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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 2
26.
Consider the following features of monochrome TV
  1. Number of lines per picture 625
  2. Interlace ratio 2 : 1
  3. Aspect ratio 4 : 3
  4. Channel bandwidth 8 MHz
As regards CCIR system B, which of the above are correct?
1, 2, 3, 4
1, 2, 3
1, 2, 4
2, 3, 4
Answer: Option
Explanation:

Channel bandwidth is not 8 MHz.

27.
In the absence of noise, if C is channel capacity in bits/s, δf is channel bandwidth in Hz and N is number of coding levels. Then
C = log2 N
C = (δf) log2 N
C = 2 (δf) log2 N
C = 0.5 (δf) log2 N
Answer: Option
Explanation:

Hartley law C = 2 δf log2N.

28.
The open loop gain of an amplifier is 50 but is likely to change by 20%. If negative feedback with β = 0.1 is used, the change in gain will be about
20%
10%
4%
0.05%
Answer: Option
Explanation:

.

Change in gain is about 4%.

29.
Audio amplifiers need
Bass control
Treble control
Both Bass and Treble control
Either Bass or Treble control
Answer: Option
Explanation:

Bass means low frequency tones and treble means high frequency tones.

30.
The open loop gain of an amplifier is 200. If negative feedback with β = 0.2 is used, the closed loop gain will be
200
40
4.878
1.212
Answer: Option
Explanation:

.

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