# FM modulation - fm deviation and carrier frequency

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#### harry456

##### Member level 1
I have the option to set the following values ​​of my signal generator: carrier frequency, frequency deviation and LF Gen. (R&S SMB100)
LF Gen is frequency of the modulation signal but why to I have to set 3 different frequencies?
Isn't frequency deviation already defined as the 1/2(fmax-fmin)/fmod and fmax is equal to fcarrier+fmod?

#### LvW

I have the option to set the following values ​​of my signal generator: carrier frequency, frequency deviation and LF Gen. (R&S SMB100)
LF Gen is frequency of the modulation signal but why to I have to set 3 different frequencies?
Isn't frequency deviation already defined as the 1/2(fmax-fmin)/fmod and fmax is equal to fcarrier+fmod?

The last expression (fcarrier+fmod) applies to AM only.
In FM, the max frequency deviation depends on the selected modulation index. There is no theoretical limit fmax because the FM spectrum is infinite (in theory).

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