Rather than being "another very narrow filter", the NR behaves more like an
expander type of circuit, implemented in software, with its threshold being
slightly above, and adjustable around, the long term average rx input level. If
the input level drops below the threshold the gain is reduced a bit and if the
level goes above, the gain is increased a bit, thus improving the S/N ratio.
I believe that the distortion/raspiness of a signal processed with the NR is
to the step-wise gain changes the DSP is making. Every time the gain is
adjusted, the signal voltage jumps instantly to the new voltage, which is heard
as high frequency raspiness. What might cure this is passing the derived gain
signal through a low pass filter before applying it to the gain stage. Either
that or the minimum gain step size is too big. Nothing we can do about it
hope that T-T is listening....
Grant Youngman wrote:
>>2. For me, the hardware NB works somewhat but the s/w NB does
> I suppose it depends on the characteristics of the noise. I have a very
> strong pulse noise in my neighborhood (don't know from what, it's a strong
> "pop" about once per second) and both the HW and SW NB's take it out
> perfectly. But my noise isn't your noise, and luckily the power company
> fixed the arcing insulator on the pole pig behind my house a couple of years
> ago. THAT was NOISE :-)
>>The DR is what does nothing for me. It operates, but it makes
>>the signals much less intelligable on SSB for a neg negative,
>>and is simply makes copying cw signals impossible in some
>>cases. I can't even use it.
> Did you mean NR? I hear a little distortion on SSB. I can't say I've found
> it makes signals "much less intelligible". For SSB I run it at "1" or "2"
> almost all the time, and it cleans things up very nicely. There is some
> distortion. I'd rather listen to a little of that than the watery sound of
> the typical external LMS noise reducer, although I hope it gets cleaned up
> in a future release.
> I spent some time rereading the manual again, and it reconfirmed some
> comments I made earlier. Which is that on CW, if you're already using a
> narrow filter, the NR may not add anything, and may in fact make things
> worse. That's partly because the NR is effectively nothing more than
> another very narrow filter around the CW signal. And partly because it's
> effectiveness can be diluted if threshold is set to a high value, either
> explicity in the menu or if RF gain is reduced. The manual is pretty clear
> on this, and has a reasonable discussion about when it will and may not be a
> plus to use NR, how to set threshold and NR levels for best performance,
> etc. It's function is to improve S/N ratio, not get rid of the noise.
> Interestingly, the II manual indicates that Threshold is automatically
> reduced when NR is turned on, and although that did happen in the Orion
> 1.xxx and was very obvious, it isn't obviously occurring in the II. The
> radio behaves like that isn't happening at all.
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