Hello - I'm an audio, not an RF guy,
I'm having difficulty Googleing concise info
regarding the basic design/theory of operation
of helical antennas. I've found pix and plans
for axial/endfire helicals, but not what has
been described as "normal"/spherical/hemispherical/omni
designs - the one with the radiation pattern
that can best be described as torroidal or omnidirectional,
rather than hypercardioidal. Any leads appreciated!
I have used a company in the UK, called
European Antennas, for these type of antennas. They
have a wide range of products for all of the applications,
and its far easier than building them yourself.
There web-site is