"Wimpie" wrote
If it is not time consuming, I would like to see what happens when you
extend the helix until it gets its second (half wave) high impedance
resonance (current maximum in the middle). I expect some gain increase
due to small change in antenna pattern and reduced ground loss.

The NEC software that I used for the results shown earlier doesn't allow
enough segments to double the length of that helix. So I reconstructed the
model in one that does -- link to screen clip from it below:

http://i62.photobucket.com/albums/h8...onopole_6m.gif