AnsweredAssumed Answered

LO Source Power Cal Problem

Question asked by andyTPE on Jun 14, 2011
Latest reply on Jun 15, 2011 by andyTPE
Hello PNA-X'ers,

I have an N5245A running A.09.33.07 and have a problem when attempting to run an SMC calibration with the LO power calibration option enabled (configuration: swept RF, fixed IF).

Step 1 of the guided calibration (source power cal for the RF source) works without any problems

However, Step 2 of the Source Power Calibration (LO source power calibration) causes a problem.  After I connect the power sensor to the LO port and hit 'Measure' I get the attached trace.  If I then hit abort and 'Remeasure', the calibration will generally (but not always succeed).

The LO is an external source - an SMA 100A running E4438/E8257 emulation mode.  I have tried controlling the instrument on all 3 interfaces (GPIB, USB and LAN) without any noticeable difference in this problem.  I do not think it is a control syntax issue - I have used the IO Monitor to examine the command set that the PNA-X sends to the SMA 100A and it understand all the SCPI commands. 

The SMA 100A 10 MHz reference is locked to the PNA-X and I do not see any synchronization/frequency lock problems - the conversion loss measurement works (and the power meter measurement is broadband any way).  It is almost as if the PNA-X is getting erroneous data from the power meter and compensating in the wrong direction on successive frequency steps.

Can anyone give me any suggestions to resolve.  The strange thing is that I o not usually see this error with an IF=100 MHz, but IF=300 MHz and higher gives me the pain.