Occupied communications channels detector - frequency demodulates IF signal and filters result and uses frequency discriminator

摘要

The detector, for automatically recognising occupied channels, ensures quick recognition in the shortest time possible by avoiding having to determine absolute noise level. Instead the signal to noise ratio is determined from the phase spectrum of the IF signal -- ie by evaluating the time derivative of phase, frequency. The IF signal (from the channel being examined) is frequency demodulated and evaluated by filtering in an HP or BP filter. The detector consists of a chain of the following in the order given: an amplitude limiter (1), a frequency discriminator, a BP filter, a rectifier, an integrator and a comparator (6).