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Spectrum Analyzer - strange measurements

Question asked by TDawe on Mar 4, 2009
Latest reply on Mar 4, 2009 by TDawe
Greetings all, first post here.  Be gentle with me. 

I am using a PSA E4448A spectrum analyzer to measure a CW power and the power levels of its 2nd and 3rd harmonics.  I had a CW at -33 and read the 2nd harmonic at -108. 

I adjusted the power of the CW to -39 and the 2nd harmonic was close to the noise floor... reading about -114.

I adjusted the power of the CW to -43 and the 2nd harmonic was below the noise floor (<-115).  So I switched on the pre-amp function.  With the pre-amp on, the 2nd harmonic reads -106.8.  I know this is wrong because if the 2nd harmonic's power level was -106.8, then I would have seen it clearly without the use of the pre-amp. I checked the power level of the main signal, and it does not alter with or without pre-amp... staying steady at -43.

I went back to the previous power level (-39) and saw the 2nd harmonic again at -114 with pre-amp off... turned the pre-amp on, and the power of the 2nd harmonic jumped to -99.8.

What could be causing this?  I suspect the spectrum analyzer is in dire need of a calibration... but I'm praying that I'm wrong, because it is an invaluable tool to us here at this point in time.