[TenTec] Questions about NR i.e. Orion

Fri Mar 24 12:43:12 EST 2006

Lin,

There are many excellent references available, but some of them make for
very dense reading.  Some of the more basic stuff can be found in Technical
notes published by Bruel and Kjaer Instruments some years ago.  Although
they specialized in audio work, it is the same principle, and the Orion's IF
is low enough to apply these same techniques obviously.  I will try and see
if I have these on the shelf someplace, and can either cite them, or perhaps
scan them into the computer.

73 de Gary

----- Original Message ----- 
From: "Lin Davis" <linbdavis at earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Thursday, March 23, 2006 9:07 PM
Subject: Re: [TenTec] Questions about NR i.e. Orion

> 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 at k6kdk.net>
> > To: "Discussion of Ten-Tec Equipment" <tentec at 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 at comcast.net>
> >>To: "'Discussion of Ten-Tec Equipment'" <tentec at 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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> >>>TenTec at contesting.com
> >>>http://lists.contesting.com/mailman/listinfo/tentec
> >>>
> >>>
> >>
> >>_______________________________________________
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> >>
> >>
> >
> >
> >
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> >
>
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