signals from the transmitter
"assume the identity" of low-frequency baseband signals at the receiver when sent
digitally.
ANS:
Aliasing
18. The output of a sample-and-hold circuit is a pulse-__________ modulated
signal.
ANS:
amplitude
19. ________ modulation is the most commonly used digital modulation scheme.
ANS:
Pulse-code
20. _________ noise results from the process of converting an analog signal into
digital format.
ANS:
Quantizing
21. ________ is used to preserve dynamic range using a reasonable bandwidth.
ANS:
Companding
22. In North America, compression is done using the ________-law equation.
ANS:
µ, mu
23. In Europe, compression is done using the _____-law equation.
ANS:
A
24. A _______ is an IC that converts a voice signal to PCM and vice versa.
ANS:
codec
25. In a PCM system, the samples of the analog signal are first converted to
________ bits before being compressed to 8 bits.
ANS:
12
26. The number of bits per sample transmitted in delta modulation is ________.
ANS:
1, one
27. Delta modulation requires a _______ sampling rate than PCM for the same
quality of reproduction.
ANS:
higher
28. _______ noise is produced by a delta modulator if the analog signal doesn't
change.
ANS:
Granular
29. In delta modulation, ________ overload can occur if the analog signal changes
too fast.
ANS:
slope
30. The ________ size varies in adaptive delta modulation.
ANS:
step
31. Adaptive delta modulation can transmit PCM-quality voice at about ________
the bit rate of PCM.
ANS:
half
32. Unipolar NRZ is not practical because most channels do not have ________
continuity.
ANS:
DC
33. In AMI, binary ones are represented by a voltage that alternates in ________.
ANS:
polarity
34. Long strings of _________ should be avoided in AMI.
ANS:
zeros
35. Manchester code has a level _________ in the center of each bit period.
ANS:
transition
36. Manchester coding provides _________ information regardless of the pattern of
ones and zeros.
ANS:
timing
37. There are _________ channels in a DS-1 frame.
ANS:
24
38. DS-1 uses a ________ bit to synchronize the transmitter and receiver.
ANS:
framing
39. In DS-1, each channel is sampled ______ times per second.
ANS:
8000
40. Data is carried over a T-1 line at a rate of _______ bits per second.
ANS:
1.544 × 106
41. A group of 12 DS-1 frames is called a _________.
ANS:
superframe
42. From a group of twelve frames, signaling bits are "stolen" from every ________
frame.
ANS:
sixth
43. ________ compression transmits all the data in the original signal but uses
fewer bits to do it.
ANS:
Lossless
SHORT ANSWER
1. Use Hartley's Law to find how much time it would take to send 100,000 bits over
a channel with a bandwidth of 2,000 hertz and a channel constant of k = 10.
ANS:
5 seconds
7. The telephone switching hierarchy is being replaced by a "flat" network topology.
T
8. A "twisted-pair" is twisted to minimize "crosstalk". T
9. The wires in a local loop are called TIP and GND. F
2. Use the Shannon-Hartley theorem to find the bandwidth required to send 12,000
bits per second if the number of levels transmitted is 8.
ANS:
2000 hertz
10. In a local loop, the red wire is positive. F
11. In a local loop, the TIP wire is positive. T
3.What is the Shannon Limit of a channel that has a bandwidth of 4000 hertz and a
signal-to-noise ratio of 15?
ANS:
16 kbps
12. Local loops can carry voice signals in only one direction at a time. F
13. Local loops carry DC current. T
4. What is the minimum required number of samples per second to digitize an
analog signal with frequency components ranging from 300 hertz to 3300 hertz?
ANS:
6600 samples/second
14. Local loops carry signaling information. T
15. Loading coils allow high-speed data loads to be carried on a local loop. F
5. What is the approximate dynamic range, in dB, of a linear PCM system that uses
12 bits per sample?
ANS:
74 dB
6. What is the approximate data rate for a system using 8 bits per sample and
running at 8000 samples per second?
ANS:
64 kbps
16. Typically, when a phone is on hook, a voltage of 48 volts appears across it. T
17. When a telephone is off hook, the DC voltage across it can drop substantially
from its on-hook value. T
18. The DC resistance of a telephone is about 2000 ohms. F
7. If bits were "stolen" from every DS-1 frame, what would the useable data-rate be
for each channel in the frame?
ANS:
56 kbps
8. Assuming maximum input and output voltages of 1 volt, what is the output
voltage of a -law compressor if the input voltage is 0.388 volt?
ANS:
0.833 volt
19. When a telephone is on hook, the DC current through it is in the range of 20 to
80 mA. F
20. Touch-Tone is a registered trademark of AT&T. T
21. DTMF is the same as Touch-Tone. T
22. DTMF uses sets of 3 tones. F
Chapter 8: The Telephone System
23. The technology to "dial" telephone numbers was invented in 1893. T
TRUE/FALSE
24. A crosspoint switch allows any incoming line to be connected to any outgoing
line. T
1. A telephone from 1930 could not work on today's public switched telephone
network. F
25. The central office uses 24 volts AC at 20 hertz to cause a telephone to ring. F
26. The local-loop is full-duplex. T
2. The public switched telephone network is changing from an all analog to a mostly
digital system. T
27. Telephones usually contain a hybrid coil or an equivalent circuit. T
3. A LATA is a local calling area. T
28. To allow for "sidetone", a hybrid coil should be slightly unbalanced. T
4. A feature of the public switched telephone system is that calls cannot be
"blocked". F
29. The signal levels in analog telephone systems have increased substantially over
the past 100 years. F
5. Telephones connect to the central office via trunk lines. F
30. The signal levels in modern analog telephone systems are still based on 19thcentury technology. T
6. Most local loops still use copper wire. T
31. To allow multiplexing, the bandwidth of voice-grade telephone signals is
deliberately restricted. T
32. The net gain of a telephone system must be greater than 0 dB for an acceptable
signal level. F
33. Too much gain in a telephone system causes "singing". T
34. Echo suppressors prevent oscillations on long-distance telephone circuits. T
35. Echo suppressors can be switched off by a subscriber's equipment. T
36. C-message weighting increases the bandwidth of a local loop. F
37. The reference level for measuring noise in a telephone system is 10–12 Watts. T
38. In a telephone system, signal strength is given relative to the zero transmission
loss point. T
2. PSTN stands for:
a. Public Switched Telephone Network
b. Private Switched Telephone Network
c. Primary Service Telephone Network
d. Primary Service Telephone Numbers
3. POTS stands for:
a. Private Office Telephone System
b. Primary Office Telephone Service
c. Primary Operational Test System
d. Plain Old Telephone Service
4. LATA stands for:
a. Local Access and Transport Area
b. Local Access Telephone Area
5. A LATA is a:
a. a local calling area
b. a type of digital local network
c. Local Area Telephone Access
d. Local Area Transport Access
c. a way of accessing a tandem office
d. a way of accessing a central office
39. TDM is being replaced by the newer FDM technology in telephone systems. F
40. DS-1 can be used to carry digital data that did not originate as a voice signal. T
41. When using DS-1 to carry data, it is common to use each channel to carry 64
kbps. F
42. Digital carriers up to T3 can use copper wires. F
43. A DS-1C signal carries twice as many channels as a DS-1 signal. T
44. A DS-1C signal uses twice the bit rate of a DS-1 signal. F
45. "Stuff" bits are used to compensate for differences in clock rates. T
46. Every "in-channel" signal is also an "in-band" signal. F
47. Common-channel signaling is being replaced by the more modern MF signaling.
F
48. Common-channel signaling reduces opportunities for stealing telephone service.
T
49. ADSL is faster than ISDN. T
50. B-ISDN is a slower version of standard ISDN. F
6. Central offices are connected by:
a. local loops
c. both a and b
b. trunk lines
d. none of the above
7. Local loops terminate at:
a. a tandem office
b. a toll station
c. a central office
d. an interexchange office
8. Call blocking:
a. cannot occur in the public telephone network
b. occurs on the local loop when there is an electrical power failure
c. occurs only on long-distance cables
d. occurs when the central office capacity is exceeded
9. In telephony, POP stands for:
a. Post Office Protocol
b. Point Of Presence
c. Power-On Protocol
d. none of the above
10. The cable used for local loops is mainly:
a. twisted-pair copper wire
b. shielded twisted-pair copper wire
c. coaxial cable
d. fiber-optic
11. FITL stands for:
a. Framing Information for Toll Loops
b. Fiber In the Toll Loop
c. Framing In The Loop
d. Fiber-In-The-Loop
MULTIPLE CHOICE
12. DC current flows through a telephone:
a. when it is on hook
c. as long as it is attached to a local loop
b. when it is off hook
d. only when it is ringing
1. DTMF stands for:
a. Digital Telephony Multiple Frequency
b. Dial Tone Master Frequency
c. Dual-Tone Multifrequency
d. Digital Trunk Master Frequency
13. The range of DC current that flows through a telephone is:
a. 20 µA to 80 µA
c. 2 mA to 8 mA
b. 200 µA to 800 µA
d. 20 mA to 80 mA
14. Loading coils were used to:
a. increase the speed of the local loop for digital data
b. reduce the attenuation of voice signals
c. reduce crosstalk
d. provide C-type conditioning to a local loop
15. The separation of control functions from signal switching is known as:
a. step-by-step switching control
c. common control
b. crossbar control
d. ESS
16. The typical voltage across a telephone when on-hook is:
a. 48 volts DC
c. 90 volts DC
b. 48 volts, 20 hertz AC
d. 90 volts, 20 hertz AC
17. The typical voltage needed to "ring" a telephone is:
a. 48 volts DC
c. 90 volts DC
b. 48 volts, 20 hertz AC
d. 90 volts, 20 hertz AC
18. The bandwidth of voice-grade signals on a telephone system is restricted in
order to:
a. allow lines to be "conditioned" c. allow signals to be multiplexed
b. prevent "singing"
d. all of the above
19. VNL stands for:
a. voltage net loss
b. volume net loss
c. via net loss
d. voice noise level
27. In DS-1, bits are "robbed" in order to:
a. provide synchronization
b. carry signaling
c. cancel echoes
d. check for errors
28. "Bit-stuffing" is more formally called:
a. compensation
b. rectification
c. justification
d. frame alignment
29. ISDN stands for:
a. Integrated Services Digital Network
b. Information Services Digital Network
c. Integrated Services Data Network
d. Information Systems Digital Network
30. Basic ISDN has not been widely adopted because:
a. it took to long to develop
b. it is too slow
c. it has been surpassed by newer technologies
d. all of the above
31. ADSL stands for:
a. All-Digital Subscriber Line
b. Asymmetrical Digital Subscriber Line
c. Allocated Digital Service Line
d. Access to Data Services Line
32. Compared to ISDN, internet access using ADSL is typically:
a. much faster
c. much more expensive
b. about the same speed
d. none of the above
20. Signal loss is designed into a telephone system to:
a. eliminate reflections
c. improve signal-to-noise ratio
b. prevent oscillation
d. reduce power consumption
COMPLETION
21. The reference noise level for telephony is:
a. 1 mW
b. 0 dBm
c. 1 pW
d. 0 dBr
1. A _________ is a local calling area.
ANS:
LATA
22. The number of voice channels in a basic FDM group is:
a. 6
b. 12
c. 24
d. 60
2. Central offices are connected together by _________ lines.
ANS:
trunk
3. One central office can be connected to another through a _________ office.
ANS:
tandem
23. Basic FDM groups can be combined into:
a. supergroups
c. jumbogroups
b. mastergroups
d. all of the above
24. In telephone system FDM, voice is put on a carrier using:
a. SSB
b. DSBSC
c. PDM
d. PCM
25. PABX stands for:
a. Power Amplification Before Transmission
b. Private Automatic Branch Exchange
c. Public Automated Branch Exchange
d. Public Access Branch Exchange
26. SLIC stands for:
a. Single-Line Interface Circuit
b. Standard Line Interface Card
c. Subscriber Line Interface Card
d. Standard Local Interface Circuit
4. With 7-digit phone numbers, _________ thousand telephones can connect to a
central office.
ANS:
ten
5. Call _________ is when it becomes impossible for a subscriber to place a call due
to an overload of lines being used.
ANS:
blocking
6. New _________ switching equipment uses TDM to combine signals.
ANS:
digital
7. Most local loops still use _________ copper wire.
ANS:
twisted-pair
8. As compared to a hierarchical network, a _________ network never needs more
than one intermediate switch.
ANS:
flat
9. _________ coils were used to reduce the attenuation of voice frequencies.
ANS:
Loading
10. In a twisted-pair telephone cable, the red wire is called _________
ANS:
ring
11. In a twisted-pair telephone cable, the green wire is called _________.
ANS:
tip
12. Of the red and green 'phone wires, the _________ wire is positive with respect
to the other.
ANS:
green
13. A telephone is said to have _________ the line when the central office sends it
dial tone.
ANS:
seized
14. The _________ functions are provided by a SLIC.
ANS:
BORSCHT
24. In FDM telephony, _________ bands separate the channels in a group.
ANS:
guard
25. Because of "bit robbing", a channel in a DS-1 frame allows only _________ kbps
when used to send digital data.
ANS:
56
26. A _________ is a group of 12 DS-1 frames with signaling information in the sixth
and twelfth frames.
ANS:
superframe
27. In DS-1C, _________ bits are used to compensate for differences between clock
rates.
ANS:
stuff
28. Busy and dial tone are referred to as _________signals because they use the
same pair of wires as the voice signal.
ANS:
in-channel
29. SS7 is the current version of _________ signaling.
ANS:
common-channel
30. SS7 is a _________-switched data network.
ANS:
packet
15. A _________ coil prevents loss of signal energy within a telephone while
allowing full-duplex operation over a single pair of wires.
ANS:
hybrid
31. In ISDN, the _________ channel is used for common-channel signaling.
ANS:
D
16. In a crosspoint switch, not all _________ can be in use at the same time.
ANS:
lines
32. In ISDN, the _________ channels are used for voice or data.
ANS:
B
17. The old carbon transmitters generated a relatively _________ signal voltage.
ANS:
large
33. Terminal equipment especially designed for ISDN is designated _________
equipment.
ANS:
TE1
18. The generic term for Touch-Tone® signaling is _________.
ANS:
DTMF
19. A ________ line provides more bandwidth than a standard line.
ANS:
conditioned
20. In the telephone system, amplifiers are called _________.
ANS:
repeaters
21. An echo _________ converts a long-distance line from full-duplex to half-duplex
operation.
ANS:
suppressor
22. _________ weighting is an attempt to adjust the noise or signal level to the
response of a typical telephone receiver.
ANS:
C-message
23. In FDM telephony, the modulation is usually _________.
ANS:
SSB, SSBSC
34. The A in ADSL stands for _________.
ANS:
asymmetrical
35. In ADSL, the speed from the network to the subscriber is _________ than the
speed in the opposite direction.
ANS:
greater, faster
SHORT ANSWER
1. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If
the loop current is 40 mA, what is the DC resistance of the local loop?
ANS:
1000 ohms
2. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If
the loop current is 40 mA, what is the DC resistance of the telephone?
ANS:
200 ohms
3. Which two DTMF tones correspond to the digit "1"? (Use the table in the text.)
ANS:
697 Hz and 1209 Hz
16. In synchronous transmission, control characters in the data require special
handling, but flag sequences in the data do not. F
4. Calculate the dB of VNL required for a channel with a 3 ms delay.
ANS:
1 dB
17. HDLC is very similar to SDLC. T
18. HDLC is a bit-oriented protocol. T
5. If a telephone voice signal has a level of 0 dBm, what is its level in dBrn?
ANS:
90 dBrn
6. A telephone test-tone has a level of 80 dBrn at a point where the level is +5dB
TLP. If C-weighting produces a 10-dB loss, what would the signal level be in dBrnc0?
ANS:
65 dBrnc TLP
19. When receiving digital data, it is possible to detect errors, but not to correct
them. F
20. In digital data transmission, bad frames are usually retransmitted. T
21. CRC codes are particularly good at detecting burst errors. T
22. Hamming codes allow errors to be corrected without requiring retransmission. T
Chapter 9: Data Transmission
23. All schemes to detect errors require adding extra bits to the data being
transmitted. T
TRUE/FALSE
24. Huffman codes are as good as CRC codes at detecting errors, but are faster. F
1. Data can be sent either in serial format or in parallel format. T
25. Run-length encoding is a data-compression technique. T
2. For practical reasons, virtually all data communications is done in serial format. T
26. A "cipher" is, essentially, a secret code. T
3. The first binary code was invented in 1914. F
4. A character code is the same as a data code. T
5. The old Baudot code is no longer used. F
27. Both "private-key" and "public-key" encryption always require the addition of
extra bits to the data. T
6. How fast data can be transferred is independent of the character code used. F
28. An advantage of public-key encryption is that it is not "computation-intensive",
meaning a computer doesn't have to do many numerical calculations to unencrypt
(decrypt) the data. F
7. Both synchronous and asynchronous transmission require bit timing. T
29. A "digital signature" does not require the use of encryption. F
8. There is no "framing" in asynchronous transmission. F
MULTIPLE CHOICE
9. A "mark" is the same as a binary 1. T
10. Digital modulation is sometimes called "keying". T
11. Due to the "bursty" nature of most channel noise, simple parity is more or less
useless. T
12. An advantage of using a UART is that "buffer overflow" cannot happen. F
13. Synchronous transmission is much more efficient than asynchronous
transmission. T
14. In synchronous transmission, the data stream is used to "lock" the receiver's
clock onto the transmitter's clock. T
15. Bit-oriented protocols are being replaced by the newer character-oriented
protocols. F
1. In practical terms, parallel data transmission is sent:
a. over short distances only
c. over any distance
b. usually over long distances
d. usually over a coaxial cable
2. The five-level teletype code was invented by:
a. the Morkum Company
b. the Teletype Company
3. Data codes are also called:
a. character codes
b. character sets
c. Western Union
d. Emile Baudot
c. they do not have any other name
d. both a and b
4. Digital data that is not being used to carry characters is called:
a. FIGS data
c. numerical data
b. binary data
d. all of the above
5. Character codes include:
a. alphanumeric characters
b. data link control characters
c. graphic control characters
d. all of the above
16. To maintain synchronization in synchronous transmission:
a. long strings of 1s and 0s must not be allowed
b. transmission must stop periodically for resynchronization
c. the clock circuits must be precisely adjusted
d. the channel must be noise-free
6. ASCII stands for:
a. American Standard Character-set 2
b. American Standard Code for Information Interchange
c. American Standard Code 2
d. Alphanumeric Standard Code for Information Interchange
17. HDLC:
a. is an IBM product
b. is a bit-oriented protocol
7. BS, FF, and CR are examples of:
a. nonstandard character codes
b. escape characters
18. The use of flags in SDLC requires:
a. "bit-stuffing"
b. different flags at either end of a frame
8. LF stands for:
a. Line Feed
b. Link Feed
c. control characters
d. none of the above
c. Line Forward
d. Link Forward
9. UART stands for:
a. Universal Asynchronous Receiver-Transmitter
b. Unidirectional Asynchronous Receiver-Transmitter
c. Unaltered Received Text
d. Universal Automatic Receiver for Text
10. In asynchronous transmission, the transmitter and receiver are:
a. frame-by-frame synchronized using the data bits
b. frame-by-frame synchronized using a common clock
c. frame-by-frame synchronized using the start and stop bits
d. not synchronized at all, hence the name "asynchronous"
11. In asynchronous transmission, the time between consecutive frames is:
a. equal to zero
c. equal to the start and stop bit-times
b. equal to one bit-time
d. not a set length
12. In synchronous transmission, the frames are:
a. about the same length as ten asynchronous frames
b. much longer than asynchronous frames
c. 128 bytes long
d. 1024 bytes long
13. Synchronous transmission is used because:
a. no start and stop bits means higher efficiency
b. it is cheaper than asynchronous since no UARTS are required
c. it is easier to implement than asynchronous
d. all of the above
14. In synchronous transmission, the receiver "syncs-up" with the transmitter by
using:
a. the clock bits
c. the CRC bits
b. the data bits
d. a separate clock line
15. BISYNC:
a. is an IBM product
b. is a character-oriented protocol
c. requires the use of DLE
d. all of the above
c. is identical to SDLC
d. all of the above
c. FEC
d. ARQ
19. The initials ARQ are used to designate:
a. automatic request for resynchronization
b. automatic request for retransmission
c. automatic receiver queue
d. automatic request for queue
20. ARQ is used to:
a. correct bit errors
b. correct synchronization problems
c. put data into a temporary buffer
d. none of the above
21. FEC stands for:
a. Fixed Error Control
b. Forward Error Control
c. Forward Error Correction
d. False Error Condition
22. VRC is another name for:
a. FEC
b. ARQ
c. LRC
23. CRC stands for:
a. Control Receiver Code
b. Correct Received Character
c. Cyclic Redundancy Check
d. Cycle Repeat Character
24. Huffman codes:
a. allow errors to be detected but not corrected
b. allow errors to be detected and corrected
c. allow alphanumeric data to be corrected
d. allow alphanumeric data to be compressed
25. Run-length encoding is used to:
a. encrypt data
c. correct data
b. compress data
d. none of the above
26. Public-key encryption:
a. allows the use of digital signatures
b. is used to convey symmetric keys
c. avoids the "password problem"
d. all of the above
d. parity
27. SDLC stands for:
a. Synchronous Data Link Control
b. Synchronous Data Line Control
28. HDLC is:
a. a bit-oriented protocol
b. based on SDLC
c. Synchronous Data Link Character
d. Synchronous Data Line Character
c. an ISO standard
d. all of the above
13. Clock sync is derived from the stream of _________ bits in synchronous
transmission.
ANS:
data
14. In the _________ protocol, each frame begins with at least two SYN characters.
ANS:
BISYNC
15. In HDLC, each frame starts with an 8-bit _________.
ANS:
flag
COMPLETION
1. Parallel transmission can be used only for _________ distances.
ANS:
short
2. The term "baud" was named after Emil _________.
ANS:
Baudot
3. Data codes are also called _________ codes.
ANS:
character
4. The _________ code is a 7-bit code commonly used in communication between
personal computers.
ANS:
ASCII
16. The first eight bits of an SDLC frame are _________.
ANS:
01111110
17. BCC stands for _________ check character.
ANS:
block
18. DLE stands for data link _________.
ANS:
escape
19. HDLC uses bit-_________ to prevent accidental flags.
ANS:
stuffing
20. _________ errors cause many consecutive bits to be bad.
ANS:
Burst
5. The two letters _________ designate the code character used to advance a
printer to the next page.
ANS:
FF
21. FEC stands for _________error correction.
ANS:
forward
6. An asynchronous frame begins with the _________ bit.
ANS:
start
22. An _________ scheme corrects errors by requiring the retransmission of bad
blocks.
ANS:
ARQ
7. An asynchronous frame ends with the _________bit.
ANS:
stop
8. At the end of an asynchronous frame, the line will be at the _________ level.
ANS:
mark, binary 1
9. An integrated circuit called a _________ is used in an asynchronous
communication system to convert between parallel and serial data.
ANS:
UART
10. When receiving digital data, _________ are used to hold data until they can be
read.
ANS:
buffers
11. Synchronous communication is more _________ than asynchronous since there
are fewer "overhead" bits.
ANS:
efficient
12. There must be sufficient 1-to-0 _________ to maintain synchronization in
synchronous transmission.
ANS:
transitions
23. Parity fails when an _________ number of bits are in error.
ANS:
even
24. CRC codes are particularly good at detecting _________ errors.
ANS:
burst
25. Huffman coding and run-length encoding are examples of data _________.
ANS:
compression
26. A _________ is an encoding scheme that is not public in order to protect data.
ANS:
cipher
27. A _________is often used to generate an encryption key because it is easier to
remember.
ANS:
password
28. If the key is _________ enough, private-key encryption can be quite secure.
ANS:
long
29. Messages cannot be _________ using a public key.
ANS:
decrypted
30. Because it is _________-intensive, public-key encryption can be slow.
ANS:
computation
9. Token passing can be implemented as a ring or as a bus. T
10. A token is used to control access to the network. T
SHORT ANSWER
11. A token is generated by a node wishing to access the network. F
1. How many different characters could be encoded using a six-bit code?
ANS:
64
12. On a bus network, all traffic shares a common channel. T
13. CSMA networks must deal with "contention". T
2. What is the numerical difference between ASCII 'a' and ASCII 'A' if you treat them
as hexadecimal (hex) numbers?
ANS:
20 hex (32 decimal)
3. The ASCII codes for the characters '0' through '9' are what hex numbers?
ANS:
30H to 39H
14. Token-passing networks must deal with "collisions" between two tokens. F
15. On a CSMA/CD network, several nodes can try to access the channel
simultaneously. T
16. A "collision" will take a CSMA network down. F
4. If an asynchronous frame is used to send ASCII characters in the form of bytes (8
bits), what is the shortest time it could take to send 1000 characters if each bit in a
frame is 1 msec long?
ANS:
10 seconds
5. Suppose an asynchronous frame holds 8 bits of data, a parity bit, and two stop
bits (it could happen). Calculate the efficiency of the communication system.
ANS:
66.7%
6. Suppose a synchronous frame has 16 bits of non-data in the front and a 16-bit
BCC at the end. The frame carries 1024 bytes of actual data. Calculate the efficiency
of the communication system.
ANS:
97.0%
17. Token rings never have collisions. T
18. CSMA works best when traffic is relatively light. T
19. A token-ring network can be implemented with a bus topology. T
20. A MAU will disconnect a defective node from a CSMA network. F
21. Token-ring networks usually operate at 100 megabits per second. F
22. Most LANs are based on the Ethernet type of network. T
23. Ethernet was originated by Microsoft with participation by Intel. F
24. IEEE 802.3 is a protocol based on Ethernet. T
Chapter 10: Local Area Networks
25. Ethernet-type networks are limited to a maximum speed of 100 Mbits per
second. F
TRUE/FALSE
26. Classic Ethernet is no longer used for new networks. T
1. The maximum extent of a local area network is one building. F
27. Originally, Ethernet used 10Base2 coaxial cable. F
2. An organization could have several local area networks in the same room. T
28. 100BaseT cable could be used in a new LAN installation. T
3. LANs can allow several people to access the same file at the same time. T
29. The "100" in 100BaseT designates the supported bit rate. T
4. LANs often use "dumb" terminals as workstations. F
30. The "Base" in 100BaseT indicates the cable carries an unmodulated signal. T
5. On a circuit-switched network, a data stream has a channel all to itself for the
duration of the connection. T
31. The "T" in 100BaseT indicates the cable is Thick coax. F
6. A "node" is a workstation or PC connected to a network. T
32. Ethernet uses CSMA/CD. T
7. In a star network, if one node fails, the entire network goes down. F
33. Ethernet type LANs use token passing. F
8. Hubs are, by definition, passive. F
34. In CSMA, a node must "listen" to the channel before trying to use it. T
35. 10BaseT cable usually uses RJ-45 connectors. T
36. 100BaseT cable requires a BNC connector. F
37. Ethernet cannot use fiber-optic cables. F
38. Packets on a CSMA/CD network must be equal to or longer than some minimum
size. T
39. On a CSMA/CD network, there will be fewer collisions if longer packets are used.
T
40. Longer packets means more bits must be retransmitted after a collision. T
41. On a CSMA/CD network, only one node actually needs to "hear" a collision. F
42. A NIC gives a unique address to a node on a network. T
43. If coax is used, the ends must be left open to avoid reflections. F
44. Typically, a NIC requires a 4-wire cable to connect to a hub. T
45. CAT-5 UTP is actually the same as ordinary twisted-pair telephone wire. F
46. Standard Manchester line encoding can be used up to 100 Mbits per second. F
2. The CD in CSMA/CD stands for:
a. Carrier Detection
b. Carrier Delay
c. Collision Detection
d. Collision Delay
3. The Internet is:
a. a network of networks
b. a very large client-server network
4. Most LANs:
a. are based on Ethernet
b. use CSMA/CD
c. a very large CSMA/CD network
d. not really a network at all
c. use UTP cable
d. all of the above
5. Dumb terminals are still used:
a. in token-passing networks
b. in networks requiring central monitoring
c. in networks that cannot provide central monitoring
d. none of the above
6. In a circuit-switched network:
a. communication is half-duplex only
b. each channel carries only one data stream
c. connection is usually done using a bus topology
d. all of the above
7. Each computer on a network is called a:
a. hub
b. token
c. node
d. circuit
47. If 10BaseT cabling is used in a multinode LAN, then a hub cannot be used. F
48. Compared to a hub, a switch reduces the chances for a collision. T
8. Compared to CSMA/CD systems, token-passing rings are:
a. slower
c. not as widely used
b. more expensive
d. all of the above
49. "Jabber" is failure mode for a NIC. T
50. "Stacking" is a failure mode for a hub. F
51. Network software is generally independent of the network topology. T
52. The same network software can be used on a token-passing network and on an
Ethernet LAN. T
53. To a user on the network, a hard drive on the server looks like it is on the
workstation. T
54. In a client-server network, each node takes a turn at being the server. F
9. The key feature of a star network is that individual workstations are connected
to:
a. a central ring
c. a node
b. a central bus
d. none of the above
10. On networks, long messages are divided into "chunks" called:
a. packets
c. carriers
b. nodes
d. tokens
11. When two or more PCs try to access a baseband network cable at the same
time, it is called:
a. a collision
c. excess traffic
b. contention
d. multiple access
55. Software that runs a client-server network must have true multitasking ability. T
12. When two PCs send data over a baseband network cable at the same time, it is
called:
a. a collision
c. excess traffic
b. contention
d. multiple access
MULTIPLE CHOICE
1. CSMA stands for:
a. Client-Server Multi-Access
b. Carrier Sense Multiple Access
c. Carrier Server Master Application
d. none of the above
13. One type of network that never has a collision is:
a. CSMA
c. token-passing
b. Ethernet
d. all networks have collisions
14. In an Ethernet-based network, a switch can be used to reduce the number of:
a. nodes
c. packets
b. users
d. collisions
15. The effect of too many collisions is:
a. the network goes down
b. the network slows down
c. the cable overheats
d. data is lost
16. MAU stands for:
a. Multistation Access Unit
b. Multiple Access Unit
c. Multiple Auxiliary Units
d. none of the above
17. The standard that describes Ethernet-type networks is:
a. EIA 232
c. IEEE 802.3
b. IEEE 488.1
d. CCITT ITU-E
18. Ethernet was invented by:
a. IBM
c. Xerox
b. INTEL
d. Digital Equipment Corporation
19. An Ethernet running at 10 Mbits / second uses:
a. Manchester encoding
c. NRZ encoding
b. Three-Level encoding
d. AMI encoding
20. A 100BaseT cable uses:
a. fiber-optic cable
b. twisted-pair copper wires
c. RG-58U coaxial cable
d. 50-ohm coaxial cable
26. UTP stands for:
a.Untwisted-Pair copper wire
b. Unshielded Twisted-Pair copper wire
c. Uninterruptible Terminal Packet
d. Unicode Text Packet
27. Compared to twisted-pair telephone cables, CAT-5 cables:
a. are cheaper
c. allow faster bit rates
b. are easier to crimp connectors onto
d. all of the above
28. A hub:
a. sends incoming packets out to all other terminals connected to it
b. sends incoming packets out to specific ports
c. cannot be used in an Ethernet-type network
d. are more common in token-passing networks
29. A switch:
a. sends incoming packets out to all other terminals connected to it
b. sends incoming packets out to specific ports
c. cannot be used in an Ethernet-type network
d. are more common in token-passing networks
30. An advantage of using a switch instead of a hub is:
a. it is cheaper when used in large networks
b. it is faster when used in large networks
c. it reduces the number of collisions in large networks
d. all of the above
21. The word "Base" in 10BaseT means:
a. the cable carries baseband signals
b. the cable has a base speed of 10 Mbps
c. it can be used as the base for a backbone cable system
d. none of the above
31. Broadband LANs:
a. modulate the data onto a carrier
b. use coaxial cables
c. are provided by cable TV companies for Internet access
d. all of the above
22. The reason a CSMA/CD network has a minimum length for packets is:
a. to increase the data rate
b. to prevent packets from reaching all other nodes during transmission
c. to make sure all other nodes hear a collision in progress
d. all of the above
32. Using one node in the network to hold all the application software is done in:
a. peer-to-peer networks
c. both a and b
b. client-server networks
d. none of the above
23. The reason a CSMA/CD network has a maximum length for cables is:
a. to increase the data rate
b. to prevent packets from reaching all other nodes during transmission
c. to make sure all other nodes hear a collision in progress
d. all of the above
24. NIC stands for:
a. Network Interface Card
b. Network Interface Cable
25. 10BaseT cable typically uses:
a. a BNC connector
b. a T connector
c. Network Interface Code
d. Network Internal Code
c. an RJ45 connector
d. an RS11 connector
33. Record locking is used to:
a. store records securely on a server
b. prevent multiple users from looking at a document simultaneously
c. prevent one user from reading a record that another user is writing to
d. none of the above
34. The software that runs a client-server network must be:
a. UNIX-based
c. multitasking
b. WINDOWS-based
d. Novell certified
35. A "thin" client is:
a. basically, a PC with no disk drives
b. a node that rarely sends data
c. same as a "dumb" terminal
d. all of the above
COMPLETION
1. A LAN is a _________ Area Network.
ANS:
Local
2. The Internet is a network of _________.
ANS:
networks
3. In a _________ network, all nodes are connected to a central computer.
ANS:
star
4. In a _________-switched network, users have a dedicated channel for the
duration of communications.
ANS:
circuit
17. A 100BaseTX cable is a_________cable.
ANS:
fiber-optic
18. Hubs can be _________ to form, in effect, one big hub.
ANS:
stacked
19. A switch looks at the _________ of each incoming packet.
ANS:
address
20. The effect of a switch is to greatly reduce _________
ANS:
contention
SHORT ANSWER
5. The _________ of a network describes how it is physically connected together.
ANS:
topology
6. Ring networks often use _________-passing.
ANS:
token
7. A _________ is a short section of a message in digital form.
ANS:
packet
8. _________ is when two nodes try to seize the same cable at the same time.
ANS:
Contention
9. A _________ occurs when two nodes transmit simultaneously on the same
baseband cable.
ANS:
collision
1. Explain how a network can be a physical bus but a logical ring.
ANS:
A token-passing network sends the token from node to node in a
prescribed order. So it doesn't matter how the physical connection is
made. It still works like a token-passing ring.
2. What is the key difference between a hub and a switch?
ANS:
A hub sends incoming packets out to all other ports on the hub. A switch
sends a packet to a specific port based on the address in the packet.
3. What is the advantage of a CSMA/CD network over a basic star network?
ANS:
If the central computer in a star network fails, the entire network is
inoperative. If a node fails in a CSMA/CD network, it can be disconnected
and the network still functions.
10. In CSMA/CD networks, all collisions must be _________.
ANS:
detected
4. Why do CSMA/CD packets have a minimum size limit?
ANS:
If a packet is too short, nodes at either end of a cable could get on, send a
packet, and get off before the packets travel far enough to collide. The
collision would not be detected.
11. Carrier-Sense means that a node "listens" for the cable to be _________ before
using it.
ANS:
quiet, free, unused, available
5. What is a NIC address, and why is it unique?
ANS:
12. A "_________" cable links clusters of computers together.
ANS:
backbone
The address is a long binary number "burned" into a NIC's memory chip
at the factory. Each factory uses a different sequence of numbers, so the
chances of two NICs on the same network having the same address is
extremely small.
13. 100BaseT cables can reliably carry up to _________ bits per second.
ANS:
100 mega
14. In CSMA/CD, packets must have a _________ length to ensure that collisions are
detected.
ANS:
minimum
Chapter 11: Wide-Area Networks and the Internet
TRUE/FALSE
15. In CSMA/CD, the _________ of a cable is limited to ensure that collisions are
detected.
ANS:
length
1. Leased lines are the least expensive way to connect a WAN. F
2. A WAN can be implemented using circuit switching. T
16. A unique numerical address is provided to a node by its _________.
ANS:
NIC
3. A WAN can be implemented using packet switching. T
4. A WAN can be implemented using analog lines. T
30. Most WANs are set up to work as extensions of the LANs they interconnect. T
5. A WAN can be implemented using digital lines. T
31. There are only two ways to set up a WAN. F
6. Packet switching uses the shortest route. F
32. The term "bridge" is another name for a repeater. F
7. With packet switching, you never get a "busy signal". T
33. Bridges must examine the address field of each packet they see. T
8. With packet switching, you always get a "real-time" connection. F
34. Bridges function at the data-link level. T
9. Packets may not arrive at the destination in the same order they were sent. T
35. Routers operate at the network level. T
10. Packets are often blocked by channels that are too full or are disconnected. F
36. TCP/IP predates ISO OSI. T
11. Packets received out of order is a failure mode in packet switching. F
37. TCP/IP contains additional levels beyond the seven described by ISO OSI. F
12. In digital communications, errors within frames are detected and corrected at
the data-link layer of a protocol stack. T
38. The task of IP is to get packets to their intended destination. F
39. IP is simple but very "robust". T
13. Protocols are the various pieces of hardware used to transmit and receive digital
data. F
40. A problem with IP is that packets can get stuck traveling the network in an
endless loop. F
14. The ISO OSI is a protocol. F
41. IP continues to function even if parts of the network are destroyed. T
15. The network layer sets up the path through the network. T
42. One task of TCP is to detect lost packets. T
16. X.25 is a protocol. T
43. One task of TCP is to reorder received packets into their correct sequence. T
17. An X.25 frame is similar to an HDLC frame. T
44. UDP is a more sophisticated version of TCP. F
18. Each frame contains a virtual circuit. F
19. Some packets only carry control bits. T
45. The Internet is a large network of other networks running the TCP/IP protocols.
T
20. X.25 gives reliable service even over relatively poor cables. T
46. The current 32-bit address scheme used on the Internet is highly efficient. F
21. Frame relay uses more error detection and correction than does X.25. F
47. A domain-name server stores the address of every computer attached to the
Internet. F
22. Frame relay requires better quality cables than does X.25. T
48. An intranet is essentially a private Internet. T
23. Frame relay is faster than X.25. T
24. Variable-length frames allow faster data rates than do fixed-length frames. F
MULTIPLE CHOICE
25. Frame relay allows for variable-length packets. T
1. MAN stands for:
a. Manchester Access Network
b. Multiple-Area Network
c. Metropolitan-Area Network
d. Multiple Access Network
2. Packet switching is based on:
a. store-and-forward
b. switched circuits
c. real-time delivery
d. all of the above
26. ATM is faster than frame relay. T
27. ATM uses relatively large fixed-length frames. F
28. ATM is designed to carry real-time information such as video. T
29. ATM is best suited to fiber-optic cables. T
3. The number of layers in ISO OSI is:
a. 3
b. 5
c. 7
d. 8
4. SNA stands for:
a. Standard Network Access
b. Small Network Access
c. Standard Network Architecture
d. Systems Network Architecture
5. The lowest-level layer in ISO OSI is called the:
a. physical layer
c. cable layer
b. link layer
d. transport layer
16. The "lifetime" of a packet in an IP network:
a. is essentially forever
b. depends on elapsed time since transmission
c. depends on number of "hops" between nodes
d. is approximately 200 milliseconds
6. Bad frames are usually detected by the:
a. frame layer
c. error-check layer
b. physical layer
d. link layer
17. HTTP stands for:
a. High-speed Transmission Test Procedure
b. High-Level Transfer Test Procedure
c. Hypertext Transmission and Transport Procedure
d. Hypertext Transport Protocol
7. A virtual circuit is set up by the:
a. user
c. network
b. link layer
d. frame
18. HTTP allows the use of:
a. dumb terminals
b. file transport
8. Frame Relay:
a. is faster than X.25
b. does less error checking than X.25
c. allows for variable length packets
d. all of the above
19. HTML stands for:
a. Hypertext Markup Language
c. Hypertext Transfer-Mode Layer
b. Hypertext Transfer-Mode Level d.High-speed Transfer-Mode Language
c. browsers
d. none of the above
9. ATM stands for:
a. Asynchronous Transfer Mode
b. Asynchronous Transmission Mode
c. Asynchronous Transmission Model
d. Automatic Test Mode
20. HTML allows:
a. telneting
b. high-speed file transfer
c. web page layout
d. all of the above
21. FTP stands for:
a. File Transfer Protocol
b. File Transport Protocol
c. File Test Procedure
d. Fast Transport Packet
10. A bridge:
a. separates a network into "collision domains"
b. looks at the address of each packet
c. operate at the data-link level
d. all of the above
22. FTP is used to:
a. transfer files between a server on the network and a user
b. test files to see if their data has been "corrupted"
c. transport packets at maximum speed through the network
d. none of the above
11. IP stands for:
a. Internet Process
b. Internet Protocol
23. SMTP stands for:
a. Short Message Transport Protocol
b. Simple Message Transport Protocol
c. Simple Mail Transport Protocol
d. Secondary Mail Transfer Procedure
c. Interconnect Protocol
d. Interconnect Procedure
12. TCP stands for:
a. Transmission Control Process
b. Transmission Control Protocol
13. Together, TCP/IP consists of:
a. 5 layers
b. 7 layers
c. Transfer Connection Protocol
d. none of the above
c. an application and a process
d. datagrams
14. IP is a:
a. connection-oriented protocol
b. virtual circuit
15. UDP stands for:
a. User Datagram Protocol
b. User Data Protocol
c. connectionless protocol
d. non-robust protocol
c. User Data Packet
d. Universal Data Packet
24. ISP stands for:
a. Internet Service Protocol
b. Internet Service Provider
c. Internet Service Procedure
d. none of the above
25. The standard Internet address (or URL) is:
a. a 32-bit binary number
b. four groups of base-ten numbers
c.running out of available values
d. all of the above
26. A DNS:
a. has become obsolete on the Internet
b. translates words to numbers
c. stores all domain addresses
d. describes the Internet address-naming procedure
27. DNS stands for:
a. Domain Name Server
b. Domain Name System
c. Domain Numbering System
d. Domain Naming System
28. An intranet connected to the Internet is often protected by:
a. a DNS
c. a "firewall"
b. a "brick wall"
d. the use of "spoofing" protocols
29. OSI stands for:
a. Open Systems Interconnection
b. Open Standard Interconnection
c. Open Systems Internet
d. none of the above
COMPLETION
1. A ________-Area Network would extend typically across a city.
ANS:
Metropolitan
2. A ________-Area Network could extend across a nation.
ANS:
Wide
3. A dedicated telephone line can be ________on a monthly basis.
ANS:
leased
4. The use of digital circuit-________ lines is cheaper than dedicated lines.
ANS:
switched
5. Packet switching is done on a store-and-________network.
ANS:
forward
6. A ________ is a hierarchy of procedures for implementing digital
communications.
ANS:
protocol
7. Voltage levels on a cable are specified at the ________ layer.
ANS:
physical
8. Bad frames are usually detected at the ________ layer.
ANS:
data-link
9. Setting up a path through the network is done by the ________ layer.
ANS:
network
10. The X.25 protocol was developed by the ________.
ANS:
CCITT
11. In X.25, the data-link layer is called the ________ layer.
ANS:
frame
12. In X.25, the network layer is called the ________ layer.
ANS:
packet
13. The physical route of a ________ circuit changes each time it is used.
ANS:
virtual
14. Frame Relay requires channels with low ________ rates.
ANS:
bit-error
15. Compared to X.25, Frame Relay does ________ error checking.
ANS:
less
16. All ATM frames contain just ________ bytes.
ANS:
53
17. Small frame size and a high-speed channel allow ________-time
communications.
ANS:
real
18. ________ simply regenerate and retransmit packets in a network.
ANS:
Repeaters
19. ________ look at the address inside a packet to decide whether or not to
retransmit it.
ANS:
Bridges
20. ________ decide the best network path on which to forward a packet.
ANS:
Routers
21. TCP/IP goes back to the ________ of the 1970s.
ANS:
ARPANET, DARPANET
22. Between ISO OSI and TCP/IP, ________was used first.
ANS:
TCP/IP
23. A ________ protocol does not track packets after they are sent.
ANS:
connectionless
24. HTTP allows the use of ________ that jump to other pages on the web.
ANS:
hyperlinks
25. The Internet "backbone" mostly uses high-speed ________ cables.
ANS:
fiber-optic
26. A ________translates words in an Internet address to numbers.
ANS:
DNS
27. Intranets usually connect to the Internet through a ________ for security.
ANS:
firewall
28. Voice over ________ is telephony done over the Internet.
ANS:
IP
29. "________" is another term for real-time transmission over the Internet.
ANS:
Streaming
30. Most people gain access to the Internet by subscribing to an ________.
ANS:
ISP
SHORT ANSWER
6. "Baud rate" is the same as bits per second. F
1. Name the three parts of an IP address as used on the Internet.
ANS:
Network number, Subnet number, Host number
2. Why is a logical channel called a "virtual" circuit?
ANS:
A logical channel is a way of keeping track of which two nodes on the
network have messages for each other. The actual physical path can
change while packets are being sent. Virtual means it behaves like direct
circuit between 'A' and 'B', but it is not a direct circuit.
3. Why is it faster to send packets of a fixed size compared to packets of variable
size?
ANS:
The processing required to store and forward packets of different lengths
is greater than that required for packets of a fixed length. More
processing implies more time per packet, which implies fewer packets
per second through the network.
7. A "mark" is a binary one. T
8. "Space" is another term for bandwidth. F
9. FSK is slow, but "robust". T
10. FSK makes efficient use of available bandwidth. F
11. FSK is used extensively in high-frequency radioteletype transmission. T
12. PSK is typically faster than FSK. T
13. "Dibit" is another term for PSK. F
14. PSK is typically DPSK. T
4. Why are the tasks involved in digital communications divided into layers in a
protocol stack? Why not just have one layer that does it all?
ANS:
Divide and conquer: it reduces complexity to a manageable job. One big
layer could not be adapted to newer media etc as easily as a system of
independent layers. Think of subroutines in a computer program.
15. QPSK is typically DQPSK. T
16. Digital amplitude modulation is called QAM. F
17. QAM uses PSK. T
5. What is a "hop"?
ANS:
Every time a packet is forwarded on to the next store-and-forward node
in the network, it is considered to be one "hop".
18. A "constellation diagram" shows the "symbols" used in QAM. T
19. CCITT is now ITU-T. T
6. What does it mean to say a packet has a lifetime measured in hops?
ANS:
Each packet contains a number representing the maximum number of
allowed hops. At each hop, this number is reduced by one. When it gets
to zero, the packet is deleted from the network.
7. Why should packets have a lifetime?
ANS:
If they didn't, then the number of "lost" packets traveling around the
network would continuously increase. At some point, there would be no
bandwidth left to carry real traffic.
20. Equalization compensates for phase and frequency distortions in a channel. T
21. Signal complexity compensates for low S/N during transmission. F
22. Receiver equalization requires a "training sequence" be sent at startup. T
23. 54 kbps is about the maximum speed you can get from a telephone line modem.
T
24. High-speed modems cannot do data compression. F
Chapter 12: Digital Modulation and Modems
25. High-speed modems cannot do error correction. F
26. MNP4 is an error-correction protocol. T
TRUE/FALSE
27. V.42 is a data-compression scheme. F
1. Little data communication is carried over voice-grade telephone lines. F
28. A computer is a DTE. T
2. The word "keying" is still used to denote digital modulation schemes. T
29. A MODEM is a DCE. T
3. ASK is rarely used for data communications. T
30. EIA-232D is the same as RS-232C. T
4. Information capacity is proportional to bandwidth. T
31. RS-232 describes a parallel port protocol. F
5. Information capacity is independent of noise. F
32. The response to RTS is DSR. F
33. RTS and CTS provide a "handshake" between a DTE and a DCE. T
34. +10 volts on an RS-232 control line is a HIGH or TRUE level. T
35. +12 volts on an RS-232 signal line is a binary ONE. F
36. A line is active when it is "asserted". T
37. "Smart" MODEMS are initialized with a string of "AT" commands. T
38. Twisted-pair telephone wire is not capable of more than about 4 kHz of
bandwidth. F
4. In the equation I = ktB, I is measured in:
a. amperes
c. bits
b. amperes per second
d. bits per second
5. In the equation C = 2Blog2M, M is the:
a. margin of noise
c. number of possible states per symbol
b. modulation index
d. maximum number of symbols per second
6. An "eye pattern" shows a good channel when:
a. the eye is maximally open
c. the eye is half open
b. the eye is maximally closed
d. the eye alternately opens and closes
7. What you see in an eye pattern is the effect of:
a. too many bits high
c. intermodulation distortion
b. too many bits low
d. intersymbol interference
39. DSL carries high-speed data over twisted-pair telephone wire. T
40. CATV cables only carry signals one way: from the head-end to the subscriber. F
41. Fiber-optic CATV cables carry analog signals. T
42. Typically, a NIC is required to interface a PC to a cable modem. T
43. A cable modem is always on. T
44. A DSL connection is always on. T
8. High-frequency radioteletype systems commonly use:
a. FSK
b. AFSK
c. PSK
d. QAM
9. Instead of a single bit, a QPSK symbol contains:
a. a byte
b. 4 bits
c. a dibit
d. a Q-bit
10. To reduce the need for linearity, π/4 DQPSK uses:
a. angles of 0, 90, 180, and 270 degrees
b. angles of 45, 135, 225, and 315 degrees
c. angles of π/4, 2π/4, 3π/4, and 4π/4
d. double phase-shift angles
45. A cable modem shares the channel with other users. T
46. A DSL connection shares the loop with other subscribers. F
47. ADSL Lite is faster than standard ADSL. F
11. For QAM, a "constellation diagram" shows:
a. location of symbols in "symbol space"
b. separation of symbols in "symbol space"
c. effects of noise on symbols
d. all of the above
48. ADSL Lite requires a splitter at the subscriber end. F
49. In practice, both ADSL Lite and a cable modem have comparable data rates. T
MULTIPLE CHOICE
12. For QAM, the two dimensions of its symbol space are:
a. amplitude and frequency
c. frequency and phase angle
b. amplitude and phase angle
d. I-bits and Q-bits
13. The specs of the old Bell type 103 modem were:
a. 300 bps, full-duplex, FSK
c. 1200 bps, full-duplex, FSK
b. 600 bps, full-duplex, FSK
d. 1200 bps, half-duplex, FSK
1. FSK stands for:
a. Full-Shift Keying
b. Frequency-Shift Keying
c. Full-Signal Keying
d. none of the above
2.PSK stands for:
a. Pulse-Signal Keying
b. Pulse-Shift Keying
c. Phase-Signal Keying
d. Phase-Shift Keying
3. QAM stands for:
a. Quadrature Amplitude Modulation
b. Quadrature Amplitude Masking
c. Quadrature Amplitude Marking
d. none of the above
14. ITU is an abbreviation for:
a. International Telephony Unit
b. International Telephony Union
c. International Telecommunications Union
d. International Telecommunications Units
15. High-speed modems equalize the line to compensate for:
a. noise and interference
b. uneven phase and frequency response
c. low SNR
d. inconsistent bit rates at either end of channel
16. The ITU is under the auspices of:
a. CCITT
b. the U.N.
c. IEEE
d. ANSI
17. The bits sent to allow equalization are called:
a. Gaussian bits
c. a training sequence
b. random bits
d. a random sequence
18. The V.90 standard is issued by:
a. the EIA
b. the TIA
c. the ITU
32. ADSL stands for:
a. Asynchronous DSL
b. Asymmetrical DSL
c. Analog DSL
d. All DSL
33. In a CATV system, HFC stands for:
a. Head Frequency Control
b. Hybrid Frequency Control
c. Hybrid Fiber-Coax
d. Hybrid Fiber Control
19. MNP2, MNP3, MNP4, and MNP10 are all:
a. data-compression schemes
b. error-correction protocols
c. both a and b
d. none of the above
34. In a CATV system, CMTS stands for:
a. Cable Modem Terminal Server
b. Cable Modem Transmission System
c. Cable Modem Terminal System
d. Cable Modem Transmission Server
20. MNP5 and V.42 bis are both:
a. data-compression schemes
b. error-correction protocols
c. both a and b
d. none of the above
35. A "splitter" at the subscriber end is not required for:
a. Any DSL scheme
c. ADSL Lite
b. ADSL
d. none of the above
21. In RS-232, flow control is done using:
a. RTS/CTS handshake
b. XON/XOFF characters
22. The official name for RS-232C is:
a. RS-232C
b. EIA-232D
23. In RS-232, a modem would be:
a. a DTR
b. a DSR
d. the ISO
COMPLETION
c. both a and b
d. none of the above
1. RTS means Request To _________.
ANS:
Send
c. ISO-232C/D
d. ANSI-232C
2. The response to RTS is _________.
ANS:
CTS
c. a DCE
24. In RS-232, a personal computer would be:
a. a DTR
b. a DSR
c. a DCE
25. On a DB-9 RS-232 connector, signal ground is pin:
a. 1
b. 3
c. 5
26. On a DB-25 RS-232 connector, signal ground is pin:
a. 1
b. 3
c. 5
d. a DTE
3. FSK stands for Frequency-Shift _________.
ANS:
Keying
d. a DTE
4. DSR stands for _________ Set Ready.
ANS:
Data
d. 7
5. QAM stands for _________ Amplitude Modulation.
ANS:
Quadrature
d. 7
27. The minimum lines required for RS-232 are:
a. TD and RD
c. TD, RD, DSR, and signal ground
b. TD, RD, and signal ground
d. TD, RD, RTS, CTS, and signal ground
6. The number of symbols per second is called the _________ rate.
ANS:
baud
7. The 2 bits of information in a QPSK symbol is called a _________.
ANS:
dibit
28. Hardware flow control uses:
a. XON and XOFF
b. TD and RD
c. RTS and CT
d. DSR and DCD
8. QPSK uses _________ different phase angles.
ANS:
four
29. Software flow control uses:
a. XON and XOFF
b. TD and RD
c. RTS and CT
d. DSR and DCD
9. DPSK stands for _________ PSK.
ANS:
Delta
30. Which voltage represents a binary zero on an RS-232 data pin:
a. +15 volts
b. +12 volts
c. +9 volts
d. all of the above
31. DSL stands for:
a. Data Signal Line
b. Digital Signal Line
c. Digital Subscriber Line
d. Double-Speed Loop
10. The QAM amplitude-phase combinations are shown with a _________ diagram.
ANS:
constellation
11. ITU stands for International _________ Union.
ANS:
Telecommunications
12. In QAM modems, _________ coding adds extra bits to improve performance on
a noisy line.
ANS:
Trellis
27. A DSLAM is a DSL Access _________.
ANS:
Multiplexer
13. _________ is used in a high-speed modem to compensate for uneven frequency
and phase response on a line.
ANS:
Equalization
SHORT ANSWER
14. The maximum allowed speed for a modem on a dial-up line is about _________
bps.
ANS:
54k
15. The nominal maximum speed on an RS-232 cable is _________ bps.
ANS:
20k
1. Calculate the bits per second capacity of a system sending 1000 symbols per
second with 16 possible states per symbol.
ANS:
4000
2. How many points will be on the constellation diagram of a QAM system using 8
phase angles and 2 amplitude levels?
ANS:
16
16. In RS-232, the _________line is asserted when the analog carrier from another
modem is being received.
ANS:
CD, DCD, RLSD
3. A CATV system has 100 cable-modem customers sharing a single channel with a
data rate of 36 Mbps. If half the modems are active at any given time, what bit rate
can a customer expect?
ANS:
720 kbps
17. Between hardware flow control and software flow control, _________ flow
control is preferred.
ANS:
hardware
4. A DMT system uses 4.3-kHz bins on a 1-MHz cable. Approximately how many bins
are there?
ANS:
230
18. A voltage higher than _________ volts should be considered a high on an RS232 receiver.
ANS:
3
5. Assuming a maximum symbol rate of 400 per second, how many possible states
must a symbol have to achieve a data rate of 1200 bps?
ANS:
8
19. A _________ modem cable is used to connect two DTEs via their serial ports.
ANS:
null
Chapter 13: Multiplexing and Multiple-Access Techniques
20. ADSL stands for _________ DSL.
ANS:
Asymmetrical
TRUE/FALSE
21. A typical CATV system is organized as a _________ network.
ANS:
tree
22. In a CATV system using cable modems, a _________ is used to put several
channels of data onto a fiber-optic backbone.
ANS:
CMTS
23. _________ is the process of synchronizing transmitted data from cable modems
to a CMTS.
ANS:
Ranging
24. _________ systems send high-speed data over a POTS line while sharing the line
with dial-up service.
ANS:
ADSL
25. The _________ version of ADSL does not require a splitter at the subscriber end.
ANS:
lite
1. Most communications systems require the sharing of channels. T
2. Multiple-access is the same as multiplexing. F
3. There are three basic ways to share media. T
4. In FDM, each transmission has a frequency band all to itself. T
5. TDM and FDM cannot be used simultaneously. F
6. FDM cannot be used on fiber-optic cables. F
7. DS-1 uses TDM. T
8. In one out of every six DS-1 frames, the LSBs are used for signaling. T
9. DS-3 is three times as fast as DS-1. F
26. _________ modulation divides the line bandwidth into many narrow bands
called tones or bins for ADSL.
ANS:
DMT
10. A "time switch" is used to increase or decrease the bit rate. F
11. A "space switch" is used to change the time slot of the samples on a bus. F
5. A DS-1 signal contains:
a. 12 channels
b. 24 channels
c. 32 channels
d. 64 channels
12. A space switch is used only with analog signals. F
13. The bus of a time switch is often called a "highway". T
14. Spread-spectrum is used on radio channels to overcome interference. T
6. The bit-rate of a DS-1 signal over a T-1 line is:
a. 64 kbps
b. 256 kbps
c. 1.536 Mbps
7. Besides data bits, a DS-1 frame contains a:
a. timing bit
b. T-bit
c. signaling bit
d. 1.544 Mbps
d. framing bit
15. A problem with spread-spectrum is that it is easily "blocked". F
16. With spread-spectrum, the signal-to-noise ratio can be less than one. T
17. Spread-spectrum is affected less by Rayleigh fading than standard RF
technology. T
18. "Frequency-hopping" is the only practical way to implement spread-spectrum. F
19. Direct-sequence spread-spectrum adds "pseudo-random" bits to the data bits. T
20. In direct-sequence spread-spectrum, the number of added bits cannot exceed
the number of data bits. F
21. Both frequency-hopping and direct-sequence require synchronization of
receiver to transmitter. T
22. CDMA uses spread-spectrum. T
23. With CDMA, all stations can be transmitting on the same band at the same time.
T
MULTIPLE CHOICE
1. TDMA stands for:
a. Time Domain Multiple Access
b. Time-Division Multiple Access
c. Tone Division Multiple Access
d. none of the above
2. CDMA stands for:
a. Code-Division Multiple Access
b. Carrier Division Multiple Access
c. Compact Digital Multiplex Arrangement
d. none of the above
3. TDMA is used instead of TDM when:
a. all the signals come from the same source
b. the signals come from different sources
c. TDM is used in RF communications
d. they mean the same thing
4. When calculating the maximum number of users, a limiting factor in FDM is:
a. the type of media used
c. the bandwidth of each signal
b. the length of the channel
d. all of the above
8. In DS-1, a bit is "stolen" out of each channel:
a. every frame
c. every sixth frame
b. every other frame
d. every twelfth frame
9. Moving signals from one line to another is called:
a. time switching
c. line switching
b. space switching
d. cross-point switching
10. Moving PCM samples from one time-slot to another is called:
a. time switching
c. signal switching
b. space switching
d. crosspoint switching
11. A digital space switch is a:
a. multiplexer
b. TDM switch
c. computerized Strowger switch
d. crosspoint switch
12. Spread-spectrum can be done by using:
a. computer-controlled frequency reuse
b. frequency-hopping
c. direct-sequence method
d. all of the above
13. The term "chip rate" is used in describing:
a. computer-controlled frequency reuse
b. frequency-hopping
c. direct-sequence method
d. all of the above
14. For a given data rate, direct-sequence systems, compared to standard RF
systems, use:
a. about the same bandwidth
c. much less bandwidth
b. much more bandwidth
d. approximately double the bandwidth
15. "Processing gain" is another term for:
a. RF gain
b. computer speed
c. spreading gain
d. improved signal-to-noise ratio
16. To calculate processing gain, divide the transmitted RF bandwidth by:
a. the digital data bit rate
c. the S/N ratio
b. bandwidth of original baseband
d. the chip size
17. A receiver for frequency-hopping spread-spectrum would be:
a. a narrowband receiver
c. a direct-conversion receiver
b. a wideband receiver
d. a CDMA receiver
18. A receiver for direct-sequence spread-spectrum would be:
a. a narrowband receiver
c. a direct-conversion receiver
b. a wideband receiver
d. a “chiprate” receiver
19. CDMA:
a. cannot be used with frequency-hopping spread-spectrum
b. cannot be used with direct-sequence spread-spectrum
c. cannot be used on an RF channel
d. allows many transmitters to use a band simultaneously
20. For optimal performance, CDMA requires the use of:
a. orthogonal PN sequences
c. true-random PN sequences
b. non-orthogonal PN sequences
d. none of the above
15. Moving PCM samples from one time slot to another is called _________
switching.
ANS:
time
16. The deep fades caused by signal-cancellation due to reflection are called
_________ fading.
ANS:
Rayleigh
17. A PN sequence is a _________-random noise sequence.
ANS:
pseudo
COMPLETION
1. Multiplexing allows many signals to _________ a channel.
ANS:
share
2. Three methods of multiple access are FDMA, TDMA, and _________.
ANS:
CDMA
3. In FDM, each signal uses part of the bandwidth _________ of the time.
ANS:
all
18. One method of spread-spectrum is frequency _________.
ANS:
hopping
19. It is _________ to jam a spread-spectrum signal.
ANS:
difficult
20. It is _________ to eavesdrop on a spread-spectrum signal.
ANS:
difficult
4. In TDM, each signal uses all of the bandwidth _________ of the time.
ANS:
part
21. The extra bits added to the data in direct-sequence spread-spectrum are called
_________.
ANS:
chips
5. Using CDMA on a radio channel, all signals can transmit _________ of the time.
ANS:
all
22. A chipping-rate of at least _________ times the bit rate of the data is common.
ANS:
ten
6. DS-1 is an example of _________-division multiplexing.
ANS:
time
23. The 'C' in CDMA stands for _________.
ANS:
code
7. The AM radio band is an example of _________-division multiplexing.
ANS:
frequency
24. In a frequency-hopping CDMA system, when no two transmitters use the same
frequency at the same time the PN sequences are said to be _________.
ANS:
orthogonal
8. A DS-1 frame contains one sample from each of _________ channels.
ANS:
24
SHORT ANSWER
9. T1 uses the _________line code.
ANS:
AMI
10. Each DS-1 frame contains a total of _________ bits.
ANS:
193
11. A DS-1 frame is transmitted at a rate of _________ bits per second.
ANS:
1.544 Meg
12. Each sample in a DS-1 frame contains _________ bits.
ANS:
8
13. A group of twelve DS-1 frames is called a _________.
ANS:
superframe
14. Switching signals from one line to another is called _________switching.
ANS:
space
1. What does Hartley's Law tell us about the relationship between time and
bandwidth for digital transmission?
ANS:
The more bandwidth, the less time it takes to send a given amount of
information. So the more bandwidth available, the higher the possible bit
rate.
2. How many signals could fit into 1 MHz of bandwidth if each signal required 100
kHz of bandwidth and the separation between adjacent channels was 10 kHz?
ANS:
9
3. Why is it difficult to jam a spread-spectrum signal?
ANS:
Jamming requires an interference signal of sufficient power in the same
part of the spectrum the information signal occupies. Because a spreadspectrum signal is, by definition, spread out over a very wide bandwidth,
jamming can interfere with only a small fraction of the total signal.
4. Why is it difficult to eavesdrop on a spread-spectrum signal?
ANS:
In a spread-spectrum transmission, the signal power at any given
frequency in its band is so low that it is virtually indistinguishable from
noise. An eavesdropper would not know a signal was being sent. And
without knowing the exact sequence being used, it is virtually impossible
to "de-spread" the signal.
5. Why is autocorrelation used to receive direct-sequence spread-spectrum signals?
ANS:
Autocorrelation allows a signal to be "pulled out of" the noise even when
the signal-to-noise ratio is less than one, as it is in spread-spectrum.
6. What is meant by "orthogonal sequences" in CDMA?
ANS:
During transmission, the PN sequences determine which parts of the
available bandwidth the spread-spectrum signal will occupy. Assume you
have two PN sequences: PN1 and PN2. At some point in time, suppose
PN1 would cause a transmission to occupy frequencies f11, f12, f13, and
so forth. Now suppose PN2 would cause the transmission to occupy
frequencies f21, f22, f23, and so forth. If the two sets of frequencies, (f11,
f12, f13, ...) and (f21, f22, f23, ...), have no frequencies in common, then
the two PN sequences are said to be orthogonal.
12. For coaxial cables, there are only a few standard values in common use. T
13. RF signals travel slower on a transmission line than they would through free
space. T
14. Energy can "reflect" from a load at the end of a cable and travel back to the
source. T
15. A "mismatched" line will cause reflections. T
16. The typical load on a cable, such as an antenna, has the same value at any
frequency. F
17. A mismatched line between a transmitter and an antenna could actually
damage the transmitter. T
18. A matched transmission line will exhibit "standing" waves. F
19. The optimum value for SWR is one. T
20. "Ghost" images on a cable TV indicate an impedance mismatch. T
Chapter 14: Transmission Lines
21 If a cable is shorter than 1/16 of the signal's wavelength, it does not really
behave as a transmission line. T
22. Shorted stubs radiate more energy than open stubs do. F
TRUE/FALSE
23. It is often better to measure SWR at the load rather than the source. T
1. A transmission line is a metallic cable. T
2. Coaxial cables are referred to as "unbalanced". T
3. "Balanced" means that both conductors are the same size. F
24. The only limit to the power that a transmission line can carry is the heat from
I2R losses. F
25. A length of transmission line can be used to match impedances at very high
frequencies. T
4. Twisted-pair telephone wire is a kind of transmission line. T
5. Cable resistance does not depend on frequency. F
26. A circular graph called a "Jones" chart is commonly used to analyze transmission
lines. F
6. Losses occur in the plastic dielectric of a transmission line. T
27. There is no practical way to connect a balanced line to an unbalanced line. F
7. Basically, a transmission line looks like an inductor in series with a small resistor.
F
28. A 1/4 wavelength transmission line can be used as a transformer. T
29. When used, stubs are usually inserted in series with a transmission line. F
8. Distributed parameters (inductance and capacitance) are characteristic of
transmission lines. T
30. Slotted-lines are only useful at lower frequencies. F
9. Transmission lines are often considered to be "lossless" at higher frequencies. T
MULTIPLE CHOICE
10. The characteristic impedance of a cable depends mostly on the resistance of the
wires. F
11. The value of the load at the end of a transmission line must be equal to or less
than Z0. F
1. SWR stands for:
a. Shorted Wave Radiation
b. Sine Wave Response
c. Shorted Wire Region
d. none of the above
2. TDR stands for:
a. Total Distance of Reflection
b. Time-Domain Reflectometer
c. Time-Domain Response
d. Transmission Delay Ratio
3. An example of an unbalanced line is:
a. a coaxial cable
b. 300-ohm twin-lead TV cable
c. an open-wire-line cable
d. all of the above
4. When analyzing a transmission line, its inductance and capacitance are
considered to be:
a. lumped
c. equal reactances
b. distributed
d. ideal elements
5. As frequency increases, the resistance of a wire:
a. increases
c. stays the same
b. decreases
d. changes periodically
6. The effect of frequency on the resistance of a wire is called:
c. the skin effect
a. I2R loss
b. the Ohmic effect
d. there is no such effect
7. As frequency increases, the loss in a cable's dielectric:
a. increases
c. stays the same
b. decreases
d. there is no loss in a dielectric
8. The characteristic impedance of a cable depends on:
a. the resistance per foot of the wire used
b. the resistance per foot and the inductance per foot
c. the resistance per foot and the capacitance per foot
d. the inductance per foot and the capacitance per foot
9. For best matching, the load on a cable should be:
c. equal to Z0
a. lower than Z0
b. higher than Z0
d. 50 ohms
10. The characteristic impedance of a cable:
a. increases with length
b. increases with frequency
c. increases with voltage
d. none of the above
11. The velocity factor of a cable depends mostly on:
a. the wire resistance
c. the inductance per foot
b. the dielectric constant
d. all of the above
12. A positive voltage pulse sent down a transmission line terminated in a shortcircuit:
a. would reflect as a positive pulse
b. would reflect as a negative pulse
c. would reflect as a positive pulse followed by a negative pulse
d. would not reflect at all
13. The optimum value for SWR is:
a. zero
c. as large as possible
b. one
d. there is no optimum value
14. A positive voltage pulse sent down a transmission line terminated with its
characteristic impedance:
a. would reflect as a positive pulse
b. would reflect as a negative pulse
c. would reflect as a positive pulse followed by a negative pulse
d. would not reflect at all
15. A positive voltage-pulse sent down a transmission line terminated in an opencircuit:
a. would reflect as a positive pulse
b. would reflect as a negative pulse
c. would reflect as a positive pulse followed by a negative pulse
d. would not reflect at all
16. A non-optimum value for SWR will cause:
a. standing waves
c. higher voltage peaks on cable
b. loss of power to load
d. all of the above
17. VSWR stands for:
a. variable SWR
b. vacuum SWR
c. voltage SWR
d. none of the above
18. The impedance "looking into" a matched line:
a. is infinite
c. is the characteristic impedance
b. is zero
d. 50 ohms
19. A Smith Chart is used to calculate:
a. transmission line impedances
b. propagation velocity
c. optimum length of a transmission line
d. transmission line losses
20. Compared to a 300-ohm line, the loss of a 50-ohm cable carrying the same
power:
a. would be less
c. would be the same
b. would be more
d. cannot be compared
21. A balanced load can be connected to an unbalanced cable:
a. directly
c. by using a "balun"
b. by using a filter
d. cannot be connected
22. On a Smith Chart, you "normalize" the impedance by:
a. assuming it to be zero
c. multiplying it by 2π
b. dividing it by 2π
d. dividing it by Z0
23. The radius of the circle you draw on a Smith Chart represents:
a. the voltage
c. the impedance
b. the current
d. none of the above
24. The center of the Smith Chart always represents:
a. zero
c. the characteristic impedance
b. one
d. none of the above
25. A TDR is commonly used to:
a. measure the characteristic impedance of a cable
b. find the position of a defect in a cable
c. replace a slotted-line
d. all of the above
COMPLETION
1. A cable that lacks symmetry with respect to ground is called ________.
ANS:
unbalanced
2. Parallel lines are usually operated as ________ lines since both wires are
symmetrical with respect to ground.
ANS:
balanced
3. Normally, a transmission line is terminated with a load equal to its ________
impedance.
ANS:
characteristic
4. Twisted-pair cables are transmission lines for relatively ________ frequencies.
ANS:
low
5. To analyze a transmission line, it is necessary to use ________ parameters
instead of lumped ones.
ANS:
distributed
6. The increase of a wire's resistance with frequency is called the ________ effect.
ANS:
skin
7. The increase of a wire's resistance with frequency is caused by the ________ field
inside the wire.
ANS:
magnetic
8. Dielectrics become more ________ as the frequency increases.
ANS:
lossy
14. SWR stands for ________-wave ratio.
ANS:
standing
15. The ideal value for SWR is ________.
ANS:
one
16. Transmission line impedances can be found using a ________ chart.
ANS:
Smith
17. Short transmission-line sections called ________ can be used as capacitors or
inductors.
ANS:
stubs
18. Any cable that radiates energy can also ________ energy.
ANS:
absorb
19. A ________-dB loss in a cable means only half the power sent reaches the load.
ANS:
3
20. It is often best to measure SWR at the ________ end of a cable.
ANS:
load
21. Besides heat from I2R, the power a cable can carry is limited by the ________
voltage of its dielectric.
ANS:
breakdown
22. To normalize an impedance on a Smith Chart, you divide it by ________.
ANS:
Z0
23.The ________ of a Smith Chart always represents the characteristic impedance.
ANS:
center
24. A ________ wavelength transmission line can be used a transformer.
ANS:
one-quarter
25. A slotted line is used to make measurements in the ________ domain.
ANS:
frequency
9. The inductance and capacitance of a cable are given per unit ________.
ANS:
length
SHORT ANSWER
10. Characteristic impedance is sometimes called ________ impedance.
ANS:
surge
11. A cable that is terminated in its characteristic impedance is called a ________
line.
ANS:
matched
12. A pulse sent down a cable terminated in a short-circuit will reflect with the
________ polarity.
ANS:
opposite
13. The apparently stationary pattern of waves on a mismatched cable is called a
________ wave.
ANS:
standing
1. A transmission line has 2.5 pF of capacitance per foot and 100 nH of inductance
per foot. Calculate its characteristic impedance.
ANS:
Z0 = 200 ohms
2. Two wires with air as a dielectric are one inch apart. The diameter of the wire is
.04 inch. Calculate, approximately, its characteristic impedance.
ANS:
386 ohms
3. If a coaxial cable uses plastic insulation with a dielectric constant ∈r = 2.6 , what
is the velocity factor for the cable?
ANS:
0.62
4. If a cable has a velocity factor of 0.8, how long would it take a signal to travel
3000 kilometers along the cable?
ANS:
12.5 ms
5. If a cable has a velocity factor of 0.8, what length of cable is required for a 90°
phase shift at 100 MHz?
ANS:
0.6 meters
6. A cable has a VSWR of 10. If the minimum voltage along the cable is 20 volts,
what is the maximum voltage along the cable?
ANS:
200 volts
10. Radio waves, like all other waves, must travel through some sort of medium. F
11. An isotropic radiator radiates in one direction only. F
12. A "point source" would be an isotropic radiator. T
13. The wavefront of a point source radiator would be a sphere. T
14. Beyond some distance from the source, we can approximate a wavefront by
assuming it is flat. T
15. The polarization of a plane wave is the direction of its magnetic field. F
7. A lossless line has a characteristic impedance of 50 ohms, but is terminated with
a 75-ohm resistive load. What SWR do you expect to measure?
ANS:
1.5
8. If a cable has an SWR of 1.5, what will be the absolute value of its voltage
coefficient of reflection?
ANS:
0.2
9. A generator matched to a line with a voltage coefficient of reflection equal to 0.2
transmits 100 watts into the line. How much power is actually absorbed by the
load?
ANS:
96 watts
10. Using a Smith Chart to analyze a 50-ohm cable, what would be the normalized
value of an impedance equal to 200 + j50 ohms?
ANS:
4 + j1
16. Polarization is either vertical or horizontal. F
17. For best results, the transmitting and receiving antennas should have opposite
polarizations. F
18. As radio waves travel outward, they are effectively attenuated by the
"spreading out" of the wavefront. T
19. A power density of 100 × 10-9 W/m2 would be a strong radio signal. T
20. An antenna is a passive device. T
21. An antenna can have a gain specification greater than one. T
22. The power absorbed by a receiving antenna depends on its shape, not its size. F
23. Reflection of plane waves off a smooth surface is called "specular" reflection. T
Chapter 15: Radio-Wave Propagation
24. Radio waves can be reflected, but not diffracted. F
25. Space waves work on a "line-of-sight" basis. T
TRUE/FALSE
26. Ground waves can follow the curvature of the earth to travel over the horizon. T
1. James Clerk Maxwell predicted radio waves in 1865 based on a set of equations
he derived. T
2. Marconi demonstrated the existence of radio-waves in 1887. F
27. Ground waves are not reliable because they are affected by bad weather. F
28. Because of refraction in ionized layers of air, sky waves appear to "bounce" off
the sky and come back down to earth far from the source. T
3. Electromagnetic radiation is in the form of TEM waves. T
29. Because of diffraction, radio waves can sometimes "bend" around a corner. T
4. Electromagnetic radiation is in the form of particles called photons. T
30. At gigahertz frequencies, radio waves are absorbed by the ionosphere. F
5. X rays are not electromagnetic radiation. F
6. Gamma rays are not electromagnetic radiation. F
7. Radio waves are electromagnetic radiation. T
31. Transmission of high-frequency (HF) radio waves is affected by "spots" on the
surface of the sun. T
32. It's possible for a radio signal to be detected 1000 miles from the transmitter
but not detected 500 miles from the transmitter. T
8. Like light rays, Radio waves can be reflected. T
33. There is no effective way to compensate for fading. F
9. Free, empty space has a characteristic impedance of 377 ohms. T
34. Communication by "bouncing" radio signals off the ionization trails of meteors is
routinely done by some organizations. T
MULTIPLE CHOICE
1. Radio waves were first predicted mathematically by:
a. Armstrong
b. Hertz
c. Maxwell
d. Marconi
2. Radio waves were first demonstrated experimentally by:
a. Armstrong
b. Hertz
c. Maxwell
d. Marconi
3. The technology that made cell phones practical was:
a. the microprocessor chip
c. high-power microwave transmitters
b. the miniature cell-site
d. all of the above
4. Cell phones reduce much of the problems of mobile communications with:
a. high power levels
c. reuse of frequencies
b. high antennas
d. all of the above
5. Which of the following are electromagnetic:
a. radio waves
c. gamma waves
b. light
d. all of the above
6. The electric and magnetic fields of a radio wave are:
a. perpendicular to each other
b. perpendicular to the direction of travel
c. both a and b
d. none of the above
7. TEM stands for:
a. Transverse Electromagnetic
b. Transmitted Electromagnetic
c. True Electromagnetic
d. none of the above
8. In free space, radio waves travel at a speed of:
a. 3 × 106 meters per second
b. 300 × 106 meters per second
c. 3 × 10 miles per second
d. 300 × 106 miles per second
6
9. Which is a possible polarization for an electromagnetic wave:
a. vertical
b. horizontal
c. circular
d. all of the above
10. Which polarization can be reasonably well received by a circularly polarized
antenna:
a. vertical
b. horizontal
c. circular
d. all of the above
11. The number of circular polarization modes (directions) is:
a. 1
b. 2
c. 3
d. many
12. An antenna has "gain" as compared to:
a. an isotropic radiator
b. a vertically polarized radiator
13. Ground waves are most effective:
a. below about 2 MHz
b. above about 20 MHz
c. a ground-wave antenna
d. none of the above
c. at microwave frequencies
d. when using horizontally polarized waves
14. EIRP stands for:
a. the E and I fields of the Radiated Power
b. the Effective Isotropic Radiated Power
c. the Effective Internal Reflected Power
d. the Electric-field Intensity of the Radiated Power
15. The "attenuation of free space" is due to:
a. losses in the characteristic impedance of free space
b. losses due to absorption in the upper atmosphere
c. the decrease in energy per square meter due to expansion of the
wavefront
d. the decrease in energy per square meter due to absorption of the
wavefront
16. Radio waves would most strongly reflect off:
a. a flat insulating surface of the right size
b. a flat dielectric surface of the right size
c. a flat metallic surface of the right size
d. a flat body of water
17. Radio waves sometimes "bend" around a corner because of:
a. reflection
b. diffusion
c. refraction
d. diffraction
18. Space waves are:
a. line-of-sight
b. reflected off the ionosphere
c. same as sky waves
d. radio waves used for satellite communications
19. Sky waves:
a. are line-of-sight
b. "bounce" off the ionosphere
c. are same as space waves
d. are radio waves used for satellite communications
20. Sky waves cannot be "heard":
a. close to the transmitter
b. far from the transmitter
c. in the "silent" zone
d. in the "skip" zone
21. A 20-dB reduction in the strength of a radio wave due to reflection is called:
a. fading
c. frequency diversity
b. diffraction
d. spatial diversity
22. "Ghosts" on a TV screen are an example of:
a. fading
c. multipath distortion
b. diffraction
d. cancellation due to reflection
23. A "repeater" is used to:
a. send a message multiple times over a channel
b. send a message over multiple channels at the same time
c. extend the range of a radio communications system
d. cancel the effects of fading
24. Cellular phone systems rely on:
a. high power
c. the radio horizon
b. repeaters
d. the reuse of frequencies
25. If the number of cell-phone users within a cell increases above some limit:
a. the cell area is increased
c. the power levels are increased
b. the cell area is split
d. the number of channels is reduced
26. As a cell-phone user passes from one cell to another:
a. a "handoff" process occurs
c. both cells will handle the call
b. a "sectoring" process occurs
d. nothing occurs
27. To receive several data streams at once, a CDMA spread-spectrum system uses:
a. a "funnel" receiver
c. multiple receivers
b. a "rake" receiver
d. none of the above
28. The troposphere is the:
a. highest layer of the atmosphere
b. middle layer of the atmosphere
c. lowest layer of the atmosphere
d. the most ionized layer of the atmosphere
29. Meteor-trail propagation is:
a. used for radio telephony
b. used to send data by radio
9. The wavefront of a point source would have the shape of a ________
ANS:
sphere
10. At a far distance from the source, a radio wavefront looks like a flat ________wave.
ANS:
plane
11. The polarization of a radio wave is the direction of its ________ field.
ANS:
electric
12. The electric field of a radio wave is ________ to its magnetic field.
ANS:
perpendicular
13. Both the electric and magnetic fields of a radio wave are ________ to its
propagation direction.
ANS:
perpendicular
14. With ________ polarization, the direction of a radio wave's electric field rotates
as it travels through space.
ANS:
circular
c. also called "ducting"
d. not possible
15. An antenna is said to have ________ in a certain direction if it radiates more
power in that direction than in other directions.
ANS:
gain
COMPLETION
16. The watts per square meter of a radio wave ________ as the wave-front moves
through space.
ANS:
decrease
1. Radio waves were mathematically predicted by ________.
ANS:
Maxwell
17. Reflection of plane-waves from a smooth surface is called ________ reflection.
ANS:
specular
2. Radio waves were first demonstrated by ________.
ANS:
Hertz
18. ________ is the "bending" of radio waves as they travel across the boundary
between two different dielectrics.
ANS:
Refraction
3. Radio waves are ________ electromagnetic waves.
ANS:
transverse
4. The propagation speed of radio waves in free space is ________ m/sec.
ANS:
300 × 106
5. Electromagnetic radiation can be thought of as a stream of particles called
________.
ANS:
photons
6. Unlike sound or water waves, radio waves do not need a ________ to travel
through.
ANS:
medium
7. The dielectric strength of clean dry air is about ________ volts per meter.
ANS:
3 × 106
8. Waves from an ________source radiate equally in all directions.
ANS:
isotropic
19. The process of ________ makes radio waves appear to "bend around a corner".
ANS:
diffraction
20. ________waves travel from transmitter to receiver in a "line-of-sight" fashion.
ANS:
Space
21.________ waves are vertically polarized radio waves that travel along the earth's
surface.
ANS:
Ground
22. ________ waves are radio waves that "bounce off" the ionosphere due to
refraction.
ANS:
Sky
23. The "fast fading" seen in mobile communications is caused by ________ waves
interfering with direct waves.
ANS:
reflected
24. The ________ zone is a region where sky waves cannot be received.
ANS:
skip
Chapter 16: Antenna
25. "Ghosts" on a TV screen are an example of ________ distortion.
ANS:
multipath
TRUE/FALSE
1. Antennas are considered to be active devices. F
26. Cell phones typically operate at a ________ power level.
ANS:
low
27. The ________ of frequencies allows many cell-phone users to share a
geographical area.
ANS:
reuse
28. ________ is when a cell-site uses three directional antennas, each covering a
third of the cell area, to reduce interference.
ANS:
Sectoring
2. Any antenna can transmit a signal as well as receive one. T
3. A half-wave dipole is an isotropic radiator. F
4. The "gain" of an antenna is often given as its performance relative to a half-wave
dipole. T
5. A half-wave dipole is sometimes called a "Hertz" antenna. T
6. A "Hertzian Dipole" is a theoretical concept and not a real antenna. T
29. The use of ________ chips makes cell phones a practical technology.
ANS:
microprocessor
7. A half-wave dipole is actually 5% longer than half a wavelength. F
8. A half-wave dipole radiates uniformly in all directions. F
SHORT ANSWER
1. A certain dielectric has permittivity of 6. 3 × 10–10 F/m and the same permeability
as free space. What is the characteristic impedance of that dielectric?
ANS:
45 ohms
2. If a point source of radio waves transmits 1 watt, what is the power density
10,000 meters from the source?
ANS:
796 pW/ m2
3. What power must a point-source of radio waves transmit so that the power
density at 3000 meters from the source is 1 µW/ m2?
ANS:
113 watts
4. If a radio receiver needs 1 nW/ m2 of power density to function, how far away
from a 1-watt point source will it continue to work?
ANS:
8.9 km
9. The horizontal radiation pattern of a half-wave dipole is symmetrical front and
back. T
10. Compared to a point-source radiator, a half-wave dipole has gain. T
11. A half-wave dipole does not have directivity. F
12. In general, the near-field radiation pattern of an antenna is not the same as its
far-field radiation pattern. T
13. The front-to-back ratio of a dipole is 0 dB. T
14. Antenna gain given in dBd is gain relative to a half-wave dipole. T
15. The input impedance of an antenna at resonance is infinity. F
16. A center-fed dipole antenna is a balanced load. T
5. A line-of-sight radio link over flat terrain needs to use antenna towers 50 km
apart. What, approximately, is the minimum height for the towers assuming all the
towers are the same?
ANS:
37 meters
17. The input impedance of a center-fed dipole increases as the separation between
the cable connections is increased. T
18. The polarization of a dipole antenna is always horizontal. F
6. A mobile radio is being used at 1 GHz in an urban environment with lots of
reflecting structures. If the car is traveling 36 km/hour, what is the expected time
between fades?
ANS:
15 msec
19. A folded dipole has a wider bandwidth than a simple dipole. T
20. A folded dipole has a higher input impedance than a simple dipole. T
21. There is actually no such thing as a "monopole" antenna. F
22. Vertical antennas typically need a ground plane. T
23. The earth itself can be a ground plane. T
24. The sheet-metal body of a car can be a ground plane. T
25. A helical antenna cannot receive vertically polarized radio waves. F
26. A helical antenna cannot receive horizontally polarized radio waves. F
27. A typical helical antenna can receive either clockwise or counterclockwise
circularly polarized waves, but not both. T
28. An antenna must be resonant at the frequency it is transmitting or receiving. F
29. A nonresonant antenna can cause a high SWR in the transmission line
connected to it. T
30. Any antenna will transmit radio waves as long as an RF current is flowing in it. T
31. A "loading coil" is used to make an antenna appear longer to a signal than its
physical length. T
32. Antennas cannot be made to appear shorter to a signal than their actual
physical length. F
33. A phased array is a driven array. T
34. A Yagi array is a "parasitic" array. T
2. A half-wave dipole is sometimes called:
a. a Marconi antenna
b. a Hertz antenna
c. a Yagi antenna
d. none of the above
3. The end-to-end length of a half-wave dipole antenna is actually:
a. one wavelength
c. slightly longer than a half-wavelength
b. one half-wavelength
d. slightly shorter than a half-wavelength
4. The radiation of energy from an antenna can be seen in the:
a. standing wave pattern around the antenna
b. SWR along the feed cable
c. radiation resistance of the antenna
d. I2R loss of the antenna
5. Measured on the ground, the field strength of a horizontally polarized half-wave
dipole antenna is strongest:
a. in one direction
c. in all directions
b. in two directions
d. depends on the number of elements
6. The ability of an antenna to radiate more energy in one direction than in other
directions is called:
a. directivity
c. active antenna
b. selectivity
d. resonance
7. The real part of an antenna's input impedance is due to:
a. the radiated signal
c. the SWR
b. the reflected signal
d. all of the above
35. A Yagi array is unidirectional. T
36. A Log-Periodic Dipole array is a "parasitic" array. F
8. An antenna's beamwidth is measured:
a. from +90° to –90°
b. from front to back
37. A Log-Periodic Dipole array is unidirectional. T
38. A Turnstile array is unidirectional. F
9. ERP stands for:
a. Equivalent Radiation Pattern
b. Effective Radiation Pattern
39. Stacked Yagis form a phased array. T
40. A parabolic "dish" can be a reflector. T
41. A flat piece of metal can be a reflector. T
42. A piece of sheet metal bent at a 90° angle can be a reflector. T
c. between half-power points
d. between the minor side-lobes
c. Equivalent Radiated Power
d. Effective Radiated Power
10. "Ground Effects" refers to the effects on an antenna's radiation pattern caused
by:
a. radio signals reflecting off the ground
b. buildings and other structures on the ground
c. fading
d. faulty connection of the feed cable ground
43. A piece of thin metal tubing can be a reflector. T
44. Only certain types of antennas, such as "horns", can be used with a parabolic
reflector. F
45. An anechoic chamber requires highly reflective surfaces.F
11. A 1-MHz monopole antenna must be:
a. mounted vertically
b. mounted horizontally
c. at least one half-wavelength long
d. at least one wavelength long
12. The typical antenna in an AM radio is a:
a. dipole
c. ferrite "loop-stick"
b. folded dipole
d. none of the above
MULTIPLE CHOICE
1. The front-to-back ratio of a half-wave dipole antenna is:
a. 0 dB
b. 3 dB
c. 10 dB
d. infinite
13. The polarization of plane waves received from a satellite is changed by:
a. gamma rays
c. helical rotation
b. Faraday Rotation
d. the distance traveled
14. A nonresonant antenna:
a. will not transmit
b. will not receive
c. will cause SWR on the feed cable
d. all of the above
15. At resonance, the input impedance to a lossless antenna should be:
a. resistive
b. inductive
c. capacitive
d. infinite
16. An antenna can be matched to a feed line using:
a. a shorted stub
c. an LC network
b. a loading coil
d. all of the above
17. As the length of a "long-wire" antenna is increased:
a. the number of lobes increases
c. efficiency decreases
b. the number of nodes decreases
d. none of the above
18. Arrays can be:
a. phased
b. driven
c. parasitic
d. all of the above
19. An array with one driven element, a reflector, and one or more directors is
called a:
a. Marconi
c. Log-Periodic Dipole
b. Yagi
d. stacked array
20. LPDA stands for:
a. Low-Power Dipole Array
b. Low-Power Directed Array
c. Log-Periodic Dipole Array
d. Log Power Dipole Array
21. The radiated beam from a parabolic "dish" transmitting antenna is:
a. collimated
b. phased
c. dispersed
d. none of the above
22. The energy picked up by a parabolic antenna is concentrated at the:
a. center
b. edges
c. focus
d. horn
23. Antennas are often tested in:
a. an echo chamber
b. an anechoic chamber
c. a vacuum chamber
d. an RF reflective chamber
24. Field strength at a distance from an antenna is measured with:
a. a slotted line
c. an EIRP meter
b. a dipole
d. a field-strength meter
COMPLETION
1. An antenna is the interface between the transmission line and ________.
ANS:
space
2. Hertz antenna is another name for a half-wave ________.
ANS:
dipole
3. The length of a half-wave dipole is about ________% of a half-wave in free space.
ANS:
95
4. The ________ resistance is the portion of an antenna's input impedance due to
transmitted radio waves leaving the antenna.
ANS:
radiation
5. Input impedance at the center feed point of a resonant half-wave dipole is about
________ Ω.
ANS:
70
6. Input impedance at the center feed point of a resonant folded dipole is about
________ Ω.
ANS:
280 – 300
7. The vertical angle of radiation is called the angle of ________.
ANS:
elevation
8. Antenna radiation patterns are typically drawn on graphs with ________
coordinates.
ANS:
polar
9. As compared to a ________ source, a half-wave dipole has a gain of about 2 dBi.
ANS:
point, isotropic
10. Antenna gain measured in ________ is with reference to a half-wave dipole.
ANS:
dBd
11. ________ is the same as the gain for a lossless antenna.
ANS:
Directivity
12. The front-to-back ratio of a half-wave dipole is ________ dB.
ANS:
0
13. The ________ of a directional antenna is the angle between its half-power
points.
ANS:
beamwidth
14. ERP stands for ________ radiated power.
ANS:
effective
15. ERP is the power input to the antenna multiplied by the antenna's ________.
ANS:
gain
16. A ________ is required to connect a coaxial cable to a center-fed dipole
antenna.
ANS:
balun
17. A horizontally mounted dipole will radiate waves with ________ polarization.
ANS:
horizontal
18. A folded dipole has ________ bandwidth than a standard dipole.
ANS:
wider, greater, more
19. A monopole antenna is typically mounted in the ________ direction.
ANS:
vertical
20. The length of a typical monopole antenna is ________ wavelength.
ANS:
one-quarter, 1/4
5. What is the ERP of an antenna with 10 dBd of gain and driven by one watt?
ANS:
10 watts
21. A monopole antenna mounted high on a tower typically uses a ________ plane.
ANS:
ground
6. A resonant antenna has an input impedance of 100 ohms and is driven by 100
watts. What is the RMS voltage at the feed-point of the antenna?
ANS:
100 volts
22. A vertical antenna has an ________ radiation pattern for ground-based
receivers.
ANS:
omnidirectional
Chapter 17: Microwave Devices
23. The number of driven elements in a Yagi antenna is typically ________.
ANS:
one
TRUE/FALSE
24. The reflector on a Yagi antenna is called a ________ element.
ANS:
parasitic
1. By convention, microwave frequencies are 1 GHz and above. T
2. Transmission line losses decrease at microwave frequencies. F
25. An LPDA is a ________ dipole array.
ANS:
log-periodic
26. If an LPDA had five elements, the number of driven elements it had would be
________.
ANS:
five
27. All the waves that hit the surface of a parabolic antenna merge at the ________.
ANS:
focus
3. Semiconductor transit time can be ignored at microwave frequencies. F
4. Leads on semiconductor devices have significant inductance at microwave
frequencies. T
5. Waveguides are essentially pipes through which electromagnetic fields
propagate. T
6. Waveguides act as low-pass frequency filters for microwaves. F
28. A ________ beam has all its individual rays parallel to each other.
ANS:
collimated
29. A microwave ________ antenna is essentially an extension of a waveguide.
ANS:
horn
30. An ________ chamber is often used to test microwave antennas.
ANS:
anechoic
7. Waveguides often have significant radiation loss. F
8. Waveguides do not have significant dielectric losses. T
9. Multimode propagation causes dispersion of a pulse as it travels through a
waveguide. T
10. Usually, a waveguide should use only one mode of propagation. T
SHORT ANSWER
11. Single-mode propagation causes some dispersion of a pulse as it travels through
a waveguide. T
1. Calculate the physical length of a half-wave dipole for use at 300 MHz.
ANS:
475 millimeters
12. Typically, waveguides carry TEM waves. F
2. How much power will a 95% efficient antenna radiate if driven with 100 watts?
ANS:
95 watts
13. In a rectangular waveguide, TE10 is the dominant mode. T
14. Circular waveguides are possible, but are not used in practice. F
3. If an antenna has 10.14 dB of gain compared to a point source, how much gain
does it have compared to a half-wave dipole?
ANS:
8 dB
4. A resonant antenna has an input impedance of 100 ohms and is driven by 100
watts. What is the RMS current in the antenna?
ANS:
1 ampere
15. The cutoff frequency for a rectangular waveguide depends on the longer
dimension of its cross section. T
16. Group velocity is how fast a signal travels through a waveguide. T
17. Group velocity is significantly less than the speed of light. T
18. Phase velocity is another term for group velocity. F
19. Group velocity increases as the signal frequency increases. T
45. A parabolic dish is commonly used with a "horn". T
20. Guide wavelength is calculated using the phase velocity. T
46. A horn is a type of impedance matcher. T
21. Guide wavelength is always shorter than free-space wavelength. F
47. A horn is a type of antenna. T
22. Phase velocity in a waveguide is always greater than the speed of light. T
48. A piece of Teflon in front of a horn can act as a lens. T
23. Waveguide impedance is a function of frequency. T
49. All radar devices rely on the Doppler effect. F
24. Waveguide impedance is always equal to or less than 377 ohms. F
50. Radar has a maximum range, but no minimum range. F
25. Impedance matching on a waveguide can be done with a brass screw. T
51. Radar can discriminate between two targets that are in the same "line-of-sight".
T
26. At microwave frequencies, a cavity in a piece of metal acts like an LC circuit. T
52. Absorption and scattering by a target can reduce the effectiveness of radar. T
27. Resonant cavities cannot be tuned.F
28. An isolator uses multiple ports to separate signals. F
MULTIPLE CHOICE
29. Circulators rely on the magnetic properties of ferrites. T
1. The microwave frequency range is considered to start at:
a. 100 MHz
b. 1 GHz
c. 10 GHz
d. 100 GHz
30. A Gunn device contains a P-N junction. F
31. A Gunn device uses its transit time to produce microwave oscillations. T
2. The UHF range is:
a. below the microwave range
b. inside the microwave range
c. above the microwave range
d. same as the microwave range
32. A Gunn device uses "negative resistance" to produce microwave oscillations. T
33. An IMPATT diode is often a 4-layer device. T
34. The frequency of oscillation of an IMPATT diode depends on its physical
dimensions. T
35. The frequency of oscillation of an IMPATT diode depends on the resonant cavity
it is in. T
36. A YIG oscillator cannot be tuned. F
37. A magnetron is actually a type of vacuum tube. T
3. The dominant mode of a waveguide depends on:
a. the shape of the waveguide
c. the point of signal injection
b. the power level of the signal
d. none of the above
4. The dominant mode of a rectangular waveguide is:
a. TE01
b. TM 01
c. TE10
d. TM10
5. The dominant mode of a circular waveguide is:
a. TE 01
b. TM 01
c. TE11
d. TM11
6. Circular waveguides use TM 01 mode because:
a. it is dominant
b. of its circular symmetry
c. it is the only mode possible
d. it is more efficient
38. A magnetron is a high-power fixed-frequency oscillator. T
39. A magnetron is easily tuned. F
40. A klystron is a vacuum tube device used for high-stability amplification of
microwave signals. T
41. Klystrons can produce power in the megawatt range. T
42. Traveling-wave tubes can oscillate, but not amplify. F
43. Traveling-wave tubes are distinguished by their wide bandwidths. T
44. A parabolic dish, like a dipole, is a type of antenna. F
7. The characteristic impedance of a waveguide:
a. is fixed
b. depends on the frequency it carries
c. depends on the longer dimension of its cross section
d. both b and c
8. Power can be coupled into or out of a waveguide:
a. with a magnetic field probe
c. through a hole in the waveguide
b. with an electric field probe
d. all of the above
9. Directional couplers for waveguides are characterized by:
a. their insertion loss
c. their directivity
b. their coupling specification
d. all of the above
22. The device commonly used in UHF transmitters is the:
a. TWT
b. klystron
c. magnetron
10. Striplines and microstrips are used to:
a. couple sections of waveguide
b. couple waveguides to antennas
c. couple components on a circuit board
d. none of the above
23. A microwave phased array is often made using:
a. slots
b. Yagis
c. Fresnel lenses
11. A resonant cavity is a type of:
a. tuned circuit
b. defect in a waveguide
24. RADAR stands for:
a. radio ranging
b. radio depth and ranging
c. antenna
d. none of the above
25. RADAR uses:
a. pulsed transmission
b. continuous transmission
13. TWT stands for:
a. Transverse Wave Transmission
b. Transverse-Wave Tube
26. The maximum effective range for pulsed radar:
a. increases with increasing repetition rate
b. decreases with increasing repetition rate
c. decreases with increasing pulse period
d. none of the above
14. An "isolator" is a device that:
a. isolates frequencies in a waveguide
b. allows a signal to pass in one direction only
c. separates signals among various ports
d. prevents microwaves from leaking out of a waveguide
COMPLETION
1. ________ is the effect of a pulse "spreading out" as it travels through a
waveguide.
ANS:
Dispersion
c. gallium astenite
d. none of the above
2. The electric field is ________ along the walls of a rectangular waveguide.
ANS:
zero
17. IMPATT stands for:
a. impact avalanche and transit time
b. induced mobility at transmission time
c. implied power at transmission terminal
d. none of the above
18. YIG stands for:
a. Yttrium-Iron-Gallium
b. Yttrium-Iron-Germanium
19. A YIG can be tuned by applying:
a. an electric field
b. a magnetic field
c. the Doppler effect
d. all of the above
27. The minimum effective range for pulsed radar:
a. increases with increasing pulse duration
b. decreases with increasing pulse duration
c. is always a tenth of the maximum range
d. none of the above
15. A "circulator" is a device that:
a. rotates signal polarity in a waveguide
b. allows a signal to pass in one direction only
c. separates signals among various ports
d. prevents microwaves from being "trapped" in a waveguide
16. GaAs stands for:
a. gallium arsenide
b. gallium assembly
d. all of the above
c. radio detection and ranging
d. remote detection and ranging
12. A TEE connector used with waveguides is:
a. an H-plane TEE
c. a "magic" TEE
b. an E-plane TEE
d. all of the above
c. Traveling-Wave Tube
d. Traveling-Wave Transmission
d. YIG
3. The waveguide mode with the lowest cutoff frequency is the ________ mode.
ANS:
dominant
4. In TE10 mode, the ________ field peaks in the middle of the waveguide cross
section.
ANS:
electric
c. Yttrium-Iron-Garnet
d. none of the above
c. mechanical pressure
d. an "exciter" signal
5. In TE20 mode, the electric field has ________ peaks in the waveguide cross
section.
ANS:
two
6. In a circular waveguide, ________ mode is used because of its circular symmetry.
ANS:
TM01
20. The device commonly used in microwave ovens is the:
a. TWT
b. klystron
c. magnetron
d. YIG
21. The device commonly used in satellite communications is the:
a. TWT
b. klystron
c. magnetron
d. YIG
7. A waveguide acts as a ________-pass filter.
ANS:
high
8. In a waveguide, group velocity is always ________ than the speed of light.
ANS:
slower
9. In a waveguide, phase velocity is always ________than the speed of light.
ANS:
faster
10. In a waveguide, impedance ________ as frequency increases.
ANS:
decreases
11. A ________ TEE is a combination of E-plane and H-plane TEES.
ANS:
hybrid
12. The Q of a resonant cavity is very ________ compared to lumped LC circuits.
ANS:
high
13. A wavemeter is a resonant ________ with an adjustable plunger.
ANS:
cavity
4. Calculate the phase velocity in a waveguide carrying a signal that is twice its
cutoff frequency.
ANS:
346 × 106 meters per second
5. Calculate the wavelength of a 2-GHz signal in a waveguide with a 1-GHz cutoff
frequency.
ANS:
173 millimeters
6. Find the maximum unambiguous range for a pulsed radar sending 10k pulses per
second.
ANS:
15 km
7. Find the minimum unambiguous range for a pulsed radar sending 2-µsec
duration pulses.
ANS:
300 meters
14. A Gunn device oscillates because of its negative ________.
ANS:
resistance
Chapter 18: Terrestrial Microwave Communication Systems
15. Both magnetrons and TWTs are slow ________ tubes.
ANS:
wave
TRUE/FALSE
16. Both klystrons and TWTs are ________-beam tubes.
ANS:
linear
1. Microwave links are still used to carry telephone signals. T
2. Microwave links carry analog data only. F
17. A ________ antenna is just a waveguide with a hole in it.
ANS:
slot
3. Microwave links carry video signals for television. T
18. A ________ antenna is a flat piece of copper on an insulating substrate with a
ground plane on the other side.
ANS:
patch
4. Microwave links are point-to-point. T
19. The radar cross section of a target is typically ________ than its actual size.
ANS:
smaller
6. Microwave links are line-of-sight. T
20. The frequency of the returned signal will be ________ than the transmitted
signal if the target is moving toward the radar antenna.
ANS:
higher
5. Microwave links are always "multi-hop". F
7. Because of reliability, microwave links typically suffer about one hour of
"downtime" a month. F
8. Microwave systems should use as few repeaters as possible. T
9. In analog microwave systems, additional links add to the noise level. T
SHORT ANSWER
10. In digital microwave systems, additional links have no negative affects. F
1. Calculate the TE10 cutoff frequency for a rectangular waveguide if the longer
dimension of its cross section is 5 cm.
ANS:
3 GHz
2. Calculate the group velocity in a waveguide carrying a signal that is twice its
cutoff frequency.
ANS:
260 × 106 meters per second
3. Find the gain in dBi of a 10-GHz horn antenna with dE = dH = 60 mm.
ANS:
14.8
11. Microwave links typically use power levels under 10 watts. T
12. The "line-of-sight" distance for microwaves is about a third longer than it is for
visible light. T
13. Diffraction is not an issue with microwave links. F
14. Antenna height for microwave links must be below the "Fresnel zone". F
15. For analog microwave systems, the carrier-to-noise ratio must exceed a certain
minimum. T
16. For microwave links, it is more convenient to use noise temperature than noise
figure. T
17. For digital microwave links, energy per bit is a key parameter. T
18. An Eb / N0 ratio of about 3 dB is sufficient for most digital microwave links. F
19. Above 10 GHz, fading due to rain is not a problem. F
20. One cause of fading in a microwave system is "ducting". T
21. Compensation for fading due to multipath reception is usually done using
"diversity". T
22. Diversity can be achieved by mounting two antennas on a tower, one above the
other. T
23. Diversity can be achieved by using two microwave frequencies. T
24. Repeaters typically receive a signal and retransmit it on the same frequency. F
25. Analog microwave repeaters can be either "baseband" or "IF" repeaters. T
8. Too much antenna gain causes:
a. a very narrow microwave beam
b. a very wide microwave beam
c. excessive noise
d. jitter
9. The microwave signal path should clear obstacles by at least:
a. 60% of the Faraday zone
c. 60% of the height of the antenna tower
b. 60% of the Fresnel zone
d. 60% of the highest obstacle height
10. Satisfactory performance of an analog microwave system is defined as:
a. a carrier-to-noise ratio that exceeds a given value
b. an ERP level that exceeds a given value
c. an energy-per-hertz level that exceeds a given value
d. none of the above
11. Satisfactory performance of a digital microwave system requires a:
a. low level of transmitted power
b. high level of ERP
c. good energy per bit per transmitted Watt ratio
d. good energy per bit per noise density ratio
12. Fading is caused by:
a. multipath reception
b. attenuation due to weather
c. ducting
d. all of the above
13. The effects of fading due to multipath reception are often reduced using:
a. diversity
b. power
c. high-gain antennas
d. all of the above
26. MMDS systems are bidirectional. F
14. Repeaters are used in a microwave system:
a. always
b. when distance exceeds line-of-sight
27. LMDS systems are bidirectional. T
MULTIPLE CHOICE
1. Another term for a single microwave link is a:
a. section
b. hop
c. skip
2. Microwave systems use:
a. FM
b. SSB
c. QAM
3. The typical reliability of a microwave system is:
a. 90%
b. 99%
c. 99.9%
15. Microwave repeaters can be:
a. IF type
b. baseband type
c. above 10 GHz
d. below 10 GHz
c. regenerative type
d. all of the above
d. jump
d. all of the above
d. 99.99%
4. A typical microwave system uses a transmitted power of about:
a. 2 watts
b. 20 watts
c. 200 watts
d. none of the above
16. An advantage of digital techniques over analog in a microwave system is:
a. less bandwidth is required
c. it requires less power
b. accumulation of noise is reduced
d. all of the above
17. MMDS stands for:
a. Multichannel Microwave Distribution System
b. Multipoint Microwave Distribution System
c. Multichannel Multipoint Distribution System
d. Multiple Microwave Distribution Systems
6. In digital microwave systems, additional repeaters increase the:
a. reliability
b. noise level
c. jitter
d. all of the above
18. LMDS stands for:
a. Local Microwave Distribution System
b. Local Multipoint Distribution System
c. Local Multichannel Distribution System
d. Low-power Microwave Distribution System
7. LOS stands for:
a. Loss Of Skip
b. Loss Of Signal
19. LMDS is:
a. bidirectional
b. unidirectional
5. In analog microwave systems, additional repeaters increase the:
a. reliability
b. noise level
c. jitter
d. all of the above
c. Line-Of-Sight
d. Line-Of-Signal
c. multidirectional
d. none of the above
COMPLETION
SHORT ANSWER
1. One microwave link is called a _________.
ANS:
hop
1. If the line-of-sight distance for an optical beam is 12 km, what would it be,
approximately, for a microwave beam?
ANS:
16 km
2. STL stands for _________-to-transmitter links.
ANS:
studio
3. A typical microwave system has about one hour per _________ or less of
downtime.
ANS:
year
4. Adding more links causes _________ in a digital microwave system.
ANS:
jitter
5. In microwave systems, it is more convenient to use noise _________ than noise
figure in calculations.
ANS:
temperature
6. In digital microwave systems, the energy per bit per _________ is a key
parameter.
ANS:
noise density
7. Multipath reception can cause 20 dB or more of _________.
ANS:
fading
8. Two antennas stacked one above the other on a tower is an example of
_________ diversity in a microwave system.
ANS:
space
9. The ability to use two frequencies simultaneously is an example of _________.
ANS:
diversity
2. A line-of-sight microwave link operating at 4 GHz has a separation of 40 km
between antennas. An obstacle in the path is located midway between the two
antennas. By how much must the beam clear the obstacle?
ANS:
16.4 meters
3. A transmitter and receiver operating at 1 GHz are separated by 10 km. How many
dBm of power gets to the receiver if the transmitter puts out 1 Watt, and both the
sending and receiving antennas have a gain of 20 dBi?
ANS:
–42.4 dBm
4. A microwave system has a feed-line loss of 2 dB and sees a sky temperature of
150 K. Calculate the noise temperature of the antenna/feed-line system referenced
to the receiver input.
ANS:
201 K
5. A microwave receiver receives –60 dBm of signal. The noise power is –100 dBm.
What is the carrier-to-noise power ratio?
ANS:
40 dB
Chapter 19: Television
TRUE/FALSE
1. Video systems form pictures by a scanning process. T
10. Microwave systems generally use less than _________ watts of power.
ANS:
ten
11. _________ are necessary in a microwave system that extends beyond the lineof-sight distance.
ANS:
Repeaters
12. Analog microwave systems use both IF and _________ repeaters.
ANS:
baseband
2. The NTSC system is used in North America. T
3. The NTSC system is used in Europe. F
4. The NTSC system is used in Japan. T
5. The PAL system is no longer used in much of the world. F
6. The SECAM system is used in Europe. T
13. Microwave digital radio techniques reduce the accumulation of _________ as a
signal goes from link to link.
ANS:
noise
7. In North America, TV uses 60 frames a second. F
8. NTSC systems use an interlaced scan. T
14. MMDS is unidirectional, but _________ is bidirectional.
ANS:
LMDS
9. The standard TV aspect ratio is 5:3. F
10. The electron beam in a TV CRT is blanked during horizontal retrace. T
11. The electron beam in a TV CRT is blanked during vertical retrace. T
12. The standard analog TV signal is called composite video. T
37. The accelerating voltage applied to the CRT in a TV receiver is several thousand
volts. T
13. A few commercial TV stations broadcast RGB video. F
38. Color TVs use a higher accelerating voltage than do monochrome receivers. T
14. Most color monitors for personal computers use RGB video. T
39. The CRTs commonly used in TV receivers use electrostatic deflection. F
15. The luminance signal controls the brightness of a scan line. T
40. The "yoke" is part of the deflection circuit. T
16. The standard synchronization for TV is called positive sync. F
41. Color TV receivers do not have a "raster". F
17. The sync pulses are said to be "blacker than black". T
42. There is very high voltage at the flyback transformer in a TV receiver. T
18. The negative peak of a video signal occurs during a sync pulse.T
19. The peak video signal occurs at the blanking level. F
20. The duration of the vertical blanking pulse identifies which picture field is
present. F
43. Most of the supply voltages in a TV receiver come from the horizontal output
transformer. T
44. A typical color CRT contains three electron guns. T
45. A typical monochrome CRT contains a "shadow mask". F
21. Closed-caption signals can be sent during the vertical blanking time. T
22. Horizontal and vertical resolution in a TV system are determined in the same
way. F
46. In a color CRT, "purity" means each electron beam hits the correct color
phosphor. T
47. "Aquadag" is a color phosphor. F
23. The resolution seen by a viewer depends to a certain extent on the TV receiver.
T
48. "Ultor" is a color phosphor. F
24. Horizontal resolution is equal to the number of visible scan lines. F
49. In a CATV system, the main antenna is at the "head end". T
25. Resolution is proportional to bandwidth. T
50. Like a PSTN central office, the typical CATV system is configured as a star
network. F
26. Because of the way people perceive color, any color can be made with red,
green, and blue. T
51. Noninterlaced scanning is called "progressive" scanning. T
27. NTSC color television is not compatible with NTSC monochrome television. F
52. HDTV uses the same aspect ratio as standard NTSC. F
28. In an NTSC color TV system, luminance is derived from the RGB signals. T
53. An HDTV signal cannot fit into the bandwidth of a standard broadcast TV
channel. F
29. Horizontal resolution for color in NTSC is much less than it is for luminance. T
54. Digital encoding and compression play a significant role in HDTV. T
30. NTSC uses a suppressed-carrier system to add color information to the video
signal. T
55. The FCC has set the phase-out of analog TV broadcasting for the year 2006. T
31. NTSC uses a type of amplitude modulation for the video signal. T
56. Color CRTs emit X rays. T
32. A standard video broadcast channel is about 4.5 MHz wide. F
MULTIPLE CHOICE
33. The audio signal in NTSC video uses FM. T
34. Color NTSC receivers use a "color-burst" oscillator to create the color signals. F
35. A standard broadcast video signal reaches zero level twice per frame. F
36. An analog television receiver uses a type of superheterodyne circuit. T
1. NTSC stands for:
a. National Television Systems Commission
b. National Television Systems Committee
c. National Television Systems Council
d. Nippon Television Systems Commission
2. The NTSC specification was drawn up by the:
a. FCC
b. IRE
c. EIA
3. RGB stands for:
a. Red-Green Burst
b. Red-Green Brightness
d. IEEE
c. Red-Green Bandwidth
d. Red-Green-Blue
4. The number of scan lines in an NTSC signal is:
a. 525
b. 625
c. 1024
d. 1250
5. The number of NTSC frames sent per second is:
a. 25
b. 30
c. 50
d. 60
6. The number of NTSC fields sent per second is:
a. 25
b. 30
c. 50
d. 60
7. The aspect ratio of a standard TV receiver is:
a. 3 : 4
b. 4 : 3
c. 525 : 625
8. Luminance refers to:
a. brightness
b. contrast
9. Luminance is measured in:
a. foot-candles
b. lumins
17. In a color TV receiver, Y I Q refers to:
a. luminance signal, in-phase color component, quadrature phase color
component
b. composite color signal, in-phase color component, quadrature phase
color component
c. composite video signal, in-phase video component, quadrature video
color component
d. a method of demodulating stereo sound
18. The modulation used for the video signal in a standard NTSC color TV receiver is:
a. SSB
c. suppressed-carrier AM
b. vestigial sideband AM
d. FM
19. The modulation used for the audio signal in a standard NTSC color TV receiver
is:
a. SSB
c. suppressed-carrier AM
b. vestigial sideband AM
d. FM
d. 625 : 525
c. chroma
d. raster
c. IRE units
d. NTSC units
20. The modulation used for the chroma signal in a standard NTSC color TV receiver
is:
a. SSB
c. suppressed-carrier AM
b. vestigial sideband AM
d. FM
10. The maximum luminance level is called:
a. max white
c. all white
b. peak white
d. whiter than white
21. The function of the "color burst" is to:
a. detect the presence of a color video signal
b. regenerate the color sub-carrier
c. to synchronize the color demodulation line by line
d. all of the above
11. The blanking level corresponds to a luminance of:
a. white
c. whiter than white
b. black
d. blacker than black
22. SAP stands for:
a. separate audio program
b. separate audio pulse
12. The sync pulse level corresponds to a luminance of:
a. white
c. whiter than white
b. black
d. blacker than black
23. The horizontal output transformer is also called:
a. the isolation transformer
c. the flyback transformer
b. the video transformer
d. the yoke
13. The vertical blanking pulse is serrated to:
a. maintain horizontal sync
c. equalize the DC level
b. maintain vertical sync
d. all of the above
24. Compared to a monochrome CRT, the accelerating voltage on a color CRT is:
a. about the same
c. much lower
b. much higher
d. color CRTs use magnetic acceleration
14. When measured in lines, horizontal resolution:
a. is greater than vertical resolution
b. is about the same as vertical resolution
c. is less than vertical resolution
d. horizontal resolution is not measured in lines
25. Deflection in CRTs used in TV receivers is done:
a. magnetically for both vertical and horizontal
b. electrostatically for both vertical and horizontal
c. electrostatically for vertical and magnetically for horizontal
d. magnetically for vertical and electrostatically for horizontal
15. The smallest picture element is called a:
a. dot
b. pic
c. pixel
d. none of the above
16. Compared to the luminance signal, the horizontal resolution for color is:
a. much greater
c. much less
b. about the same
d. resolution does not apply to color
26. AFPC stands for:
a. allowed full picture chroma
b. automatic frequency and phase control
c. automatic frequency and picture control
d. none of the above
c. sync amplitude pulse
d. sync audio pulse
COMPLETION
18. SAP stands for ________ audio program.
ANS:
separate
1. ________ is a conductive coating on both the inside and outside of the CRT in a
TV.
ANS:
Aquadag
19. The second anode of a CRT is often called the ________.
ANS:
ultor
2. The ________ standard for TV has been in use since 1953.
ANS:
NTSC
20. The accelerating voltage for a color CRT is about ________ kV.
ANS:
20 to 30
3. Video systems form pictures by a ________ process.
ANS:
scanning
21. The inside of a CRT's face-plate is coated with ________ to generate the picture.
ANS:
phosphor
4. During the horizontal blanking interval, the electron beam ________ from right
to left.
ANS:
retraces
22. The horizontal output transformer is called the ________ transformer.
ANS:
flyback
5. The NTSC specifies a ________ video signal.
ANS:
composite
23. A good way to separate luma from chroma is to use a ________ filter.
ANS:
comb
6. The ________ ratio of a CRT screen is the ratio of width to height.
ANS:
aspect
24. The color ________ turns off the color circuitry when a color TV is receiving a
monochrome signal.
ANS:
killer
7. Brightness information is called ________.
ANS:
luma, luminance
25. Signal levels in cable TV systems are usually measured in ________.
ANS:
dBmV
8. Color information is called ________.
ANS:
chroma, chrominance
26. The antenna for a CATV system is located at the ________ end.
ANS:
head
9. The blanking period before the sync pulse is called the front ________.
ANS:
porch
27. A ________ shows a color-bar signal with predetermined levels and phases.
ANS:
vectorscope
10. Odd and even fields are identified by the ________of the vertical sync pulse.
ANS:
position
28. Color intensity is called ________.
ANS:
saturation
11. Each horizontal scan line takes ________ microseconds, not including blanking.
ANS:
62.5
29. The ________ of the chroma signal represents the color hue.
ANS:
phase
12. Horizontal blanking lasts ________ microseconds.
ANS:
10
30. The ________ controls in a color TV adjust the electron beams to strike the
correct color phosphor dots.
ANS:
purity
13. Vertical blanking lasts about ________ milliseconds.
ANS:
1.3
14. Picture elements are called ________.
ANS:
pixels
31. The ________ controls in a color TV adjust the electron beams to strike the
correct triad of phosphor dots.
ANS:
convergence
15. The maximum number of scan lines under NTSC is ________.
ANS:
525
Chapter 20: Satellite Communications
16. The human eye is most sensitive to the color ________.
ANS:
green
TRUE/FALSE
17. The color sub-carrier frequency is approximately ________ MHz.
ANS:
3.58
1. Communications satellites could be just passive reflectors. T
2. A typical communications satellite can cover half of the earth's surface. F
25. Conventional analog satellite transponders cannot be used with digital data
signals. F
3. Most communications satellites are in a geosynchronous orbit. T
26. It is possible to transmit signals from one satellite to another. T
4. Most communications satellites are in a geostationary orbit. T
5. "Geostationary" means the same thing as "geosynchronous". F
6. A geosynchronous orbit is about 3,600 km above the equator. F
7. Signals from satellites in a geosynchronous orbit suffer a great deal of free-space
attenuation. T
27. In practice, the beamwidth of a parabolic reflector is independent of its
diameter. F
28. Communications satellites are particularly well suited to long-distance
telephony. F
29. With TDMA, more than one hundred earth stations can use the same satellite
transponder. T
8. It is easier to reach a geosynchronous satellite from higher northern latitudes. F
30. LEO communications satellite systems have been a great commercial success. F
9. At the frequencies satellites use, the ionosphere has negligible effect. T
10. The closer a satellite is to earth, the faster the velocity it needs to stay in orbit. T
MULTIPLE CHOICE
11. In the Northern Hemisphere, an antenna must face south to reach a satellite. T
1. The height of the geosynchronous orbit above the equator is about:
a. 3,578 km
c. 357,800 km
b. 35,780 km
d. depends on satellite velocity
12. You cannot communicate with a geosynchronous satellite from the Southern
Hemisphere. F
13. You cannot communicate with a geosynchronous satellite from the South Pole.
T
14. Typically, ground antennas must be movable to "track" a geosynchronous
satellite. F
15. The azimuth and elevation needed for an antenna to "see" a certain satellite
depend on the location of the antenna on the ground. T
16. The power in the uplink signal to a typical communications satellite is in the
range of 50 to 240 watts. F
17. The power in the downlink signal from a typical communications satellite is in
the range of 10 to 250 watts per transponder. T
18. The EIRP of a satellite depends on the gain of its antenna. T
19. The EIRP of a satellite is the same anywhere reception is possible. F
20. It takes over half a second for a signal to go from point A to point B and back
again via geostationary satellite. T
21. The useful life of a communications satellite is over when it runs out of fuel. T
22. The maximum useful life of a communications satellite is about three years. F
23. Using the C band for satellites may conflict with terrestrial microwave
communications. T
24. Ku-band antennas can be smaller than C-band antennas. T
2. The high and low points of a satellite's orbit are called, respectively,:
a. apogee and perigee
c. uplink and downlink
b. perigee and apogee
d. downlink and uplink
3. The area on the earth that is "covered" by a satellite is called its:
a. earth station
c. footprint
b. downlink
d. plate
4. The velocity required to stay in orbit:
a. is constant
b. is zero (freefall)
c. is lower close to the earth than far from the earth
d. is higher close to the earth than far from the earth
5. An antenna is aimed by adjusting the two "look angles" called:
a. azimuth and elevation
c. declination and elevation
b. azimuth and declination
d. apogee and perigee
6. The power per transponder of a typical Ku-band satellite is in the range:
a. 5 to 25 watts
c. 500 to 2500 watts
b. 50 to 250 watts
d. depends on its orbit
7. The power level for an earth station to transmit to a satellite is on the order of:
a. 101 watts
b. 102 watts
c. 103 watts
d. 104 watts
8. The "payload" on a communications satellite consists of:
a. transponders
b. batteries
c. solar cells
9. "Station-keeping" refers to:
a. antenna maintenance
b. power-level adjustments
d. all of the above
c. orbital adjustments
d. none of the above
10. DBS stands for:
a. decibels of signal
b. down-beam signal
c. direct-broadcast system
d. direct-broadcast satellite
11. LNA stands for:
a. low-noise amplifier
b. low north angle
c. low-noise amplitude
d. low-noise array
4. The _________ is the signal path from the satellite to the earth station.
ANS:
downlink
5. Non-geostationary satellites are sometimes called _________satellites.
ANS:
orbital
12. A reduction in TWT power for linearity is called:
a. backdown
b. backoff
c. power-down
d. EIRP drop
6. A geosynchronous orbit is about _________ km above the earth.
ANS:
35,780
13. TVRO stands for:
a. television receive only
b. television repeater only
c. television remote origin
d. none of the above
14. TDMA stands for:
a. transponder-directed multiple antennas
b. television distribution master antenna
c. time-division multiple access
d. transmit delay minimum aperture
15. VSAT stands for:
a. video satellite
b. video signal antenna terminal
9. The _________ is the distance of a satellite's closest approach to the earth.
ANS:
perigee
c. very small antenna terminal
d. very small aperture terminal
17. A typical VSAT system is configured as a:
a. star
b. mesh
c. ring
7. A satellite in geosynchronous orbit takes _________ hours to complete one orbit.
ANS:
24
8. All satellite orbits are _________ in shape.
ANS:
elliptical
16. On the uplink from a terminal, a VSAT system uses:
a. high power to a small antenna
c. low power to a large antenna
b. low power to a small antenna
d. LEO satellites
18. LEO stands for:
a. long elliptic orbit
b. low-earth orbit
3. The _________ is the signal path from the earth station to the satellite.
ANS:
uplink
10. The _________ is a satellite's farthest distance from the earth.
ANS:
apogee
11. An antenna's _________ is its angular direction between east and west.
ANS:
azimuth
12. An antenna's _________ is its vertical angle with respect to the earth's surface.
ANS:
elevation
d. repeater
13. An antenna's _________ is the angle by which it is offset from the earth's axis.
ANS:
declination
c. lateral earth orbit
d. longitudinal earth orbit
19. For real-time communication, LEO systems require:
a. a constellation of satellites
c. very high power
b. tracking dish antennas
d. all of the above
14. Satellites using the _________ band operate on 12 GHz.
ANS:
Ku
15. The time for a signal to make a round trip via satellite is about _________
milliseconds.
ANS:
500
20. The frequency bands used by Ku-band satellites are:
a. 4 GHz and 6 GHz
c. 20 GHz and 30 GHz
b. 12 GHz and 14 GHz
d. none of the above
16. A _________ is a type of repeater used on communications satellites.
ANS:
transponder
COMPLETION
17. Both the gain and the beamwidth of a dish antenna depend on its _________.
ANS:
diameter
1. A _________ is an outline of the area on the earth's surface that a satellite
broadcasts to.
ANS:
footprint
2. A satellite in a _________ orbit appears to stay directly above one spot on the
equator.
ANS:
geostationary
18. VSAT systems commonly use a _________ network configuration.
ANS:
star
19. To date, LEO satellite systems have been a financial _________.
ANS:
failure
20. C-band antennas are _________ than Ku-band antennas.
ANS:
larger
14. In AMPS, some control functions are done over the voice channels. T
15. Paging signals are sent over voice channels in AMPS. F
SHORT ANSWER
16. For efficient handoff, an optimum cell-site radius is a bit less than 0.5 km. F
1. A receiving antenna with a gain of 44.4 dBi looks at a sky with a noise
temperature of 15 K. The loss between the output of the antenna and the input of
the LNA is 0.4 dB, and the LNA has a noise temperature of 40 K. Calculate the G/T.
ANS:
25 dB
17. With AMPS, a cell phone can receive a voice channel and a control channel
simultaneously. F
2. A receiver has a noise figure of 1.7 dB. Find its equivalent noise temperature.
ANS:
139 K.
19. There is no encryption in AMPS. T
18. "Blank-and-burst" control signaling is done over the voice channel. T
20. The MIN represents the 10-digit phone-number of the cell phone. T
3. A receiving antenna with a G/T of 25 dB is used to receive signals from a satellite
38,000 km away. The satellite has a 100-watt transmitter and an antenna with a
gain of 30 dBi. The signal has a bandwidth of 1 MHz at a frequency of 12 GHz.
Calculate the C/N at the receiver.
ANS:
38 dB
21. The MIN is stored in the NAM. T
22. If used, the ESN must be keyed in by the cell phone user. F
23. Both the ESN and the MIN are required for proper billing. T
24. The power a cell phone transmits is controlled by the land station. T
Chapter 21: Cellular Radio
25. It is possible to have a "collision" when two cell phones try to use the same
control channel at the same time. T
TRUE/FALSE
26. The DCC is used to tell a cell phone it is "roaming". F
1. AMPS was the original mobile phone system in America. F
27. With AMPS, handoffs always involve a change in the voice channel. T
2. AMPS is an analog system. T
28. With AMPS, handoffs result in a 100-msec interruption of the voice signal. T
3. AMPS is a circuit-switched system. T
29. The AMPS system was designed to ensure privacy. F
4. Originally, only one carrier was allowed to operate an AMPS system in any given
region. F
30. It is relatively easy to "clone" an AMPS cell phone. T
5. High path loss makes it easier to reduce interference in a cellular system. T
31. The AMPS system is full-duplex. T
6. Adjacent cell sites usually have some overlap. T
32. Analog cell phones require linear RF amplifiers. F
7. Portable handheld cell phones have a maximum ERP of 4 watts. F
33. The optimum size of a cell depends on the amount of traffic. T
8. All cell sites in a region are connected to a central office. T
34. Calls can never be blocked on a cell phone. F
9. AMPS provides for direct cell phone-to-cell phone connection. F
35. Calls can be "dropped" when a cell phone moves into another cell. T
10. AMPS reuses frequencies over a relatively short distance. T
36. Capacity can be increased by using fewer cells. F
11. AMPS uses narrowband FM. T
37. Digital data cannot be sent over an AMPS system. F
12. With AMPS, each individual cell uses all available voice channels. F
38. Digital cellular systems actually use less bandwidth than analog systems. T
13. Besides voice channels, AMPS uses a set of control channels. T
39. Digital cellular systems in North America use the same frequencies, power
levels, and channels as AMPS. T
40. Privacy using the digital cellular system is much better than using AMPS. T
MULTIPLE CHOICE
1. AMPS stand for:
a. American Mobile Phone System
b. Analog Mobile Phone Service
c. Advanced Mobile Phone System
d.Advanced Mobile Phone Service
2. PCS stands for:
a. Personal Communications Service
b. Personal Communications Systems
c. Personal Cell phone Service
d. Portable Communications Systems
3. RCC stands for:
a. Radio Common Carrier
b. Radio Cellular Carrier
4. MSC stands for:
a. Mobile Switching Center
b. Mobile Service Cellular
7. NAM stands for:
a. Numerical Access Mode
b. Numerical Assignment Mode
13. DCC stands for:
a. Digital Color Code
b. Digital Communications Code
c. Digital Communications Carrier
d. Direct Channel Code
14. SAT stands for:
a. Station Antenna Tower
b. Supervisory Audio Tone
c. Regional Cellular Carrier
d. none of the above
c. Maximum Signal Carrier
d. Minimum Signal Carrier
5. MTSO stands for:
a. Minimum Transmitted Signal Output
b. Maximum Transmitted Signal Output
c. Mobile Telephone Switching Office
d. Mobile Transmission Time-Out
6. MIN stands for:
a. Manual Identification Number
b. Mobile Identification Number
12. The SID is used by a cell phone to:
a. identify the type of system (analog or digital)
b. recognize an AMPS system
c. set its transmitted power level
d. recognize that it is "roaming"
c. Supervisory Access Tone
d. none of the above
15. CMAC stands for:
a. Control Mobile Attenuation Code c. Central Mobile Access Control
b. Control Mobile Access Code
d. Carrier Mode Attenuation Control
16. The CMAC is used to:
a. control access to the cell site
b. set the access code of the cell phone
c. set the transmit power of the cell phone
d. select the transmit channel for the cell phone
17. In an AMPS system, voice is sent using:
a. AM
b. FM
c. FSK
d. CDMA
18. In an AMPS system, control-channel signals are sent using:
a. AM
b. FM
c. FSK
d. CDMA
c. Maximum In-band Noise
d. Minimum In-band Noise
c. Number Access Module
d. Number Assignment Module
19. The ERP of a typical handheld AMPS cell phone is:
a. less than 600 µW.
c. between 1 and 2 watts
b. less than 600 mW.
d. 4 watts
20. BSC stands for:
a. Base Station Controller
b. Base Signal Controller
c. Basic Service Contract
d. Basic Service Code
8. ESN stands for:
a. Electronic Serial Number
b. Emitted Signal Number
c. Emission Strength Number
d. none of the above
21. The combination of the mobile cell phone and the cell site radio equipment is
called the:
a. BSC
b. MTSO
c. RF interface
d. air interface
9. SCM stands for:
a. Service Class Mark
b. Station Class Mark
c. Signal Class Mark
d. Serial-Code Mode
22. The optimum cell-site radius is:
a. 2 km
b. 0.5 km
c. as small as possible
10. SCM identifies the:
a. code number of a cell phone
b. base-station class
11. SID stands for:
a. Sequential Interrupt Demand
b. Standard Identification Number
c. signal classification (analog or digital)
d. maximum power level of a cell phone
c. System Identification Number
d. Signal Intensity Descriptor
23. Phone traffic is measured in:
a. calls
b. erlangs
c. number of user
d. none of the above
d. number of blocked calls
24. One way to increase the capacity of a cell phone system is:
a. increase the number of cells
c. increase the ERP
b. decrease the number of cells
d. decrease the ERP
25. CDPD stands for:
a. Code-Division Packet Data
b. Cellular Digital Packet Data
c. Coded Digital Packet Data
d. Cellular Digital Pulse Data
16. A cell phone moving into a site with no available frequencies will have a
_________ call.
ANS:
dropped
COMPLETION
17. The reduction in cell size to increase traffic is called cell _________.
ANS:
splitting
1. AMPS uses the _________-MHz band.
ANS:
800
18. A _________site is a very small unit that can mount on a streetlight pole.
ANS:
microcell
2. _________ is still the most common cellular phone system in North America.
ANS:
AMPS
19. Very small cells called _________ are used for reliable indoor reception.
ANS:
picocells
3. Frequency _________ is what makes cellular phone systems complex.
ANS:
reuse
20. Compared with AMPS, digital cellular phones require _________ bandwidth.
ANS:
4. A _________ occurs when an in-use cell-phone moves from one cell site to
another.
ANS:
handoff
5. If a cell-site radius drops below _________ km, handoffs will occur too
frequently.
ANS:
0.5
SHORT ANSWER
1. Give two reasons why digital cell phone systems are more secure than analog cell
phone systems.
ANS:
6. The number of ERP classes in AMPS is _________.
ANS:
three
7. A cell phone permanently installed in a car would be ERP class _________.
ANS:
I, one
8. The maximum ERP of class III cell phones is _________.
ANS:
600 mW
9. A portable, handheld cell phone would be ERP class _________.
ANS:
III, three
less
1. Digital is inherently more secure because of its format.
2. Digitized voice signals are easily encrypted.
2. If a 28.8-kbps modem is being used over a cell phone, how many words of text
would be lost during a 100-msec handoff interruption assuming 10 bits per letter
and 5 letters per word?
ANS:
57.6
3. A certain cell site contains 200 cell phones. The probability that a given cell
phone is being used is 15%. What is the traffic in erlangs?
ANS:
30
4. What is "trunking gain"?
10. Mobile transmitter power is controlled by the _________.
ANS:
land station
ANS:
For a given probability of being blocked, the maximum allowable traffic
per channel increases as the number of channels increases.
11. A MAC is a mobile _________ code.
ANS:
attenuation
12. For security, you should always assume that AMPS transmissions are
_________.
ANS:
public
Chapter 22: Personal Communications Systems
TRUE/FALSE
13. A mobile switching center is also called an _________.
ANS:
MTSO
1. There are three competing, and incompatible, PCS systems in North America. T
14. The optimum size of a cell site depends on the amount of _________.
ANS:
traffic
2. The current PCS systems are "true" personal communications systems in their
performance. F
15. Telephone call traffic is measured in _________.
ANS:
erlangs
3. Current PCS systems are referred to as "third-generation", with AMPS and digital
cell phones being the first and second generations. F
4. Europe has basically one PCS system based on GSM technology. T
30. The Walsh code is used for error detection in CDMA systems. F
5. GSM is used in North America. T
MULTIPLE CHOICE
6. One reason for developing PCS was that the 800-MHz band was too crowded. T
7. The North American PCS band is 1.9 GHz. T
1. Current PCS systems are referred to as:
a. first-generation
b. second-generation
c. third-generation
d. digital-generation
8. PCS cells are typically smaller than AMPS cells. T
9. All first generation cellular systems are analog. T
10. Current digital technology is not as efficient as analog FM in its use of
bandwidth. F
2. The frequency band designated for PCS in North America is:
a. 800 MHz
b. 900 MHz
c. 1.9 GHz
d. 12 GHz
3. The "forward" PCS channel is:
a. from the base to the mobile
b. from the mobile to the base
c. from mobile to mobile
d. same as the uplink
4. Compared to AMPS, PCS cell sites are:
a. bigger
b. smaller
c. distributed
11. Today, roaming is easier with PCS than it is with AMPS. F
12. IS-136 PCS is usually just called TDMA PCS. T
13. In TDMA PCS, control frames are mixed in with frames carrying voice. T
14. GSM is a TDMA system. T
15. GSM is not as sophisticated as IS-136. F
5. AMPS was designed for:
a. POTS
b. voice
d. higher-power
c. use built into an automobile
d. all of the above
6. The number of competing PCS systems in North America is:
a. 2
b. 3
c. 4
d. many
16. In GSM PCS, control frames are mixed in with frames carrying voice. T
17. GSM uses extensive frequency hopping for spread-spectrum. F
18. Frequency hopping lessens the impact of multipath fading. T
7. CDMA technology was invented by:
a. AT&T
b. Lucent
8. GSM is used in:
a. Asia
b. Europe
c. Bell Labs
d. Qualcomm
d. all of the above
c. North America
19. The SIM used in a GSM phone helps prevent unauthorized use. T
20. GSM security is not as good as it is in IS-136. F
9. In GSM, voice channels are called:
a. traffic channels
b. voice channels
c. bearer channels
d. talking channels
21. IS-95 PCS uses CDMA technology. T
22. IS-95 allows a "soft" handoff. T
23. A "soft" handoff is done without interrupting service. T
24. IS-95 can achieve space diversity by using antennas in separate cell-sites. T
25. One drawback of IS-95 is its lack of frequency diversity. F
26. Security with CDMA is not as good as it is in GSM. F
27. Unlike AMPS, CDMA PCS does not require the cell phone to adjust its ERP. F
28. Potentially, CDMA makes the best use of available bandwidth. T
29. In CDMA it is common for the signal power in the receiver to be less than the
noise power. T
10. AMPS uses:
a. CDMA
b. TDMA
c. spread-spectrum
d. none of the above
11. Other things being equal, battery life in a GSM phone should be:
a. less than in a TDMA phone
c. greater than in a TDMA phone
b. no better than in an AMPS phone
d. no better than a TDMA phone
12. It is necessary to send control information on traffic channels in:
a. no PCS system
c. TDMA only
b. GSM only
d. both GSM and TDMA
13. GSM uses:
a. frequency hopping
b. direct-sequence modulation
c. CDMA
d. all of the above
14. In GSM, SIM stands for:
a. Short Inbound Message
b. Subscriber-Initiated Message
c. Subscriber ID Module
d. Subscriber ID Method
15. IMSI stands for:
a. Integrated Mobile Subscriber Identification
b. International Mobile Subscriber Identification
c. Interim Mobile Subscriber Identification
d. Intermodulation System Interference
9. The orthogonal PN sequences used in CDMA are called a __________ code.
ANS:
Walsh
16. IS-95 uses:
a. frequency hopping
b. TDMA
11. PN stands for Pseudo-__________ Noise.
ANS:
random
17. IS-136 uses:
a. frequency hopping
b. TDMA
10. Unlike other systems, in CDMA __________ frequencies are used in all cells.
ANS:
all
c. CDMA
d. all of the above
12. __________ diversity is inherent in any spread-spectrum system.
ANS:
Frequency
c. CDMA
d. all of the above
18. In CDMA:
a. all frequencies are used in all cells
b. each cell uses half the available frequencies
c. each cell is assigned a frequency by the base
d. the frequency is selected by the mobile phone
19. CDMA uses a set of PN sequences that are:
a. common
b. unique
c. rotating
13. RF channel S/N ratios __________ than zero are typical in CDMA systems.
ANS:
less
14. CDMA uses a __________-rate vocoder.
ANS:
variable
15. A phone user typically talks less than __________% of the time during a
conversation.
ANS:
50
d. orthogonal
20. The next generation of PCS is expected to have:
a. faster data rates
c. wider roaming area
b. Internet access
d. all of the above
COMPLETION
1. PCS stands for __________ Communications System.
ANS:
Personal
2. Current PCS systems are called __________-generation systems.
ANS:
second
3. In North America, PCS is assigned the __________-MHz band.
ANS:
1900
16. CDMA requires __________-loop power control to work properly.
ANS:
closed
17. GPRS stands for General __________ Radio Service.
ANS:
Packet
18. IMT stands for International __________ Telecommunications.
ANS:
Mobile
19. UPT stands for __________ Personal Telecommunications.
ANS:
Universal
20. UWT stands for Universal __________Telecommunications.
ANS:
Wireless
21. W-CDMA stands for __________ CDMA.
ANS:
Wideband
4. Compared to AMPS, PCS cells are __________ in size.
ANS:
smaller
SHORT ANSWER
5. Besides TDMA and CDMA, __________ is also used in North America for PCS.
ANS:
GSM
6. The spread-spectrum technique used in IS-95 PCS is __________.
ANS:
CDMA, direct sequence
7. The spread-spectrum technique used in GSM is __________.
ANS:
frequency hopping
8. Unlike AMPS, CDMA allows for a __________ handoff.
ANS:
soft
1. What is the advantage of a "soft" handoff?
ANS:
No calls are dropped.
2. If CDMA receivers hear all frequencies all the time, how do they pick a specific
frequency?
ANS:
Each frequency is modulated using a separate orthogonal PN sequence.
To demodulate, the receiver uses the PN sequence specific to the channel
it wants.
3. What is the effect of cochannel interference in CDMA?
ANS:
It increases the background noise level, but CDMA can tolerate a lot of
such noise.
4. How does GSM achieve frequency diversity?
ANS:
It uses limited frequency hopping.
12. The IEEE 802.33 covers wireless LANs. F
13. Few companies actually use the IEEE 802 wireless LAN specifications. F
14. Wireless LANs typically use a spread-spectrum modulation. T
15. IEEE 802 allows up to 1 watt of transmitter power. T
5. Why was PCS assigned to 1.9 GHz instead of the 800-MHz band used for AMPS?
ANS:
The 800 MHz band was already overcrowded.
6. Why would a battery in a GSM phone be expected to last longer than a battery in
a TDMA phone?
ANS:
A TDMA phone is active during one out of every three time slots. A GSM
phone is active during one out of every eight.
7. What is the advantage of using offset QPSK over standard QPSK?
ANS:
With standard QPSK, the transmitted power repeatedly goes to zero.
With offset QPSK, it never goes to zero. Linearity requirements are less
strict for offset QPSK transmitters.
8. What is the "near/far" effect in CDMA, and what causes it?
ANS:
A stronger station farther away can "drown out" a weaker station that is
near. This happens when the power transmitted by mobile units is not
well controlled by the base.
16. The typical range of a wireless LAN in an office environment is about 10 meters.
F
17. The range of a Bluetooth system in an office environment is about 0.01 meters
to 10 meters. T
18. Any Bluetooth device should be able to communicate with any other Bluetooth
device. T
19. Bluetooth has a channel bit rate of 100 Mbps. F
20. Bluetooth devices communicate automatically once they are in range of each
other. T
21. Bluetooth uses spread-spectrum modulation. T
22. Bluetooth uses frequency hopping. T
23. Bluetooth is designed for audio as well as data. T
Chapter 23: Paging and Wireless Data Networking
24. Currently, no wireless LAN uses light-wave transmission. F
TRUE/FALSE
25. A wireless LAN based on light waves would need direct line of sight for
connections. F
1. Traditional paging systems use low-power transmitters. F
2. Traditional paging systems use widely spaced transmitters. T
MULTIPLE CHOICE
3. Pagers use the VHF band. T
1. Pagers use:
a. the VHF band only
b. the UHF band only
c. both the VHF and UHF bands
d. the VHF band, the UHF band, and the ISM band
4. Pagers use the UHF band. T
5. Pager messages typically require a lot of bandwidth. F
6. Each pager has a unique address. T
7. Typically, pager systems keep track of each pager's location. F
8. Satellite systems are used by pagers. T
9. All pagers are one-way only. F
10. Wireless LANs are typically slower than wired LANs. T
11. Wireless LANs are typically more expensive than wired LANs. T
2. ISM stands for:
a. IEEE Standard Message
b. IEEE Secure Message
c. Industrial, Scientific, and Messaging
d. Industrial, Scientific, and Medical
3. CAPCODE is:
a. an encryption scheme used for pagers
b. an addressing scheme used for pagers
c. an error-detection scheme used for pagers
d. a digital modulation scheme used for pagers
4. The IEEE specification covering wireless LANs is:
a. 802.10
b. 802.11
c. 802.12
d. 802.13
19. Infrared networks:
a. cannot penetrate walls
b. can use diffused infrared beams
5. In a one-way pager system:
a. all pages are sent from all transmitters
b. each transmitting antenna covers a wide area
c. transmitters use relatively high power
d. all of the above
20. The maximum range of a typical wireless modem is:
a. 1 meter
c. several hundred meters
b. several meters
d. several thousand meters
6. POCSAG stands for:
a. Pager Operations Common Standards Advisory Group
b. Pager Operations Code Standardization Advisory Group
c. Post Office Code Standardization Advisory Group
d. Post Office Common Standards Advisory Group
7. A typical pager system does not:
a. require "handoffs"
b. allow "roaming"
c. can use reflected infrared beams
d. all of the above
COMPLETION
1. Each pager has a unique address called a _________.
ANS:
capcode
c. require error detection
d. all of the above
8. The IEEE 802 spec for wireless LANs uses the:
a. VHF band
b. UHF band
c. ISM band
2. Many pagers can share a frequency using _________.
ANS:
TDMA
d. infrared band
3. The POCSAG was devised by the British _________ Office.
ANS:
Post
9. The IEEE 802 document for wireless LANs specifies the use of:
a. CSMA/CA
b. CSMA/CD
c. CDMA
d. all of the above
4. A POCSAG message uses a _________-bit error correction code.
ANS:
10
10. BSS stands for:
a. Basic Service Set
b. Basic Service System
5. IEEE _________ covers wireless LANs.
ANS:
802.11
11. Bluetooth uses:
a. CDMA
c. Bluetooth Service System
d. none of the above
6. The IEEE document specifies a maximum power of _________ for wireless LANs.
ANS:
1 watt
b.frequency hopping
c. QPSK
d. all of the above
7. Bluetooth uses the _________ band.
ANS:
ISM
12. Bluetooth uses the:
a. VHF band
b. UHF band
c. ISM band
d. infrared band
13. TDD stands for:
a. Time-Division Duplex
b. Time-Delayed Duplex
c. Time Delay Difference
d. Total Distance Delay
14. A Bluetooth "piconet" has:
a. 2 nodes
b. 2 to 4 nodes
8. A network of 2 to 8 Bluetooth devices is called a _________.
ANS:
piconet
c. 2 to 8 nodes
15. Two or more connected piconets forms a:
a. micronet
b. multinet
c. TDD net
9. A Bluetooth scatternet consists of 2 or more _________.
ANS:
piconets
d. 2 to 16 nodes
10. An IRDA system is deliberately restricted to a range of _________.
ANS:
1 meter
d. scatternet
Chapter 24: Fiber Optics
16. The basic range of a Bluetooth device is:
a. 10 cm to 1 meter
c. 10 cm to 100 meters
b. 10 cm to 10 meters
d. within 10 feet
17. IRDA stands for:
a. Infrared Data Association
b. Infrared Digital Association
18. The range of an IRDA system is:
a. 1 meter
b. 10 meters
TRUE/FALSE
1. An optical fiber is a waveguide for light. T
c. Infrared Restricted Data Area
d. Infrared Roaming Data Area
2. Fiber has greater bandwidth than copper cable. T
3. Optical fiber has greater loss per kilometer than copper cable. F
c. 1 foot
d. 10 feet
4. Fiber is immune to crosstalk. T
30. A LASER diode can be turned on and off at a rate of 10 GHz. T
5. Optical fiber carries a very small amount of current. F
MULTIPLE CHOICE
6. Optical fiber is easy to "tap". F
7. Optical fiber is easy to splice. F
1. Compared to the core, the index of refraction of the cladding must be:
a. the same
c. less
b. greater
d. doesn't have an index of refraction
8. Optical fiber can be used safely in an atmosphere of explosive gas. T
9. Optical fiber can be used to connect a radio transmitter to an antenna. F
2. Fiber-optic cables do not:
a. carry current
b. cause crosstalk
c. generate EMI
d. all of the above
10. The core has a higher index of refraction than does the cladding. T
11. Single-mode fiber causes less dispersion than does multimode fiber. T
3. Single-mode fiber is made from:
a. glass
c. both a and b
b. plastic
d. none of the above
12. Single-mode fiber is always made from glass. T
13. The core of a single mode fiber is on the order of 1000 µm. F
14. Single-mode fiber is free of all dispersion effects. F
4. Fiber-optic cable cannot be used:
a. in an explosive environment
b. to connect a transmitter to an antenna
c. to isolate a medical patient from a shock hazard
d. none of the above
15. Dispersion can be expressed in units of time. T
16. The terms "linewidth" and "bandwidth" are equivalent for fiber. T
5. A single-mode cable does not suffer from:
a. modal dispersion
c. waveguide dispersion
b. chromatic dispersion
d. all of the above
17. Dispersion increases with cable length. T
18. Glass fiber-optic cables have a loss of about 3dB per km. F
6. Scattering causes:
a. loss
b. dispersion
c. intersymbol interference
d. all of the above
19. Plastic fiber-optic cables have a loss of several hundred dB per km. T
20. The losses due to splicing can be greater than the losses due to the cable itself.
T
21. The purpose of the cladding is to add strength to the fiber-optic cable. F
22. The terms "splice" and "connector" are equivalent for fiber. F
7. The loss in single-mode fiber-optic cable due to the glass is about:
a. 40 dB per km
b. 4 db per km
c. 0.4 dB per km
d. zero loss
8. The loss in single-mode fiber-optic cable due to a splice is about:
a. 0.02 dB
b. 0.2 db
c. 1 dB
d. 3 dB
9. The loss in single-mode fiber-optic cable due to a connector is about:
a. 0.02 dB
b. 0.2 db
c. 1 dB
d. 3 dB
23. A typical splice has a loss of 0.2 dB or less. T
24. Unlike copper cables, it is not possible to make an optical power splitter. F
25. Like copper cables, it is possible to make an optical directional coupler. T
10. Which of the following is a type of fiber connector:
a. ST
b. SC
c. SMA
d. all of the above
11. The quantum of light is called:
a. an erg
b. an e-v
d. a phonon
c. a photon
26. It is possible to make an optical switch. T
27. Energy can be expressed in electron-volts. T
28. LEDs are commonly used to drive single-mode fiber cables in communications
systems. F
29. PIN diodes are used as receivers on single-mode fiber cables in communications
systems. T
12. LASER stands for:
a. Light Amplification by Simulated Emission of Radiation
b. Light Amplification by Stimulated Emission of Radiation
c. Light Amplification by Simulated Emitted Rays
d. Light Amplification by Stimulated Emitted Rays
13. APD stands for:
a. Avalanche Photodiode
b. Advanced Photodiode
c. Avalanche Photo Detector
d. Advanced Photo Detector
14. In a PIN diode, leakage current in the absence of light is called:
a. baseline current
c. dark current
b. zero-point current
d. E-H current
15. For a light detector, responsivity is measured in:
a. amps per watt
c. mA per joule
b. µW per amp
d. µsec per µW
COMPLETION
1. In the core, the angle of incidence equals the angle of _________.
ANS:
reflection
2. The core is surrounded by the _________.
ANS:
cladding
3. The _________ angle is where refraction changes to reflection.
ANS:
critical
14. The optical fiber is not free to move around in a _________ cable.
ANS:
tight-buffer
15. A _________ is a short length of fiber that carries the light away from the
source.
ANS:
pigtail
16. Good connections are more critical with _________-mode fiber.
ANS:
single
17. A _________ diode is the usual light source for single-mode cable.
ANS:
laser
18. The quantum of light is called the _________.
ANS:
photon
19. A _________ diode is the usual light detector for single-mode cable.
ANS:
PIN
20. For safety, you should never _________ at the end of an optical fiber unless you
know it is not connected to a light source.
ANS:
look
4. An electron-volt is a measure of _________.
ANS:
energy
Chapter 25: Fiber-Optic Systems
5. The numerical aperture is the _________ of the angle of acceptance.
ANS:
sine
TRUE/FALSE
6. Optical fiber relies on total _________ reflection.
ANS:
internal
1. Most new telephone trunk cables are fiber-optic. T
2. Cable TV systems use fiber-optic cable. T
7. Chromatic dispersion is also called _________ dispersion.
ANS:
intramodal
8. With optical fiber, _________ light is more common than visible light.
ANS:
infrared
3. Many data network cables are fiber-optic. T
4. Fiber-optic cable is not practical for telephone trunk cables. F
5. CATV uses analog modulation on fiber-optic cables. T
9. In multimode fiber, _________ index has less dispersion than step index.
ANS:
graded
10. For laser diodes, the term _________ is used instead of bandwidth.
ANS:
linewidth
6. Usually, splicing losses can be disregarded in loss-budget calculations. F
7. The rise time of a transmitter limits its bandwidth. T
8. RZ encoding allows twice as much pulse spreading as NRZ. F
11. Dispersion can be expressed in units of _________ rather than bandwidth.
ANS:
time
12. _________ interference is when one pulse merges with the next pulse.
ANS:
Intersymbol
13. The optical fiber is free to move around in a _________ cable.
ANS:
loose-tube
9. The product of bandwidth times distance describes dispersion in a multimode
fiber-optic cable. T
10. Regenerative repeaters for fiber-optic cables typically convert the light signal to
an electrical signal, and then back to light. T
11. Optical amplifiers are not suitable for digital signals. F
12. Dispersion effects accumulate when optical amplifiers are used. T
9. Typically, repeaters are not required for fiber-optic cable lengths up to:
a. 1000 miles
b. 100 miles
c. 100 km
d. 10 km
13. Most fiber-optic systems use TDM. T
14. Fiber-optic cables shorter than 100 km typically do not require repeaters. T
10. In SONET, OC-1 stands for:
a. Optical Carrier level one
b. Optical Coupler unidirectional
c. Optical Channel one
d. Optical Cable type 1
15. SONET operates at a base speed of 25 Mbps. F
16. SONET solves many of the timing problems in synchronizing digital signals. T
11. In SONET, STS stands for:
a. Synchronous Transport Signal
b. Synchronous Transport System
c. Synchronous Transmission Signal
d. Synchronous Transmission System
17. SONET is typically used on LANs. F
12. A commonly used fiber-based system for LANs is:
a. FDDI
c. gigabit Ethernet
b. high-speed Ethernet
d. all of the above
18. FDDI can be used on a LAN. T
19. Soliton pulses can travel down a fiber-optic cable with no dispersion. T
13. The use of solitons on fiber-optic cables is:
a. common
b. experimental
20. TDR cannot be used on fiber-optic cables. F
MULTIPLE CHOICE
1. FDDI stands for:
a. Fiber Digital Data Interface
b. Fiber Distributed Data Interface
2. FITL stands for:
a. Fiber In The Loop
b. Fiber Input Timing Loss
c. Fiber Distribution Delay Interface
d. Frequency-Division Data Interface
c. Frequency Input to The Loop
d. Fiber Input Timing Loop
3. FTTC stands for:
a. Fiber Transmission Timing Constraint
b. Fiber Transmission Technology Committee
c. Fiber Telephone Transmission Cable
d. Fiber To The Curb
4. SONET stands for:
a. Simple Optical Network
b. Standard Optical Network
c. Synchronous Optical Network
d. none of the above
c. type of pulse
d. type of optical network
d. not possible
14. OTDR stands for:
a. Optical Time-Delay Response
b. Optical Timing Delay Requirement
c. Optical Time-Domain Reflectometer
d. Optical Time-Division Relay
15. Using fiber-optic cable in a telephone system except for the connection to the
subscriber's phone is called:
a. FDDI
b. FTTC
c. FITL
d. SONET
COMPLETION
1. FTTC stands for Fiber To The _________.
ANS:
Curb
2. FITL stands for Fiber In The _________.
ANS:
Loop
5. DWDM stands for:
a. Digital Wavelength-Division Modulation
b. Dense Wavelength-Division Modulation
c. Double Wavelength-Division Modulation
d. Dense Wavelength-Division Multiplexing
6. A Soliton is a:
a. defect in the glass
b. type of particle
c. obsolete
3. SDH stands for Synchronous Data _________.
ANS:
Hierarchy
4. WDM stands for _________-division multiplexing.
ANS:
Wavelength
5. SONET stands for _________ Optical Network.
ANS:
Synchronous
6. FDDI stands for Fiber _________ Data Interface.
ANS:
Distributed
7. Adding bits to synchronize one digital signal to another is called:
a. bit stuffing
b. bit-synch
c. SDH
d. WDM
7. Optical amplifiers use _________-doped glass.
ANS:
erbium
8. Power above the minimum required by an optical receiver is called:
a. gain margin
b. system margin
c. excess gain
d. overdrive
8. Optical amplifiers use a _________ laser.
ANS:
pump
9. Dense _________ allows many different wavelengths of light to share a cable.
ANS:
WDM
10. The OC-1 line rate is _________ Mbps.
ANS:
51.84
11. SONET does not use bit _________ to synchronize two digital signals.
ANS:
stuffing
12. SONET uses a _________ to denote the starting position of an information
frame.
ANS:
pointer
13. FDDI systems use two _________ rings to carry signals.
ANS:
token
14. The two rings of an FDDI system carry data in _________ directions.
ANS:
opposite
15. Each _________ in an FDDI system acts as a regenerative repeater.
ANS:
node
16. FDDI uses _________ mode cables.
ANS:
multi
17. The data rate of an FDDI system is _________ bps.
ANS:
100 M
18. SONET frames have considerably more _________ than do DS frames for
information about signal routing and setup.
ANS:
overhead
19. The number of bytes in a SONET frame is _________.
ANS:
810
20. The number of bytes in the payload of a SONET frame is _________.
ANS:
774
21. The number of rows in a SONET frame is _________.
ANS:
9
22. The total number of overhead bytes in a SONET frame row is _________.
ANS:
4
23. The number of path overhead bytes in a SONET frame row is _________.
ANS:
1
24. SONET frame rows contain path overhead and _________ overhead.
ANS:
transport
25. In SONET, SPE stands for synchronous payload _________.
ANS:
envelope
SHORT ANSWER
1. What is the bandwidth of a first-order LPF with a rise time of 350 nanoseconds?
ANS:
1 MHz
2. Calculate the total rise time for a fiber-optic system if the transmitter, receiver,
and cable each have a rise time of 50 nanoseconds.
ANS:
86.6 nanoseconds