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9320B Drift In RF amplitude Measurement?

Question asked by sr on Jan 30, 2014
Latest reply on Feb 4, 2014 by fanfansimon
Sent out instrument for Calibration recently and came back with all spec tolerances within test limits per Agilent spec sheet.

*Few notes:*

Some of the test specs Frequency Response preamp off: Reads 0.67dB

Input reference level of 10dB reads 10.45dB. (within spec of +/- 0.5dB)

Actual Measurement: 

Input path to the Rf chain from synthesizer -5dbm to -2dBM (path of measurment where spectrum analyzer used)

  Usual readings/measurement for DUT at  64MHz: 5.4dB, 360MHz: 17dB, 295MHz: -13.5dB, 280MHz: 17.5, 15Mhz: 4.4dB

After recent drift in Spectrum analyzer measurements (Please note RF internal alignment performed)

64MHz: -6.7dB, 360MHz: 19dB, 295MHz: -12.3dB, 280MHz: 19.2dB, 15MHz: 5dB

We have observed close to 1dB shift in the readings on the spectrum analyzer.

What would cause such an issue? Looking for some help and advice in this regard.