Just playing devels advocate here, but, as you state "If you put X watts
into one antenna and extract Y watts from an antenna coupled to it, and
measure the efficiency of the "transformer" the same way as you did the
conventional transformer, you'll find it has lousy
efficiency.", does that refer to the 377 ohms (or so) free space coupling
impedence, or could that effeciency be improved by having the antenna's
matched radiation resistance approach that 377 ohms? (I.E. max transfer of
power is at Z0 (in) matches Z0(out)! or, is this academic for this?
Perhaps, better for Dr. Shorza Gitchigoumi of CQ fame, or Larson E. Rapp of
ARRL fame (both with bad habit of only presenting articles in the 4th month
of the year in their respective publications) ! But, I'd thought I had
better ask! Jim NN7K


"Roy Lewallen" wrote in message
...
I hope you'll pardon me for amplifying this a little.

If you put X watts into the primary of a transformer and extract Y watts
from the secondary, the efficiency is Y/X by definition.

If you put X watts into one antenna and extract Y watts from an antenna
coupled to it, and measure the efficiency of the "transformer" the same
way as you did the conventional transformer, you'll find it has lousy
efficiency. Why? Because a goodly fraction of the power you applied to
the "primary" antenna never gets to the "secondary" antenna because it's
radiated instead. As far as the "secondary" is concerned, it might as
well have been converted to heat.

If you look at the impedance of the "primary" antenna, you'll find an
excess of resistance -- just enough, in fact, to account for the "lost"
(radiated) power.

This isn't a statement about how well coupled antennas function as
antennas, whose purpose is to radiate after all. It's a statement about
how well they function as a transformer. Poorly.

Roy Lewallen, W7EL