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Incidental AM using N5531S?

Question asked by NIARMetrologist on Nov 5, 2010
Latest reply on Dec 8, 2010 by NIARMetrologist
I am trying to run the performance verification procedure of an HP 8657A using an N5531S in place of the 8902A. Two tests are giving me failing results, the Incidental AM and Residual FM above 123 MHz.

I am satisfied with just running the Residual FM tests below 123 MHz as the procedure notes "Tests performed at these frequencies will verify that in all probability, the instrument meets its specifications". But I must get the Incidental AM test to completely pass.

The Incidental AM spec of the UUT is <0.1% peak in a 300 Hz to 3 kHz BW. The 8902A indicates 0.03% and the N5531S reads 0.291%.

I have manually set the IF BW of the N5531S to 50 kHz versus its default of 58.960 kHz for a result of 0.144%. This is the lowest result I can manage.

Is this measurement beyond the capability of the N5531S, or do I need to do some fine tuning of its other operational parameters?

Any help would be appreciated.