Some scattered observations on my recent attempts at engaging an improved CHARD_Y loop

• The loop is stable and works fine at the beginning of a lock stretch. When I tried to engate it after a few hours into a lock, it is right away unstable
• The first plot shows the trend of a few ASC signals during a lock stretch
  • at the beginning I engaged the new CHARD_Y controller, and it worked ok. The red trace in the second plot shows the error signal spectrum
  • after a couple of hours, there is clear oscillation rising at 3.36 Hz (blue trace in the second plot). There is also increased motion at ~ 0.5 Hz
  • at that point, to save the lock, I switched back to the old CHARD filter, but left the RPC off. This stabilized the ASC behavior, and the oscillation moved to 3.42 Hz (green trace in the second plot)
  • after a while I put back the RPC (brown trace in the second plot): this helped only marginally for the 3.42 Hz oscillation
  • there was a new risign oscillation at 1.30 Hz (pink trace in the second plot), as does the 3.42 Hz peak
• Looking at a long lock stretch with the nominal CHARD_Y controller, one can still see a worsening of the CHARD_Y error signal over time (third plot): the peak at 1.3 Hz increases as does the 3.42 Hz peak. Also, CHARD is noisier everywhere