Re: A test fixture for common-mode current chokes AKA 1:1 baluns #measurement

Peter Ide-Kostic <on7yi.pik973@...>


I think you should have a look at the change request recently introduced
for nanovna-saver, it contains two links about the way to use a vna to
measure the CMMR of a ballun .

The trick is to make two successive S21 measurements and to use a formula
to calculate the CMMR based on those two successive S21 measurements. The
change request to nanovna-saver is about nanovna-saver doing the
calculation instead of the user.

In both measurements CH0 is connected on the single-ended side of the balun
(so the coax or tx/rx side)

In the first S21 measurement, CH1 is connected between GROUND and one of
the two output wires on balanced side (so the antenna side) of the balun
In the second measurement, CH1 is connected between GROUND and the other
output wire on the balanced side of the balun

On Sat, Jul 11, 2020 at 6:42 PM yvandelaserge via <yvandelaserge=> wrote:

Hi all,

Someone here mentioned some Youtube videos about baluns, a few days ago.
They are named TRX bench. I watched the videos and the guy gets some
impressive results with his baluns.
To measure the common mode rejection ratio, he uses a fixture I never saw
before. I made a drawing of it.
In fact he uses a spectrum analyzer and a tracking generator. But I wonder
if a nanoVNA could be used instead.
What do you think?


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