Danny, Hang, Stefan, Daniel

Daniel hooked up two IFR function generators to simulate the ALS DIFF and COMM beat notes.

1) Just injecting a lot of noise (up to 100kHz broadband) into ALS_COMM did not produce enough cross-talk - only about 1/200 of the injected signal in COMM shows up in DIFF (plot 1)

2) However, when we started to simulate COMM noise by lowering the beat note strength enough that the PLL started missing beats, the noise also showed up in DIFF at about 1/4th the strength (about the ratio we see when COMM locks) (plot 2).

3) In situation 2, changing the COMM PLL feed-back gain actually reduced the noise coupling - I don't know whether that was already tried with the arm signal.


In all plots, the references are from arm locks yesterday. The COMM is always noisy (brown). DIFF has a noisy (dark blue, COMM locked) and a quiet (black, COMM unlocked) reference.