[TowerTalk] Test Fixture for Common Mode Chokes

[David Gilbert]

That is of course great advice, but in my case almost all of my coax is 
either on the tower or buried underground.  Climbing up and down the 
tower several times taking measurements along the line (the process is 
useless if you only do it in one spot since as you say it could be a 
current minimum) has limited appeal for me when instead I could maybe 
just get a reasonable indication of the impedance of a CMC to have some 
confidence that it would work when I install it.

Dave AB7E



On 1/25/2026 10:31 AM, jim.thom jim.thom at telus.net wrote:
> ##  why don't you folks just use a clamp on RF ammeter, and actually
> measure the CM current,  at several different places along the coax cable
> ??   The CM current will vary along the length of the coax due to swr on
> the outside braid of the coax, even though the ant swr may well be  1:1.
>
> ##  Mark the coax with tape, where u take the readings from.  Then if you
> swap to a different CM choke at the feedpoint, or  a 2nd, 3rd CM choke
> downstream, or 2 x chokes in series, you can compare CM current results
> asap.
>
> ##  The whole idea is to minimize  CM current.   If you don't actually
> measure it,  you really don't know what you are dealing with.
>
> ## and when taking measurements use the same PO as before.  IE:  1 kw  CXR.
>
> Jim  VE7RF
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