On 3 abr, 00:42, "Richard Fry" wrote:
Followup -- the link below compares the relative current distribution,
directivity and radiation efficiency of a helical and a linear radiator
system when the helical radiator described in my earlier post is operating
at the frequency of its first self-resonance, and the linear monopole height
is set for its first self-resonance at that same frequency.

It is interesting to note that linear form has better performance than the
helical form.

http://i62.photobucket.com/albums/h8...inear_1st_Reso...

Hello Richard Fry,

Why is this so interesting, as it is what I expect (and I think you
expect this also)? The current*(physical length) product is more, so
given same feed current it produces more field (hence more radiated
power). This results in higher input impedance, hence reducing the 10
ohms ground loss.

The small change in shape of pattern is just due to the less isotropic
array pattern of the 0.25 lambda radiator (w.r.t. to the array pattern
of the 3 m radiator).

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.

¡Very informative thread!

73, Wim, PA3DJS, www.tetech.nl.