I used the auxiliary 1811 as an out-of-loop RAM monitor. The RF from the 1811 is mixed with the PDH LO, and then low-passed at 1.9 MHz.
I'm not sure about the RAM calibration here. I took the raw spectrum (in V/rtHz), multiplied by 10^(4/20) (assuming 4 dB conversion loss in the mixer), then divided by the measured dc voltage (about 20 mV), then divided by 40 (because of the different dc/ac tranimpedances).
Anyway, the point is that the 200 Hz hump we see in the beat seems to be from the north RAM.