Hier der letzte update von G7VGG:
After much work I have decided to end the Triple Delta experiment for now.
The impedance conveniently turned out be be around 50 Ohms, allowing it to be fed unbalanced, directly with 50 Ohm coax, or balanced with a 1:1 balun at the feedpoint and 50 Ohm coax.
I discovered that the closley spaced double loop arrangement was acting a bit like a huge loading coil, greatly reducing the length of wire needed for resonance by several metres.
Before cutting it down to length the Twin Delta was resonant on several HF bands...The first resonance was just above top band and the second was in the middle of the 60m band.
I needed to bring the lowest resonance, at about 2 mhz, up to 3.6 mhz so I could use the 40m Twin Delta from 80m and above, as planned, but after cutting over 6m off the length to move the second resonance back to to 40m from 60m it still wasn't short enough to resonate on 80m (It got up to about 2.7-2.8mhz) and if I had cut off any more wire, then I could not have supported such a small antenna with my current loop support system!
I also tried several different baluns...a 1:1, a 1:2, a 2:1, a 3:1 and even a 4:1...Not surprisingly the 1:1 balun seemed to give the best match but it was still not a perfect match.
The only solution I could think of it to try using either 3 core wire, to form three series connected 40m loops (the "Triple Delta") or use 4 core wire, to form four series connected 40m loops (the "Quad Delta"), in the hope that I can tune it from 160m and above and the resonances might possibly sort themselves out.
Right now though I have gone back to my a standard, single core, stranded wire 40m Delta Loop, only this time I moved the feedpoint to the middle of one of the sides to convert it to horizontal polarisation, and it appears to working better than ever, as this minimises ground reflection and lowers the angle of radiation even more.