stefan.ballmer@LIGO.ORG - posted 11:05, Wednesday 04 December 2013 - last comment - 11:44, Wednesday 04 December 2013(8811)
EOM RF return loss measurement after the latest phase jump
Kiwamu, Stefan Attached is a new RF return loss measurement for the EOM cable taken at the PSL rack end. This was taken after the latest RF phase jump. As before, the marker labeled 24.08MHz is at the actual IMC modulation frequency of 24.078360MHz. Compare this to alog 7959 (before RF jump).
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Kiwamu repeated the measurement directly at the EOM, and he was able to jump between the two setting by pushing at the EOM's Sam connector. Conclusion: a bad connector at the EOM is responsible for our phase jumps.
The resonant frequency of the notch appears to have changed such that one could reasonably account for the phase shift. The million dollar question is how? Either the tuning has bistable states (such that a mechanical tuning screw clicks between two states) or the external loading changes due to a bad connection to the EOM. It seems the latter has just been identified by Stefan...