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Re: grounding question



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 12:49 PM 10/9/2006, you wrote:
Original poster: Mddeming@xxxxxxx
In a message dated 10/9/06 1:27:38 P.M. Eastern Daylight Time, tesla@xxxxxxxxxx writes:
Original poster: John <guipenguin@xxxxxxxxx>

If I cant drive a grounding rod for RF ground, what is this counter
pose under the coil I hear people mention?

Thanks,

     John.

Hi John,

A counterpoise is a type of "virtual ground". consisting of foil, wire mesh (chicken wire etc.) or radial wires arranged in a daisy wheel at least as long and broad as the coil is high or the topload diameter, whichever is greater. This is placed underneath the unit with RF ground end of secondary attached to it. The topload "sees this as ground and all works. A foil one is cheapest and easiest, but wastes somewhat more power in eddy currents. Radial wires are the most efficient, but hardest to do and keep straight. a large square or circle of wire mesh is a good compromise. NOTE: During operation, the counterpoise is floating at unknown high potential with respect to earth ground. DO NOT TOUCH!!!!!


For the latter reason, the counterpoise SHOULD be connected to the "green wire" safety ground. I'd use a RF Choke of some sort, just to keep RF off the building safety ground.


Hope this helps,

Matt D.