spectrum analyzer rbw

Hi all,
I want too know the relationship of resolution bandwidth (RBW) and measured power level in a spectrum analyzer.
why the noise floor of displayed and measure dsignal become lower with decreasing RBW?

what is the power of measured signal and IF output power?
thanks to attension.

regards

Hi, This due to the relation "Noise bandwidth " the absolute noise floor is know when you know the temperature. the receiver noise floor will be lower if the bandwidth over which you mearue the energy (RBW) is smaller.

regards,

Paul.

Accurate power measurement should be done with linear frequency characteristic over the spectrum bandwidth of signal. All spectrum components must be "weighted" with same constant. It is possible with wide bandwidth or square shaped one. Spectrum analyzer IF filter has something like sin^2 shape and can have different width (RBW). Measured result can be simply explained as sum of products of filter shape and power of each individual spectral component. Measured result is not correct.
Right measuring result is possible only for each spectral component separately.