DEPARTMENT OF ECE
QUESTION BANK
Subject Code 6304
Subject Name: Analog and Digital Communication
UNIT -I
Year/Sem:II/III
PART- A (2 MARKS)
As related to AM, what is over modulation, under modulation and 100% modulation?
Define modulation index of an AM signal
A transmitter radiates 9 kW without modulation and 10.125 kW after modulation.
Determine depth of modulation.
Define the transmission efficiency of AM signal.
Draw the phasor diagram of AM signal.
Advantages of SSB.
Disadvantages of DSB-FC.
What are the advantages of superhetrodyne receiver?
Distinguish between low level and high level modulator.
Give the parameters of receiver.
Define sensitivity and selectivity.
Define fidelity.
What is meant by image frequency?
Need for modulation.
Application of AM.
What is meant by diagonal clipping and negative peak clipping?
Define envelope.
Distinguish between linear and non linear modulator.
What are the limitations of AM
Draw the envelope of AM
Differentiate phase modulation and frequency modulation.
When a signal m(t) = 3 cos (2p x 103t ) modulates a carrier c(t) = 5 cos (p x 106t),
find the modulation index and transmission bandwidth if the modulationisAM.
What do you mean by narrowband and wideband FM?
Give the frequency spectrum of narrowband FM?
Define frequency deviation in FM?
state Carson’s rule of FM bandwidth?
Differentiate between narrow band and wideband FM.?
What are the advantages of FM.?
Define PM.
what is meant by indirect FM generation?
Draw the phasor diagram of narrow band FM.
Write the expression for the spectrum of a single tone FM signal.
Define modulation index of FM and PM.
Differentiate between phase and frequency modulation.
A carrier of frequency 100 MHz is frequency modulated by a signal x(t)=20sin
(200¶x103 t ). What is the bandwidth of the FM signal if the frequency sensitivity of themodulator is 25
KHz per volt?
39. What is the bandwidth required for an FM wave in which the modulating frequency signal is 2 KHz and the
maximum frequency deviation is 12 KHz?
40. Determine and draw the instantaneous frequency of a wave having a total phase
41. angle given by ø(t)= 2000t +sin10t.
PART- B (16 MARKS)
1.(i) What is the principle of Amplitude modulation? Derive expression for the AM wave and draw its
spectrum. (8)
(ii) Describe the frequency analysis of Angle modulated waves. Explain their Bandwidth requirements. (8)
2) (i) A modulating signal of 2 cos5000t is amplitude modulated over a carrier signal of 5cos20000t .
Derive expressions for the modulation index, LSB and VSB frequencies, Bandwidth and the ratio of
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Side Band Power in the Total Power of AM wave. (8)
(ii) Explain the principle of Angle Modulation. Derive and explain phase deviation, Modulation index,
frequency deviation and percent modulation. (8)
3) (i) Write short notes on : (1) AM voltage distribution. (4) (2) AM power distribution. (4)
(ii) An audio frequency signal 10 sin 2w500t is used to amplitude modulate a carrier of 50 sin
5*3.14*10^5 t. Calculate (1) Modulation index (2) (2) Side band frequencies (2)
4) (i) Compare FM and AM. (12)
(ii) The phase deviation constant in a phase modulation system is K = 0.01 rad/v. Calculate the
maximum phase deviation when a modulating signal of 10 V is applied? (4)
5) In angle modulation, explain frequency deviation, percent modulation, phase deviation and modulation
index with suitable example.
6) (i) Derive the expression for a Amplitude Modulated wave and draw its spectrum. (10)
(ii) Obtain a relationship between carrier and side band powers in an AM DSBFC wave and explain
how power distribution takes place in AM DSB FC system. (6)
7) (i) Define modulation index for FM and PM and obtain the relation between modulation index and
modulating signal for FM and PM.
(ii) Compare the advantages and disadvantages of angle modulation with amplitude modulation.
8) (i) Distinguish between FM and PM by giving its mathematical analysis. (8)
(ii) Derive the relationship between the voltage amplitudes of the side band frequencies and the carrier
and draw the frequency spectrum. (8)
9) In an AM modulator, 500 KHz carrier of amplitude 20 V is modulated by 10 KHz modulating signal
which causes a change in the output wave of ｱ 7.5 V . Determine :
(1) Upper and lower side band frequencies
(2) Modulation Index
(3) Peak amplitude of upper and lower side frequency(4) Maximum and minimum amplitudes of envelope
UNIT - II
PART – A (2 MARKS)
1. Differentiate coherent and non coherent digital modulation methods
2. What is correlative coding?
3. Compare bandwidth of Mary PSK signal And Mary FSK signal
4. Sketch the waveform of PSK for binary sequence 1100101.
5. Differentiate QPSK and BPSK.
6. Differentiate ASK and FSK.
7. What are the type of digital data format.
8. Define minimum Shift keying.
9. Define Duobinary encoding
10.Define DPSK.
11 What are the advantages of QPSK?
12 Define Nyquist sampling theorem.
13 Define information capacity and bit rate.
14. Draw PWM and PPM waveforms.
15. What is the relation between bit rate and baud for a FSK system?
16. What are the advantages of digital transmission?
17. Define ASK, PSK and FSK.
18. What is meant by antipodal signal and give one example?
19. Why is ASK called as ON-OFF keying?
20. What are the differences between QASK and QPSK?
PART – B (16 MARKS)
1. (i) Draw FSK Transmitter and explain. Describe its Bandwidth Considerations. (8)
(ii) For a BPSK modulator with a Carrier frequency of 70 MHz and an input bit rate of 10 Mbps, determine the
maximum and minimum upper and lower side frequencies, draw the output spectrum, determine the minimum
Nyquist bandwidth, and calculate the baud (Assume f= 5MHz)
2) (i) Draw and explain the operations of Non-coherent and coherent FSK modulators. (8)
(ii) Draw QPSK modulator and explain. Describe its Bandwidth considerations. (8)
3) (i) Explain the principle of FSK transmitter and receiver. (10)
(ii) Write short notes on the spectrum and bandwidth of FSK. (6)
4) (i) Compare the various types of digital modulation techniques. (8)
(ii) Explain the eyepattern in base band digital transmission with a neat diagram. (8)
5) Describe FSK transmitter and FSK receiver.
6) Explain in detail carrier recovery with a suitable block diagram.
7) (i) Describe with neat diagram, the operation of a QPSK modulator. Draw its phasor and constellation diagram.
(ii) Explain the bandwidth considerations of QPSK system. (6)
8) What is carrier recovery? Discuss how carrier recovery is achieved by the squaring loop and Costas loop circuits.
9) Draw the block diagram of FSK receiver and explain the operation. Determine the : (i) peak frequency deviation
(ii) minimum bandwidth (iii) baud for FSK signal with a mark frequency of 49 kHz, space frequency of 51 kHz, and
input bit rate of 2 kbps.
10) Draw the block diagram of QPSK modulator and explain its operation. For QPSK modulator, construct the truth
table, phasor diagram and constellation diagram.
11) What is known as Binary phase shift keying? Discuss in detail the BPSK transmitter and Receiver and also
obtain the minimum double sided Nyquist bandwidth.
12) (i) Illustrate the concept of 8 QAM transmitter with the truth table. (8)
(ii) What is the need for carrier Recovery? Explain the Costas loop method of carrier recovery. (8)
UNIT III
PART – A (2 MARKS)
1. State sampling theorem.
2. What is aliasing?
3. How to avoid aliasing effect.
4. Define eye pattern.
5. Define PAM.
6. Construct NRZ and RZ format for 011010.
7. Define adaptive equalization.
8.Define ISI.
9.Define Nyquist Criteria.
10.What is the interpretation obtained from eye pattern?
11. Define Nyquist sampling theorem.
12. For the signal m t3 cos 500 wt 4 sin 1000*3.14 t , Determine the Nyquist sampling rate.
13. Draw PWM and PPM waveforms.
14. Draw the Eye pattern and indicate how ISI is measured from it.
15. What are the advantages of digital transmission?
16. Define companding.
17. Define dynamic range.
18. Determine the Nyquist sample rate for a maximum analog input frequency of (a) 4 KHz (b) 10 KHz.
19. Distinguish between DM and ADM.
PART –B (16 MARKS)
1. State and prove Sampling theorem.
2. Explain various data formats with clear example.
3. What is eye pattern. What are the interpretations obtained from it?
4. Write notes on Intersymbol Interference.
5. Explain in detail the Nyquist criterion for distortionless transmission of baseband PAM signal
6. Write notes on adaptive equalization.
7. (i) Describe in detail the PCM technique with focus on its sampling rate, and signal to quantization Noise ratio.
(ii) What is ISI? Explain the applications of eye pattern to detect ISI. (8)
8. (i) With a block diagram, explain the adaptive Delta Modulation technique. (8)
(ii) What is DPCM? Explain its principle with neat block diagram. (8)
9. (i) Explain the elements of PCM system with a neat block diagram. (12)
(ii) What is companding? (4)
10 (i) Find the signal amplitude for minimum quantization error in a delta modulation system if step size is 1 volt
having repetition period 1 ms. The information signal operates at 100 Hz.
(ii) Describe the operation of DPCM system with a relevant diagram.(12)
11. For a PCM system with the following parameters, determin (i) Minimum sampling rate
(ii) Minimum number of bits used in the PCM code (iii) Resolution and
Maximum analog input frequency = 4 KHz
(iv) Quantization error
Minimum dynamic range = 46 dB.
Describe DPCM transmitter and receiver with suitable block diagram.
13. (i) Draw the block diagram of a PCM transmitter and explain the function of each block. (6)
(ii) What are the types of sampling? Explain the operation of the sample and hold circuit. (10)
14. Draw the block diagram and describe the operation of a delta modulator. What are its advantages and
disadvantages compared to a PCM system? (16)
15. What is companding? Explain analog companding process with the help of block diagram.
16. How does delta modulation differ from PCM? Explain delta modulation transmitter with the help of a block
diagram.
17. (i) Explain in detail the Delta modulation transmitter and Receiver. (10)
(ii) Discuss the draw backs of delta modulation and explain the significance of adaptive delta modulator. (6)
UNIT V
PART – A (2 MARKS)
1. Define pseudo noise sequence.
2. Define spread spectrum technique
3. Differentiate Slow and fast FH SS technique.
4. Differentiate TDMA and FDMA.
5. Define processing gain for DS SS technique
6. What are the advantages of Spread Spectrum techniques?
7. Differentiate DS –SS and FH-SS.
8. Define processing gain for FH SS technique
9. What are the disadvantages of DS SS techniques?
10. What are the advantages of FH SS techniques?
11. What are the applications of spread spectrum modulation?
12. Design processing gain in spread spectrum modulation.
13. Define effective jamming power and processing.
14. What is the principle of frequency hopping spread spectrum?
15. A spread spectrum communication system has the following parameters;information bit duration Tb = 4.095 ms,
PN chip duration Tc = 1 ms. Determine Processing Gain.
16. What is meant by slow frequency hopping and fast-frequency hopping?
17. What is frequency hopping?
18. What is meant by an orthogonal code?
19. Define Pseudonoise sequence?
20. What are the different types of multiple access techniques?
21. What is the significance of PN sequence?
22. What are the types of FH spread spectrum technique?
PART –B (16 MARKS)
1. Explain in detail the transmitter and receiver of DS SS technique.
2. Explain in detail the transmitter and receiver of FH SS technique.
3. Explain in detail the characteristics of PN sequence
4. Explain the two common multiple access technique for wireless communication.
5. Differentiate direct sequence and frequency hop spread spectrum technique
6. Compare and contrast TDMA and CDMA techniques.
7. (i) Draw the circuit of a P-N sequence generator and explain. (8)
(ii) Describe the concept of FHSS in detail. (8)
8. (i) Explain the principle of DSSS with coherent binary PSK. (8)
(ii) Compare between the TDMA and CDMA wireless communication systems.
9. (i) Write a short note on frequency hop spread spectrum. (10)
(ii) Explain the applications of spread spectrum techniques. (6)
10. (i) Give a detail account of the different types of multiple access techniques. (10)
(ii) Compare TDMA and CDMA. (6)
11. Discuss the frequency HOP spread spectrum with suitable block diagram.
12. Explain the source coding of speech for wireless communications.
13. (i) What is a PN sequence.? Explain its important properties. (8)
(ii) Describe with block diagram, DS SS binary PSK spread spectrum system. (8)
14. (i) Describe the operation of a CDMA multiplexing system. (10)
(ii) List the advantages of CDMA over TDMA multiple access scheme.(6)
15. With the help of block diagram explain how DSSS can be implemented. Draw the input and output waveforms.
16 Explain the frequency – hopped spread spectrum with a block diagram.
How PN sequences are generated?
17.(i) What is a Pseudo noise sequence? What are the properties of Pseudo noise sequence? (8)
(ii) Describe the application of CDMA in Wireless communication system. (8)
18. (i) With a block diagram explain, DS spread spectrum with coherent binary PSK. (10)
(ii) Explain the near-far problem in spread spectrum modulation? (6)
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