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Entry  Tue Jul 29 01:03:17 2008, rob, Configuration, IOO, MC length measurement 
    Reply  Tue Jul 29 09:12:43 2008, Koji, Configuration, IOO, MC length measurement 
Message ID: 752     Entry time: Tue Jul 29 01:03:17 2008     Reply to this: 753
Author: rob 
Type: Configuration 
Category: IOO 
Subject: MC length measurement 
rob, yoichi

We measured the length of the mode cleaner tonight, using a variant of the Sigg-Frolov method. We used c1omc DAC outputs to inject a signal (at 2023Hz) into the AO path of the mode cleaner and another at DC into the EXT MOD input of the 166MHz IFR2023A. We then moved an offset slider to change the 166MHz modulation frequency until we could not see the 2023Hz excitation in a single-bounce REFL166. This technique could actually be taken a step further if we were really cool--we could actually demodulate the signal at 2023Hz and look for a zero crossing rather than just a powerspec minimum. In any case, we set the frequency on the Marconi by looking at the frequency counter when the Marconi setting+EXT MOD input were correct, then changed the Marconi frequency to be within a couple of Hz of that reading after removing the EXT MOD input. We then did some arithmetic to set the other Marconis.

The new f2 frequency is:

New              OLD
--------------------------
165983145        165977195

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