﻿ What is space wave propagation? from Physics Communication Systems Class 12 CBSE
What is space wave propagation?

The mode of wave propagation in which the radio waves emitted from the transmitter antenna reach the receiving antenna through space in a straight line is known as space wave propagation. Space waves are the radio waves of frequency-range from 54 MHz to 4.2 GHz.
Space wave propagation is used in line of sight communication and satelite communication.
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Radio waves of constant amplitude can be generated with
• Filter

• Rectifier

• FET

• Oscillator

D.

Oscillator

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In an amplitude modulated wave for audio-frequency of 500 cycles/sec, the appropriate carrier frequency will be
• 50 cycles/sec
• 100 cycles/sec
• 500 cycles/sec
• 50,000 cycles/sec

D.

50,000 cycles/sec
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State various modes of propagation of electromagnetic waves. Explain briefly using a proper diagram, the mode of propagation used is the frequency range from a few MHz up to 40 MHz.

Electromagnetic waves are propagated through the following modes:
(i) ground wave propagation
(ii) sky wave propagation, and
(iii) space wave propagation.

For transmission of signal having frequency range from a few MHz up to 40 MHz, sky wave propagation mode is used.

Sky wave propagation:

The mode of wave propagation in which the radiowaves emitted from the transmitter antenna reach the receiving antenna after reflection by the ionosphere.

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What is 'amplitude modulation'? Represent the process graphically. Write the limitation of amplitude modulation.

In amplitude modulation, the amplitude of the carrier wave is varied in accordance with the amplitude of the audio frequency modulating signal.
In this case, the frequency of the amplitude modulated wave remains the same as that of the carrier wave.

Limitation of amplitude modulation:

1. The amplitude of modulated signal obtaind can be transmitted only by amplifying it first and then fed to an antenna of appropriate size for radiation.
The size of the antenna matters.

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The process of superimposing signal frequency (i.e.,) audio wave on the carrier wave is known as
• transmission

• reception
• modulation

• detection

C.

modulation

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