On 12/25/22 2:05 AM, Jim Brown wrote:
Hi Paul,
I made S21 measurements using a test jig quite similar to Steve's. His
measurement technique seemed quite good. The (major) shortcoming of
his work is that he measured only chokes on only a few cores, failing
to understand the contribution of production tolerances to
reproducible designs.
What are the dominant sources of variation? Material or "assembly"
The material datasheet claims 20% uncertainty in the properties
(although I don't know if that is "run to run" or "piece to piece within
a run") - They're sintered from a powder, and having just looked a a
bunch of micrographs of gas line filters made using a similar process, i
was surprised how much variation there is in that process, within a batch.
I would think there is substantial variation due to how the turns are
wound on the core (how tight, spacing, etc.) Particularly in terms of
parasitic C between turns.
A limitation on the precision of my data is that my fixture had to
allow measurement of many hundreds of chokes on many cores, not a few.
73, Jim K9YC
On 12/25/2022 12:02 AM, Paul Christensen wrote:
Jim (K9YC),
When making Rs measurements are you using the S11 or S21 method? Steve,
G3TXQ was an advocate of S21 while Owen, VK2OMD claims S11 results in
better
accuracy with high Rs values.
I've been using S21 with G3TXQ's VNA adapter on a PC board. It's
shown at
the bottom of the page in the link below:
http://www.karinya.net/g3txq/chokes/
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