It looks like the Y21 method is a bit better, especially with increasing
frequency, but the S21 is a decent proxy as is mentioned on the web page
article already. And a real indictment of S11... Wow.
I bought one of those gadgets as well after seeing the video - because
it makes the process of getting setup to do the test quick and easy and
that's a real benefit here. When I'm looking at a CMC on the VNA, most
of the time I'm wanting to compare two chokes and as long as the
measurement setup is consistent I can do that even spread over time.
The other part is I'm looking for the relative Z vs. frequency in the
case of a wider-banded application which makes me wonder what sort of
OSL implementation there is. But I'm guessing that the lengths & strays
involved over HF ranges is going to be minimal. Seems like it will be a
handy addition to the little setup here.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 1/23/2026 5:05 PM, Brian Beezley wrote:
AB7E said:
"Any thoughts on this text fixture?"
Dave, use the Y21 method instead of the conventional S21 method to
suppress any shunt capacitance in the test fixture. This S-parameter
plotter implements both methods. Scroll down to see a comparison of
results for the two methods for a common-mode choke:
https://k6sti.neocities.org/sp
K6JCA's explanation and derivation of the Y21 method:
https://k6jca.blogspot.com/2020/07/the-y21-method-of-measuring-common-mode.html
Brian
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