Thanks Rik & Chris
> ground losses (or better environmental losses) depend on a number of things:
> - 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 noise
towards lower frequencies. The noise on the feedline is usually attenuated by
the common mode choke at the feedpoint. But they are ineffective at VLF, and I
expected the rod resistance near 0 ohm. Instead it is a lot higher and thus the
remaining noise voltage. The rod is shared by the feedline screen and antenna
ground, so the noise gets injected into the antenna circuit. Not good.
I incidentally have another antenna 30m away with its own rod, and that does
not show this problem. I already inserted a 1:1 isolation transformer at the
shack to prevent current flow from rx to screen. That improved a lot, but the
remaining capacity coax-screen-to-environment still allows some noise to occur.
So I hoped to lower the rod resistance, but if it is pretty ineffective at low
frequencies then I need to solve it differently. That's why I used the DC
method. I need a DC connection in order to provide supply current to the
electronics at the feedpoint
Would a non corroding surface (like stainless steel) improve anything? As long
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
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
>
> 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.
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
TV: Winradio G305 / Fly2000 + video noise filter & variable IF BW
FM: Downconverter + Perseus + Speclab as WFM demod.
MW: staggered 300m Beverage 320°, 30 x 4m EWE 320°, Winradio & Perseus
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
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