On Thu, 11 Dec 2008 04:22:39 GMT, "Harry H"
wrote:

I am wondering if its possible to build a 6 element "round" quad antenna,
that is the elements are circular instead of square.

Yes. It's called a "disc yagi". It was commonly used for various
wireless TV schemes in the 1970's.
http://www.supernec.com/diskyagi.htm
http://www.idealantenas.com.br/produto/yagi%20disc19/yagidisc19_ing.htm

I want to use it for DFing and have the centre frequency of 438 mhz.
I will be mounting the elements on an insulator above the boom, will the
boom have to be non conductive?

It should be non-conductive. You'll have plenty of entertainment
value figuring out how to run the feed line. I suggest a triangular
mounting contrivance rather than a stright pole. It keeps the coax
mostly out of the way, but also is more rigid than a stright pole. If
you're only going to have 6 elements, you can mount it by the
reflector end. However, methinks you'll want or need more than 6
elements in order to do direction finding. The big problem is
reflections off buildings and hills, You need good resolution to
identify and seperate these with a rotating antenna direction finder.
That means a narrow 3dB antenna beamwidth.

I intend to use 1/8" alloy wire for rigidity, and make the element mounts
out of insulating material so they can be slid along the boom, will the
frequency to wire diameter ratio have any effect on the length of each
element?

Ideally, the center boom should be an insulator but could also be
metal if sufficiently small diameter. A disk yagi doesn't use any
wire (except for the driven element).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558