## Non-coherent FSK detection

One of the simplest ways of detecting binary FSK is to pass the signal through two bandpass filters tuned to the two signalling frequencies and detect which has the larger output averaged over a symbol period. This is in essence a non-coherent envelope detector for the equivalent two ASK streams with a comparator at the output. Because it takes no account of the phase of the respective symbols, this method, as expected from our discussions on ASK detection, will not perform as well as coherent FSK detection systems. |

There are several alternative methods for discriminating between the incoming frequencies. One simple digital method involves counting the zero-crossings of the carrier during a symbol and hence directly estimating the frequency on a symbol-by-symbol basis. A third, often used method involves a phase-locked loop which is described next.