On 3 abr, 21:11, "Richard Fry" wrote:
"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

Hello Richard Fry,

Thanks for taking the time to do the simulation.

It seems from your graph that the electrically half wave (180 degr)
helical has slightly more gain than the physically and electrically
quarter wave (90 degr) radiator (5.61 dBi for the helical versus 5.14
dBi for the quarter wave whip).

Given the about 4 kOhms for 1/(Re(Y)), the loss in the 10 Ohms ground
resistance is negligible (so at can be significantly higher before
presenting significant loss). 900Vp at the feed point (100W input)
will not give problems with matching.

With kind regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely