"Marijan Miletic, S56A" wrote:
> >Looking at the filter there are only 4 crystals.
> Each crystal has series and parallel resonance which makes 8 pole filter!
Well, formally that's correct, but for ages it has been customary
to indicate number of poles according to the equivalent low-pass
filter. For bandpass filters this means 4 crystals = 4 "poles".
> It is difficult to achieve 1 kHz filter shape factor better then 1:3 at 9
> MHz.
Inrad has much better shapes at much lower bandwidths.
73,
Sinisa YT1NT, VA3TTN
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