# effect of modulating signal freq in freq modulation

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#### Indian

##### Junior Member level 3
Can anyone tell me the effect of freq of the modulating signal in freq mod. if possible post the spectrum diagram also
thanks

#### the_risk_master

In frequency modulation, the carrier frequency is varied upon the amplitude of the modulating frquency (information signal) without affecting the carrier's amplitude. As the modulating signal reaches the maximum peak amplitude, the carrier frequency is at it maximum, and if the modulating signal reaches the lowest peak (negative cycle), the carrier frequency is at minimum. In other words the carrier frequency is dependent on the paek amplitude of the modulating signal (information signal) hence its name, frequency modulation.

If the signal to be sent is

xm(t)
and the sinusoidal carrier is

xc(t) = Acos(2πfct)
where fc is the carrier's base frequency in hertz and A is an arbitrary amplitude, the carrier will be modulated by the signal as in

xc(t) = Acos(2πf(t)) = Acos(2π[fc + fΔx(t)])

#### Borber

In other words the carrier frequency is dependent on the peak amplitude of the modulating signal
Not true. The carrier frequency is dependent on instantaneous value of modulating signal. At the amplitude peak it just reaches it's deviation peak.

About influence of modulation signal frequency to spectrum of FM you may find a lot informations on web. Basically the spectral components of FM spectrum are spaced for fmod apart.

#### jeffttan

##### Member level 2
the frequency of the modulating signal in FM determines how fast the frequency of the carrier signal changes. the frequency of the modulating signal also produces the sidebands of the FM signal. theoretically, a single frequency modulating a carrier signal, in FM, would result to an infinite number of sidebands. but in practice, only a number of significant sidebands are taken and sent through the transmitter.

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