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Date: Mon, 25 Mar 2002 12:29:03 +0000
To: rsgb_lf_group@blacksheep.org, 
 "Alexander S. Yurkov" <fitec@omskcity.com>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: Re: LF: Ground loss
In-reply-to: <Pine.LNX.3.95.1020323150701.284B-100000@fitec.omskcity.com >
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At 15:19 23/03/2002 +0000, you wrote:

>Hello, lowfers!
>
>I wonder is any methods to estimate theoretically groung loss resistance
>of transmitting LF antenna (T-antenna with wire conterpoints mainly but
>others antennas also).
>I have good expirience in theoretical physics but I do not know, how solve
>the problem correctly...:-( My attempt to use EZNEC-2 was unsucsesfull.

Dear Alexander, LF Group,

I am not aware of any reliable way of calculating ground loss resistance - 
The problem with using EZNEC or similar is that it does not provide a 
realistic way of modelling a buried ground system. Some old antenna books 
provide some info about ground losses, but this data is concerned with big, 
professional LF antennas, and does not seem to be representative of the 
performance of much smaller amateur antennas. From a theoretical point of 
view, a small LF antenna could probably be modelled as a lossy capacitor - 
but this requires a knowledge of the dielectric properties of the soil 
under the antenna, and the field distribution around the antenna, which are 
usually not known with any accuracy.

Practical figures for ground loss of amateur top-loaded vertical antennas 
at 136kHz vary from around 10-20 ohms to a few hundred ohms at the extremes 
- typically, tens of ohms can be expected - the larger or higher the 
antenna, the lower resistance gets. The loss resistance of a particular 
antenna is frequency dependent, very approximately proportional to 1/f. 
Environmental effects are significant - if there are many trees or 
buildings near the antenna, loss will increase. However, even in an "ideal" 
location in an open field, the loss resistance is not greatly reduced. On 
the whole, people have been disappointed with the effects of improving 
ground systems using radials, counterpoises, and earth rods - the actual 
resistance of the ground connection seems to be only a minor factor in the 
overall losses.

Will be interested to hear about any of your investigations on this 
subject. Also, I'm sure many of us would be keen to try and receive your 
136kHz sigs - using QRSS or similar modes, you can go a long way with low 
power and quite small antennas.

Cheers, Jim Moritz
73 de M0BMU