To better show the applications of a noise source (sometimes called noise generator), today I used the Rover Instruments HD Touch STC meter - a top of the class professional meter.
The left picture shows the CATV band with just the noise source, while the right picture shows the spectrum with the LTE filter inserted:
With the HD Touch it is possible to use a stored spectrum picture as a back picture. It will be shown as a blue contour.
The photo shows the stored spectrum (using just the noise source) superimposed by the live spectrum, but this time a LTE filter is applied between the meter and the noise source. This filter blocks frequencies from 790MHz upwards, as used by LTE (mobile internet). The LTE signal is infamous for interfering with DVB-T/T2 transponders at close frequency ranges.
As can be seen, the generated noise signal is not exactly flat, but still usable. On a spectrum analyzer with memory function or the possibility to overlay a stored spectrum (like the HD Touch) it can still be used to measure attenuations due to faults in the distirbution network.