Transistor multichannel v.h.f. communication and navigation receiver for aircraft

The receiver is an all-transistor triple superheterodyne with remote selection of 560 channels with spacing of 50kc/s between 108 and 136Mc/s. A novel signal/noise-operated squelch or muting system is incorporated. The introduction of v.h.f. transistors for the first time in an airborne application raised several aspects of circuit design for reliable operation of equipment in the extreme conditions encountered in aircraft. The problem of spurious responses in multiple superheterodynes is discussed with particular reference to the operation and limitations of the semiconductor mixer. Difficulties encountered with operation on simultaneous offset frequency transmissions of the `climax¿ type are examined. The compromise necessary between mechanical layout for maximum electrical efficiency and ease of maintenance is considered.