Below is the transfer function of the PDH box from the SWEEP input to the output. This input will be used for the closed-loop measurements of the gyro loops, so we need to know this information. It appears that the TF is flat at 0 dB up to around 10 kHz, where there is some strange behavior. It also appears to be independent of the gain setting, which is a nice feature. The two seemingly arbitrary gain settings chosen to test this are 1) 0.5: the setting at which we took the IN -> OUT TFs, and 2) 7.0: the typical running setting for the gyro.

Trying to take a TF with the BOOST on (to emulate the state of the system while running the gyro) proved fruitless, as this causes the output to rail regardless of how low you make the source or whether you go in at SWEEP or INPUT. This is problematic because we would like to do the closed-loop measurements on the actual (BOOST on) running state of the gyro. It is possible that engaging the boost produces an unwanted offset, and this would explain why doing so with the cavity locked sometimes causes it to drop. I will take a look at the schematic to see if something is obviously wrong with the circuit.