Study of adjacent and co-channel FM interference reduction

The reduction of FM interference caused by the reception of adjacent or co-channel signals is examined. Techniques to allow the demodulation of a weak FM signal, when in the presence of a stronger one, are described. The description is extended to include methods where the residual interference is reduced independent of which signal is being demodulated, i.e. the normal FM capture effect is enhanced. FM interference reduction from co-channel sources cannot be perfect and is subject to distortions arising from the format of the signal modulations. Such distortions may be tolerable in certain cases. The magnitude and frequency of these distortions can be assessed through the performance of a wideband phase-shifting process which ideally has to provide an exact and absolute quadrature shift.<>