## Coherent FSK detection

Coherent detection of FSK is very similar to that for ASK but in this case there are two detectors tuned to the two carrier frequencies. As for ASK, coherent detection and matched filtering minimize the effects of noise in the receiver. Recovery of the carrier references in the coherent receiver is made simple if the frequency spacing between the symbols is made equal to the symbol rate (Sunde's FSK), as the modulated spectrum contains discrete spectral lines at the carrier frequencies. The drawback of using Sunde's FSK is that the bandwidth of the FSK signal is approximately 1.5 to 2 times that of an optimally filtered ASK or PSK binary signal. |