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Message-ID: <3.0.1.16.20000621135302.12f7ace4@mail.cc.kuleuven.ac.be>
Date: Wed, 21 Jun 2000 13:53:02
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: CFA Antenna: miraculous?
In-reply-to: <E134iLB-0001Lr-00@post.thorcom.com>
References: <3.0.1.16.20000621103659.0af713fc@mail.cc.kuleuven.ac.be> <394F7643.7AC83ACF@club-internet.fr>
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>I found only two papers reporting field strenght measurement, one 
>from supporters and one from a dectractor of CFAs:
>
>1) WA6HZT and N6YIP in Antennex (June 2000) report a loss of 24 db 
>respect to the filed strenght predicted by models for a 
>quarter wave monopole with 120 radials, for their 1.6-m high CFA on 
>160 meters. However they declare that this result is provisional, 
>while they are still trying to build better tuning networks.
>
>2) VE2CV in the same journal reports a radiation efficiency of about 
>1% for his 1.2-m high CFA on 80 meters

This would mean that a 0.015 lambda CFA has a gain of about -20dB (2) and a
0.01 lambda CFA has a gain of about -24dB (1). 
Extrapolating this figures would lead to -30/-35dB for a 10m high CFA on
136kHz (about 0.005 lambda) and -35/-40dB for 6m high CFA.
These are values that one can achieve with a decent T or inverted-L antenna
of the same height.

I do not doubt that the CFA principle works, but when the size of the
antenna becomes very small (compared to wavelength) you will get high
losses. For a short vertical these are mainly in the 'surrounding'
(grounds, nearby objects) while for the CFA (as for the magnetic loop)
these are probably within the antenna. This could make the CFA a valid
alternative for those sufferering from very high groundloss.

73, Rik  ON7YD