spectrum analyzer noise floor

Dear all,

I want to use spectrum analyzer to measure the noise floor of my laboratory. Since there are large vacuum pump beside my lab. I suspect that it will increase noise floor as it is operating. Therefore, I want to use spectrum analyzer to measure it. I am interested in 3-5GHz band. So, what is the spectrum analyzer setting in order to get a correct noise floor measurement? Why is this setting? Actually, I have tried to set RBW=1Hz only. The measured noise flooris =-130dBm. However, I set the RBW=1MHz. It shows the noise floor =-80dBm. Why? Which one I should trust?

Thanks

wccheng

Spectrum analyzers are notorious for poor noise figures. You should put a low noise high gain amplifier between your antenna and analyzer. Then subtract the amplifier gain from the measurements.

I would suspect that any noise from motors and relays would not be large at the frequency you specify. They would have other problems of putting transients on the mains which would affect other equipment.

Do you have any reference notes for me?
I want to take a look of the setup. Thanks