A few thoughts... One old-time rule on Helical antennas is that it takes about twice the amount of wire to accomplish what a straight piece of wire would do;, so, for this case, that would be about 75/2, or and effective wire length of 37.5 feet, or ~125 Meters (of I did my math right). That length represents between 1/2 and 5/8 wavelength at 20 Meters, so it (theoretically) would be ground-plane independent with a very low angle of radiation.
Sounds like it's working in any case! Congrats... Happy New Year to the group, Gary, WA6HZT
