I had an MFJ 1026 noise cancelor for a while. I found it quite effective at
removing various noise sources but there were problems with it. I had an
outside noise antenna for it. The noise antenna did not hear the noise as
well as my normal antenna. So I typically had to reduce the signal from the
normal antenna to match the strength from the noise antenna. Then I would
have to adjust the phase to get the noise to cancel. This usually took
about a minute to get everything adjusted properly and all the noise
removed. At that point the signal I was trying to hear usually left and was
gone! I sold my noise cancelor a few months ago.
Carl Moreschi N4PY
121 Little Bell Drive
Bell Mountain
Hays, NC 28635
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Monday, January 29, 2007 4:56 PM
Subject: Re: [TenTec] Orion 2 HW Noise Blanker
> On Mon, 2007-01-29 at 16:26 -0500, joel hallas wrote:
> > Jerry,
> >
> > That not quite what Toby's talking about.
> >
> > The old noise blankers used a noise sample in a wideband receiver to
> > perform a short (not extended by selective filters) duration receive
> > mute, much like current noise blankers operate except they pull a sample
> > at the operating frequency from early in the receiver.
> >
> > The noise cancelers work in a different way. Instead of shutting off
> > the receiver they have a phase and amplitude adjustment that allows the
> > noise reduction signal to cancel the input from the regular antenna.
> > This allows removal of even CW signals, or in band QRM if the directions
> > are different. See Aug 06 QST, p 45 for more, if you like.
> >
> > 73, Joel Hallas, W1ZR
> >
> Yah, I saw "noise xxxxxer" with separate antenna and thought noise
> blanker with 40 MHz noise input.
>
> Noise cancelers at the antenna work on the noise antenna capturing full
> strength noise but not much for signal which to me seems more than a
> little serendipitous, especially with more than one noise source. Using
> elevated directive antennas for both leads me to believe that the
> "noise" antenna wouldn't get the noise the same strength as the main
> antenna but would often acquire unwanted signals on the same frequency
> from the direction the noise antenna was aimed. Might as well listen
> with a vertical, "equally noisy in all direction." Seems to me the
> directive antenna (admittedly its inconvenient to get directivity on 160
> meters on a city lot with anything larger than a 2 meter diameter multi
> turn loop) may be a better investment in S/N unless the noise source is
> extremely local and then it might be most profitable to cure that noise
> on the ham's own premises.
>
> I could envision three towers with identical beams all pointed the same
> direct (that of the desired signal and some DSP processing with three
> front ends to determine the direction of the unwanted and then to do
> some directional enhancement, but I question whether it would do better
> than just phasing the extra beams for better horizontal and vertical
> directivity.
>
> E.g. I think the MFJ device (which they did NOT invent) will fail to
> make an improvement more often that it makes an improvement. And one in
> the receiver would do no better.
>
> --
> 73, Jerry, K0CQ,
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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