Digital communications
Unit-1
1.The advantage of Manchester encoding is [ c ]
A) less band width requirement B) less bit energy required for
transmission
C)
less probability of error D) less bit duration
2. The Nyquist's
rate of sampling of an analog signal S(t) for alias free reconstruction is
5000samples/sec. For a signal x(t) = [S(t)]2 ,the corresponding sampling rate
in samples/sec is 10,000
3. The sampling
rate in Delta Modulation is More than
PCM.
Uniit-2
1. The minimum band width required to multiplex
12 different message signals each of band width 10KHz is [ b]
A) 60KHz B)
120KHz C) 180KHz D) 160KHz
2. Companding results in [ c]
A)More S/N ratio at higher amplitudes of the base band signal
B) More S/N ratio at lower amplitudes of the base band signal
C) Uniform S/N ratio throughout the base band signal
D) Better S/N
ratio at lower frequencies
3. A uniform quantizer is having a step size of
.05 volts. This quantizer suffers from a maximum quantization error of [ b ]
A) 0.1V B)
0.025 V C) 0.8 V D) 0.05 V
4. Granular Noise in Delta Modulation system can
be reduced by [ c ]
A) using a square law device B) increasing the step size
C) decreasing
the step size D) adjusting the rate of rise of the base band signal
5. Tapped
Delay Line Filter is used as a
Predictor in a DPCM transmitter.
6. A
signal extending over -4v to +4v is quantized into 8 levels. The maximum
possible quantization error obtainable is 0.5v
V.
7. The
sampling rate in Delta Modulation is more
than PCM.
Unit-3
1.In 8-PSK system, adjacent phasors differ by
an angle given by ( in degrees) [ a ]
A) n/4 B) n/8 C) n/6 D) n/2
2. Band Width
efficiency of a Digital Modulation Method is [ c ]
A)
(Minimum Band width)/ (Transmission Bit Rate)
B)
(Power required)/( Minimum Band width)
C) (Transmission Bit
rate)/ (Minimum Band width)
D) (Power Saved during transmission)/(Minimum Band
width)
3. The minimum
band width required for a BPSK signal is equal to [d ]
A) one fourth of bit rate B) twice the bit rate C)
half of the bit rate D) bit rate
4. In Non-Coherent demodulation, the receiver [ b
]
A) relies on carrier
phase B) relies on the carrier amplitude
C) makes an error with less probability D) uses a
carrier recovery circuit
5. Non-coherent detection of FSK signal results in More Probability of error
6. The phases in a QPSK system can be expressed as 0,
90, 180,270
7. The Synchronization is defined as The use of same clock to maintain the
order of transmission
Unit-4
1. The
Auto-correlation function of White Noise is [ a]
A) Impulse function B) Constant C) Sampling
function D) Step function
2. A Matched filter is used to minimizes the probability of error
3. The bit error Probability of BPSK
system is same that of QPSK.
Prepared by
Jyosthna
Prepared by
Jyosthna