This signal consists of a sequences of sharp pulses and of tones:
Zoom around the tone:
Aligning the signal in frequency to the beginning of the tone, it becomes visible that there are two tones in three intervals. It might be a coincidence but the length of the intervals is close to 6/128 seconds which may or may not be relate to the information (here or here):
It is interesting that some residual modulation is visible, i.e., the phase is not perfectly constant or linearly rising.
The next three plots show abs(z) assuming different frame lengths:
- 854 samples (9.11/128 sec):
- 844 samples (9/128 sec):
- 281 samples (3/128 sec):