Gary,
I'm interested in learning more about this technique. Can you recommend any
reference material on the subject?
Thanks,
Lin
WB1AIW
Gary Hoffman wrote:
Incidentally, I also have professional experience with adaptive noise
elimination.
I agree completely with the comments below. Has nothing to do with
bandwidth as measured on a scope.
Obviously, we all know narrow filters help - a lot !
But in software, with enough processor, one can simply delete bits which are
noise bits, and leave in bits which are signal bits. Then go through D to A
and one reconstructs the original signal, minus the noise. Bandwidth
having nothing to do with it.
This works exceptionally well.
73 de Gary, AA2IZ
----- Original Message -----
From: <k6kdk@k6kdk.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, March 23, 2006 5:22 PM
Subject: Re: [TenTec] Questions about NR i.e. Orion
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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