Art Sowers wrote:
For a nice-sounding CW filter, I have used an audio frequency equalizer
(picked up mine from a thrift store for $5, its a Realistic [Radio Shack]
jobber). I max boost 500 Hz sliding pot on both channels, and max depress
the pots on all other frequencies, and feed speaker output into input of
one channel, output of that channel into input of the other channel, and
run output of other channel into input of an amplifier driving either a
speaker or earphones. Bandwidth "sounds" (not measured) like maybe about
300-400 Hz. The next frequencies above and below 500 Hz are 250 Hz and
1 kHz. I might get narrower if I boost at 250, etc, but tone is too low
for my ears. I thought I wasn't getting any detectable ringing at all
on this setup. The calibrations are max/min 12 db, so that should put
unwanted frequencies down 24+ db per channel, or 48 db for both, no?

You might try setting the filters on the two ears a little bit different,
so that higher tones are to the right and lower tones are to the left. I
find this helps pick out signals from a pileup.

The filters on those cheap EQs are probably fairly wide; you can measure the
Q with a meter and a signal generator if you want to really know.

Scott, for AM on the R-390: are you sure its the filter? Not distortion in
the audio string? Have you tried any other post detection path (eg. a
separate receiver, even an old AM radio where you feet the 455 kc output
from the R-390 to the input of the IF on the AM radio and see what audio
quality you can get? I'm not familiar with the R390 (does it have
mechanical filters?).

There is lots of distortion in the audio string, although the line output
is definitely much cleaner than the speaker level output. However, there is
just outrageous amounts of ringing on the 8KC filter. If I go to the 16 KC
filter it's much cleaner but of course there's a wider bandwidth too.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."