Attached are plots of the injection locking error signal and the servo transfer function.  Note that
the servo transfer function measurement does not include the SR560 low frequency boost stage that was
added before the O2 run.  This measurement was taken with
  - servo gain = 1.00 V
  - reference level = -1.30 V
  - error point offset = 0.20 V
which are the same ones in use for yonks.  The transfer function is comparable to the measurement taken
from before the observing run.

    As noted from yesterday, the RF summing box was placed on to an insulating plastic bag to isolate
it from the front end laser breadboard (and hence the table).  Touching the box did not appear to affect
the injection locking.  However I did notice that the frequency servo went into oscillation whenever I
touched the box and table.

    Suspected grounding problem.  Probably not noticed, or paid attention to, before because we rarely
touch the RF summer.  Will be chasing this up over the next few weeks.