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Re: phase shift with coax



Multiply the free space length by the velocity factor for the coaxial cable.
The velocity factor depends on the type of dielectric used but it should be
on the manufacturer's data sheet. The length of the T and barrel adapters
shouldn't matter much at 2 meters.

73,

John
KD6OZH

----- Original Message -----
From: "Stan Vandiver" <Stan@Vandiver.com>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, 08 July 2001 20:00 UTC
Subject: [amsat-bb] phase shift with coax


> 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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