I know the title doesn't make a lot of sense. What I am trying to ask is; let's say that I have a spectrum analyzer, a tinysa ultra, with 800MHz bandwidth, which claims to be calibrated to 5.3GHz in ultra mode. It uses some kind of harmonic mixing and spur removal algorithms but I am not quite sure how it works yet.
I am going to buy some transistors and schottky diodes to build radio frequency receivers and some testing equipment like a return loss bridge and signal sources.
What kind of fmax should I aim for? Should I limit myself to transistors with fmax<800MHz? Maybe 5.3GHz? I know there is no hard rule about this kind of thing and also that it is pretty much impossible to actually get any gain at fmax from a transistor. Most of them seem to be specified for about a third of their transition frequency.
What kind of scares me is that I will buy these transistors, build some circuits and then they will oscillate at some very high frequency that I can't detect, though I suppose it is not very likely that a transistor can be made to oscillate at frequencies near fmax especially considering that the rest of the circuit will have some loss even if I were to try and make it oscillate.
I am thinking of getting some BFP183 for amplification/oscillators and some cheap medium barrier schottkies for mixers. I've already got lots of lower frequency transistors and I've been building RF circuits as a hobby for about 10 years or so. It's just that seeing "GHz" in a datasheet kinda scares me
BFP183 seems to have an fmax of about 10.3GHz based on its fT, Rbb and Ccb. I figure I can just run it at a lower than ideal current to lower its fT, although I will need to run it at a higher current to drive those schottky diodes for mixers. Maybe I can buy a more powerful but slower transistor to do that. The reason I am considering it is because it seems to be quite cheap. Another reason is that I need a low noise figure for some weak signal projects.
I am open to transistor-diode suggestions and thanks in advance for your answers.