Gentlemen,
These noise cancelors work far better than most people give them credit.
Clearly the best solution is to find and cure the source of the noise,
but that's not always possible.
I bought my first one almost 15 years ago.
It was called the "QRM-Eliminator", and was manufactured by S.E.M.
electronics, on the Isle of Mann.
(The name was a misnomer but the device works great.)
I doubt that Paul (the owner of S.E.M.) invented the technology, but it
was the first time I saw this technology available commercially in ham
channels and I accredit him as introducing it to our ham community.
Paul sent a unit to the states to a company called JPS for evaluation,
in the hopes they would resell it.
They sent the device back and declined his offer.
Soon after they brought their own product to market called the ANC-4.
Later that same product became available through TimeWave.
And several years later, MFJ brought out an amazingly similar product.
Hmmmm.
My first experience: at the time the NoName computers were more or less
random noise generators. My QRM eliminator was able to drop an S9 noise
created by the computer to just S1. Of course I followed the advice
stated earlier and sold the darn computer to a friend who lived about
400 miles away.
Being a traveling contester, I have used the device many times at remote
locations.
I have both the S.E.M. and the ANC-4.
A few years back I got an emergency call from a group of guys from my
contest club, the BCC, who were in Tobago for CQWW.
They had terrible noise on the low bands and asked me to send my noise
cancelor.
One of their team members had not left Munich yet, so he swung by and
picked it up and took it with him.
When they returned, the entire team purchased ANC-4's.
YES, you should fix your noise at its source, but if noise unexpectedly
pops up and you need to operate (e.g., for a contest weekend), often
these devices will save the day.
Of the two units I have, both work equally well, but the ANC-4 is easier
and faster to adjust.
It is recommended by the manufacturer that the noise pickup antenna be
of opposite polarity to the antenna you are using to receive on.
So if you are using a beam, you should use a vertical for the noise
pickup antenna - so they say. I usually just stretched a wire to
whatever support was available.
What does not work very well, unless the noise happens to be inside your
shack, is the dinky whip antenna that sits on top of the ANC-4.
S.E.M. did not even bother to incorporate one.
Ten-Tec's new OMNI VII actually has provisioned for inserting such a
device directly in the RX antenna line, but the connections are inside
the box and may be easily extended to the two SPARE jacks on the back
panel before using. Yaesu's new FT-2000 has 2 jacks on the back panel
which can accept one of these devices. The industry is beginning to
accomidate to our needs.
73
Rick
DJ0IP (NJ0IP)
Dr. Gerald N. Johnson wrote:
>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.
>
>
>
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