# Frequency Modulation

**Frequency Modulation** is a Modulation Scheme where the incoming signal modulates the frequency of the Carrier Signal by a tiny fraction. Used e.g. in FM Radio.

A variation of Frequency Modulation is sometimes also used for digital Transmissions, this is then called *Frequency Shift Keying* or FSK-Modulation.

## Visualisation

*it would be nice to have a gnuplot picture here, is it possible to upload the gnuplot script for toying, too?*

## Mathematical Setting

The output voltage of a FM modulator with input voltage <math> u_{in} </math> is described by

where <math> \Delta f </math> is the frequency deviation from the center frequency at <math> u_{in} = 1V </math>.

## Aquired Bandwidth

...can be determined using Carson's Bandwidth Rule: two times sum of the peak deviation <math> \Delta f </math> from the highest frequency occuring in the spectrum of the modulating signal <math> (f_m) </math>:

## Noise Immunity

is higher than the one of Amplitude Modulation Schemes since athmospheric disturbances and noise usually don't shift the frequency of a signal but add their contribution to the amplitude of the transmitted signal. Amplitude variations don't affect FM much.