[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

Paul Christensen w9ac at arrl.net
Thu Jan 4 07:17:45 EST 2018


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?

"...To complicate the field, G3TXQ describes a 'S21 method' for high Z
measurements, a method that is a
combination of the shunt and series through method in that the unknown is
connected as in the series through
configuration and port one also has a shunt 50+j0 loadΩ. It is not clear
that this delivers any benefit for high Z
measurements, but it does introduce another element of uncertainty (the
value of that shunt load), and it
decreases the level reaching port two by up to 6dB."

Paul, W9AC 

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Steve
Sent: Thursday, January 4, 2018 6:31 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Measuring Common Mode Choke with Anritsu VNA

For completeness, here's the data referred to by G3RBJ in his paper:

Notice how the self-capacitance falls as the number of turns increases.

Steve G3TXQ

On 04/01/2018 11:25, Steve Hunt wrote:
> Wes,
> Thanks, I hadn't spotted that one!
> Steve G3TXQ


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