[RFI] Oh, happy daze!!

Lee K7TJR k7tjr at msn.com
Wed Dec 5 21:39:41 EST 2012

Hi Charlie,
   In a previous life I sold fence chargers and other farm supplies for a
 living. A couple things I remember. You are very right in that a good
 ground is needed. Some of the application notes suggested using
 multiple rods in poor ground areas. Lacking a good ground will cause
 the return pulse current to come back through the power cord line
 ground making your local grounds and power poles hot with pulse
 noise. I would suggest a very good ground and then using the toroid
 as suggested by Jim on the power cord to the unit to keep the pulse
 current off the local wiring.
   In addition, one of the application notes I read years ago suggested
 an inductor be placed in the fence line right at the charger output if
 radio interference was a problem. Their claim was that it lowered the
 speed of the risetime causing less high frequency energy. Right or
 wrong I have not looked at that in detail. Their inductor suggested
 was about 4 to 5 inches in diameter and about 8 to 9 inches long. It
 appeared to have 15 to 20 turns. Remember, the voltage levels we
 are talking about here are in the 10 to 20 KV range.
   Lee  K7TJR  OR

>My question is has anyone tried using say, several turns
of wire around a #31 toroid core (or other filter) at the 
output of a fence "charger" to reduce/eliminate any 
noise from that particular source?  

I realize a filter is not going to affect any spark noise from
somewhere out on the line, but just asking about the 
filter at the charger output.  I was thinking that the inductance
might take the "edge" off the voltage spike generated by the 
fence charger.

Any input most welcome!

Charlie, N0TT

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