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Strange things after calibration

Question asked by Desmosedici on Jun 26, 2007
Latest reply on Jun 28, 2007 by Desmosedici

hi guys,

 

I am working on a project using a VNA (old one but enought for my measurements : HP8720B) . But I had observed strange things on the screen on my VNA

 

Details :
I had done a One port calibration, after placed OPEN ,Load, Short kit and computing cal coef my calibration had been done between   130MH and 20GHz ( full  bandwith on my VNA !) . After all calibration , I always placed the cal kit ( OPEN,SHORT, LOAD) just to verify if the cal is good. But recently, after a calibration when I placed 3 elements on the VNA and placed  VNA in mode Smith Chart : Load is correctly centred, but OPEN or SHORT, I see the same phenomena :  a large circle turning  on smith chart !!!!?? Normally I must see a small line at left (Imaginary part ~0 )Xaxis ) for the OPEN and a small line at right (Imaginary part ~0 ) for the SHORT

 

Could you help to understand this?

 

For your information : My VNA is just coming from Agilent for a full chekup and calibration period. I had discussed on phone with the Agilent technician , the guy was not sure but he said to me that is normal!?

 

NB: sorry for my english  

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