[TowerTalk] electric fence qrn

[Jim Lux]

At 07:39 PM 12/8/2003 -0600, Mark Brown wrote:
>Hi All
>         I have a new neighbor who has horses and put up an electric 
> fence. It is
>giving off an s9+ pulse on the lower bands and is hearable on 2m ssb when I
>point that way. Any suggestions to fix it? I confirmed it is the fence and
>the neighbor is willing to work with me to fix it.
>                                                                         Mark

The usual electric fence puts a single high voltage pulse out every couple 
seconds, which normally won't make much RFI, because there isn't any real 
current flowing, unless...  If there's something arcing (a wet insulator, 
or weeds) then the current flowing causes it to radiate.  Check the wire 
from the charger to the fence (is it HV wire... spark plug wire works 
nicely, so does neon sign wire (GTO15)... house wire (romex) or automotive 
hookup type wire does not...)

Corrosion or such on "gate connectors" (i.e. spring loaded hooks) can also 
result in problems.

Does the charger have a good ground?  Does it have a line filter?

Is the pulsing frequent, or just once a second or so?  Does the pulse have 
any "structure" to it (i.e. are you hearing harmonics of a switching 
regulator, or is it just a "pop")

If it's a single pop, then what you need to do is make the rise and fall 
time a bit longer (say, > a few microseconds) so that there isn't any 
significant power in the HF bands.  A resistor in series may be all it 
takes.. Or, perhaps, a ferrite core like is used on computers to knock down 
the RFI.


Have you called the mfr of the fence charger?  It's presumably a Part 15 
incidental radiator, and, while the owner of the device is ultimately 
responsible, and you don't really want to hassle your neighbor (after all, 
he's trying to do the right thing)... a decent manufacturer should have 
used "good engineering practice" to "minimize the risk of harmful 
interference".

I also seem to recall seeing RFI filters in a fence charger manual...