S11 distortion

[LeCont]

Hello,
Tried different versions: 1.01, 1.0. 0.53, etc. S11 graph looks always distorted:
http://lecont.net/wp-content/uploads/2019/06/0000018.jpg
Minor distortions (steps) are also visible on other graphs.

From the other hand, original EU1KY firmware does not have this issue (same hardware used):
http://lecont.net/wp-content/uploads/2019/06/00000017.jpg

Do appreciate your feedback.
Evgeny

[ted051]

I tried to confirm your problem, with CEC V1.01.
I cannot confirm this error, my screen is as expected.
Please let me know your concrete testing conditions.
73, Wolfgang, DH1AKF

[LeCont]

Hi Wolfgang, thanks for your prompt response.
After I have reduced a number of turns on choke (now there are 4, before - 6) and relocated it on the side of the board, the issue apparently resolved.
http://lecont.net/wp-content/uploads/2019/06/IMG_6697.jpg
Strange thing is that I have experienced the same issue on 3 different devices and only on CEC firmware, not on EU1KY one.
Could you please advice what is the right type of ferrite for the choke and what is the most optimal number of cable turns on it?
Thanks, Evgeny

[ted051]

Even Juri Kuchura (EU1KY) did not provide more precise information on the core. I used cores from an old VGA cable, µ about 800nH/w². 4 turns 50 Ohm Teflon coax.