Quote:
Originally Posted by Radio Wrangler
After the FM band got occupied up to 108MHz they had to require aircraft to switch to broadcast-proof radios, or fit special filters.
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Given that the USA had the 88 to 108 MHz FM band from mid-1945, would not aircraft travelling internationally have needed suitably immune VHF airband receivers from that time? 88 to 108 MHz was also the Region II FM band from 1947. ITU Region III was 87 to 108 MHz from 1947, although not all countries used the whole band. Europe/Region I was in fact the outlier with 87.5 to 100 MHz originally, extended upwards to 104 MHz and then to 108 MHz. Japan had VHF channels in Band II from c.1953, with channel J3 sound at 107.75 MHz.
The brief descriptions of the Park Air airband receivers available in Wireless World etc., indicate that from the late 1960s, dual-gate mosfets were used in the front ends and linear ICs in the IF strips. This suggests that they paralleled FM tuner technology developments of the time if not using exact FM circuits.
Cheers,