Jerry,
Taking your point regarding filter response shape (ideally, rounded
edges, steep slopes, and flat passband), and looking at the
response curves for the Inrad CW filters, they look pretty incredible.
http://www.qth.com/inrad/graphs/759.gif
http://www.qth.com/inrad/graphs/750.gif
http://www.qth.com/inrad/graphs/763.gif
I don't know if these are actual plots of sampled 400Hz filters, or
'marketing' plots. But, using these filters, I can say that they
are very, very good for weak signal listening in noisy conditions.
They don't have the incessant roaring (noise power) in the passband
like the TT 500Hz filter.
73 bill n4lg
At 03:25 PM 6/16/2007, you wrote:
It is possible to have sharp corners, flat frequency response, steep
skirts, and a good time response but that is ungodly expensive in
hardware because the design has to use many extra resonators to
correct
the phase response. In a digital filter it is handier to have the
extra
poles to achieve both goals, at the cost of total time delay.
>
> > I almost always have easier and clearer copy on weak cw signals
> > when I use the 1.8 kHz filter vs. the .5 or .25 kHz filters
in my
> > 6.3 MHz IF. I've got nothing in the N1 position. Is this the
way
> > it's supposed to be?
>
> --
> 73 DE N7WIM / G8UDP
> Kevin Purcell
> kevinpurcell@pobox.com
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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