Frequency Modulation:

Frequency modulation is specially known for its good clarity of sound. When the sound signal and the carrier waves mixed in such manner that the amplitude of the carrier waves remains unchanged but its frequency changes with the amplitude of he sound signal then this type of modulation is called

the frequency modulation or more commonly as FM.
The rate at which the frequency of the carrier waves changes depends on the frequency of he sound signal. Thus the frequency of the carrier waves depends on both the amplitude and the frequency of the sound signal in this type of frequency modulation. Clarity of transmitted sound signal and low noise is the benefit of the frequency modulation technique. It is necessary to keep the frequency of the carrier waves at a very high level in the FM transmission. The FM range for radio broadcast is from 88MHz-108MHz.

In FM the total transmitted power always remains constant and useful. Frequency Modulation is a non-linear modulation process. Consequently the spectrum of a FM wave is not related in a simple manner to that of the modulating wave.

Several Test points are available for waveform observations. They are

• Modulated RF waveform
  
• Intermediate Frequency signal of the FM i.e. 100.7MHz
  
• Discriminator output
  
• Oscillator signal
  
• Amplified output of the oscillator
  
• Pure AF signal
  
• The final output of the whole circuit.