NEC-LIST: CFA

This was recently posted on rec.radio.amateur.antenna.

Roy Lewallen

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As some may remember, I posted a few months back some info about a
colleague who had made measurements on one of the CFA antennas in
Egypt. I made reference to his remarks without attribution, because I
didn't know whether he wished to be publicly connected to his
findings.

He has since made some brief public remarks in a broadcast engineering
e-news letter, which I quote below. These are from the Gonsett
Communicator.

Gray

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Dr. Bill Bayha of Harris and I traveled to Egypt to make measurements
of the actual performance of the Hatley/Khabbary antenna. Because the
Nile Delta is an area of very high conductivity (much like parts of
the California Central Valley) and because of its ease of access to
Cairo, we requested that the measurements be made at the Tanta
installation. Tanta is the largest city in the Delta between Cairo
and Alexandria, and the antenna is located at the edge of the city,
adjacent to agricultural land for many kilometers to the north.
Although we made very careful observations of the potential for
reradiation from other antenna structures on the site, and of the
measured field from the antenna, we were unable to verify the power
input to the antenna or its impedance/bandwidth characteristics,
because we were not given access to the input matching system, despite
earlier assurances of access.

  From these measurements, and from observation of the approximate
power fed to the antenna from the transmitter used, a very ancient
Tesla 30 kW unit operating at somewhat lower power, we have determined
unambiguously that the antenna efficiency is almost exactly what would
be expected from a moderately lossy very short radiator. The antenna
did not appear to cause significant carrier shift or other serious
bandwidth limitation, and the modulated signal received on an FIM-21
did not exhibit obvious impaired fidelity due to bandwidth limitation.

  Until valid repeatable measurements by independent observers with
properly calibrated equipment can be made of both field strength and
input power and impedance, it is not possible to say much more. In my
view if the input impedance circumstances can be resolved favorably
the antenna may have some application for specialized uses, but it not
a good solution for very many if any medium wave broadcast situations.
Dr. Alberto Fassio of RAI in Italy is constructing one for just such
tests, and when completed his installation should resolve the
exaggerated claims for this antenna's performance.

  Ben Dawson

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