Exercise: Communication Systems

Questions for: Communication Systems

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
A:
5 ms
B:
2.5 ms
C:
1 ms
D:
0.1 ms
Answer: C

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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
A:
the input to the modulator is essentially constant
B:
the modulator is going through slope overload
C:
the accumulator is in saturation
D:
the speech signal is being sampled at the Nyquist rate
Answer: A

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

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In a CD player the speed of CD is
A:
constant at 500 rpm
B:
constant at 200 rpm
C:
varies from 200 to 500 rpm
D:
none of the above
Answer: C

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.

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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
A:
115.2 kbps
B:
28.8 kbps
C:
57.6 kbps
D:
38.4 kbps
Answer: C

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.

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Fields are said to be circularly polarised if their magnitudes are
A:
equal and they are in phase
B:
equal but they differ in phase by ± 90°
C:
unequal and differ in phase by ± 90°
D:
unequal but are in phase
Answer: B

Magnitudes should be equal and phase angle ± 90°.

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