It may be of interest that mechanical filters are a component that hams
with metal machining capability can design and construct. The Collins type
employing "drum head" vibration mode might be a little tricky, but a simple
transmission line approach using compression or torsion vibration is
straightforward. See:
"Magnetorestriction Devices and Mechanical Filters for Radio Frequencies"
Parts I, II, & III QSTs June, July, Aug 1953 by Roberts.
Suitable metals have Qs somewahat smaller than that of quartz, for example:
Aluminim 4000
Dural 8000
NiSpan C 900
Srainless steel 1500
Robert's filter characteristic design approach examples were analogous with
transmission line section filter design. Get the bandpass and skirts you
want!
73 Jim
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* Jim Headrick (W3CP) ---> headrick@radar.nrl.navy.mil *
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