dave at nk7z.net
Thu Aug 30 10:21:26 EDT 2012
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...
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