Re: LF: how to get ground rod ressitance low

[Andy Talbot <andy.g4jnt@gmail.com>]

I installed about 20 earth rods around the periphery, with a couple in the centre region,  of a small garden abt 6m x 12m with heavy clay soil.  Each rod consisted of as much 15mm copper water pipe as I could bash in before it buckled, typically 0.6 to 0.8m each.  There were also about 4 or 5 proper full length rods.  All these were wired together with thick bare single strand wire which was also buried just under the surface.  

 

The DC resistance measured to mains earth / neutral (PME system in use) was in the region of 3 ohms, and stayed reasonably constant whatever the weather / ground sogginess.    The whole lot was bonded to mains earth with three runs of 10mm^2 cable (and yes,  I know IEE wiring regs say only one bond of 16mm^2 should be used, but that's a practical thing of being able to check, not an actual safety rule  I wanted better RF resistance, so three).

 

At RF, resistance of the Tee antenna system - which is mostly due to ground losses is :

73kHz   180 - 220 R

137kHz  90 - 130 R

503kHz  25 - 28 R

1.9MHz  10 - 13 R

Higher than this antenna transmission line effects become significant.

 

All originally determined from V / I measurements and recently confirmed with DG8SAQ NetAn.

 

Andy

G4JNT

 

 

On 10 February 2011 08:23, Jurgen Bartels <jurgenb2@3sdesign.de> wrote:

I just discovered that my ground rod isn't ideal by having the assumed 0 ohm to
earth. Measuring with 10VDC the current from neutral/waterpipe to the rod gives
about 140 ohms.
I use a 8mm rod 1m long in wet soil. I put in another one and tried several
places nearby and got it a bit lower, but far away from ideal.
So I assume the surface size is too small, one the other hand I want a small
rod that can be pulled out with ease in spring when the season is over.

What resistance do you get usually and what size do you use?

Stefan, you wrote yesterday that you got 65 ohms with your rod on sunday.
That's still pretty high



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