First thank you for the reply.
By bandwidth I literally mean for example the 3-dB or what ever you specify as bandwidth and I dont look for jitter either.
If you have a small RBW, lets say 1Hz, then what do you see? I would guess the sweeping filter which could be Gaussian.
But basically my question is: if you put a sine wave from a signal generator into a spectrum analyser, would it make sense to measure the 3-dB bandwidth for example? And what would you measure if you for example used 1 Hz RBW?
Kind regards