ANALOG AND DIGITAL COMMUNICATION Question Bank

ANALOG AND DIGITAL COMMUNICATION

Part 1

1) Define coefficient of modulation and percentage modulation for an AM system.
2) Determine the improvement in noise figure for a receiver with an RF bandwidth equal to 200KHz
and an IF bandwidth equal to 10KHz.
3) A 20MHz carrier is frequency modulated by a sinusoidal signal such that the peak frequency
deviation is 100KHz.Determine the modulation index and approximate
bandwidth of the FM signal if the frequency of the modulating signal is 50KHz.
4) How will you convert a frequency modulator into a phase modulator?
5) Why are synchronous modems required for medium and high speed applications?
6) What is μ-law companding?
7) Determine the bandwidth and baud for the FSK signal with a mark frequency of 49KHz and a
space frequency of 51KHz and a bit rate of 2Kbps.
8) Write the differences between PSK and FSK.
9) State the ‘run property’ of maximum length sequences.
10) How will you compact the effects of multi-path in a slow fading channel?

PART-B

11) a) i) Define amplitude modulation. Derive the relation between the total transmitted power and
carrier power in an AM system when several
frequencies simultaneously modulate a carrier
ii) For an AM DSBFC wave with a peak unmodulated carrier voltage
Vc=10Vp, a load resistance RL=10?, and a modulation coefficient m=1, determine
(1) Powers of the carrier, upper and lower side bands
(2) Total power of the modulated wave
(3) Total side band power
(4) Draw the power spectrum.
(or)
b) i) Draw the block diagram of an AM super heterodyne receiver and explain
function of each block.
ii) A super heterodyne radio receiver has a mixer that translates the carrier frequency ƒc to a fixed IF
frequency of 455KHz by using a local oscillator
of frequency ƒLO. The broadcast frequencies range from 540 to 1600KHz.
iii) Determine the range of tuning that must be provided in the local oscillator
(1) When ƒLO is higher than ƒc and
(2) When ƒLO is lower than ƒc.

12) a) Compare direct and indirect FM modulators. Draw the block diagram of a direct
FM transmitter and describe its operation.
(or)
b) Draw the circuit diagram of a radio detector for FM demodulation and explain. State the
advantages of a radio detector over slope detector and Foster-Seelay
Detector.

13) a) i) Draw the block diagram of typical DPCM system and explain.
ii) In a binary PCM system, the output signal to quantization noise ratio is to be a minimum of 40dB.
Determine the number of required levels, and find the
corresponding out signal to quantization noise ratio.
(or)
b) i) Draw the eye diagram and explain its importance in data transmission.
ii) Write short notes on Vertical and Horizontal check Schemes for error detection.

14) a) Draw the block diagram of a QPSK transmitter and explain. Derive the bandwidth requirement
of a QPSK system
(or)
b) Draw the block diagram of a non-coherent receiver for detection of binary FSK signals and the
probability of symbol error for a non-coherent FSK system.

15) a) What is frequency hop spread spectrum? Explain the generation of slow frequency hop spread
M-ary FSK and fast frequency hop spread M-ary FSK . with appropriate diagrams
(or)
b) i) Compare Time division Multiple Access and Frequency Division Multiple Access.
ii) A spread spectrum communication system has the following parameters:
Information bit duration Tb=4.095ms, PN chip duration Tc=1μs, the energy to
noise ratio Eb / No=10. Calculate the processing gain and Jamming margin.