15 Jul 2011

More VLF earth-mode tests

8.76kHz QRSS3 signal at 3.8km
Recently the water company repaired some pipes right outside our property in the road. I was informed the pipes are/were NOT metallic.

Today, just as a check, I tried 8.760kHz earth-mode running my usual 5W into 20m spaced earth electrodes just to see if the repair work made any difference to signal levels some kilometres away.

At my favourite roadside test site 3.8km from home I set up my RX and tried 2 different loops on the ground (a) my 30t 80cm square loop and (b) a large single turn loop.  Using QRSS3 the signal was copied on both antennas at the usual strength. This makes me think any "utilities assistance" is NOT purely from metal water pipes in the road.

My next planned test is to see how well an earth-mode signal propagates along one of the many fenland water channels using one TX electrode actually in the water and one on dry land. For RX I'll either use another earth electrode pair (one in and one out of the water) or a loop or E-field probe. The next couple of weeks are pretty busy with family matters, so this fenland river test may not take place until sometime in August.


Anonymous said...

From what I read from Cave radio analysis, it might be important how the underlying rocks/sediment form an electrical path from one ground electrode to another. The separation distance between electrodes is usually quite large.. 100m or so in cave radio.
One theory is that the ground current loop couples to the above air/free-space, but with your 6km only, you might still be working just resistive earth potential gradients? At ELF, Ground probes are also very good, but the coupling mechanism is not good under about 1KHz, so you cannot see the Schumann resonances, but you can see atmospheric 'tweaks' and submarine transmitters fine, so I guess there must be a mechanism for coupling from ground to free-space... Happy paddling in the fens with laptop, but make sure you don't end up at Fulbourne Hospital ! Regards, Hugh G6AIG

Roger G3XBM said...

Hi Hugh

Well some policemen and farmers have asked me what I'm doing. When I explain they nod politely, HI.