RF Spectrometer Sees Inside - Hackaday
For example, you can tell what elements are in a star or an incandescent based on the spectrum of light they emit.
An oscilloscope-resident function generator creates a signal that he feeds to an amplifier because you need a fair amount of power going out.However, you also need to sense a very tiny amount of power coming back, and that requires a special circuit that will block high-power signals while passing low-level signals.Because of the low level of signals involved, you do need some special RF techniques.The actual science behind this is the same idea as what happens with nuclear resonance imaging.The end of the video has a detailed explanation of what makes it work.