Richard Fry wrote:

... I am asking for comments on what I wrote -- ...

Comment: good stuff, and a couple of additional comments.

The term "accept power" is interesting. To me, it's just a measure
of the input impedance of the antenna. If the resistance (radiation
plus loss resistance) is zero, you're not going to get it to absorb
power no matter what you do.

Yes. And the input conditions depend on the ability of the radiator to
generate EM fields. No current can enter and "flow through" a radiator if
it doesn't have some place to go. If a radiator is not electrically long
enough to allow differential current to exist along its length, it cannot
generate EM fields. It is the di/dt along the radiator length that
generates those fields.

Adding a matching network at the antenna input doesn't change the
instrinsic
ability of an antenna to radiate. That is determined by the factors
described in the paragraph above. A matching network can permit the tx to
increase its rated, safe output power while driving that poor antenna, but
any extra power available at the antenna input because of that will be
subject to the same poor radiation efficiency as if the matcher wasn't
used.
And much of any added power from the tx may get dissipated in lossy output
system components other than the antenna, rather than being radiated.

The feedline has a certain efficiency. A matching network at the antenna
has a certain efficiency. If the matching network at the antenna is much
more efficient than the feedline, then it may be a reasonable solution.
An SGC-230 tuner mounted at the base of a 22 foot vertical makes a
reasonable antenna for 40m-10m operation. Feeding that same antenna
through coax from an SGC-230 in the shack makes for a pretty poor
antenna on most bands except 30m. Same antenna, same tuner, different
configuration = wildly different results.

The
antenna itself will still have the same directivity/gain that it had before
the matching network was added.

Yes, but the SGC-230 at the base of the antenna may be operating at
50% efficiency while, if you moved the tuner back to the shack, the
feedline might be operating at 10% efficiency. The choice is clear
(if there are no thieves around. :-)

Improving the ability of a poor antenna to generate EM fields per unit of
source power is possible in a limited way only by increasing its electrical
length. "Capacity hats" and inductances incorporated into the radiating
structure can be used, as examples. This also raises the antenna radiation
resistance and reduces the reactance at the antenna input -- making it
easier to match into, and reducing system losses.

Someone gave an example of a pager antenna or something that had a
rated gain that was below isotropic. It'd be interesting to see where the
losses were.

This is covered in my comments above, I believe.

--
73, Cecil http://www.qsl.net/w5dxp

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