Sparking noise is causes by the line voltage rising to the point where it
reaches the breakdown point across a leakage path. Mike describes
in his posting, all the places that leakage can occur.
This breakdown leads to much higher current flow. The rise time of this
current wave can be very fast - in the 10-100 ns range. Once the current
flows, it takes a less voltage to stop the flow. So the currnt wave isn't
a symetrical square wave. Still, due to the rise time, this wave has
frequency components well into the UHF range.
However, as the frequency rises, the strength goes way down, and the distance
over which it can be heard. Above 300MHz, you've got to be within 20 feet
of the noise to hear it in a 5kHz BW, on most receivers available today.
This is why hunting with higher and higher frequencies helps localize the
source.
Marv's recent QST article shows an excellent way to use a TV signal to
find the type of noise.
Note:sparking noise is the starting, and stopping of current flow, due to
breakdown of a leakage path. Cornoa noise is a different mechanism.
KR
-----Original Message-----
From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On Behalf
Of Cortland Richmond
Sent: Sunday, March 20, 2005 8:59 AM
To: rfi@contesting.com
Subject: [RFI] Direct DFing of arcing hardware (was PG&E IR line faultdetection
advertisements)
Some 20 years ago I had occassion to track down widespread interference
caused by medium-voltage power-line-related arcing. I found HF DF of
limited use due to RF conducted along powerlines and other conductors to
be radiated elswhere. I had to go into VHF to narrow down the general area.
Then I had to go to 450 MHz to get a bead on the specific pole and
hardware. The hardware involved was almost resonant there, so the *direct*
emission could be DF'd.. Luckily, it turned out to be at a local airport
and had been bothering the control tower's reception for some time; when
THEY complained, the utility showed right up.
This calls for beams, not loops, of course, and I had to build one.
Nowadays I have 2450, 1700, 1250, 900 MHz, and 2/440 as needed.
Cortland
KA5S
> [Original Message]
> From: Kevin J. Rowett <krowett@rowett.org>
>
> Almost all the source of HF RFI is sparking noise caused by current
> "arcing" over between one of the conductors and ground. This
> usually only happens with the medium (15-48kV) voltage distribution
> lines and the even high voltage lines (> 55kV).
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