From: "Jurgen Bartels" <jurgenb2@3sdesign.de>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 10 Feb 2011 11:39:47 +0100
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Subject: Re: LF: RE: how to get ground rod ressitance low
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Thanks Rik & Chris
=20
> ground losses (or better environmental losses) depend on a number of thi=
ngs:
> - frequency : losses are increasing at lower frequencies (so measuring=
 DC
> resistance is not very meaningfull)

That's interesting, because all got started when I noticed increasing nois=
e =20
towards lower frequencies. The noise on the feedline is usually attenuated=
 by=20
the common mode choke at the feedpoint. But they are ineffective at VLF,=
 and I=20
expected the rod resistance near 0 ohm. Instead it is a lot higher and thu=
s the=20
remaining noise voltage. The rod is shared by the feedline screen and ante=
nna=20
ground, so the noise gets injected into the antenna circuit. Not good.=20
I incidentally have another antenna 30m away with its own rod, and that do=
es=20
not show this problem. I already inserted a 1:1 isolation transformer at=
 the=20
shack to prevent current flow from rx to screen. That improved a lot, but=
 the=20
remaining capacity coax-screen-to-environment still allows some noise to=
 occur.=20
So I hoped to lower the rod resistance, but if it is pretty ineffective at=
 low=20
frequencies then I need to solve it differently. That's why I used the DC=
=20
method. I need a DC connection in order to provide supply current to the=
=20
electronics at the feedpoint
Would a non corroding surface (like stainless steel) improve anything? As=
 long=20
as it is deep in the soil, corrosion should not take place, they say

It also make me wonder how good a lightning rod is? If a single one shows=
 60=20
ohms, then I better don't think of the resulting voltage during a strike=
 :-(
I use to have a single one (4m long) to ground my TV antenna on the roof

> >  measuring DC resistance is not very meaningfull
>=20
> Absolutely! The soil charges up. It's quite fun to do. Take your
> multimeter into the garden, put it on the > Ohms range and put the
> meter prods into the soil some distance apart. The resistance starts
> quite low then rises.=20

Will measure it with 50Hz AC to see if there's a difference


Jurgen Bartels  Suellwarden, N. Germany
hor. Antennas: 11-ele 45-87MHz 13-ele Band-III, 48-ele UHF, FM: 15.11=20
TV: Winradio G305 / Fly2000 + video noise filter & variable IF BW
FM: Downconverter + Perseus + Speclab as WFM demod.
MW: staggered 300m Beverage 320=B0,  30 x 4m EWE 320=B0, Winradio & Perseu=
s
http://dx.3sdesign.de/tv_offset_list.htm
http://dx.3sdesign.de/station_list.htm

http://fewo.3sdesign.de  - Vacation home: DX right at the Northsea coast