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..._Resonance.gif