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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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Radio waves of constant amplitude can be generated with
  • Filter

  • Rectifier

  • FET

  • Oscillator


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

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

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

  • reception
  • modulation

  • detection


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