On Tue, 31 May 2011, Scott Dorsey wrote:
Edmund H. Ramm wrote:
In (Scott Dorsey) writes:
Rockwell-Collins still makes the size J filters. From the 2005 catalogue:
[...]
Dave Curry Longwave Product's mechanical filters (exact replacements
for Collins ones) reportedly have less insertion loss and better skirts.
See Electric Radio magazine for more info.
Does 'better' mean tighter or less ringing?
There are sure times when I wish I had a less nasty-sounding filter for
AM on the R-390.
--scott
I'll have to put on my "to do" list that I need to search the web for
sources of these filters (as well as ER magazine). And, see if Collins has
a website of their own (I should have done that, too, but I have variable
lazyness...and I'm not in a big hurry on this project).
I did send to that Collins email address a request for further information
and have not, as yet, received an answer (I notice email responses to
email queries can be all over the spectrum from minutes later to days
later to no answer at all).
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?
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?).
--
"C'est un Nagra. C'est suisse, et tres, tres precis."