[amsat-bb] phase shift with coax

["Stan Vandiver" <Stan@xxxxxxxxxxxx>]

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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