Today I replaced the Qubig PD back to the one with DC output (simply called DC-Qubig later), whose change was done about one month ago (elog2801). Note that I just temporarily set up DC-Qubig, whose cables are still not deployed properly since it's hard to do by myself

After putting DC-Qubig back, to have a decent loop gain, I adjusted DDS2 channel CH1 amplitude from 1/4 to 1/2. After that, I took a measurement of open-loop transfer function. The unity gain frequency was around 13kHz. At the same time, the Rampeauto attenuation is 0, the Rampeauto gain is 8.

The setting for AA is shown in Fig.1. The setting for z_corr is shown in Fig.2. 

In the first minute of Fig.3, the filter cavity is controlled with PDH and z_corr. After using setting of Fig.1 for AA, the filter cavity transmission is stabilized. This figure shows about five minutes. But longer lock such as about 20min was observed tonight as well.