Roy

I'm a real slopy builder. So, I do alot of half-assed things. I might
begin with a 100 watt light bulb inside the "icebox" to establish a
referance temperature. maybe even a 50 watt and even a 25 watt. And, if
the antenna could be modeled at some frequency where I could build an ice
box thats sufficiently transparent to RF, like 6 Meters, I'd build a full
size antenna for use as a referance.

I've never done something like this. It just sems very practical, since a
100% efficient antenna wouldnt introduce any heat. But , a 50% efficient
one might produce about the same heat as a 50 watt light bulb.

I'd not declare this "ice box" to be a Lab Standard. But, if there was
need, I'd sure try to evaluate the concept.

When people like you cast doubt on anything I tink up, I begin to doubt
myself.

Jerry



"Roy Lewallen" wrote in message
...
There's a fundamental problem in making a scale model of an antenna to
determine loss -- the wire conductivity has to be scaled with frequency.
Of course, the wire diameter can be changed from the normally scaled
size in order to create the same loss, but then the antenna might behave
differently.

It's not clear to me how you could get quantitative data from
measurements in a styrofoam container. Let's say you put 100 watts into
the antenna for five minutes and the temperature rise (of the coil?
helical winding? air?) was 10 degrees C. How would you calculate the
loss or efficiency from that information?

Roy Lewallen, W7EL

Jerry Martes wrote:

Youve gotten too refined. I mostly know about basic antenna theory
and
modeling. But building a VHF model of a 40 meter antenna with #12
copper
wire wound around a 4 inch mandril might be impractical.
But, if the "wonder antenna" is small enough to be enclosed (mostly)
in
something transparent to the RF but not to the thermal thats generated
by
any I^2* R losses, wouldnt the temperture rise inside the enclosure give
a
decent indication of efficiency?

If this "wonder antenna" designer claims to be able to shape the
radiation
pattern with an antenna significantly shorter that a 1/4 wave stub, He
really has something. I suspect that the something he has is mental
illness.

I've been following this info on the RI antenna and have considered it
to
be so 'snake oilish' that it would never see the light of an auditorium.

Your post about attending the lecture made me wonder if anyone asked
about
*any* simple (approximations) measurements like the styrofoam radome to
get
some idea of the I^2*R power lost in the antenna. If he has an antenna,
and
a transmitter and enough room to build a foam igloo it seems that alot
of
data on efficiency could be obtained.
If I had any interest in describing an antenna I'd built, I'd at least
use
an infared thermometer on the section of the antenna suspected as being
the
most lossy.

Jerry