[amsat-bb] Re: [Mw] Fwd: Power splitters circular polarization?

Joe v Murray k0vty at juno.com
Fri Jun 11 09:17:12 PDT 2010

My apologies gents

The attached was the second reply to Gary (WE9Y) that was not sent to the
As you can see after reading the attached a few pictures would have been
a must to really get into
a axis discussion about my original query.
I took a chance that Gary might have had some secret way of lining up the
axis of those two antennas in his back yard.

Dom ( I8CVS) I still have your bench lab alignment pictures from years
It has been a long dry spell for us.

And as usual Dr. Johnson (K0CQ) can add helpful information which we are
all thankful for.

My problem as you all now can grasp is outdoors , far field , 23 feet
about ground using prime dish problems.
Assuming good focus alignment on that dish and since it is AZ/EL mounted
constructing the measurement 
ability on the selfsupporting tower 48 feet distant seems simple at first
However the desire to have the measurement capability be no worse than
1dB or the axial ratio results
begins to provide tight axis alignment of the bore sight even using a
single spinning dipole.

I apoligize again for stirring up a problem by not sending the second
post to the BB


Joe Murray K0VTY
----- Forwarded Message -----
From: Joe v Murray <k0vty at juno.com>
To: gary.reed at sbcglobal.net
Date: Thu, 10 Jun 2010 20:51:52 -0500
Subject: Re: [Mw] Fwd: Power splitters-errors circular polarization?

I have been trying to determine a way to accomplish the line up of the
two axis
before I begin the construction.
Keeping  the entire system and measurement off the ground is a
As we know on a CP antenna the minimum axial ratio is the measure that
must be delivered or 
the notion of CP does not mean much.
In my case I am using a 54 inch diameter spun aluminum dish mounted at 23
feet off the ground.
A mono axial mode helical feed is used with > 22 dB return loss. 
A second self supporting tower at 48 foot distant is the location for the
measurement dipole system
However so far I have not convinced myself of a sure fire way to manage
the axis alignment.
Even when I make the measurement end adjustable I still have not arrived
at a good enough way.
So when you came up with your suggestion I thought maybe you have devised
a method of aligning 
those axis with in some reasonable method.
I do not believe that eye balls will cut the needed accuracy if 1dB of
axial ratio is the goal.

I should have provided the above in the first place Gary

Thanks Gary

Joe Murray K0VTY
On Thu, 10 Jun 2010 17:59:12 -0700 (PDT) Gary K Reed
<gary.reed at sbcglobal.net> writes:
Well, I would say mount the dipole through a piece of PVC pipe of say 1
inch diameter. Make the pipe 3 feet long. Run the pipe through a PVC
"Tee" of appropriate size. Mount that "Tee" on a stand of some sort. I
would suggest more PVC for that - no metal of course.
Then, site down through the pipe at the other antenna. Far field would be
about 25-30 feet at 1296  so you should be able to see that far easily.
(Far field depends on the antenna aperture so it varies. Large arrays
would entail longer distances.)

Don't know if this helps, but it might be a start.

Gary WE9Y
--- On Thu, 6/10/10, Joe v Murray <k0vty at juno.com> wrote:

From: Joe v Murray <k0vty at juno.com>
Subject: Re: [Mw] Fwd: Power splitters-errors circular polarization?
To: gary.reed at sbcglobal.net, amsat-bb at amsat.org
Date: Thursday, June 10, 2010, 8:42 PM

Hi Gary

Any good suggstions on how to keep the axis of the rotating dipole 
lined up with the axis of the CP antenna in the far field?


Joe Murray  K0VTY
On Thu, 10 Jun 2010 17:24:55 -0700 (PDT) Gary K Reed
<gary.reed at sbcglobal.net> writes:
> To measure axial ratio, why not rotate a dipole in front of the yagis 
> (or other antenna) , and measure the signal strength. If the axial 
> ratio is 1 then there should be NO change in signal strength as the 
> dipole is rotated. It would necessary to stay in the far field.
> Or have I been working too long today?
> Gary WE9Y
> _______________________________________________
> Microwave mailing list
> microwave at lists.valinet.com
> http://www.valinet.com/mailman/listinfo/microwave
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