I contacted Dick, WA3USG, who had actually built and used a synchronous
noise blanker. He was kind enough to give me some observations based upon
his use.
Most importantly, he provided URLs to two wave files that demonstrate the
effect of the noise blanker he built. One demonstrates removal of a single
noise source; the second allows you to hear him remove first one and then a
second source.
I think that one sound demo may not be the same 10,000 words as a picture is
reported to be, but it certainly suggested to me that this would be an
useful tool to have. In addition, it is a simple, low cost circuit that
should be able to be built by most of us should we wish to do so.
Tod, K0TO
----------------------------- Dick's message is below ------------
-----Original Message-----
From: Richard Goodman [mailto:wa3usg@comcast.net]
Sent: Tuesday, February 13, 2007 5:13 PM
To: Tod-ID
Subject: RE: Synchronous noise blanker
Todd,
The noise blanker works very well on 60 Hz mains related noise. Back when
I built it, I was using a fairly large multi turn loop for a receiving
antenna. I had it mounted on the house and it picked up quite a bit of noise
from TV's, Halogen lamps with dimmer controls (the bane of LF work), and
other things I never really identified. Let me say that it works GREAT for
getting trid of halogen dimmer noise. For TV horizontal oscillator noise, it
doesn't help. I moved the loop away from the house ... that got rid of about
50% of the noise ... I was still using the noise blanker to get rid of
Halaogen dimmer junk from the neighbors over 100 feet away. Then I put up
the AMRAD E-Field Probe ... about 100 feet from the house & 30 feet in the
air, now I'm not bothered by noise much at all. I haven't used the blanker
in quite awhile. The E-Field probe is absolutely fantastic! It way
outperforms my loop or any other antenna I've ever tried. I live fairly
close to W3EEE, Steve Dove, the Grabulator guy, and see everything just
about as good as he does. There is no substitute for a quiet location ...
however .... if you've got a lot of the loud, heavy, raspy, 60/120 Hz buzz
that is mains related, the synchronous blanker will work quite well.
I only ever used it on LF .... below 400 KHz. Most importantly, it only
will get rid of 60 Hz mains related noise. It uses a gate to actially shut
off the signal getting to the receiver when the noise pulse is present, and
that noise pulse must be synchable (not sure that's a word) to the 60 Hz
reference transformer in the blanker.
Probably the best way for you to evaluate how it works is to actually
hear it in operation. Here are two WAV files that I made using it. The link
below demonstrates using it to null out noise from a single interfering
source (halogen type of interference):
http://home.comcast.net/~wa3usg/FILT_OPS.WAV
In this case, you initally hear extremely bad interference, it goes away
as I synch the blanker to the noise ... it comes back after I pass through
the null ... then is eliminated when I re-null the blanker.
In the next case, there are two interfering noise sources. Since I built
the blanker with two channels, I can get rid of two sources of interference.
If you listen, you'll hear both sets of 60 /120 Hz buzzes. One will go away
as I null the first channel, then the second will be completely nulled out,
leaving a reasanably quiet passband:
http://home.comcast.net/~wa3usg/FILT_2S.WAV
Hey ... there have been times that I needed more then 3 channels!
Hope this helps.
Best of 73
Dick, WA3USG
-----Original Message-----
From: Tod-ID [mailto:tod@k0to.us]
Sent: Tuesday, February 13, 2007 4:13 PM
To: wa3usg@comcast.net
Subject: Synchronous noise blanker
Dick:
I am exploring the utility of a synchronous noise blanker.
During a web search I got a message that you wrote some time ago
******************************************
Richard Goodman wa3usg at compuserve.com Fri Feb 11 10:55:59 CST 2000
****************************************
In the text you said,
" This noise blanker almost COMPLETELY gets rid of it ... it's amazing.
I went from total overload to being able to copy the AMRAD beacon perfectly
(with Spectran). You can barely tell the interference is there.... after
awhile I switch the filter off to see if the interference has gone away
(but with the filter out it's as bad as ever). It seems to raise the
noise floor just a little bit but I'm still able to do serious weak signal
work with the filter running.... BEST WORKING PROJECT THAT I'VE EVER BUILT!
"
I wonder if you are still using that noise blanker? What bands did you use
it on? Any additional information you might wish to share would be
appreciated.
73, Tod, K0TO
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