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Message ID: 580     Entry time: Thu Jun 26 22:08:33 2008
Author: Jenne 
Type: Update 
Category: Electronics 
Subject: 3.7MHz bandstop filter in MC Servo  
The 3.7MHz elliptical bandstop filter that I made during my SURF summer is now installed in the MC servo loop to reduce the noise at 3.7MHz.

I have taken transfer functions with and without the filter between TP1A and TP2A, with EXCA at -20dBm, using the HP4195A Network Analyzer. I have also taken power spectra of TP1A with and without the filter, and time domain data with the filter of OUT2 on the MC Servo Board and Qmon on the Demod board just before the MC servo board. The filter is between Qmon and OUT2 in the loop.

The UGF and phase margin don't change noticeably with and without the filter, and the MC still locks nicely (after the minor fiasco this afternoon), so I think it's okay. The UGF is around 57kHz, with about 38 degrees phase margin.

1 July 2008: I redid the plots. Same info, but the traces with and without the filters are now on the same graph for easier readability.
Attachment 1: MCLoopGainBoth.png  43 kB  Uploaded Tue Jul 1 12:27:56 2008  | Hide | Hide all
MCLoopGainBoth.png
Attachment 2: TP1ASpectrumBoth.png  14 kB  Uploaded Tue Jul 1 12:28:09 2008  | Hide | Hide all
TP1ASpectrumBoth.png
Attachment 3: QmonWithFilt.png  5 kB  Uploaded Tue Jul 1 12:32:25 2008  | Hide | Hide all
QmonWithFilt.png
Attachment 4: MCOut2WithFilt.png  5 kB  Uploaded Tue Jul 1 12:32:30 2008  | Hide | Hide all
MCOut2WithFilt.png
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