After discovering that the MPC polarization controller creates a peak at 27kHz in the EX PLL noise spectrum, I decided to take some more measurements at the end station with the controller off.

PLL Servo Board

• Input 1 enable: ON
• Input 1 pol: NEG
• Input 1 gain: 0db (unless otherwise specified)
• Common Comp: ON
• Fast Option: ON
• Fast pol: POS
• Fast gain: -8dB
• Boost 1: ON/OFF

PDH Servo Board

• Input 1 enable: ON
• Input 1 pol: POS
• Input 1 gain: -7db (unless otherwise specified)
• Common Comp: ON
• Boost 1: ON
• Boost 2: ON/OFF

PLL error signal measured out of PFD IMON, and PDH error signal measured out of demod IMON.

The lowest RMS comes from the PLL Boost 1: OFF, and the PDH Boost 2: ON. With the PLL Boost 1 off there is no gain peaking and the the OLTF of the PLL is stable with a UGF of 22kHz and a phase margin of 50 deg. I need to take an OLTF with the PDH Boost 2 on.