Ahhhh Hummm... I agree w/ "Buck".. (speaking as a software-type here..) a
true NR system implemented in software is capable of "intelligently
manipulating" noise and signal in a way that can not be detected on a scope.
It is fully possible (in software) to make determinations about which bits
are noise which are information, pass and reject the bits on the fly,
interpolate the intelligence through (create it artificially and insert it
into the bit stream for later D/A) and a whole host of other "tricks" to
improve intelligence throughput for a human user. You will never see this
manipulatiuon on a scope no matter how hard you try.
For some more informatiuon on these type of schemes see Flex Radio
documentation on their site about what they call "NB2". I mentioned before
on a previous post that I thought TT should outsource the NR to NCT
Technologies who developed many such audio/ human listener NR codes under
military contract. They now will license it out for a price.
I don't want to bore you with recounts of my past victories in this realm.
Nothing is worse than listenting to some retired software guy tell you how
he could do it with one hand tied behind his back, but I once got paid a
bunch to write just such code for a customer of ours that had severe noise
(from RF interference) into a SMPTE time code track on his very expensive
little black boxes. His boxes could no longer "hear" the information stream.
We cleaned that right up for him, no problem !
73s -Dan K6KDK
==================snip=========================
I submit the only way to check the NR function is by listening. It either
works or it doesn't.
It hasn't worked since version 1.371.
K4ia "Buck"
Fredericksburg, Virginia USA
----- Original Message -----
From: "Grant Youngman" <nq5t@comcast.net>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Thursday, March 23, 2006 9:36 AM
Subject: Re: [TenTec] Questions about NR i.e. Orion
> > MDS, S/N and similar measurements with NR on must be peformed
> > completely with the signal present, and not by switching the
> > signal on and off.
>
> > This means that the only way to do it is by spectral
> > analysis, with due care paid to subtle issuses like windowing
> > functions, bin size, etc.
>
>
> I've been poking at NR on and off for a couple of days now on 2.032.
Using
> an Elecraft N-gen noise generator to a Daven RF attenuator (to control the
> fixed output of the N-gen), with an 8640B providing the signal, and both
fed
> to the radio through a TT 651 hybrid. And watching the whole thing on
> Spectrum Lab. AGC off (really very fast), and the RF gain reduced enough
to
> keep the signal out of the AGC range.
>
> With no signal present, NR drops the noise output to about -30dB
(relative).
> But the baseline noise level increases with the application of a signal to
> about -18dB. NR drops both signal and noise level when turned on relative
> to the levels without. The noise component in the passband is rolled off
> fairly gently by what appears to be a a very broad filter effect, so it's
> most likely that SNNR is increased, but I'm not sure how to measure it
from
> what appears on the display. The signal peak actually seems to decrease
by
> 2-3 dBu relative to the noise at the baseline right in the vacinity of the
> signal, but there is noise rolloff above and I think below the signal
> (although the lower side is harder to ascertain). It shows up best if
SPOT
> is set relatively high, such as around 1 Khz.
>
> There is no indication of any very narrow or steep-sided bandpass filter
> being applied, so the filter itself looks relatively simple and quite
broad.
> Actually, it looks much like what I see from a couple of external
> audio-based DSP gizmos.
>
> My recollection of pre-1.372 NR performance, on SSB signals, is that the
> high frequency rolloff in particular was possibly more pronounced.
>
> Grant/NQ5T
>
>
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>
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