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Wide band power measurements with MXA N9020A

Question asked by ljo on Mar 14, 2014
I am trying to carry out RIN_OMA measurements: signal from an optical transmitter is fed through O/E converter to a power meter (required back reflection controls etc. included in the setup) and the power is measured with modulation of the transmitter on and off.

The best way to measure the power would be to use RF power meter with its broadband frequency coverage. However, I don’t happen to have one on hand but we have a MXA signal analyser available, but how reliable MXA’s band power measurements are when I need to measure really wide band (approx. DC to several GHz)? Especially when the measured noise signal is very close to the noise floor of the instrument?

Attached spectra as an example:
Yellow: modulated, band power (10 MHz – 3.6 GHz) -16.90 dBm
Cyan: unmodulated, band power -50.54 dBm
Purple: noise floor, band power -52.09 dBm

Which result in reasonable RIN value of 129 dB/Hz, but is this method at all trustworthy?