I've been planning for a while to build a tracking generator for my spectrum analyzer, but because time seems to be a rare commodity these days, I had to look for some quick alternatives that could get the job done. I had a crack at building several noise sources, but was not too happy with the result and since I didn't want to spend too much time on it, I went ahead and purchased one of those cheap noise sources from eBay.
They currently sell for about 20 pounds and they're advertised to work well up to 1.5 GHz. I need a lot better than this, but for my current project it was enough.
When buying a noise source, keep in mind that they can't replace a tracking generator. The power of the signal generated by the noise source will be spread across the entire spectrum, so every time you reduce your RBW, the displayed signal level will also drop, since less power will make its way inside the filter. It's easy to get fooled by this, so if you do get a noise source, make sure you're aware at all times of the total power that's present at the spectrum analyzer input, so you don't exceed the maximum limits.read more