Topband: Boradband noise on 160 meters tracked down toapartmentcomplex
goldtr8 at charter.net
Mon Dec 15 20:45:52 EST 2014
Thanks for your comments in the email below.
I have a 80m noise that is from a local house source and your comments below
have me thinking about how to implement a vertical noise sense antenna.
I believe the noise to be vertically polarized as my horizontal loop does
not have the same noise receive issue as my 80m vertical does. Thus my plan
was to set up a vertical antenna outside and connect it to my ANC-4 noise
nulling system as the sense antenna. I currently used the ANC-4 with a wire
strung in the basement with the target to null out plasma tv noise and this
was reasonably successful until the new noise showed up. My current sense
system does not hear the noise at all so something else needs to be set up.
The vertical element I was going to use was a simple 102 inch whip, however
based on your comment I am thinking a longer vertical element would be
better but I am not sure how to pick a vertical length.
I have concluded based on driving around this weekend with a simple
direction loop that it is less than 1/2 mile away from me and its comes from
a house. It was active this Sunday morning and using the simple loop I am
confident that it is from a specific house. It is not power pole noise that
is something that I recognize easily with my mobile operations.
So specifically noise is 80m and I want to null it so I can use 80m again.
My thought is a vertical sense antenna, my first thought was a 102 inch whip
but I can make something longer. I know the direction of the noise so I
can put the sense antenna where needed so I am open for suggestions.
This was the noise that showed up and then disappeared and now has returned
intermittently so I need to attempt to try and null it out.
2014 3905CC Top Gun :-)
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From: Tom W8JI
Sent: Monday, December 15, 2014 10:08 AM
To: Don Kirk ; W2PM
Cc: topband at contesting.com ; jim at audiosystemsgroup.com
Subject: Re: Topband: Boradband noise on 160 meters tracked down
> Mfj Nuller will not work because the signal is in the same direction of my
> 300 deg pointing pennant.
There are a lot of popular misconceptions about this. The noise does always
not have to be a different direction, or even just one source.
The MFJ nuller and other similar systems will remove noise when:
1.) The sense antenna is much closer to the noise, or picks up the noise
much better compared to signals than the listening antenna does. This is
true no matter what the desired signal direction. In this case you are
eliminating a source by having a sense antenna hear the noise much stronger
than the sense antenna hears desired signals.
2.) The noise is one or multiple sources from the same direction and the
sense antenna is reasonably close to the RX antenna and the correct
direction from the RX antenna. The noise has to be a significantly different
direction than the RX direction. You are just eliminating the general noise
direction in this case.
3.) The noise can be from multiple sources radiating from the same point. A
long power line with multiple insulators arcing that is passing by close,
and conducting emissions to that point, might be an example. You are
nulling the point of coupling, rather than the noise generator's location.
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