The only way I know of to know for sure if the noise is direct radiation or
re-radiation of conducted noise is to use an ultrasonic detector to test for
direct noise. You'll only pick up noise from a direct source with ultrasonic
equipment. You need to completely search all sides & angles of a pole with a
UT device before ruling it out as the source.
You can and should use RF to track the noise to possible sources, but a good UT
device will allow you to confirm the right pole and even perhaps what hardware
on the pole is the culprit generating the noise. Certain mfr squirrel guards
and loose software are the usual culprits.
The was an interesting story in the last ARRL letter about powerline
interference that you don't see everyday. Here's a copy of the story from"The
Letter":
***************
The ARRL Letter
Vol. 21, No. 22
May 31 , 2002
***************
IN THIS EDITION:
* +Odd interference case resolved in Ohio
==>OUT-OF-THE-ORDINARY INTERFERENCE CASE RESOLVED
In what FCC Special Counsel for Enforcement Riley Hollingsworth called "a
textbook example" of FCC-ARRL cooperation, a case of strange interference
involving a power company and an AM broadcast station has been
substantially resolved. As a result of their follow-up investigation, six
Cincinnati-area amateurs were awarded the ARRL Certificate of Merit.
In January, the FCC wrote Cincinnati AM radio station WLW and Cinergy
Corp--the electric utility serving the region--to help resolve the unusual
and longstanding interference situation that was affecting local amateurs.
Apparently spurious signals associated with WLW transmissions had been
monitored over a wide area and frequency range and were severely affecting
some amateur bands.
The investigation focused on utility towers carrying 345-kV lines in the
vicinity of the WLW broadcast tower. Jay Adrick, K8CJY--a member of the
amateur team involved in tracking down the problem and one of those
honored--explained at the Dayton ARRL Forum earlier this month that the
primary problem seemed to stem from so-called static lines on the towers,
which do not carry electrical power. The static lines, he pointed out,
were not sufficiently RF-bonded to the tower structure. "They're actually
loose-fitted," he said. "At 60 Hz, it's a reasonable ground." But at RF,
it acted as a non-linear junction, and the static wires acted as a huge
antenna. The result was something that sounded a bit like a spark gap
modulated by WLW's audio on several amateur bands.
Success did not come easily, and mop-up operations continue. Hollingsworth
called the situation "a history-making RF interference case" that
generated more investigative analysis than any other case in his years
with the FCC.
Ohio ARRL Section Manager Joe Phillips, K8QOE, said the local amateurs
brought the matter to the FCC's attention after working with WLW and
Cinergy for almost two years to pin down the cause of the spurious
signals.
Honored with certificates at the ARRL Forum in Dayton in addition to
Adrick were team leader Bob Reiff, WA8ULW; Ted Homan, WB8WFG; Herb
Nichols, W3EOA; Geoff Mendenhall, W8GNM; and Paul Jellison, WD8KMX.
Jellison is regional engineering manager of Clear Channel Communications
which owns WLW. Also honored were non-amateurs Jeff Antoni and Kelly
McMahan, both of Cinergy Corporation.
The certificates were signed by ARRL Great Lakes Division Director George
Race, WB8BGY, and ARRL Lab Supervisor Ed Hare, W1RFI, who assisted in the
efforts to resolve the interference situation. The amateurs were cited for
"creating an example of longtime and continuing corporate-amateur radio
cooperation in an interference abatement of high power RF signals."
Though some interference remains, Phillips said, the local amateurs and
both corporations discovered many possible sources of trouble and have
established a working procedure for clearing them up.
"Saying the interference is all cleared up would be foolhardy given the
complex nature of the engineering involved," said Phillips, who
recommended the awards, "but the two words that describe this historic
work would be 'patience works.'"
Under FCC Part 15 and Part 73 rules, incidental noise radiated by power
company equipment or spurious emissions from a broadcast transmitter must
be corrected if they cause harmful interference to radio communications.
> -----Original Message-----
> From: Wendell Wyly W5FL
> I have very loud received noise that is about 10 db over S9 on 10,12,15,17,
> and 20 meters. When I plot the pattern using the noise as a constant source
> from the 10 meter antenna, 15 meter antenna, and 20 meter antenna, I get
> three similar overlaid patterns corresponding to the actual antenna patterns
> but all three pointing exactly to 210 degrees and all with almost the same
> maximum S meter reading on these five bands.
>
> I am on a rural hilltop location with 20 mile line of sight from a 64 foot
> tower. Most houses are on 5 acre or larger sites here. I assume the noise
> is line noise, but have not confirmed that either. Am I looking at the noise
> source directly with the antenna or can the exact direction be camouflaged
> if the noise is conducted for a long ways and then re-radiated? Is there an
> easy way to determine whether the noise is primarily radiated or conducted.
>
> The noise blanker on the Yaesu 1000MP knocks the noise way down (6 or 7 S
> Units)as the noise has a very high peak to average ratio (arc?).
>
>
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