The power ratio of the beatnote signal vs. the 216kHz sideband has been measured.
The measured ratio was -55 dB, which is smaller by about 20 dB than Aidan's estimation.
To confirm this fact we should check the modulation depth of the end PDH somehow.
The below is a picture showing the sidebands around the beatnote locked at 66.45 MHz.
Other than the +/-216 kHz sidebands, we can see some funny peaks at +/- 50 kHz and +/-150 kHz
I wonder if they come from the servo oscillation of the MC servo whose UGF is at 24 kHz. We can check it by unlocking the MC.
So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.
Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.