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40m Log |
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Wed Jan 25 15:41:29 2017, Lydia, Update, IMC, 29.5 MHz modulation depth measurement plan
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Wed Jan 25 17:30:03 2017, Koji, Update, IMC, 29.5 MHz modulation depth measurement plan
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Wed Jan 25 19:39:07 2017, gautam , Update, IMC, 29.5 MHz modulation depth measurement plan
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Fri Jan 27 21:25:11 2017, Lydia, Update, IMC, 29.5 MHz modulation depth
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Sat Jan 28 01:25:51 2017, gautam, Update, IMC, 29.5 MHz modulation depth 
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Mon Jan 30 19:07:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 01:07:20 2017, Lydia, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 13:46:34 2017, rana, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 14:17:48 2017, gautam, Update, IMC, RF AM stabilization box pulled out
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Tue Jan 31 22:07:13 2017, gautam, Update, IMC, RF AM stabilization box revamp
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Tue Jan 31 22:28:39 2017, Lydia, Update, IMC, RF AM stabilization box pulled out
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Wed Feb 1 11:51:19 2017, Koji, Update, IMC, RF AM stabilization box pulled out
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Wed Feb 1 16:45:56 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan
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Wed Feb 1 20:49:34 2017, rana, Update, IMC, RF AM stabilizer box Modification Plan
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Wed Feb 1 23:13:30 2017, Lydia, Update, IMC, RF AM stabilizer box Modification Plan
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Sun Feb 5 21:56:50 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Tue Feb 7 12:01:10 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Tue Feb 7 17:00:55 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 02:14:10 2017, gautam, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 11:41:43 2017, Lydia, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 13:24:28 2017, rana, Update, IMC, 29.5 MHz stabilizer box replacement
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Fri Feb 10 18:21:21 2017, gautam, Update, IMC, IMC Demod board
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Fri Feb 10 19:32:15 2017, Koji, Update, IMC, IMC Demod board
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Sun Feb 12 01:16:57 2017, gautam, Update, IMC, IMC length loop - summary of changes    
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Mon Feb 13 11:55:14 2017, rana, Update, IMC, IMC length loop - summary of changes
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Mon Feb 13 13:34:44 2017, gautam, Update, IMC, IMC length loop - bad SMA cable replaced
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Mon Feb 13 19:44:55 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Mar 1 21:15:40 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Mar 1 23:56:09 2017, gautam, Update, IMC, Front panel for 29.5 MHz amplifier box
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Thu Mar 2 20:32:18 2017, Lydia, Update, IMC, Front panel for 29.5 MHz amplifier box
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Wed Feb 15 23:54:13 2017, gautam, Update, IMC, IMC saga continues... 
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Fri Feb 17 20:10:18 2017, gautam, Update, IMC, WFS servos turned back on
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Sat Feb 18 14:09:06 2017, rana, Update, IMC, WFS servos turned back on
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Sat Feb 18 21:50:48 2017, gautam, Update, IMC, WFS servos turned back on
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Sun Mar 5 12:41:23 2017, gautam, Update, IMC, WFS servo-steppin  
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Message ID: 12782
Entry time: Tue Jan 31 22:28:39 2017
In reply to: 12775
Reply to this: 12783
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Author: |
Lydia |
Type: |
Update |
Category: |
IMC |
Subject: |
RF AM stabilization box pulled out |
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[rana, gautam, lydia]
Today we looked at the schematics for the RF AM stabilizer box and decided that there were an unnecessary amount of attenuators and amplifiers cancelling each other out and adding noise. At the end of the path are 2 HELA-10D amplifiers which we guessed based on the plots for the B version would have an acceptable amount of compression if the output of the second one is ~27dBm. This means the input to the first one should be a few dBm. This should be achieved with as simple a path as possible.
This begged the question, do we need the amplitude to be stabilized at all? Maybe it's good enough already when it comes into this box from the RF distribution box. So I tried to measure the AM noise of the 29.5 MHz signal that usually goes into the AM stabilizer:
- I first measured the power to be 12.8 dBm with the AG4395.
- I sent the signal through a splitter, then sent one side attenuated by 3 dB to the LO side of a level 7 mixer, and the other side attenuated by 10 dB to the RF side of the mixer.
- The output of the mixer went through a lowpass filter at 1.9 MHz (with a 50Ω inline terminator). Initially I connected this directly to a DAQ channel (C1:ALS-FC_X_F_IN), but the ADC noise was stronger than the AM signal.
- To fix this I used the SR560, AC coupled with a gain of 10^4. Attachment 1 is a spectrum of the noise measured with everything connected as described, and also for separate portions of the signal chain:
- I measured the ADC noise by connecting a terminator to the cable going to DAQ.
- I measured the mixer noise by putting a terminator on the RF input (and the end of the cable that was connected to it), while still driving LO.
- I measured the SR560 noise by putting a terminator on the input.
It seems like I'm getting mostly noise from the SR560. Maybe it would be better to use an SR785 to take data instead of DAQ, and then skip the SR560? At low frequencies it seems like the AM noise measurement may be actually meaningful. In any case, if the actual AM noise from the crystal is lower than any of these other noise sources, it means we probably don't need to stabilize the amplitude with a servo, which means we can simplify the AM stabilizer board considerably to just amplify what it gets to 27 dBm. |
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