Summary:
We swapped the 45MHz EOM driver under the PSL table. This box contains the RFAM stabilization board.
Old one: S1500117
New one: S1500118
Related: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=20392
We need some time to assess the impact of this swap.
Phasing:
In the PSL room, we roughly measured the phase of the driver output VS input by inserting a splitter to the input and measure the zero-cross time difference between the input and the output using a scope.
In the old one the output was 6.9ns ahead of the input, but in the new one it was 6.7ns, so there should be 0.2ns or about 3 degrees more delay.
Later we measured the transfer function from the H1:LSC-ASAIR_A_RF45_I_ERR to Q phase while the MICH was free swinging (PRM, SRM and ETMs are all misaligned). The phase between I and Q was basically 0 degrees as it should be.
| atan(Q/I) [mean(error)] in degrees | |
|
Before (according to above mentioned alog) |
76.4(6) |
| After, no cable change | 78.7(0.1) |
| After, removing one male and one female N barrel | 74.7(0.2) |
| After, replace two barrels with one N elbow | 77.3(0.03) |
We decided to go with 77.3deg, which is within 1 degree of the old phasing.
For diagnostics purposes the old unit has been setup in the CER using the 9MHz channels. Instructions how to unhook have been posted there.
The RF glitches are still present and do not depend on the EOM driver. However, they don't seem to show up on the old unit installed in the electronics room.