On Fri, 2009-10-09 at 15:14 -0400, Mike Hyder --N4NT-- wrote:
> Somewhere along the line I got the notion that the difference between the
> filters centered at 750 Hz and centered at 500 Hz was only the capacitors on
> the filter board.
>
> Did I make this up or can anyone shed light on it?
>
> Mike N4NT
>
More properly its the frequency of the crystals that set the center
frequency, the capacitors set the coupling between crystals, and the
bandpass. Dragging the crystals with different capacitors might work but
would change the filter terminal impedance that would probably cause
increased insertion loss. 250 Hz shift on a 9 MHz filter wouldn't
require a change in capacitors at all, just the crystals.
73, Jerry, K0CQ
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