christofire wrote:

... and when you get back, let's see some proof that all this wacky
'new-age' theory is of any practical use to mankind.

I'd be willing to bet, say, 100 UK pounds that Professor Unwin can't create
an antenna in hardware that radiates isotropically, that is, over a whole
sphere within, let's say +/-1 dB with respect to any chosen (but constant)
polarisation. Anyone wish to up the ante?

Chris

I'd be glad to, but there's no way to prove it. Measurement accuracy and
repeatability just aren't that good, especially if you're trying to do a
full 3D measurement. The closest I've seen to a 3D measurement system
actually measured just one hemisphere. It was at what used to be NRAD
(Naval Research and Development center) and before that NOSC in San
Diego, consisting of a large (100 foot diameter if I recall correctly)
rotating circular platform with a semicircular arch overhead. By
rotating the platform and moving the detector along the arch, a full
hemispherical measurement could be made. The models were physical scale
models of Navy ships having appropriately scaled antennas. Even then,
though, engineers there told me that when the measured results differed
from NEC computer model results, they tended to believe the computer
results. It's extremely difficult to make highly, or even moderately,
accurate field strength measurements.

A while back I designed an antenna for a consulting job which was simply
a two-sloping-radial ground plane made with fairly wide traces on a
low-loss PC board. George Brown, the inventor of the ground plane
antenna, had observed an omnidirectional pattern in the horizontal plane
with only two radials, but the marketing department at RCA insisted on
adding two more to make it look symmetrical before selling them. Hence
the ubiquitous 4-radial design. (The pattern of the 4 radial version is
more circular above and below the horizontal plane, but not by a whole
lot.) Anyway, I was concerned that maybe the PCB or the relatively wide,
flat conductors might have a detrimental impact on the pattern
circularity, so I took it to a local lab that has a high quality
anechoic chamber and ran the pattern. When the plot was finished, the
lab technician muttered "Holy $/!%", hit the print button, grabbed a
camera, and ran into the chamber to take a picture of the antenna. Then
he went around to the other folks at the lab with the picture and plot.
Seems that it was circular within about a dB, better than their $10k
reference antenna. The prototype, by the way, was made with adhesive
copper tape and an X-Acto knife and looked as crude as it was. I can't
claim that the pattern was really better than their reference antenna
because small differences in positioning of the feedline (even though
decoupled), the antenna, and anything else in the chamber can easily
cause a couple of dB of pattern deviation.

Roy Lewallen, W7EL