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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 2
21.
Fields are said to be circularly polarised if their magnitudes are
equal and they are in phase
equal but they differ in phase by ± 90°
unequal and differ in phase by ± 90°
unequal but are in phase
Answer: Option
Explanation:

Magnitudes should be equal and phase angle ± 90°.

22.
Three analog signals, having bandwidths 1200 Hz, 600 Hz, 600 Hz are sampled at their Nyquist rates, encoded with 12 bit words, and time division multiplexed. The bit rate for the multiplexed signal is
115.2 kbps
28.8 kbps
57.6 kbps
38.4 kbps
Answer: Option
Explanation:

The total message bandwidth = 1200 Hz + 600 Hz + 600 Hz = 2400 Hz

Sampling frequency = 4800 samples/sec.

Hence, Bit rate = 4800 x 12

57.6 kbps.

23.
In a CD player the speed of CD is
constant at 500 rpm
constant at 200 rpm
varies from 200 to 500 rpm
none of the above
Answer: Option
Explanation:

Since the circumference of outer tracks is more than that of tracks near the centre, the speed of disc is varied from 200 rpm to 500 rpm.

24.
In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 < t < t2. This indicates that during this interval
the input to the modulator is essentially constant
the modulator is going through slope overload
the accumulator is in saturation
the speech signal is being sampled at the Nyquist rate
Answer: Option
Explanation:

In delta modulator, when consecutive pulses of polarity are opposite then signal is constant.

25.
A fascimile reproduction has a specification of 200 lines per frame, progressive scanning and 5 frames per second. The time to scan one line is
5 ms
2.5 ms
1 ms
0.1 ms
Answer: Option
Explanation:

.

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