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

73
HarryH

Hi Harry

Many years ago scaled a quad from the RSGB handbook from 1296 to 432MHz.
It used "round" elements of flat aluminium about 15mm wide for parasitic
elements and a copper piece for the DE. All were directly bolted to the
boom (30mm dia Aluminium pipe) with no insulator.

The DE was fed direct connect balun style with the coax shield soldered
at the element/boom point, then crossing to the other side of the circle
and splitting inner/shield to each side of the element.

Worked well! (Was 23 elements I think)

I would say yes to the length question, but I dont have a handle on how
critical..

I also made a few circular/helix antennas which are for less critical
dimension wise. That might be another option for DF mode...

Cheers Bob VK2YQA

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.
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?
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?

73
HarryH

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

Here's a pair of 27 Quad -loops I built for contesting. They were scaled
from the G3JVL 23cm design. They worked really well. Gain of each is
19dBi measured on sun-noise.

Http://www.b-howie.demon.co.uk/70cm%20ant.jpg.

An antenna programme like MMANA will handle Octagonal loops ( which is
close enough) if you want to optimise before building. I've got an MMANA
model for the 27ele , however the antennas are constructed out of strip
elements, so I had to guess it a bit.

The boom can be conductive as long as the insulation is at least half
the boom diameter. Mine are bolted to the boom ; it's a low voltage
point. Driven element is copper strip fed by flexi-rigid cable at the
top and fed through the bottom on a bush. Matching is done by making
the DE slightly oval by squashing it then soldering the flexi-rigid at
the boom

Brian GM4DIJ
--
Brian Howie

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

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

73
HarryH

Hi Harry

Your post seems to refer to making an antenna from wire or tube. Would
you consider using an antenna modeling program, like EZNEC? Roy has a
program that allows you to make loops of any size and shape with any
spacing. It would be very easy to model any configuration you desire.

Jerry KD6JDJ