The clicking type of fence charger has a relay in the primary of the power
supply which is indeed a high voltage step up transformer at low current.
The relay is configured to pull in, and thus break a pole which is supplying
its coil with power, thus it immediately drops out and the cycle repeats.
The contact that momentarily is made is stepped up by the transformer, since
you have a pulse like a crude AC. You can get RFI both from the low voltage
side of the relay, and the high voltage contacts side, as they spark. You
can also get it when the weeds growing into the wire fence are being burned.
On the one I had on the farm, it did not have a different mode for weed
burning, it just naturally did that if the weed was green and shorted the
wire!
73,
Stuart K5KVH
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