Quote:
Originally Posted by Peter.N.
Being VHF there's not to much noise about anyway, especially in an aircraft or the middle of an airfield.
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The biggest sources of interference are the aircraft's own ignition system [shielded HT leads/spark-plugs are ubiquitous] - which of course travels everywhere with you - and the problem of front-end-overload if flying near to FM broadcast-band transmitters.
To comply with international aviation-standards the front-end design of modern VHF-airband radios is most intriguing: multiple varactor-tuned circuits (designed more like cavity-filters or helical resonators) with D/A converters and ROM-based lookup-tables fed from the frequency-synthesizer in order to generate the varactor voltages. It's strange at first 'aligning' a radio's front-end by entering 8-bit values into a computer, but it does give you 'correct' tracking at 254 points across the receiver's coverage!