can you give some comments about the fluctuation of VNA reading when cable connecting the VNA and probe moving?sergio mariotti said:The answer may be splitted into 2 topics:
- The measuring method
- The tip & trips
The measuring method is mainly related to the calibration method, SOLT, TRL, E-Cal, etc.
Generally the U(s11) (uncertainty related to s11) is higher if the observed value is near the external Smith-Chart's circle.
A TRL Calibration is one of the most accurate.
SOLT is less accurate than TRL but still remain very accurate.
@gilent TRL* has poor accuracy for high values of s11.
To be accurate when you observe high values of s11, try a SOLT and a
S, offset S,L,T and compare the results.
To be accurate when you observe low values of s11, try a S,O,slidingL,T,
...
tip&trips
instrument coax cables and connectors should be in exellent conditions.
Also the Standards should be in exellent conditions.
Don't move the coax cables. Fix it in many points with scotch tape. Dont' make any torsion to the coax. Be the contact metals cleans. Etc. Etc.
Set sweep mode to step, set power > -10 dBm,
Read @gilent AN 1287 series
Read @gilent AN "Principles of connectors care"
Read @gilent PN 8510 series
DJ said:rinjic,
As you said the peaks come from resonances of the ring. If the peaks move it means the resonance frequency is moved. I suppose the exact resonance frequency is a function of the material and its dimensions and also the edges condition around it. When you took off and put back the ring, it might moved a litte bit toword one side and it changed its resonant frequency.
sergio mariotti said:To: asdfaaa:
To: rinjic
If you have a 3 samplers (or mixers) VNA, like hp 87xx whit NO opt 400 installed, a ripple may be given by the instrument. That ripple may by in the range of +/-0.1 dB around the |s21| and/or +/- 0.03 (linear) around |s11| (look the s11 on Smith Chart )
But... are you sure that the ripple is generated by the VNA? May be the real response of the DUT?
To undertand better, coul'd you post a plot of your measurement?
There is a rough check test wrote on the user manual of the Agilent (formally GoreTex) cables.rinjic said:sergio mariotti said:To: asdfaaa:
To: rinjic
If you have a 3 samplers (or mixers) VNA, like hp 87xx whit NO opt 400 installed, a ripple may be given by the instrument. That ripple may by in the range of +/-0.1 dB around the |s21| and/or +/- 0.03 (linear) around |s11| (look the s11 on Smith Chart )
But... are you sure that the ripple is generated by the VNA? May be the real response of the DUT?
To undertand better, coul'd you post a plot of your measurement?
I think it is not due to the DUT because I tried using other materials. The ripple is always there. Next time I measure them, I will post a plot here. But do u think it is possible the cable has a problem? if it does, how can I check it? Thanks for ur help!
rinjic
g579 said:Hi marotti,
Please answer my question repeated here:
You stated, that
"@gilent TRL* has poor accuracy for high values of s11"
Please explain shortly why is it so, and where can I get info on that statement.
Thanks
g579
rinjic said:hi mariotti,
I searched @gilent website and didn't find "principles of connectors care" Application Note. The only thing I found is a training course overview of "cable and connector care" which is not the Application Note. I also looked my VNA manual, it does say something about the care but not too much. Could u please upload "principles of connectors care" here?
Thanks !
rinjic
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