[TowerTalk] CM Choke

[Richard (Rick) Karlquist]

On 10/13/2017 5:49 AM, Wes Stewart wrote:

>> On 10/11/2017 6:46 AM, Wes Stewart wrote:
>>> With a decent vector network analyzer, the ports are already 
>>> well-known (50 Ohm) terminations.  If the round robin you mention was 

This is probably largely true, especially as to ham radio
frequencies; it would be hard to imagine an error of more
than a few percent, which would be insignificant for
measuring chokes.

However, if you really want to do things right, you need to
do a full two-port calibration on the network analyzer.
This "calibrates out" any imperfections in the source
and load impedances of the ports.  I don't believe the
hobbyist type analyzers are capable of this, because they
don't have a reflection bridge in port 2.  (Correct me
if I am wrong).  This becomes important at microwave
frequencies where even Agilent can't realize a perfect
50 ohm source.

A poor man's way to fix source mismatch is to simply
pad down the ports with precision attenuators.  If you
can stand the loss of dynamic range, this works well.

(Biographical note:  I used to design network analyzers
for Agilent).

Rick N6RK