WP 7075

To further proceed with the 72 MHz WFS (Wave Front Sensor)s (37042), today I made the hardware changes (mostly cabling), as summarized below, while the interferometer was in a violin-mode-damping state.

I am going to leave the hardware configuration as it is. If this new setup doesn't cause extra noise in the interferometer, they will stay semi-permanently.

Here is a summary of the new configuration:

• We have the 118 MHz RF modulation signal applied to the EOM with the full RF power (+33dBm@PSL rack).
• And we have the 72 MHz RF local oscillator signal sent to the HAM6 area, providing the 72 MHz WFS signals.

[The modifications]

• I plugged the new 72 MHz RF source to the unused RF Heliax cable so that the signal is sent from the CER to the ISC R3 rack (by HAM6).
  • Additionally, I newly installed a balun at the HAM6 side which was missing for some reason.
• At the ISC R3 rack, I routed the 72 MHz to the distribution amplifier which had been used for the 90 MHz demodulators.
  • In this configuration, the distribution amplifier feeds the WFS demodulators which had been also used for the 90 MHz but now with the 72 MHz signal.
• At the ISC R3 rack, the 90 MHz RF cable was rerouted so that it directly feeds the demodulator for ASAIR_B_RF90.
• I adjusted the RF power level by inserting appropriate RF attenuaters while looking at the EPICS readouts from the distribution amplifier and WFS demodulators.
• In the LSC, I changed the FM8s for LSC_ASAIR_B_RF90_(I|Q) from +3 dB to -1 dB in order to keep the same level of signals. See the attached screenshots for the changes that I made.
  • Also, I have changed the digital demodulation phase of ASAIR_B_RF90 such that the signal is maximized in I when the interferometer was locked at 30 W.