In this experiment students will study the demodulation of received signal in the frequency modulation receiver. In frequency modulation receiver, the intelligence to be recovered is not in amplitude variations; it is in the variation of the instantaneous frequency of the carrier, either above or below the center frequency. So the receiver should be programmed in such a way that the output amplitude varies linearly according to the instantaneous frequency of the incoming signal.

In frequency demodulator, a discriminator is used followed by an AM demodulator. Discriminator converts frequency variations in the received frequency modulated signal to amplitude variations i.e.; its output signal varies in both amplitude and polarity as the input signal varies in frequency. This signal can thus be demodulated using simple amplitude demodulation. Figure 1 shows the scheme of FM demodulation as implemented in the FlexTrainer.

Figure 1: Frequency demodulation 

At the end of this experiment, students can observe the effect of different discriminators and low pass filter types on FM demodulation.