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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 4
31.
A directional microphone gives an output of 0.5 mV whereas an omnidirectional one gives an output of 0.5 μV in the same position for the same sound pressure. The directivity of the directional microphone is
120 dB
90 dB
60 dB
30 dB
Answer: Option
Explanation:

Directivity =

= 60 dB.

32.
If Eb, the energy per bit of a binary digital signal is 10-6 watt sec. and the one sided power spectral density of the white noise N0 = 10-5 W/Hz, then the output SNR of the matched filter is
26 dB
10 dB
20 dB
13 dB
Answer: Option
Explanation:

O/P SNR = 10 log10 [2 x 10-6 x 10-5].

33.
Consider the following statements about Rhombic antenna
  1. It is non resonant
  2. It is a broad band antenna
  3. It is ideally suited for HF transmission
Which of the above are correct?
1, 2, 3
1, 3 only
2, 3 only
1 only
Answer: Option
Explanation:

All the three features are correct.

34.

Assertion (A): A composite video signal has synchronising pulses.

Reason (R): It is necessary to synchronise the scanning process in the transmitter and receiver.

Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Answer: Option
Explanation:

Synchronisation of scanning process at transmitter and receiver is necessary for proper reproduction at TV receiver.

For this purpose synchronising pulses are sent as a part of video signal.

35.
Noise with uniform power spectral density of N0ω/Hz is passed through a filter H(ω) = 2 exp (-J ω ty) followed by an ideal low pass filter of bandwidth B Hz. The output noise power in watts is
2 N0B
4 N0B
8 N0B
16 N0B
Answer: Option
Explanation:

Output spectral power density

= | H(ω) | x I/P spectral power density

= 2 x 2N0 4N0

Output power = 4 N0B.

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