Richard Fry wrote:

"Wayne" wrote

Dead on explanation. Some have insisted that inefficiencies
result from antenna size and not from matching challenges.
_______

Kindly note that the radiation efficiency of an antenna _system_ is related
to its radiation resistance compared to other resistive losses present in
that antenna system.

It is possible to perfectly match the impedance at the feedpoint of an
antenna system to the impedance of the transmission line connected there.
But that antenna system still can have very poor radiation efficiency at
that frequency.

An example of this is a Z-matched, but electrically short vertical monopole
driven against a poor r-f ground connection such as a few buried ground
rods. Most of the available transmitter power is dissipated in the r-f
ground resistance, rather than being usefully radiated as e-m waves.

That is true. But the statement you were responding to was made in
response to a specific example where the RF loss resistance was much
smaller than the 0.49.ohm radation resistance. And the whole
discussion arose from the suggestion that short antennas are
*necessarily* inefficient because they cannot radiate without loss.
Your example is a good one of a system with a large loss resistance
which needs a higher radiation resistance monopole to feed the
combination efficiently in series. It is a perfectly good example, but
shows nothing about the intriinsic radiation efficiency of a short
antenna, just about its practical usefulness in a certain situations.


--

Roger Hayter