[RFI] Electrical transfomer near shack, a problem?

[N1BUG]

I was surprised by one of the things we found here this past summer. 
One of my stronger noise sources was being heard on all bands 1.8 to 
50 MHz. It may have extended well beyond that but I don't have 
higher bands at my station. It was about -85 dBm at 50 MHz with 7 
element yagi (10 dBd). I tracked it to a particular pole three 
quarters of a mile away. Conduction was definitely involved. I 
initially had some trials pinpointing the source but UHF eventually 
left no doubt. The power company thought it was a lighting arrestor.

Fortunately the day they worked on this one the noise investigator 
came out with the line crew. Replacing the lightning arrestor and 
tightening hardware did nothing, so he directed them to go get a new 
pole transformer. Problem solved. If I had to make a wild, 
uneducated guess, I'd guess sparking on the high voltage lead inside 
the transformer. Conducted noise was on the 13.2 kV lines.

I was surprised at this level of RFI from a source *apparently* 
inside a pole transformer. I was even more surprised they replaced 
it without more "prompting" by me. I like it when the investigator 
comes out with the line crew. It isn't standard practice, but seems 
like it should be. Far more was accomplished that day than all the 
other days combined.

Paul



On 01/10/2013 10:47 AM, Frank N. Haas KB4T wrote:
> RFI from an overhead transformer propagates by both radiation and
> conduction. In my experience conduction is the bigger problem and
> is often difficult to pinpoint.
>
> In my exprience, transformer RFI is pretty rare. Ham antennas
> fairly close to a transformer-based source can easily pickup such
> RFI due to being close to the radiating field produced within the
> enclosure or RFI conducted by the attached wires and radiating
> from those wires. Yet the entire field of influence extends only
> a few hundred feet and is often heard only up to 8 to 10 MHz
> (usually because the RFI signal is weak compared to an arcing
> lightning arrester or bolt/nut combo out in the clear.


-- 
Paul Kelley, N1BUG
RFI Committee chair,
Piscataquis Amateur Radio Club
http://www.k1pq.org