This is probably of interest to all the CFA fans. It was posted on
Topband, but is probably worth cross posting.
My only comment is this is similar to what happen the first time
the Cross-Field hysteria hit, around 1980 or so. It was debunked by
the IEEE or someone (I can't recall the exact group) and it died a
well deserved death. It was recently resurrected from the grave by
an article on Antennex, and now has died once again before the
NAB.
When you read this, keep in mind there is no free lunch.
Forwarded text follows:
I attended the NAB convention this week, including the presentation
by Stewart and Kabbary on the Egyptian broadcast installations of
the Crossed-Field Antenna. I offer this report on that event for the
Top
Band Reflector.
First, their claims -- The antennas used are 20 to 30 feet high, or
two
to three percent of a wavelength. They are used at four stations, on
603 to 1161 kHz, operating at 7.5 to 100 kW power. Radiated field
strengths were claimed to be 215 to 252 mV/meter at one mile
(0.9 to 2.2 dB better than the 195 mV/m spec for a 1/4 wave
vertical).
They reported that radiation was 4 to 10 dB better than a co-located
1/4 wave vertical at one of the sites. Very few technical details were
included in the paper (not unusual for an NAB paper).
Next, there was an off-the-record rebuttal that took part outside the
public presentation -- A major broadcast manufacturer hired a well-
known
and respected consultant to evaluate the Egyptian installation. The
result
of his independent evaluation was the the antenna's radiation is
nowhere
near what is claimed.
The diplomatic conclusion from the manufacturer was, "it wasn't
bad for
a very short antenna." The real answer is that the measurements
showed
the antenna to be more than 10 dB down from a "standard" 1/4
wave
vertical broadcast installation.
Personal conclusions:
At best, the CFA is a valid first attempt to synthesize an RF signal
from
a point source. Some of the data can be interpreted to suggest
that the
CFA, despite its inefficiency, creates independently-controlled E
and H
field components.
At worst, the CFA operates simply as a very small vertical, with
extra
losses due to its complex feed system. Analysis and
measurements
suggest that this is the case.
CU in Dayton,
Gary Breed, K9AY
73, Tom W8JI
w8ji@contesting.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|