Communication Systems

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

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

The maximum line-of-sight distance d_M, between two antennas having heights h_T and h_R above the earth is

• $\sqrt{\mathrm{R} ({\mathrm{h}}_{\mathrm{T}} + {\mathrm{h}}_{\mathrm{R}})}$

• $\sqrt{2\mathrm{R}/\left({\mathrm{h}}_{\mathrm{T}} + {\mathrm{h}}_{\mathrm{R}}\right)}$

• $\sqrt{{\mathrm{Rh}}_{\mathrm{T}}} + \sqrt{2{\mathrm{Rh}}_{\mathrm{R}}}$

• $\sqrt{2{\mathrm{Rh}}_{\mathrm{T}}} + \sqrt{2{\mathrm{Rh}}_{\mathrm{R}}}$

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

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

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

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

In satellite communication

1. the frequency used lies between 5 MHz and 10 MHz.
2. the uplink and downlink frequencies are different.
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

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

• total internal reflection

• reflection

• refraction

• dispersion

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.