(Evan, Kiwamu. Daniel)
We installed the 45.5MHz EOM driver in the PSL room. It is located below the PSL table and replaces the RF amplifier at the same location. The drive power has been adjusted to be the same as before at 23.2dBm. This is now controlled remotly through medm.
Calibration:
- For the front panel BNC of Mon1 and Mon2 the calibration is 105V/V relative the output signal. The DAQ readbacks RF45_ERR and RF45_AC have an additional gain of 20.
- The DC output at the fron panels have a gain of 0.578V/V relative to the output signal. The DAQ readback RF45_DC has an additonal gain of 2.
- To caluclate the RF AM in dBc one has to divide the AC/ERR values by the DC value.
The RF phase shift was compensated by cable length to within 1°.
The RF phase has a slightl dependence on the RF level. At 45.5MHz with 23dBm output level the phase advance of the entire chassis is 121°. The relative phase shift at 17dBm is +4.8° (advance), +8° at 13dBm, and 12.8° at 5dBm—or –0.8°/dBm.
The attached plot shows the RF AM RIN in dBc/Hz for both the in-loop and out-of-loop sensor (double-sided). At 100Hz with 23dBm output we are achieving-170dBc/Hz.
We kept track of the RF phase shift by keeping the interferometer in a freeswinging Michelson configuration while watching the time series of AS45I and AS45Q. Before the swap, we had arctan[Q/I] = arctan[42.0(3)/10.3(3)] = 76.2(4)°. After the swap, we found that the signals had shifted by +144°. [Note that just watching the freeswinging I and Q time series only determines the phase shift modulo 180°. We locked the Michelson and found that instead of the expected dark fringe lock, we got a bright fringe lock—indicating that the phase shift must lie somewhere between +90° and +270°.]
Then we experimented with adding extra cable length between the 45 MHz distribution spigot and the EOM driver. In the end Kiwamu and Daniel made a 150 cm LMR 195 cable, which brought the phase of AS45 back to arctan[41.8(6)/10.1(4)] = 76.4(6)°.
I assume the following SDF setting changes are related to this work, so I have accepted them into the LSC safe.snap for future restores.
