LF: Today's 8.7605kHz earth-mode tests (so far)

[Roger Lapthorn <rogerlapthorn@gmail.com>]

An interesting discovery this morning. I've been trying long continuous carriers with short breaks for ID purposes.

At my usual roadside test site (3.6km from TX) my signal was about 20dB over noise with Spectran on 0.18Hz bandwidth. At a new test site (5.4km),  believed to be well away from buried pipes, the signal was not visible at all with Spectran and the 80cm 30t loop. So, as an experiment I moved some 10-20m away from the road into a field which was bordered on one side by a fenland water irrigation channel. An earth-electrode pair was improvised with a baseline of 18m. One electrode (a large croc-clip) was dropped into the water and the other end (another large croc-clip) buried about 3cm into the peat soil as far away as possible from the water channel. 

With Spectrum Lab I got good lock on GQD and my long test TX carrier on 8.7605kHz was clearly visible, but no trace at all was seen on Spectran with 0.18Hz BW. SL was running with around 11mHz FFT bandwidth. To confirm it was my signal, I got my wife back home to drop the carrier for 5 minutes. The attached screen-shot (LF reflector only) shows the carrier clearly visible before and after the 5 minute break. Note the 0.1Hz low frequency as the crystal oscillator had cooled and drifted when the carrier was turned back on.

So, this is more evidence that the fenland water channels are involved in my earth-mode propagation. Further tests are now needed to see if the signal is detectable at even greater distances by using earth-electrode pairs with one electrode in the fenland water channels. At the TX end the usual earth-electrode pair (one connector to the house water pipes and one an earth rod 20m away at the bottom of the garden) was used. The TX power is still just 5W from a TDA2003.

The propagation is clearly conduction but this discovery opens up new places to try to receive the signal. Results at around 1kHz and lower will be considerably better than at 8.76kHz. 

So much still to try and this is without radiating a signal!

73s
Roger G3XBM

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