Hello,
I use N5242A PNA-X with FW 9.90.21. I am trying to perform pulse profile measurements according to the appnote "Active-Device Characterization in Pulsed Operation Using the PNA-X". I perform a frequency sweep at desired power level, then I turn on "Update source power calibration with leveling data" and change leveling to open loop. Next, I change the pulse sweep to pulse profile. In order to get highest time resolution I would like to perform measurements using 15 MHz IFBW. However, the displayed power level measured by the PNA-X is different for different IFBW. The generated power is correct, since the power measured by the external power meter is correct. How to measure b/r waves in pulse profile mode?
Best regards,
Pawel
So, a little complicated answer:
The IF frequency changes as the IF BW changes. Normally it is around 7 MHz, but we can't have a 7 MHz IF freq with a 15 MHz IF BW. The 15 MHz BW came in with the DSP5 and so we have a fully digitial IF with a programmable IF freq. above 600 kHz the IF is increased for increases in IF BW. And the IF has some rolloff so if you increase IF BW the loss in the IF changes. Now for S-parameters this almost doesn't matter, because the loss is almost the same for each IF so the ratio stays the same. But for power, of course it matters.
When we introduced the spectrum analyzer application (and by the way, it is very handy to have an SA in the VNA), we added an IF calibration that removes the roll-off effect (In fact I did the coding for that, along with Jvall). So with the SA introduction it solved the issue you are seeing. That will be rev 10.40.xx and above.
The solution to this issue in your firmware set is to do the calibration in the 15 MHz BW. Then the offset will be included in the user cal. You can try turning on point-mode averaging to reduce noise during the calibration. Or upgrade to latest A or better yet to B-version.