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From: John Rabson <john.rabson@numeo.fr>
Date: Sun, 8 Jan 2012 18:14:53 +0100
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To: rsgb_lf_group@blacksheep.org
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Subject: LF: Re: improving ground
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Thank you everyone for your helpful comments. I have done some more =
tests on my inverted L system with the following results (please note =
that E1 means a measurement made with the first earth connection, E2 the =
second and so on):

Feed-point resistance at 137kHz in ohms: E1 =3D 156, E2 =3D 156, E3 =3D =
200, all in parallel =3D 135 (this figure is about 15 ohms less than the =
value obtained last month).

Individual earth resistances: E1 =3D 41, E2 =3D 41, E3 =3D 85  (in each =
case in series with 7 ohms inductive), all in parallel =3D 17.  These =
measurements were made by taking 2 earth connections at a time, =
measuring the loop impedance and estimating the individual components.

Taking the differences: E1 =3D 115, E2 =3D 115, E3 =3D 115, all in =
parallel =3D 118. It looks as if this very nearly constant figure =
represents the resistances of the return paths from the remote ends of =
the horizontal section to the nearest earth spikes.  This means there is =
nothing to be gained by adding more earth spikes.

Deploying an 8 by 4 metre loop on the ground below one end of the flat =
top, and connected to the nearest earth spike, reduced the 135 figure =
above to 126.=20

Measurements were made with a GR1606A bridge.  The generator and =
detector were both isolated from the instrument with double-wound =
transformers. The case of the instrument was connected to the earth =
system under test in accordance with the manufacturer's instructions.  =
Note that the earth resistance measurements were the same whichever way =
round the earth connections were).

Note also that the transmitter system is isolated from the antenna by a =
double-wound transformer, so as to isolate the RF side of the station =
from the domestic electricity earth.

Tomorrow's step is to put a loop at the other end of the horizontal =
section and see what effect it produces.

John F5VLF