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How do I to measure noise with spectrum analyser

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Posts: 1090
Feb 28th, 2018 at 10:19am  
Q: How do I to measure noise with spectrum analyser ?

My answer was:

On the spectrum analyser select MARKER NOISE FUNCTION ON. Move the marker to somewhere on the noise floor and read off the noise power spectral density in dBW/Hz.

This is very important as spectrum analysers are calibrated to give measurements assuming an unmodulated CW input signal only, not noise !.

The  MARKER NOISE FUNCTION ON automatically adjusts for the bandwidth and shape of the resolution bandwidth filter and the characteristics of the internal voltmeter and the way noise does not look like a sine wave.

Approx adjustments are x1.2 for bandwidth, x1.05 for detector and 2.5dB for log. Much better to let the MARKER NOISE FUNCTION do if for you !!

Read more: http://uspas.fnal.gov/materials/11ODU/AN150-4.pdf

Read more: http://www.ab4oj.com/test/docs/5966-4008E.pdf

if you are measuring low level signals pull out the input cable and observe that the 'noise floor' drops at least 20 dB.  If not, you are measuring the noise of the analyser itself and you need an external pre-amplifier.  The input attenuation will normally need to be set to zero but be careful - don't burn out the analyser with high level input or DC
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