Techniques and Circuits for Implementing Predetection Diversity Combiners.

摘要

Following a brief discussion of the theory of predetection diversity combining, this report is devoted to developing the detailed circuitry and design equations of the major components for implementing an AM/AGC weighted combiner. An optimum two-channel combining circuit is described as well as a multichannel combiner with near optimum characteristics. The circuitry for a wide dynamic range, noncoherent AM detector with output proportional to the absolute value of signal plus noise is developed. A differential phase-locked loop configuration in conjunction with a 10-MHz to tape-carrier (900-kHz) down converter is analyzed. A sensitive, wide dynamic range, digital phase-frequency detector incorporating ECL Schmitt triggers and a set-reset flip-flop is presented. The VCO requirements for the combiner application are discussed and a suitable design using an LC oscillator with varactor diode control is given. A two-channel AM/AGC weighted combiner using the circuits described in this report has been constructed and shown to outperform a conventional AGC weighted combiner. (Author)