I used the Agilent 4395A and the GPIB network bridge to measure the MC error spectrum at the MC servo board.

I looked at various settings of the FSS Common and FAST gains.

Here is the spectrum of various Common gain settings, with a fixed FAST setting of 23.5:

The peak at 34k is smallest at the largest Common gain setting of 13.0 (probably expected).  The other higher frequency peaks are higher, though, such as the ones at 24.7k, 29.6k, 34.5k, etc.:

Here's a blow up of the peak at 1.06M, which peaks at about 9dB of common gain:

 Here's the spectrum with a fixed Common gain of 10.5, and various FAST gains:

and here's a zoom around that 1.06 MHz peak, which is smallest at a FAST gain of 23.5 dB:

I'm not sure yet what this points to as the best gain settings.  We can of course explore more of the space.  I'm going to leave it at 13/23.5, which leaves the PC RMS at ~1.5 and the FAST Monitor at ~6.0.

If this does turn out to be a good setting we'll need to adjust some of the alarm levels.

Various settings:

MCS
  in1 gain: 15
  offset: 1.174
  boost enabled
  super boost: 2
  VCO gain: 25

FSS:
  input offset: -0.8537
  slow actuator: 0.6304

I include the python scripts I used to remotely control the AG4395 to take the measurements, and make the plots.

PS: I made some changes/improvements to the netgpib stuff that I'll cleanup and commit tomorrow.

#!/usr/bin/env python

import os
import sys
import time
import numpy as np
sys.path.append('/opt/rtcds/caltech/c1/scripts/pylibs/')
import pyezcalib as ca
sys.path.append('/opt/rtcds/caltech/c1/scripts/general/netgpibdata/')
import netgpib

#!/usr/bin/env python

import os
#import numpy as np
from pylab import *

#name = sys.argv[1]

#atten = 10 # 10dB