Very-high-frequency single-channel receiver

A superheterodyne with a.v.c., squelch and noise-limiter circuits, for ground-station reception of signals in the range 118-136 Mc/s. The low i.f. selected to obtain the required selectivity made two double-tuned r.f. stages and a tuned aerial stage necessary for high image rejection. The coils are of stout Ag-plated Cu wire, self-supported on the variable capacitors to obtain the highest possible Q. The local oscillator is crystal-controlled; the crystals are of the third-harmonic type and give frequencies between 27.9 and 32.4 Mc/s, with an overall stability of plusmn1 part in 20 000 between temperature limits of -25deg and +75degC. Complete circuit details are given. Tests at major airports under severe noise conditions were very satisfactory.