My apologies gents
The attached was the second reply to Gary (WE9Y) that was not sent to the BB 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 ago. 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 brush. 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 [email protected] To: [email protected] 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 requirement. 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
Joe Murray K0VTY ====================== On Thu, 10 Jun 2010 17:59:12 -0700 (PDT) Gary K Reed [email protected] 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 [email protected] wrote:
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 [email protected] 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?
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