[cpollock]

Thanks, that makes a lot of sense.  At 1MHz it is equivalent to a 1 ohm short to ground, so the size of the cap makes sense. It could probably be smaller, perhaps 1/3 that size and still function, but clearly it needs to be in the 0.01 uF range to serve as a short to ground for the AM band.

 If I were to use a polarized plug, where one side is always neutral (assuming the house is wired right), would it be sufficient to only put a cap to the neutral?  That would eliminate the "AC tingle" but still provide a path for RF to ground.

Or, on the other hand, if a current path through the second antenna terminal, such as running a line to ground ground, or using a loop antenna,   is provided, are the caps necessary?.

Clif