[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

Steve Hunt steve at karinya.net
Thu Jan 4 07:43:03 EST 2018

Hi Paul,

No, I no longer use the 50 Ohm termination at the jig. I originally 
included it because I was using long RG174 patch leads between the VNA 
and the jig and wanted to minimise coax loss at the higher frequencies. 
For the last year or so I've been using the jig arrangement shown here 
without any termination:

Steve G3TXQ

On 04/01/2018 12:17, Paul Christensen wrote:
> Steve,
> Over the last week, I've been collecting articles and data on various S11
> versus S21 methodologies for use with RF choke CM measurements.   In your
> S21 measurements, are you still using a resistive 50-ohm source generator
> termination on your test jig? (See quote below from Owen Duffy, Ex-VK1OD)
> If so, is it because the generator does not see Z=50+j0 that's present at
> the VNA's detector port owing to the fact that a series complex Z (the RF
> choke) is placed between ports?  Is the termination necessary to obtain a
> reasonably accurate complex Z and phase result as complex Z increases?

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