[TowerTalk] Understanding Coax Loss Measurements

[Wes]

That doesn't work.  No matter how you choke the analyzer connection to the 
computer, it is still an unbalanced load.  And you must consider it as a load, 
particularly if you're using an open/short load s11 method as described by 
Chipman or you're measuring a line of significantly different impedance from the 
measurement system impedance.  In either event, the msmatched load is also a 
generator for the reflected waves and the analyzer is an unbalanced load for 
those reflections.

I thought to update my ladderline work using lower frequency instruments than 
what I had available 30 years ago.  I have several VIAs and a couple of VNAs.  
Three of the VIAs, are battery-powered and I thought that would solve the 
unbalance issue. It didn't; I got wildly variable results until I started adding 
a bead balun (I know you don't like that word).  I ran out of beads at 32" of 
RG142 and it was still not enough at 2 MHz.  At that point I gave up and moved 
on to more interesting things.

Wes  N7WS

On 11/28/2020 6:14 PM, Jim Brown wrote:
>
> The potential issue with 2-wire line though is that if the analyzer is running 
> from a computer, it can unbalance the line, so it should be seriously choked 
> and floating from anything grounded.
>
> 73, Jim K9YC
>
>
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