J. Kissel

I've come in to Ed mentioning that we've had intermittent RF45 glitching (see LHO aLOG 24789, LHO aLOG 24797), and there are concerns that the new PCAL lines are the source of the problem. I don't think this can be true. Here's why:

(1) The PCAL system is in no way related to the control servo for the 45 [MHz] modulation depth.
(2) The 2.5 [kHz] line (and 4 [kHz] line) had been on for ~6 hours before the first evidence for excess glitch rate / noise from RF45.
(3) The noise/glitchiness from the 45 [MHz] servo is taking on the "classic" behavior of intermittency (~15 minutes from Patrick, on and off for Ed).
(4) The amplitude of the PCAL line (with a ~0.1 [Hz] BW ASD) is just barely above the noise floor, much lower than any other sharp feature (i.e. the violin modes) above 1 [kHz], so I don't think it's a case of these new lines, say, saturating the OMC DCPDs (which is known to cause elevated noise / gltiching, etc.)
(5) The region surrounding these lines is feature free, so it's not a case of these new lines interacting with violin modes and ringing *them* up.

However, in order to get this "high" an amplitude, we are having to drive the Xend PCAL near the limit of it's range. It's not out of the realm of possibility that the PCAL's optical follower servo (OFS) is glitchy / non-linear near the edge of it range. However, again, because both the 4 and 2.5 [kHz] lines had been running for hours before any excess noise or glitchiness had shown up, I don't think this is the case either.