﻿ Which of the following statement is wrong ? | Communication Systems

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# Communication Systems

#### Multiple Choice Questions

31.

1000 kHz carrier wave is amplitude modulated by the signal frequency 200-4000 Hz. The channel width of this case is

• 8 kHz

• 4 kHz

• 7.6 kHz

• 3.8 kHz

32.

A carrier frequency of 1 MHz and peak value of 10 V is amplitude modulated with a signal frequency of 10 kHz with peak value of 0.5 V. Then the modulation index and the side band frequencies respectively are

• 0.05 and ± 0.010 MHz

• 0.5 and 1 ± 0.010 MHz

• 0.05 and 1 ± 0.005 MHz

• 0.5 and 1 ± 0.005 MHz

33.

The maximum line-of-sight distance dM, between two antennas having heights hT and hR above the earth is

34.

The frequency band used in the downlink of satellite communication is

• 9.5 to 2.5 GHz

• 896 to 901 MHz

• 3.7 to 4.2 GHz

• 840 to 935 MHz

35.

In amplitude modulation, the bandwidth is

• twice the audio signal frequency

• thrice the audio signal frequency

• thrice the carrier wave frequency

• twice the carrier wave frequency

36.

A diode AM detector with the output circuit consisting of R = 1kΩ and C = 1 µF would be more suitable for detecting a carrier signal of

• 0.1 kHz

• 0.5 kHz

• 10 kHz

• 0.75 kHz

37.

In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is

• 2 million

• 10 million

• 0.1 million

• 1 million

38.

In satellite communication

1. the frequency used lies between 5 MHz and 10 MHz.
3. the orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°.

In the above statements

• only 2 and 3 are true

• all are true

• only 2 is true

• only 1 and 2 are true

39.

The principle used in the transmission of signals through an optical fibre is

• total internal reflection

• reflection

• refraction

• dispersion

# 40.Which of the following statement is wrong ?Ground wave propagation can be sustained at frequencies 500 kHz to 1500 kHz. Statellite communication is useful for the frequencies above 30 MHz. Sky wave propagation is useful in the range of 30 to 40 MHz. Sky wave propagation takes place through tropospheric space.

C.

Sky wave propagation is useful in the range of 30 to 40 MHz.

In ground wave propagation, radiowaves travel along the surface of the earth (following the curvature of earth). Ground wave propagation can be sustained only at low frequencies  (∼500 kHz to 1500 kHz) or for radiobroadcast at long wavelengths.

Satellite communication is useful for the frequencies above 30 MHz which takes place through tropospheric space. The phenomenon involved in the sky wave propagation is total internal reflection.