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Re: [RFI] Help Identifying RFI

To: rfi@contesting.com
Subject: Re: [RFI] Help Identifying RFI
From: "Dave Cole (NK7Z)" <dave@nk7z.net>
Date: Mon, 25 Sep 2017 04:03:10 -0700
List-post: <mailto:rfi@contesting.com>
If you can get a portable SDR, say an RSP-1 using an Raspberry Pi, then you can use your loop to track down very selected RFI sources by watching the spectrogram of that RFI as you turn the loop.

A small subset of signals will fade in and out as you rotate the loop, this will help you separate out which are the really offending ones... I use the process described at:

http://nk7z.net/sdr-rfi-survey-p1/

to initially locate what RFI I want to track, then I zoom in time wise, and use a loop to follow just that source by looking at the nulls as I turn the loop. This way I see only a few signals fade, out of the many RFI signals... This allows me to select what signals I want to track.

Takes a bit of practice, but once I got the hang of it, it shortened the locate time down to minutes in most cases...

73s and thanks,
Dave
NK7Z
http://www.nk7z.net

On 09/24/2017 08:32 PM, Kam Sirag (Yahoo) via RFI wrote:
Looking for some help with the following problem, if possible, (I'm going

to 'throw a handful of rice at the side of the barn and see if any sticks'

wrt to background information - just in case some of the ancillary info is

actually more useful than I might have thought.

Every year I seem to need to track down some sort of new RFI here at the Ti5W

station in northern Costa Rica. Two years ago it was a faulty sensor for a

sodium streetlight and last year it was a sodium streetlight itself.

This year's nut has been a bit harder to crack. The RFI peaks in a

particular direction (about 335 degrees) and is s9 at some spots on the 15m

band. It is broadband, and can be heard on all the bands, but is worst on

15m, noticeable on 10m and less so on 20m. (Presently I don't have WARC

band antennas, but I'm guessing 17m and 12m pick it up also.) It can be

heard on the low bands, but is in the noise floor. This noise started

intermittently about three months ago and gradually became more frequent

until it's now on 24/7. Rain doesn't seem to affect it these days (I don't

really recall if rain affected it at all.) One interesting thing is that

the noise has gone from something that the noise blanker on my FT5000 would

easily kill to one that the NB seems to have minimal effect on (I'm assuming

it is the same noise - but that's not a 100% given.)

I have an AM mode recording WAV file of the noise that I'm happy to share if

anyone cares to listen.

Although the noise is broadband, there are a couple of frequencies where it

is highly attenuated. For example 21.260Mhz seems to be a null. But there

are not many nulls. That's the only one on 15m.

My attempts so far at tracking it down have been somewhat successful - today

there was a serendipitous power outage only in my immediate neighborhood.

The noise did not go away, which led me to believe it was farther away than

I thought. It is also loudest on the highest antenna - another vote for not

being in close proximity.

So, I flew my camera drone in a line with the peak RFI heading on my yagi to

see what may be out there farther away. At about 2.7km away, the pastures

gave way to a road with several businesses and homes in the 'target zone.'

I built up a loop antenna, fixed it in the bed of my pickup truck, put a

K3 in the passenger seat and listened as I drove to the area.

The noise seemed to peak when I got very close to a particular utility pole

in the target zone. I still need to figure out how to be 100% sure that the

pole is the culprit, since the interference is worst on 15m, and it seems

like the RFI may be radiating on some of the power lines around that area.

I was wondering if anyone could take a listen to the recording I made of

the noise, and possibly identify it, or have any other suggestions on how to

approach this. I've tracked down a reasonable number of RFI issues in

Maryland, and also a couple down here, but none has involved a utility pole

potentially being the culprit. I tried comparing the noise to the ARRL RFI

noise database, but am not confident I can say it matches anything. The

main reason I'd like to have as much/overkill information as possible is

that down here in Costa Rica, it is harder for me to communicate effectively

in order to explain an issue like this and also it's difficult to get the

utility company to act, or to ask entry into someone's home. So I guess I'm

trying to be as sure as I can be about what is going on before I try to pull

any action triggers.

Thanks for reading and please feel free to reply in the group or directly to

me.

73,

Kam

N3KS

Ti5W

..

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