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Entry  Mon Dec 22 15:46:58 2014, Kurosawa, Summary, IOO, Seven transfer functions MC_OLTF.pdf
    Reply  Mon Dec 22 21:53:08 2014, rana, koji, Update, IOO, Seven transfer functions MC_OLG.pdf
       Reply  Tue Dec 23 01:55:35 2014, rana, koji, Update, IOO, Seven transfer functions MC_FSS_TF.pdf
          Reply  Tue Dec 23 20:50:39 2014, rana, koji, Update, IOO, Seven transfer functions MC_OLTF.pdfMC_OLTF2.pdfmatlab.zip
             Reply  Sun Jan 4 22:08:46 2015, rana, Update, IOO, MC loop characterizations: PZT/EOM crossover MC_OLGs.pdfMC_xover.pdf
             Reply  Mon Jan 5 23:36:47 2015, ericq, Update, IOO, AO cable reconnected 
Message ID: 10832     Entry time: Mon Dec 22 21:53:08 2014     In reply to: 10829     Reply to this: 10833
Author: rana, koji 
Type: Update 
Category: IOO 
Subject: Seven transfer functions 

Today we were looking at the MC TFs and pulled out the FSS box to measure it. We took photos and removed a capacitor with only one leg.

Still, we were unable to see the weird, flat TF from 0.1-1 MHz and the bump around 1 MHz. Its not in the FSS box or the IMC servo card. So we looked around for a rogue Pomona box and found one sneakily located between the IMC and FSS box, underneath some cables next to the Thorlabs HV driver for the NPRO.

It was meant to be a 14k:140k lead filter (with a high frequency gain of unity) to give us more phase margin (see elog 4366; its been there for 3.5 years).

From the comparison below, you can see what the effect of the filter was. Neither the red nor purple TFs are what we want, but at least we've tracked down where the bump comes from. Now we have to figure out why and what to do about it.

* all of the stuff above ~1-2 MHz seems to be some kind of pickup stuff.

** notice how the elog is able to make thumbnails of PDFs now that its not Solaris!

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MC_OLG.pdf
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