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Power Spikes on High Power Network Analyzer

Question asked by steveor on May 21, 2014
Latest reply on May 27, 2014 by Dr_joel

I've configured a 8753ES Opt 011 (No test set) to be a high power network analyzer.  Please see my configuration in the attached file.

When calibrating S11 with a three term correction model I found I was blowing up my load standards on the calibration substrate.  I had set the calibration power to 5 dBm and these resistors are spec'd to handle 0.25 W (24 dBm).  I then replaced Probe 1 with the power sensor and see the power is indeed 5 dBm, but I see spikes at the beginning of each frequency sweep.  For a short time, the power jumps up to 32 dBm.  

I read the excellent application note AN 1287-6 at:  Page 10 discusses some cases where the power of the analyzer may spike during the source pre-tune calibration.  It seems this is what is happening and causing power spikes during the calibration and measurement.

I tried turing off the PLL Auto tune in the service menu, but I still see the power spikes.  I'd like to try the second suggestion, using frequency-offset mode, but I'm unsure what this requires.  Does this require a second signal generator?

What other paths should I try?  I'm even willing to purchase a new VNA, but I'm unsure these will prevent the damaging spikes.  I'm also eager to get some measurements quickly.  Is there something I can do to prevent the power spikes with the equipment I have on hand?


Steve Ortiz