Receiver especially for use as a diversity combining receiver with channel selection capability

摘要

A receiver especially for use as a diversity combining receiver is adapted to recover a single signal from among a plurality of cochannel signals transmitted from a plurality of sources. When recovering signals from a plurality of sources, the various sources transmit signals having PSK modulation and having, in addition, pilot tag modulation uniquely associated with each source. The output from each of the diversity branches is combined and the combined output is mixed with the output signal generated by a free-running oscillator to produce a loop signal uniquely identified by one selected tag. The processing is arranged so that when this loop signal is mixed with each branch input, the resulting sideband product of the loop signal and the one received signal having the selected tag contains a distinctive cophasing phase angle but is stripped of its PSK information and tagging modulation. However, the resulting sideband product of the loop signal and any unselected received signal contains some unremoved modulation or tagging and it is, therefore, distinguishable. Only the one modulation-free product derived from the received signal having the selected tag, is mixed with the total branch input and thus only the transmission having the selected tag contributes to the cophased combined output. The present arrangement provides a precise loop signal, and the loop will remain locked despite slight variations of either one or both of the input signal frequency or the injection frequency generated by the free-running local oscillator.