[CQ-Contest] Electric Fence QRN

[Duane Grotophorst]

Having been both in farming and ham radio at the same
some years ago I can attest that electric fences can
be electrically quiet. When I was still on the farm we
had miles of the stuff, some of it within 50 ft of my
antennas, I had very little trouble with noise from
it. My experience was that it is not the weeds growing
into the fence and arching that generate the noise,
including the "weed" burner type of fence charger. It
is almost always instead a poor connection between
fence segments, or between the fence charger and its
ground system/rod.

Think about a 3-6 KV (@ a few ma) circuit (being
pulsed for .1 - .8 second durations) coupling to a
high impedance antenna (the 1000's of feet of fence)
through a spark gap (the poor connection). That is
essentially a spark gap transmitter!!! However in the
case of the weed growing into the fence it would be an
arc through a relatively low impedance to ground.
Since the weed stem is resistive and is also a short
distance to ground it would not generate much, if any
radio noise, even though the arching was very audible
when you'd walk by it.

When I was building electric fence I always used a
"linemans" splice to connect different wire segments
using minimum of 8 - 10 turns when joining sections.
For areas that needed a gateway I always made sure
that the wire that made up the gate would be pulled
quite tight when connected to its hook. The bottom
line that it came down to was making sure that all
electrical connections were mechanically solid and
proper. A sloppy job of making the connections didn't
really hurt the fence's performance all that much for
keeping the critters in there proper places, but it
did make a big difference for RFI issues.

Duane
N9DG


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