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Message ID: 10173     Entry time: Thu Jul 10 02:09:20 2014
Author: Jenne 
Type: Update 
Category: PSL 
Subject: FSS Fast gain set 

I have put in a new nominal value for the FSS fast gain:  21.5 dB. 

There is an oscillation peak in the MC error point spectra around 41.5 kHz if the FSS gain is set too high.  I used the 4395 to have a look at the MC error point, and saw that if I set the FSS fast gain any lower than about 18 dB, the peak wasn't getting any smaller than -41 dBm.  If I set the fast gain any higher than about 26 dB the peak wouldn't get any larger than about -34 dBm. 

However, if I set the gain to 19.5dB, the PC RMS drive is consistently above 2 V, which isn't so good.  If I crank the gain up to 27 dB or more, the PC RMS will stay below 0.9 V, which is great. 

As a compromise, I have decided on 21.5 dB as the new FSS fast gain.  This puts the oscillation peak at about -39.5 dBm, and the PC RMS around 1.6 V.

I changed the nominal gain by ezcawrite C1:PSL-STAT_FSS_NOM_F_GAIN 21.5.  This sets the nominal value so that the FSS screen's fast slider doesn't turn red at the new value.  And, since the MC autolocker reads this epics channel and puts that into the gain during the mcup script, the MC autolocker now uses this new gain.  For reference, it used to be set to 23.5 dB.

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