Measuring AM modulation
The tinySA has some problems when measuring AM modulation. This is clearly visible in below 100kHz wide scan of a 10kHz and 50% depth AM modulated 6MHz signal.
This weird effect of the many signals is caused by the internal AGC that completely fails. You either have to ensure the carrier of input signal is below -50dBm by manually increasing attenuation or you have to disable the AGC
Increasing the manual attenuation creates a better picture
With a minimum RBW of 3kHz the lower limit of modulation that can be observed in frequency mode is indeed 3kHz
For even lower modulation frequencies it is advised to go to zero span mode (time mode) and a linear unit to show the signal strength versus time where the modulation depth of 50% can clearly be observed