Newer ones can be fed a reference spectrum, remember it, and divide a later spectrum by that. So if your signal (or noise) source isn't flat, it can correct for that. Sweep the generator without the filter, then with the filter, and divide (or subtract the logs.) We do this at work with our Aeroflex.
This wouldn't work well with noise, I'm thinking. It would be fine for a comb. A little division by zero never killed anybody.
Well, get a spectrum analyzer with a tracking generator! Or buy a cheap VCO and triangle sweep it with a function generator.
It will be hard to generate a GHz-wide noise source that has any usable power density in a 50 mHz slice. If there's a microwatt in every 50 mHz, you'll need a 20 kilowatt noise generator.
Yes. Onsemi mostly, some Arizona Microtech and Micrel.
Analog Devices makes some comparators that have 40 ps edges. They should generate combs well into the GHz range.
I once managed a survey of twisted-pairs in the NY subway system. I designed a comb generator, 1 KHz to 200 KHz I recall, and had one guy connect it to one end of a pair at one station, and another photograph a spectrum analyzer screen at the other. That saved a lot of time.
Geez, I've done a lot of weird stuff.
John