Topband: Electric fences

Tree tree at
Tue Dec 27 14:19:51 EST 2005

On Tue, Dec 27, 2005 at 12:12:25PM -0600, Charles Bibb wrote:

> First, what does electric fence RFI noise sound like?  

I have heard two kinds of electric fence noise.  One is a "click" that is
very quick (less than a millisecond) and repeated every .6 to 2 seconds.

A second is a buzzing sound that is perhaps 25 ms long - again repeated 
every second or so.

If you can download big files, here is a concert of electric fences (about 9
or them):

> Second, how far away can electric fence noise be heard.  

I have one that is over a mile away.  I haven't tracked down exactly where it 
is, but have the general area pinned down.  However, typically fences that are
more than 1/2 mile away tend either to not cause much of a problem, or get 
repaired after a period of time.

> I live on the 
> outer edge of a small town, and I've scoped out every place I can think of 
> where animals might be penned, but find no electrified fences.  Perhaps I 
> am not looking far enough away?

A good technique is to use your AM radio way up the band and drive around.
Some cars have too much QRN to do this with the motor running however.

If you find a fence - a good way to determine if it is the fence you are
looking for, you can time the pulses and compare.  Count off 20 or more of
them and use a stopwatch.  

If you have a concert of fences like the one above, I wrote a program that
will take a .WAV file and determine what fences are present (with their
tick period).  Run the .WAV file for about 15 seconds and run the program

The first four files in that directory are from an electric blanket that
had a poor design in the power supply.  The company got in trouble with
the FCC and has replacements.  So, if you hear this noise, you know what
to look for.

73 Tree N6TR
tree at

More information about the Topband mailing list