PARAMETRIC UPCONVERTER STUDY.

An investigation was conducted to determine the feasibility of the parametric upconverter technique as a UHF communications receiver preselector. It was determined that adequate preselection would allow simultaneous operation of ANARC-51 transceivers and operation in the presence of interfering equipment with a minimum of modification of the aircraft or associated electronic systems. Basically, a preselector will have the effect of passing the desired carrier frequency while sharply attenuating undesired frequencies which are causing interference in the receiver. Alternative methods for preselection were explored, and comparisons were made with the upconverter system finally chosen. It consists of a varactor upper side-band upconverter exhibiting wide dynamic range followed by a highly selective, low loss, fixed tuned filter tuned to the upconverter output frequency, and a resistive mixer downconverter. Input tuning of the upconverter over the band 225-400 MHz is provided by an electronically tunable pump source. This method of preselection offers significant performance advantages compared with preselectors consisting of tunable filters. These include Reduction of saturation, intermodulation distortion, and cross modulation effects in the presence of strong interfering signals. Preselection with no sacrifice of sensitivity to desired signals. High Q filtering at a fixed frequency eliminating mechanically tuned filters. Electronic tuning with no sacrifice of selectivity, such as would be required with lower Q electronically tunable YIG or varactor-tuned filters.