John ..
> However there is distortion on weak signals.
Very true.
> This sort of makes sense. I find that raising RF gain and
> lowering the AGC threshold is necessary to reduce NR distortion.
Also true in my experience. You may recall that in earlier (1.371 and
earlier, given some of the late release changes I'm not sure), when NR was
turned off, Threshold was automatically reduced to somewhere around the
minimum value to give the DSP as much as possible to work with. So far at
least, I'm still finding that to be necessary.
> Of course if the signal is strong enough to raise the S-meter
> then I can reduce noise just as well with AGC threshold
> and/or RF gain.
I haven't found that to be the case. On a very weak signal, you stand to
lose the signal at the same time if you lower gain or raise threshhold.
What I'm finding on CW is that S/N ratio is improved, over what one can do
with narrow bandwidths and gain/theshold fiddling, for signals very close
to, but distinguishable from band noise. Subjective opinion, of course.
I also think on anything but the very weakest SSB signals, that NR does in
fact reduce noise a bit further than one can manage by just reducing the
gain or runnning up Threshold. On very weak SSB signals, NR isn't very
effective. The better audio NR boxes failed to deliver anything approaching
understandable speech in the same conditions as well (I have owned and given
up on virtually everything made by JPS and Timewave, and some others). In a
roundtable environment, particularly, with signals of widely ranging
strengths, cranking up Threshold or dropping RF gain is likely to flush
someone off the bottom. And if you leave enough gain in the system to hear
the puny stations, you can't improve the noise situation on the stronger
signals as much.
My take on the whole thing is that (1) expecting miracles with NR is a kick
start down the road of disappointment, and (2) the NR (at least in the II)
is more effective than it's currently being given credit for, based on much
of the grumbling. If it improves S/N then it's conributing. It does work
better for weak CW than it works for weak SSB. ON SSB, once the signals get
a couple of S-units or so above the band noise it starts working pretty well
overall.
Grant/NQ5T
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