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Re: phase shift with coax



At 08:00 PM 7/8/01 +0000, Stan@Vandiver.com wrote:

This is what I use, The old Cushcraft AOP-1.  I was never impressed with 
the phasing they used on the 2 meter array.  Making a new harness with 90 
degree phase shift and equal power to both arrays is a tough to do.  This 
thread is a
good one.


>Hi all,
>
>This is probably a no-brainer, but I will ask anyway. I'm needing to
>make a new phasing harness for a Cushcraft A144-20T to generate
>circular polarization.  I have 2 of the 3 pieces that are original, and
>they seem to be somewhat shorter than I expect (about 10-5/8").
>
>Is the "free space" formula for 1/4 wavelength (246 * velocity factor /
>freq in MHz) = length in feet) the correct way to calculate the
>lengths for these pieces? Do I need to factor in a little length to
>account for the barrel connector between the parallel phasing line
>and the delay line? Or account for the "T" connector that splits to
>the horizontal and vertical sections of this beam?
>
>The connectors might explain why the Cushcraft pieces seem a
>little short.  But also I do not know the velocity factor of the coax
>that they used, so I'm kinda confused on how to replace them. I'm
>thinking of replacing all of them, but maybe the better choice would
>be to just make one to replace the missing piece (which is one of
>the RG-59 75-ohm legs)?
>
>Will there be any good way for me to judge the effectiveness of the
>circular pattern.... or is SWR the only measurement I can make?
>
>Your comments are welcome!
>
>73 de Stan/W4SV
>
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