REVIEW QUESTIONS
DIGITAL COMMUNICATIONS
ENCIRCLE YOUR ANSWER
1. Assigning of codes to absolute
magnitude.
a. Sampling
b. Quantizing
c. Filtering
d. None of the above
d. All of the above
7. As the bit rate of an FSK signal
increases, the bandwidth ____.
a. decreases
b. remains the same
c. increases
d. doubles
2. Which of the following methods
does not provide for
synchronization.
a. RZ
b. NRZ-L
c. B8ZS
d. HDB3
8. For a given bit rate, the minimum
bandwidth for ASK is _____ the
minimum bandwidth for FSK.
a. Equivalent to
b. Less than
c. Greater than
d. Twice
3. Which of the following is most
affected by noise?
a. ASK
b. FSK
c. PSK
d. QAM
9. For FSK, as the difference
between the two carrier
frequencies increases, the
bandwidth _____.
a. decreases
b. increases
c. remains the same
d. doubles
4. Which conversion type involves
modulation of a signal?
a. Analog to digital
b. Digital to analog
c. Digital to digital
d. All of the above
10. RZ encoding involves ______
level(s) of signal amplitude.
a. 1
b. 2
c. 3
d. 4
5. Which conversion type needs
sampling of a signal?
a. Analog to digital
b. Digital to analog
c. Digital to digital
d. All of the above
11. Which quantization level results
in a more faithful reproduction of
signal?
a. 4
b. 8
c. 16
d. 32
6. The bit rate always equals the
baud rate in which type of signal?
a. FSK
b. QAM
c. 4-PSK
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II. ANSWER THE FOLLOWING
1. Given a BW of 6,500 Hz (1000 – 7,500 Hz), draw the full-duplex ASK diagram of the
system. Find the carriers and the BWs in each direction. Assume there is 500Hz gap
between the bands in 2 directions.
2. Find the max bit rates for an FSK signal if the BW of the medium is 12,000 Hz and
the difference between the carriers must be at least 2000 Hz. Transmission is in fullduplex mode.
3. Find the BW for a 16-PSK signal transmitting at 8000 bps. Transmission is in halfduplex mode.
4. The data points of a constellation are at (4,0) and (6,0). Draw the constellation. Show
the amplitude and phase for each point. Is the modulation ASK, PSK, or QAM? How
many bits per baud can one send with this constellation?
5. What are the steps in converting analog signal to digital using PCM? You can use
drawing and example to describe the steps.
6. HDB3 was used to generate the signal below, decode the signal to get the binary
equivalent using HDB3.
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