Hi Roger,
 Try more.
 The following grabber site has used the two electrodes earth antenna
and good receiving QRSS/DFCW at 136kHz.
http://www16.ocn.ne.jp/~macoco/grabber.html
 Depending on the circumstance the two electrodes earth antenna detects
E-field between two electrodes. If this assumption is correct, lake side
or shore side including on the sea using buoy make two electrodes short
condition.
  We will try to do experiment at 2200m band.
73
Rick - 7L1RLL

On Fri, 2010-12-10 at 20:12 +0000, Roger Lapthorn wrote:
> A further observation from my 8.76kHz earth mode test today: with 17dB
> above the noise signals at 5.1km using QRSS3 there is plenty of
> (theoretical) range still to be had with utilities assisted earth
> mode, even using just 5W.
> 
> Assuming 18dB loss every time distance is doubled (an inverse cubed
> attenuation rate for induction/conduction - is this right?) then
> almost 10km should just be possible, assuming the utilities that are
> aiding propagation are still there in the ground. Going from QRSS3 to
> QRSS30 should give another 8-10dB (see
> http://www.qsl.net/on7yd/136narro.htm#QRSS). Increase power from 5W to
> 100W gains another 13dB, so QRSS30 and 100W could give a range of some
> 20km by utilities assisted earth mode in favourable places based on my
> limited tests so far.
> 
> So, in some locations using the utilities buried in the ground all
> around us could offer some quite decent ranges with an earth electrode
> "antenna" at the TX end that requires minimal matching and no large
> loading coils, just a step-up transformer.  
> 
> What is less clear to me is what exactly is the signal being carried
> along? Water pipes (often these are plastic now), overhead mains
> cables, gas pipes (usually non-metallic), phone lines, rivers even?
> And what about the propagation along a sea coast with one electrode on
> a buoy 100m out from the shore?
> 
> Not radiated VLF DX, but fascinating.
> 
> 73s
> Roger G3XBM
> 
> -- 
> g3xbm-qrp.blogspot.com/
> www.g3xbm.co.uk
> www.youtube.com/user/g3xbm
> G3XBM   GQRP 1678    ISWL G11088