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R&D (FilterCavity)
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YuhangZhao - 16:05, Thursday 18 July 2019 (1482)Get code to link to this report
The measurement of PLL phase noise for CC and PP when filter cavity is locked or not locked

Here I attach the measurement of PLL phase noise. The measurement has some disconnect points although I used V/sqrt(Hz) as a unit. The result is summarized as following.

  filter cavity locked filter cavity free running
cc-phase noise(RMS) 18mrad 12mrad
pp-phase noise(RMS) 28mrad 8mrad

The lock of filter cavity make RMS phase noise increase by a factor of 1.5/3.5

Images attached to this report
1482_20190718090133_ccphase.png 1482_20190718090139_ppphase.png
Comments related to this report
EleonoraCapocasa - 09:47, Saturday 20 July 2019 (1490)

The excess of high frequency noise measured last summer when the cavity is locked (see entry #903) seems disapeared. This is good but the reason is not clear to me.

Note that in order to sum the line into the PZT  for the calobration we have reconnected the ramp potentiometer which was disconnected last summer,  following Pierre's advice,  in order to reduce the rampeato noise (see entry #875).

We have left it connected for now. It would be interesting to compare the difference in the error signal spectrum when it is connect and disconnected as done last summer (entry #883).