Extracting carrier phase information from an MSK signal

I’m looking to show the long-term phase stability (or actually
perturbations) of a very-stable
MSK-modulated signal. I currently have the 200-baud signal running
through a 300Hz-wide filter,
and then (among other things) run through a complex-to-arg conversion
to extract the instantaneous
phase angle. I then split positive and negative values and average
them separately.

I’m nearly 1000km from the transmitter, so the results are somewhat
noisy, but by looking at the
complex-to-arg output, you can clearly see that “bits” are being
encoded. My goal isn’t to demodulate
the signal, but rather to use it as a stable phase reference, for
measuring ionospheric disturbances, which
can impart phase hits to the received signal (actually, given that the
ionosphere isn’t exactly a stable
reflector/refractor, there will always be a certain amount of small
phase disturbances).

Is my approach even close to reasonable?

Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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