Message-ID: <1834.200012091431@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Sat, 9 Dec 2000 14:34:15 +0000
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Subject: LF: CFA Antennas
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Dear Martin and LF Group,

The CFA antenna has been doing the rounds for a while - the 
problem is, like most "miracle" antennas, it does not seem to live 
up to it's claims in real life.

Nobody, including the inventors, seem to be able to get 
reproducible results from the CFA; clearly, it does radiate some 
signal, but as amateurs are well aware, just about any bit of metal 
can be coaxed into radiating a reasonable signal some of the time. 
At least one Australian broadcast station found that their CFA 
antenna worked better tuned against ground in a conventional 
manner, rather than using the "crossed field" principle.

The anecdote about the Egyptian broadcast station does not really 
stand scrutiny - a lambda/4 MF broadcast antenna should have an 
efficiency of 80% or more, so to get 6dB improvement, the CFA 
would have to radiate 4 times more power, ie. 320% efficiency, or 
more than 3 times as much power as is being fed into it from the 
transmitter. The other possibility is that the comparison antenna 
was extremely inefficient, for reasons unknown.

A 6.5m tall CFA scaled from 1.16MHz to 136kHz would be 55m tall - 
basically funnel shaped, a solid metal cylinder around10 metres in 
diameter, with a big cone made of mesh about the same diameter 
as the height for top loading, driven against a solid metal ground 
plane. So it really should be quite efficient, whether it embodies 
any new operating principles or not, and could not be called "small" 
by amateur standards.

Unfortunately, the CFA seems to have got surrounded by a lot of 
"pseudoscientific" hype, so it is difficult to tell serious information 
about it from the junk.

Cheers, Jim Moritz
73 de M0BMU