AnsweredAssumed Answered

User Cal kit and Migrating Load Trace

Question asked by SOLT_guy on Feb 16, 2011
Latest reply on Feb 17, 2011 by SOLT_guy
Dear Sir:

      I have experienced an unusual problem with regard to how my calibration kit responds to my load. 

      I own a 8753C network analyzer and I am conducting a S11 one port calibration with a user cal kit. 

      This is the circumstances of my calibration, the load that I am using comes from the HP 85033C Cal kit. 

      I made a homemade short for testing purposes and I am not using the HP 85033C open for my calibration. 

      If I conduct the S11 one port calibration using the cal kit specified by HP (HP 85033C)  which is installed on my NA, there are no problems with the calibration. 

      When I use my user calibration kit for the S11 one port cal  (where I have specified the open and the homemade short) the calibration appears to be OK, until I go to test my load (the same load used I used in calibration).  My load trace is unstable I can see a trace from the 3 o'clock position to the 50 ohm center position and my load trace is migrating toward the center of the Smith Chart (very unstable).   In my calibration kit, I have specified the load exactly the same way it is specified in the 85033C kit.   There is nothing out of the ordinary with respect to how I have specified my open and short in my cal kit.   In fact, if I conduct a response calibration with the open and short using my homemade cal kit I experience no problems measuring the load.  

      Can you tell me where the source of my error lies with regard to  how I have specified my cal kit?    Experience will probably know best in this situation.