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Message-ID: <3.0.1.16.19991116181457.2d97e9f0@mail.cc.kuleuven.ac.be>
Date: Tue, 16 Nov 1999 18:14:57
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Earth or counterpoise?
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A question to Dick :

>A.  Antenna plus counterpoise in free space: radiation resistance 17.8
milli-ohm

Did you calculate the capacitance of this 'free-space' model ?

I ask this because further you mention that the antenna against ground had
a capacitance of 176pF while the antenna against the counterpoise has a
capacitance of 74pF.

I wonder of this 74pF is completely a 'direct' capacitance between antenna
and counterpoise or there is also a 'antenna to ground to counterpoise'
component.
This last component could be very 'lossy' (and unwanted).
The fact that there is so little difference in antennacapacitance between
the counterpoise direct under the antenna and the counterpoise opposite to
the antenna could suggest that the main part of the antennacapacitance is
not direct antenna - counterpoise but first antenna to ground and then
ground to counterpoise.


Mike, G3XDV mentioned in his mail that with counterpoise he had much less
antennacurrent. He also said that both antenna and counterpoise had their
own loadingcoil and both seperately were tuned to ground. This procedure
should favour the current from the antenna to ground and then from ground
to counterpoise, instead of a direct antenna-counterpoise current. This
could explain the low current.
Maybe it would be better to tune counterpoise and antenna against each
other (if they each have their own coil) or just use 1 big coil as Dick
suggests.

73, Rik  ON7YD