On Mar 24, 3:32*am, Art Unwin wrote:
On Mar 23, 9:35*pm, Tim Shoppa wrote:



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(butthiswas
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.

But Tim Maxwells equations are accepted every where and appear to be
valid.
Because of this antenna computer programs are based on these
equations.
Thus when a optimiser is added the program can change the input to one
that satisfies
Maxwells equations. Assuming programers did a good job in focusing on
the Maxwell equations then we are provided with an array that meets
Maxwells equations.
What more can we possibly need other than a program that accounts for
all forces involved for the generation of ALL radiation available for
communication use that can be propagated
If we have a distrust in the programers or in Maxwells laws then one
should ditch the arrays
supplied by an optimiser and find what some refer to as a "new
technology." Until one comes along we first have to delegitemise
Maxwell and we have been unable to do that!

up to here this is the most lucid thing i think i have seen art
write... and then he starts going down hill.


Maxwells equations can be justified via all known laws in physics
including making static laws dynamic. and adhering to the absolute
requirement of equilibrium *with respect to physics laws. The main
problem we have is misinterpretations we add by using lumped loads etc
which Maxwell never included same. This also is the case with the yagi
where
Maxwell never supplied anything with respect to planar or even a
stipulation that elements must be straight, parallel, resonant,
etc ,only EQUILIBRIUM. where all data can be placed on one side of an
equal sign and where on the other side MUST equal zero..
So we dance with the one that 'brung' us
Regards
Art

the planar designs are a _result_ of maxwell's equations plus some
basic mechanical engineering considerations. coupling between
parallel wires or tubes is predictable and easily controlled by
adjusting length and spacing, all in accordance with maxwell's
equations, to make a family of easily designed and constructed
antennas. are they the ultimate, no, i quoted you a book probably a
couple years ago where an optimizer was used and came up with planar
elements that were more like a wavelength long but shaped like a cross
section of a bowl. a 3d optimizer can do other things, but then you
loose some of the important characteristics of the Yagi-Uda arrays,
like the control of polarization and ease of construction. and yes,
you can use maxwell's equations to model lumped elements, you just
have to model them on the appropriate scale with a program that
handles very small segments.