On Mar 23, 1:50*pm, "Joel Koltner"
wrote:
Hi Tim,

"TimShoppa" wrote in message

...
On Mar 22, 9:24 pm, "Joel Koltner"
wrote:

I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point.

Agreed -- the controversy comes into play in that he ends up computing
electrically-small loop antennas as being upwards of 70-90% efficient, when
everyone "knows" that such antennas are typically 10% efficient. *He even
goes after Chu/Wheeler/McLean/etc. in suggesting that the fundamental limits
for the Q of an ESA are orders of magnitude off (slide 47), and that's pretty
sacrosanct terriority (see, e.g.,www.slyusar.kiev.ua/Slyusar_077.pdf*-- even
the Ruskies buy into the traditional results :-) ).

Hence, while I don't really have the background to know precisely how much of
what Underhill promotes is true or not, it's definitely intriguing to me, and
I'm looking around for various rebuttals by those more skilled in the art than
I am.

One link I found:http://qcwa70.org/truth%20and%20untruth.pdf(but this was
written before the PowerPoint presentation I originally linked to).

I'm pretty sure that it is not so easy to just measure power in, heat
lost, and assume that everything else is being usefully radiated.

I think that after you've modeled and then built an antenna, that heat
loss and temperature measurements are valuable to determine if the
assumptions you put into the NEC model regarding loss etc. are correct
or not, and where you need to improve your model, especially of
materials like dielectrics.

Even the heat loss measurements require some fairly heavy modeling
just to convert the IR camera images to actual watts per square cm.
Think it's purely radiative? Sometimes yeah, but make the wrong
assumption when really it's convective and you can be off by a factor
of ten to thirty.

Tim.