On Jul 1, 2007, at 8:18 AM, Bob Henderson wrote:
CW offset is indeed adjustable from the front panel and I believe
sidetone
pitch tracks CW offset. What is not adjustable is filter centering,
which
is fixed at 800Hz. If you're happy listening to a tone between
600-1000Hz
this works fine with cascaded filters as narrow as 500Hz. However, if
your
preferred receive tone is 450Hz this doesn't work nearly so well. The
problem is significantly exagerated if 250Hz filters are used. Years
ago, a
bunch of folks had filters made with lower centre frequency, so as to
deal
with this problem. I'm not sure but I suspect Inrad made the filters
and I
believe they were centred somewhere around 600Hz.
Bob has this right. You can go ahead and set the CW tone offset and if
you want to use a narrow CW filter in the NAR position (the 9 MHz IF)
you are stuck in the passband (fixed) of the 9 MHz CW filter. If you
like to hear CW at the lower notes (below 500 Hz, like I do), you'll
suffer loss at the edge of the filter response. Of course, you can use
your PBT control to work with the 6.3 MHz CW filters, no problem there,
but the NAR filters in the 9 MHz position have fixed center frequency
and you can't move that (well you can realign the radio...)
Yes, Ten Tec asked Network Sciences to make them a filter to deal with
this, I was probably the original guy to ask for, and to receive, a
model 221 CW filter. This is the 250 Hz CW filter for the 9 MHz IF
with a 500 Hz center frequency, beats heck out of the model 219 for
listening at the lower tones, allows me to hear "down into the noise"
quite well. The model 219 filter is 250 Hz wide with the 750 Hz
center frequency, if you try to listen down at 500 Hz you suffer awful
loss (and with my 221, if you wanted to listen up at 750 Hz you'd
suffer the same sort of loss).
Clark
WA3JPG
Clark Savage Turner, J.D., Ph.D.
Professor of Computer Science
Cal Poly State University
San Luis Obispo, CA. 93407
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