[Lowfer] Pounding in a ground rod - NOT FUN

[John RABSON]

May I add a few comments, based on earth loop antennas for cave radio work at 87 kHz, and on my 136 kHz installation in central France ?

For cave radio in the north of England, we were often faced with a thin layer of soil over limestone where it was not practicable to drive rods of any great length.  Frequently we could not do better than about 1 foot.  Short rods connected in parallel and separated by at least twice their length gave good results.  

Here in Burgundy, with sandy soil over limestone/granite with a thin layer of calcite in between, I find four 1 metre ground spikes in parallel give about 20 ohms resistance at 980 Hz.  The resistance at 1.8 MHz would be about double that.  I can't quote a figure for frequencies in between because my measuring equipment for LF suffered in a flood and is not yet back in service.  

Pouring a bucket of concentrated salt solution down two of the holes reduced the resistance of the individual spikes by a factor of between two and three, but I am not sure I want to make a habit of this.  

Another reason for having several spikes is to avoid the situation where you have driven one long one and made an unhappy choice of location.  Even over a range of a few metres here the resistance of individual spikes ranged from 80 to 130 ohms.

73
John Rabson 
F5VLF/G3PAI
58800 Cervon
France
JN17vg