Jeff wrote:
> The only reason I am continuing to beat the dead horse is that the filter,
> when pressed in double-duty CW service as well as RTTY service, a wider
> number than necessary for RTTY may cause an a drop in user happiness - if
> the bandwidth were allowed to grow too wide.
I'm not so sure that's a major concern. Maybe I am atypical, but on
average I tend to use narrower IF filtering in RTTY than I do in CW.
I have a K3 with the "250 Hz" (actually 370 Hz) roofing filter,
configured to cut in at the 350 Hz setting. On RTTY I move my DSP filter
settings back and forth between 400 Hz (with a 500 Hz IF filter) and 350
Hz (370 Hz IF filter). I can't say I feel that one is all that much
better on average than the other, but it's psychologically comforting
(if nothing else) to have the choice. On reasonably strong signals with
nearby very strong signals I sometimes narrow the DSP filter down even
more, but as Chen says, on weak signals this is counter-productive.
On the other hand, in CW I don't use the narrower filter as much as I do
in RTTY, except in very specific situations. I find that narrower
filtering doesn't help me all that much most of the time in CW. Indeed,
it can actually make the wetware filtering less effective by making the
noise sound more like the signal. Anyway, so much of the interference
problem in CW is due to keying clicks and phase noise that I am not
convinced that using narrower IF filters is all that much help on
average. To put it another way, although narrower AF or DSP filtering
can be useful in a number of situations in CW, I am not sure that doing
the narrower filtering at IF is all that much better, other than when
the neighbouring station is pumping your AGC, and you often have other
weapons at your disposal to deal with that (turning the RF gain down
and/or turning off AGC, combined with AF or DSP filtering).
Be that as it may, I also have the impression, rightly or wrongly, that
RTTY contesters actually tend to crowd in closer to one another than CW
contesters typically do, although that might be a function of the types
of contests I am most likely to be active in. It seems to me as if RTTY
contesters are used to sidling up right beside one another, whereas CW
contesters tend to stay far enough apart so that the key clicks from
neighbouring stations aren't too distracting, regardless of what filters
they are using.
Just a thought...
73,
Rich VE3KI
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