I’ve been thinking about the possibility of using the moku phasemeter to track the exponential ringdown (of frequency) of a system. So far, I’ve been doing this in the least sophisticated way imaginable - I have knowledge of the starting frequency, so I simply run the Spectrum Analyzer with a 1 or 2 kHz span (so I have sufficient frequency resolution), acquire data, find the peak frequency, and then set the center frequency for the next iteration of the SA measurement to be the position of the last found peak. This sort of works because I didn’t need to know the instantaneous frequency at particularly high sampling frequency.
I am wondering if others have used the phasemeter instrument for similar applications? In principle, as long as one can arrange for the phasemeter to be locked to the frequency at the start of the ringdown, and provided the fastest rate of change of frequency is within the phasemeter bandwidth, I can track all parameters (amplitude, frequency and phase). The trouble is that the signal whose frequency I am trying to track has a few spurious peaks, and the phasemeter appears to lock onto these frequencies as the main signal frequency rings down. Is there some clever way to bypass this limitation? A bunch of software notches won’t do the job, as I guess the phasemeter will lose lock whenever the spurious spectral peaks (but also the signal frequency) get notched out. Do I have to do this programmatically, forcing the phasemeter to re-acquire lock every time the detected frequency stays constant for > some threshold time?