Signal switching and combining systems for diversity radio receiving systems

Claim 1

A signal switching and combining system for a radio communication system having two receivers each providing a coherent radio signal output and an output proportional to the signal to noise ratio of the radio signal, the two radio signals being approximately in phase and of approximately equal amplitude, which includes a comparator operable to determine at any instant which of the two signal to noise ratio outputs is greater, a threshold detector including means for determining the difference between the signal to noise ratios and operable to determine whether at any instant the difference between the two signal to noise ratios exceeds either of two of predetermined threshold levels, a gating network responsive to the output of the comparator and of the threshold detector to derive one or more control signals, a switching circuit responsive to said one or more control signal outputs to connect to an output load either one of the coherent radio signals or a combination of the two coherent radio signal outputs in one of a number of predetermined ratios, and a matching network connected to the switching circuit for presenting an electrical impedance and a radio signal amplitude to the load such that said impedance and signal amplitude remain substantially constant.