Non line-of-sight (NLOS) 481THz paths from home QTH

Before venturing out, I have been trying to plot possible NLOS paths with the optical TX at home (inside) and the RX at a convenient roadside spot at a moderate (local) distance. One possible path is VERY remote down very uneven fenland roads which would have to be navigated in the dark with my wife driving the car. I am thinking about her driving the car. I am not allowed to drive as a result of my stroke.  Many of the NLOS paths are blocked by nearby houses and trees. It is a surprisingly hard task.

 Back to Google Earth to see where might be worth trying. From previous tests it is necessary to aim very carefully.

Earth electrode antenna conclusions (472kHz)

With some further tests today I am now able to arrive at some conclusions from my experiments with an earth electrode antenna at 472kHz. Many people including Jim M0BMU and Rik OR7T have been particularly helpful in analysing the data.

My current 472kHz earth electrode "antenna" - can you see it in the grass?

These are my conclusions:

1. The earth-electrode antenna at 472kHz (2 earth rods in the soil 15-20m apart fed from the TX output) behaves like an H-field loop transmitting antenna.
2. It has directivity, with strongest signals in the line of the loop and weakest signals at right angles to it.
3. It works as an effective RX antenna too.
4. In my environment the loop looks like about 50-60 ohms resistive, so a good match to my transverter directly without matching.
5. The structure works because much of the return current flows deep within the soil and rock beneath the earth-electrode antenna. In my case Rik OR7T calculated that the loop area in the ground is effectively 290m sq with a radiation resistance of 0.017 ohm and a loss resistance of 66 ohms.This is a BIG loop!
6. Performance compared with my 9m high top loaded Marconi antenna averages only around 8dB down, not a bad figure at all, even with the connecting wire on the ground and not elevated at all.
7. Where no other antenna option is available, the earth-electrode antenna is well worth trying both on 472kHz and on 136kHz both for RX and TX. Although it works well here, your geology may be different and results not the same.

These last few days have been most interesting and, with the help of many people - listeners giving me WSPR reports, advice from others on the Internet forums, suggestions by email - I have been able to do some quite useful science. Thank you one and all.

Best DX yet on 8.97kHz earth-mode: 6km QRSS3

Today I went out to my usual test sites to check the performance of my latest VLF earth-mode system. For the first time, my RX loop and preamp could be optimally tuned in the field. At 1.6km the 8.978kHz QRSS3 beacon signal was rock solid (see first image).

5W 8.978kHz QRSS3 earth-mode signal at 1.6km (STRONG)

5W 8.978kHz QRSS3 earth-mode signal at 6.0km (10dB S/N in 0.67Hz BW)

I then moved on to a number of other locations eventually arriving at a spot 6km from the 5W TX where previously I'd only ever managed copy with a constant carrier or QRSS30 (30 second dot CW). This time the signal was about 10dB over noise in 0.67Hz bandwidth on QRSS3, my best ever result at this range (second image).

In the coming week I'll be looking for a new RX test location around 7km or further from the home QTH in the hope of increasing my through-the-ground DX record.