dave at nk7z.net
Thu Aug 30 13:25:50 EDT 2012
Thank you for that information... As soon as the homeowner tells me
what he has discovered I will assist him. At this point, I have only a
rough idea that it is the power supply, he is reticent to allow me in
his home, but very helpful otherwise.
http://www.nk7z.net for equipment reviews, propagation, and more...
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On Thu, 2012-08-30 at 12:11 -0500, Dale Svetanoff wrote:
> 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.
> 73, Dale
> > [Original Message]
> > From: Dave Cole <dave at nk7z.net>
> > To: <rfi at contesting.com>
> > Date: 8/30/2012 9:21:37
> > Subject: [RFI] Success!!!!!
> > Hello,
> > 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:
> > http://nk7z.net/rfi-at-my-home-qth/
> > 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.
> > --
> > Thanks,
> > Dave
> > http://www.nk7z.net for equipment reviews, propagation, and more...
> > For JT65 Discussions:
> > https://groups.google.com/forum/?fromgroups#!forum/jt65
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