From: "Hans-Joachim Brandt" <hajo.brandt.dj1zb@t-online.de>
To: rsgb_lf_group@blacksheep.org
References: <000201bf643a$c5701140$29c2883e@lvm>
Subject: Re: LF: Re.Ground Loss
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Date: Sun, 23 Jan 2000 20:19:33 +0100
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Dear Lawrence,

remembering the few results on ground resistance measurements published on this 
server I would regard your 120 ohms somewhat above average for 136 kHz. My own 
value is in the order of 80 ohms when using the house ground, and also when 
using an insulated radial system consisting of 28 wires of 10 m to 30 m in 
length, depending on the space in the relevant direction. Someone who had used 
his 160 meters ground system with several long buried radials also for LF had 
reported a value of 50 ohms at 136 kHz.

I have just heard of two reports of house grounds of about 25 ohms; in this 
cases a tube 12 meters deep into the ground is employed, or an extended wire 
ground system also deep in the ground.

Paralleling different grounds may be a special problem. Direct paralleling often 
results in an INCREASE in ground resistance. Therefore some stations use link or 
transformer coupling between feeder cable (connected to the house ground) and 
the antenna ground, to avoid the bad effect of direct paralleling. 

But if both ground systems are tuned against each other the resulting resistance 
may be the same as one ground system alone, or luckily somewhat lower, but never 
the value that is expected due to the paralleling of two resistances.

>>From next spring onward I will do further experiments with bare radials buried 

flat into the ground, before settling on a final solution.

73 Ha-Jo, DJ1ZB 


LAWRENCE MAYHEAD schrieb:
> I have just measured my TX ant impedance(R term) and it is 120 ohm! much
>  higher than I originally thought.It is of course all ground loss,I am using
>  3 ground rods close to the TX and the house water/mains system.I wonder
>  wether anyone can  offer me comparitive figs for impedance and details of
>  ground systems?
> To improve I will have to put in an awful lot of radials! or consider
>  counterpoises.
> 73s Laurie.
>