On Jun 25, 2:14*pm, wrote:
On Jun 25, 9:45*am, Tim Shoppa wrote:

I have been playing with homebrew crystal filters (following W7ZOI and
Bill Carver/K6OLG) for CW, as well as audio filters, and can tell you
that on CW the difference between a super-sharp-in-frequency
Chesbyshev filter (typical in ham equipment for a long time now) and a
more constant-delay (e.g. Gaussian to 6dB or 12dB, or equiripple
linear phase) filter is like night and day.

You wouldn't happen to know the group delay variance
of the filters you mentioned? *Rough values are okay.

I haven't actually measured group delay but I'm sure that what I hear
is group delay.

If you look at published group delay graphs for commercial Chesbyshev
filters, a 500 Hz 8th-order crystal filter has a delay around 2ms in
the middle of the passband, but within 100 Hz of the edge of the
passband the delay peaks up enormously to 4ms and then back down again
over the very steep skirt.

Maybe you can turn the 2 ms variation into some inter-symbol/intra-
symbol limit for some digital modes. It rings like the dickens when
hit with QRN, that's for sure!

Tim N3QE.