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Re: Cross Boom



List,

Thanks to Hasan, Joe & Ed. I know this thread is focused on crossed
yagis and appreciate the advice offered to my off topic question.
I am especially appreciative to the comments that the issue is not
as simple as generally thought.

To that end I decided to take a systematic approach and see if I could
make some sense of this on my own.
Thanks to Brian Beezley, K6STI, I was able to accomplish this quite easily.
I used Brian's source for a 10 turn axial mode helix at 435MHz to
generate data that I thought I could use to show the impact of a
conductive cross boom poked into a helix.

First, I generated data files using a vanilla version of Brian's
code. Then, I hacked Brian's code to model a 1-1/2 inch dial wire
4 foot long, stubbed into the centerline of the helix axis. I added
another wire at right angle and midway along the length of the boom.
The second wire is about 7 inches in dia. and about 12 inches long to
approximate a rotor. 

After regenerating the data files, examination showed that there did
not seem to any significant degradation of circularity or pattern.
This was not what I expected and leads me to believe that I have
overlooked something. That being the case, I've decided to take the
safe way out and use an non conducting boom.

If you are interested in the work and resultant files, you may
download them from:

http://www.whiskey7.net/ham/sat/ant/boom.html

Constructive input welcome.

On Thu, Mar 06, 2003 at 09:09:15AM -0600, k0vty@juno.com wrote:
> Hi Joe
> 
> The subject is a bit more complicated than what appears on this BB.   
> If you know what all future antennas will be and design to those
> requirements there are many things that can be done .    but they are all
> reference to your particular system.
> Having said all that however , If we need to make a single statement of
> what is best for a circular polarized (CP) antenna then it is simple to
> say use a non metallic cross boom.
> Lots of seemingly little things can and do impact CP installations.
> There is no doubt that the pattern is effected by any metallic material
> within the aperture of the CP elements of a yagi style antenna or in the
> aperture (front) of a dish .
> Included in the metallic material is the coax.    keep the coax out of
> the aperture of the antenna but keeping it behind ( to the rear ) the
> driven dipoles and let it hang loose with a large loop.
> Keeping apertures from over lapping is another example .
> Loading down a cross boom in such a way as to have reduced need of metal
> materials and keeping the cross boom in balance so the elevation rotor
> has mimimum stress is another goal .
> CP is no doubt the best for space use.    How you do yours is unique .
> 
> Have fun Joe
> 
> Joe  K0VTY
> Amsat # 860
> Amsat area coordinator for NE
> 
> 
> On Thu, 6 Mar 2003 06:56:28 -0700 Joe Ennis <joe@whiskey7.net> writes:
> > Lots of feedback on crossed yagis but:
> > 
> > Wondering if there are any results from using a conductive cross

--trunc

-- 
Joe Ennis - w7net
AMSAT 20606
http://www.whiskey7.net/
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