Today's test was a quick one; measure the capacitance required, add it in series with the earth antenna and observe the difference it makes in the signal at the grabber. I brought with me a number of different value 3 kV ceramic capacitors and I tried different combinations of these capacitors until my scopematch unit indicated a perfect match (zero degrees difference between voltage and current). I also added a (not very well calibrated) RF ammeter in series to measure the actual current.
The following graph shows the results of the test. From 23:30 UTC to 00:00 UTC, I was transmitting on the ~250m long earth base, as I did last time. This is the baseline configurations. Between 00:00 UTC and 00:55 UTC I was trying different capacitor configurations. Then at a bit before 01:00 UTC, I transmitted with about 2 nF which produced the maximum current on the earth antenna. At 01:20 UTC I switched to 1.6 nF which produced the best matching according to the scopematch, but less current. Finally, at 01:55 UTC I switched back to the ~2 nF for maximum current.
The difference between the scopematch tuned and highest current tuned is quite obvious, around 3 dB. I need to understand exactly what's happening here.
The wobbly dashes that were observed last time are probably due to a component, probably an inductor in the LPF circtuit, getting too hot. The heat sink of the FET was also too hot to touch when the transmitter was not connected to a load as close to 50+j0 as possible. I suppose, that's normal.
"Tuning" the earth antenna indeed provides a better signal at the receive location. Unrelated to this test, slowly we are building a bit of theory that seems to be gaining momentum rapidly.
I have been studying the earth probe experiments done by Renato Romero. His findings I think are in agreement with the behaviour of the earth antenna. I think it behaves more like a loop rather than a dipole. So, there is loop directionality which explains last experiment's results.
Go back to the main earth antenna page.
Dimitris Tsifakis, VK1SV