Further update on the filters mentioned below.  I am convinced that any
filter has enough tolerance variations that experimental "tweeking" is
necessary for minimum ringing.  Most of us are using 800 hertz center
frequencies obtained from a crystal source.  This signal was then gated
by a function generator (a morse keyer works just fine too!) while
carefully adjusting all poles.  Sometimes interchanging pole position is
valuable!  The conclusion is that experimentation is more valuable than
calculation for these filters!   Cliff K7RR



On Mon, 15 May 2000, Cliff Buttschardt wrote:

Christer and the group.  I was delighted to get the two URL's
containing the 30 Hz filter and noise blanker.  You might
remember
some years ago the "HDO" phase linear filter.  That was when I
was W6HDO rather than K7RR.  For years that filter served us
well.  I really enjoyed the experimental way of finding least
ringing, so I placed variable resistors in the old design
using
an automatic key.  Even the old Williams textbook approach

benefited from experimental "tweaking". 73 Cliff K7RR

C Andersson wrote:

> > >Could you post a brief text summary of your design?

> >73, Bob ZL2CA

> > PA0LQ filter descriptions:

> http://www.alg.demon.co.uk/radio/136/af_filter.htm
> http://home5.swipnet.se/~w-54761/pa0lq_filter.htm

> > 73

> Christer, sm6pxj