[amsat-bb] Help with crystal filter

William Leijenaar pe1rah at yahoo.com
Thu Nov 16 00:13:04 PST 2006


For a (small) transponder design I am checking
different kinds of filters. I need something small and
cheap, and I tested some of the monolitical 10M30A
crystal filters.

The problem is that I can not get the ripple less than
2dB, where the specs say 0.5dB. I can see the 2 poles
with a kind of bath-tube in the middle. I think the
problem is the matching of the 5000 ohm impedance in
the specs. 

In my design I used small 5mm transformers, that
doesn't work at all. More tests with a "pigs nose"
transformers work better, only not better than 2dB

Maybe someone has experience with these monolitical
crystal filters (especially the wideband 10M30A) ??
I wonder how sensitive these filters are to an
impedance miss-match, and how to get the optimum out
of these filters ??

Specs can E.g be found here:

73 de PE1RAH
William Leijenaar

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