Some years ago, we tried using a small loop to couple a Heyphone (4 W output on 
87 kHz) into a running rail in a disused railway tunnel in the English Midlands 
(we had permission from the owners of the line).  A similar setup was used for 
receive and we achieved a range of 1.6 km along the line.

73
John F5VLF

On 3 Feb 2011, at 20:36CET, Jacek Lipkowski wrote:

> trying to couple to large structures is an interesting experiment, both for 
> receiving and transmitting (only by induction of course :). think about power 
> lines, phone lines (but unfortunately nowadays most are very short, and the 
> rest is done via fiber), natural gas pipelines, railways etc. this is an 
> example rx experiment: http://www.youtube.com/watch?v=sWsdaSmWg7E , these 
> structures are usually very well grounded at regular intervals, but still 
> some vlf will slip through the ground system, so they can be also used for tx 
> too. a few miliamps at 9kHz into a large structure is detectable from a few 
> hundred meters.
> 
> actually the "utilities-assisted earth mode" works not only on transmit. a 
> loop antenna near a long conductor will pick up a stronger signal (and also 
> more qrm, so this doesn't always raise S/N).
> 
> this might not be ham radio (or not radio at all), but is very interesting 
> nevertheless
> 
> VY 73
> 
> Jacek / SQ5BPF
> 
>