power spectral density measurements

Hello,

I'm looking in some ultra wideband papers where the PSD output is measured. In some papers, the output is very smooth and in some papers the output has lot of spectral components. Can anyone explain why this is happening?. I'm attaching two figures for reference. Both uses same type of modulation.

Thanks in advance.

FCC tests use quasi peak measurements with video filtering to resemble the bandwidth of audio spectra within the IF and video filter combined. The rationale was that EMI of carriers should not introduce audio noise in communication bands.

The video filter is a peak detect and slow decay filter on the sweep so that information on deep nulls is ignored.
The quasi means it is BW limited to ~20kHz on peak detect, so that ns/us peaks in carrier are filtered out if they exist.

Thank you for the information.

Do all spectrum analyzer have access to the video bandwidth?.

yes they do