﻿ 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 | 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 is2 million 10 million 0.1 million 1 million

D.

1 million

The frequency for optical communication

But only 2% of the source frequency is available for TV transmission.

∴    v' = 2.5 × 1014 × 2 %

or   v' = 2.5 × 1014 × $\frac{2}{100}$

or   v' = 5 × 1012 Hz

∴  Number of channels = $\frac{\mathrm{v}\text{'}}{\mathrm{bandwidth}}$

or  number of channels =

or  number of channels =

= 106

= 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.