svetanoff at earthlink.net
Thu Aug 30 13:11:06 EDT 2012
Thanks for sharing your success story. Very interesting, indeed.
One comment: You say that the homeowner will be replacing the noise-making
power source. The problem is that the replacement is highly likely to be
another switching power supply that might be just as bad as the present one
(or even worse!). It might be worth your while to ask the gentleman (glad
to hear he is cooperative) just what the specs are on that unit. (Output
voltage and current are almost always provided on the label or molded into
the case of power supplies - wall warts, if you will). If the output is
something common, such as 6VDC, 9VDC, or 12 VDC, it might be possible to
replace the noise-maker with a linear power supply. One caveat: be certain
that any linear supply has a regulated output. Yes, it will run warm, but
it won't generate the hash. You may have to help him locate a source for a
regulated linear supply, since they seem to be getting less-common by the
week. They don't meet "Energy Star" requirements.
The alternative, of course, if he gets another noisy switcher, is to visit
K9YC's website (discussed many times on this list) and apply absorption
and/or filtering techniques as applicable. Good luck.
> [Original Message]
> From: Dave Cole <dave at nk7z.net>
> To: <rfi at contesting.com>
> Date: 8/30/2012 9:21:37
> Subject: [RFI] Success!!!!!
> I finally located my 20 to 40 DB over S9 noise source on 40 Meters! It
> was a home, about 1500-2000 feet away from my antenna! The homes in the
> source area have underground wiring, so I was not suspecting them...
> Turns out, whatever device the homeowner had going was generating enough
> RFI to show as 40 to 50 DB over S9 while in the home owners drive way,
> and only on 80/40/20. No VHF component.
> The signal was traveling through his house wiring, into the underground
> transformer, spewing RFI from the transformer grate, and then traveling
> via underground cable about 700 feet to a riser cable running up the
> side of a pole...
> From that pole the signal traveled about 1000 feet down a single aerial
> 7.2 KV strand, across my front yard, and then via RF about 500 feet to
> my vertical antenna. This path generated a 20DB to 40 db over S9 signal
> 15 to 20 hours of the day on my 756 PRO III with preamps off, using AM
> at 6 KHz width...
> I was very close to involving the FCC, (pointing them at the local Power
> Company), but decided to wait a bit. That was a good decision. Now
> that I knew the RFI was coming from the underground area, I reworked the
> location where the RFI was emitting from the vault and decided to try
> each house up and down from the transformer, using the mobile rig tuned
> to 40 meters. The suspect home was the strongest...
> To make a long story short, the home owner was very kind, and a pleasure
> to deal with. He and I went through the breaker killing routine, he
> found the noise source in his garage, and has it off now. He will be
> replacing it shortly. I have no idea what the source, other than he
> thinks it is a Wall mounted transformer used for his security system, he
> was reticent to allow me in his garage.
> They have lived in the home for only three months, and I believe I can
> see the same pattern of on/off times, prior to his move in, so I expect
> he is correct. If interested, there are about six months of graphs up
> at the web site...
> The 20 to 40 DB over S9 noise is gone, This of course uncovered another
> level of noise sources at S8.5 to S9, on 40 Meters. I will have graphs
> and sound cuts up at:
> if anyone is interested...
> This does offer an opportunity to show one noise source overlaid on
> another, and then it being removed, thus showing what is under it...
> I will be putting those graphs up later today, as I need to generate the
> graph for today/last-night.
> Many thanks to all involved here who helped me, and let me vent here.
> I bought Loftness's book, "AC Power Interference Handbook" and located
> the noise source within 24 hours... I suspect there is a connection.
> That book covers how RFI moves down utility lines, so it helped me in
> understanding the paths that might be taken... Seriously, had someone
> suggested a path as odd as this I would have thought them daft...
> Sorry for the long post! I will be able to RTTY contest on 40
> again!!!!!! See you all this weekend in the Russian RTTY WW.
> http://www.nk7z.net for equipment reviews, propagation, and more...
> For JT65 Discussions:
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> RFI at contesting.com
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