I remember the wireless modem jacks on 3.53 MHz very well.
What I learned in those days what that, for the most part, emissions from
devices plugged in to house wiring exhibits two phenomena:
1. They are essentially point sources, making direction finding pretty easy.
2. Their emissions decay rapidly with distance near the source
When the wireless modem jacks were causing interference on 80 meters, I built a
small 80-m loopstick antenna. It was surprisingly sensitive and highly
directive. When I pointed the antenna at a small source, the null quickly
pointed me right to the source. It was bidirectional, so I had to triangulate
at times, but that was still pretty easy.
So, I was sent to Phoenix for an ARRL convention. I packed the loopstick and an
FT-817. When I got back to the hotel, I went out on my 2nd floor lobby with
the loop and '817, to see what I could hear. The band was pretty normal. I
then tuned near 3.53 MHz and, lo and behold, there was a wireless modem jack,
exhibiting all the tell-tale signs. I had a rental car, so, got a direction,
then headed in that direction, to see if I could triangulate it.
I got to the neighborhood, got a bearing and headed in that direction. It got a
bit louder, so I stopped and got a different bearing, and pretty much figured
out where it was. I had to drive up and down about three streets, but I soon
found the house that was doing all the emitting. It was about a half mile from
the hotel!
I was able to drive past the house and, while driving, keep the null pointed at
the house, so this technique works up close or at some distance. If you use a
non-resonant loop, it won't be very sensitive, so you will have to get close to
the house the noise is coming from, but it is much better to find the house
than to get possibly misleading information about "what is it?"
If you have a cooperative resident, you may be able to turn off breakers one at
a time, then go on a hunt in the room powered by the breaker that causes the
noise to go away.
Ed, W1RFI/0
________________________________________
From: RFI [rfi-bounces@contesting.com] on behalf of Cortland Richmond
[ka5s@earthlink.net]
Sent: Sunday, October 28, 2018 4:34 PM
To: rfi@contesting.com
Subject: Re: [RFI] Signals on 160
Ed will remember the AT&T modems on 80 meters.
I had good luck tracking them down in Petaluma and locating each one to
specific rooms in a development of single-story duplexes.
It was Super Bowl Sunday and when people sharing cable co. services saw
someone with antennas on his car and a "sniffer" (AOR 8000 with an
untuned loop) they were running behind their houses to remove the
illegal taps.
A 3-6 inch loop of rigid or even fairly stiff coax can be directive
enough to find these harmonics and then at lower frequencies march right
up to the source. H-field coupling drops off VERY fast away from a
radiating conductor.
Cortland
KA5S
On 10/28/18 3:54 PM, Hare, Ed W1RFI wrote:
> "What is it?" is the wrong question. If someone said that it is a model Z-123
> Netstuff modem, that really wouldn't help much. The real question is: "Where
> is it?" Finding the house or location where the noise is originating is what
> you will get to eventually, so start with that question.
>
> Many noisy devices can sound similar, so if someone tells you that it is a
> Z-123, and it is really a lighting ballast instead, you will be on a
> wild-goose chase.
>
> Ed, W1RFI
>
>
> ________________________________________
> From: RFI [rfi-bounces@contesting.com] on behalf of donovanf@starpower.net
> [donovanf@starpower.net]
> Sent: Sunday, October 28, 2018 3:04 PM
> To: rfi@contesting.com
> Subject: Re: [RFI] Signals on 160
>
> Hi Gary,
>
>
> Of course, the first thing you should do is turn off all of the AC
> power -- including UPSs -- in your own home to determine if any
> of the RFI disappears.
>
>
>
> I don't think anyone will be doing you a favor by helping you guess
> what these signals might be. By far the best way to determine what
> they are is to build -- or if necessary buy -- a simple small loop antenna.
> A loop antenna has a deep, narrow azimuth null off of each side of
> the antenna that allows to quickly identify the RFI source.
>
>
> Good luck!
>
>
> 73
> Frank
> W3LPL
>
> ----- Original Message -----
>
> From: "Gary Smith" <Gary@ka1j.com>
> To: rfi@contesting.com
> Sent: Sunday, October 28, 2018 5:31:51 PM
> Subject: [RFI] Signals on 160
>
> I've been encountering some strong signals
> on 160 recently. I made some approximate
> guesses at the frequency using the P3
> markers to measure them. Here's the
> signals at 1:20PM local time with a center
> frequency of 1.848.67
>
> The main signals are about 42 KHz apart.
> The lesser spikes in-between appear at
> somewhat regular intervals.
>
> http://doctorgary.net/spikes-on-p3.jpg
>
> Here's the measured values of the main
> signals
>
> http://doctorgary.net/frequencies.jpg
>
>
> Any idea what might be the source of
> signals spaced like this?
>
> 73,
>
> Gary
> KA1J
> _______________________________________________
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>
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