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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 3
26.
The minimum step size required for a Delta modulator operating at 36 samples/sec to track the signal (here u(t) is the unit step function) x(t) = 125t (u(t) - u(t - 1)) + (250 - 125t) (u(t - 1) - u(t - 2)) So that slope overload is avoided, would be
2-10
2-8
2-6
2-4
Answer: Option
Explanation:

To avoid slope overload

|m(t)| ≥ Δ . fs or |x(t)| ≥ Δ . fs

125 ≤ Δ . 25 . 210

27 ≤ Δ . 215 Δ ≥ 2-8.

27.
An FM signal with a deviation δ is passed through a mixer, and has its frequency reduced 5 fold. The deviation in the output of the mixer is
5/δ
Intermediate
δ/5
δ
Answer: Option
Explanation:

Deviation depend on amplified of signal not on frequency.

28.
In PCM, if the number of quantization levels is increased from 4 to 64, then the bandwidth requirement will approximately be increased __________ times.
8
16
3
32
Answer: Option
Explanation:

Bandwidth for PCM system

= 2nN fm Hz for N >> 1, n >> 1

where n is no. of channel, N is no. of bit.

B1 = 2n N1 fm

B2 = 2n N2 fm

2N1 = 4 N1 = log24 N1 = 2

2N2 = 64 N2 = log264 6

.

29.
A tweeter should be fed from the input through a
low pass filter
high pass filter
band pass filter
band stop filter
Answer: Option
Explanation:

Tweeter is high frequency loudspeaker covering the range above 5000 Hz.

30.
The modulation index is, if fm = 500 Hz, Δf = 2.25 kHz
2.25
4.5
9
18
Answer: Option
Explanation:

Δf = 2.25 kHz, fm = 500 Hz

.

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