Communication Systems - ECE Questions and Answers

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The ratio for 100% amplitude modulation with identical total transmitted power (m_f is modulation index of FM) is

m_f²

m²_f

m_f³

m³_f

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The function of a modulator is to

separate two frequencies

extract information from the carrier

amplify the audio frequency signal

impress the information on to a RF carrier

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Which of the following radio waves are not reflected by ionosphere?

Waves above 1 kHz

Waves above 1 MHz

Waves above 10 MHz

Waves above 30 MHz

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Square law modulators utilise

linear range of V-I characteristics of a diode

linear range of V-I characteristics of a triode

non-linear region of V-I dynamic characteristics of a diode

non-linear region of V-I dynamic characteristics of a triode

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Which of the following is a disadvantage of Vestigial Sideband (VSB) system?

Low video frequencies are attenuated

Bandwidth is conserved resulting in a saving of 2 MHz per channel over DSB system

It results in a power boost of two video frequencies

It possess the advantages of both DSB and SSB system

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The maximum permissible distance between two samples of a 2 kHz signal is

1000 μ sec

500 μ sec

250 μ sec

2000 sec

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When the video signal is applied to the picture tube in a TV receiver, the strength of video signal is about

1000 V

200 V

50 V

1 V

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In the above case if the modulating frequency is increased to 20 kHz the bandwidth will be

0.05 MHz

1 MHz

2 MHz

4 MHz

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Assertion (A): In FM all power amplifiers can be operated in class C

Reason (R): FM is a constant amplitude modulation system.

Both A and R are correct and R is correct explanation of A

Both A and R are correct but R is not correct explanation of A

A is correct but R is wrong

A is wrong but R is correct