I found that a good method is to use the MFJ259/269 as
an RF source driving a 50 ohm pad in parallel with the
open stub under test using a T-connector. I connect the
output of the pad to a spectrum analyzer (you could also
use a general coverage receiver, but it would be less
convenient as you would have to tune the receiver to track
the signal). This method provides a very sharp null at the
resonant frequency of the stub. I cut long, determine the
resonant frequency of the first-cut stub, and then calculate
how much I need to trim off to move the stub resonance
up to the frequency where I want it centered. Works great.
73 de Mike, W4EF.............................
----- Original Message -----
From: <TexasRF@aol.com>
To: <k6rix@earthlink.net>; <towertalk@contesting.com>
Sent: Thursday, July 14, 2005 8:55 AM
Subject: Re: [TowerTalk] Measuring electrical length of coax...
>
> In a message dated 7/14/2005 10:12:08 A.M. Central Standard Time,
> k6rix@earthlink.net writes:
>
> Hello John, how do you test your lines and what equipment do you use?
>
> I've experimented with the MFJ 259B for stubs and phasing lines, but if
> it
> is critical, I'll order lines from M2. I'd sure like a good method that
> I
> could employ myself. Also, do you short the end of the coax or leave it
> open. The MFJ book lists both methods.
>
>>...but I even measure the actual phase shift for each delay line of solid
>>dielectric coax, if the application is critical.
>>
>>And with foam coax it is MANDATORY to TUNE (trim) each delay line to the
>>correct electrical length.
>>
>>--John W0UN
>
> Dino...k6rix@earthlink.net
>
_______________________________________________
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