Hello - I'm an audio, not an RF guy,
and 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 www.european-antennas.co.uk