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.

attachment:AM_wrong.jpg

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

attachment:AM_reduced.jpg

With a minimum RBW of 3kHz the lower limit of modulation that can be observed in frequency mode is indeed 3kHz

attachment:AM_3kHz.jpg

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

attachment:AM_linear.jpg


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TinySA-AMModulation (last edited 2020-10-16 11:08:29 by RudolfReuter)