On 27 Sep 2005 14:44:43 -0700, "Harry" wrote:

Would someone please explain that for me?

Hi Harry,

Because the media, space, does not have DC continuity, but acts rather
more like an infinite succession of inductances and capacitances that
transforms the original waveform (a) into (b) whose DC average is zip.
It should be said that this is not due strictly to the antenna, but
all paths within the complete communication circuit.

And to anticipate the yahoos who interject that yes there is an R
component, its contribution (short of the æther turning into a plasma)
is of no consequence to the outcome you observe.

This is an answer, but it may fall quite short of an explanation.

73's
Richard Clark, KB7QHC