FM modulation encodes information by varying the instantaneous frequency of a carrier wave, rather than its amplitude as in AM. To generate an FM signal, the radio carrier frequency is changed in line with the amplitude of an incoming audio signal. The modulation index indicates the amount the carrier frequency deviates from the center frequency and is determined by the maximum audio frequency.

1. FM Modulation
In telecommunications and signal processing, frequency modulation (FM) is the
encoding of information in a carrier wave by varying the instantaneous frequency of the
wave. This contrasts with amplitude modulation, in which the amplitude of the carrier
wave varies, while the frequency remains constant.
To generate a frequency modulated signal, the frequency of the radio carrier is changed
in line with the amplitude of the incoming audio signal.
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6. frequency modulation index
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7. FM General Equation
Modulation Index
Modulation Index (β) = 1
Here, the maximum frequency (fmax) causes a maximum deviation of 1*fmax in the
carrier. From the modulation index formula:
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8. Modulation Index (β) = 5
Here, the maximum frequency (fmax) causes a maximum deviation of
5*fmax in the carrier. From the modulation index formula:
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9. Modulation Index (β) = 25
Here, the maximum frequency (fmax) causes a maximum deviation of 25*fmax
in the carrier. From the modulation index formula:
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10. Phase modulation (PM)
is a method of impressing data onto an alternating-current
(AC) waveform by varying the instantaneous phase of the
wave.
The technique in which carrier phase varies based on analog
baseband information signal to be transmitted using wireless
device.
If a constant amplitude as well as constant frequency sine
wave carrier is given to the phase shifter the output is phase
modulated signal.
Phase modulation is referred as indirect frequency
modulation due to the fact that phase modulation produces
frequency modulation.
The effect of variation in amount of phase shift is
proportional to change in the carrier frequency.
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