On Wed, 16 Sep 2009 22:27:13 -0300, John Coppens wrote:

> I have never heard about 60 kHz crystal filter. I'm quite sure those are
> "mechanical filters", but not piezoelectric.

I think mechanical filters would be more the norm, although active filters
are probably more common.  The stock CMAX et al receivers-on-a-chip use basic
quartz crystals to filter though; usually several different ones in parallel
to allow the same hardware to decode MSF, DCF, etc.  The datasheets don't
tend to give too much away though.  I've also seen quartz filters as low as
10KHz mentioned, but no references - now that must be some serious kit.


> Normal crystal have way too high Q to make a practical filter at that
> frequency (say Q of 40000, would give a filter of only 1.5 Hz!)

I think that's exactly my problem; I need to reduce the Q a bit to widen
the bandwidth and get a decent transition time.

Regards,

Pete Restall
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