Re: VHF filter, Aerial Facilities Ltd
It is a "Helical filter"
The coils are not connected at the top end and are self resonant within their cavity. The cavity with helix has a lower resonance frequency than the cavity alone would give. Tuning screws add an adjustable C at the hot end for fine trimming. The PTFE bits can be used to trim coupling through the apertures in a fairly fine way.
The input and output are to taps low down on the end helices.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
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