[TowerTalk] Measuring electrical length of coax...

[Michael Tope]

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 at aol.com>
To: <k6rix at earthlink.net>; <towertalk at 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 at 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 at earthlink.net
>