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Entry  Mon Sep 19 23:19:40 2011, Keiko, Update, IOO, AM modulation mistery 
    Reply  Tue Sep 20 23:01:37 2011, Keiko, Update, IOO, AM modulation mistery 
       Reply  Wed Sep 21 16:44:18 2011, Keiko, Update, IOO, AM modulation mistery P9210138.JPGP92101381.jpg
          Reply  Wed Sep 21 17:42:35 2011, rana, Update, IOO, AM modulation misery 
             Reply  Wed Sep 21 18:53:03 2011, Keiko, Update, IOO, AM modulation misery AM0.pngAMratio1.pngAMratio50.png
                Reply  Wed Sep 21 21:13:35 2011, rana, Update, IOO, AM modulation misery 
                   Reply  Thu Sep 22 17:29:42 2011, Keiko, Update, IOO, AM modulation mistery AMmod0MICH.pngAMmod1e-1MICH.pngAMmod0SRCL.pngAMmod3e-3SRCL.pngAMmod3e-3SRCL-AS55I.png
                      Reply  Sat Sep 24 09:55:42 2011, Keiko, Update, IOO, AM modulation mistery 
Message ID: 5538     Entry time: Sat Sep 24 09:55:42 2011     In reply to: 5520
Author: Keiko 
Type: Update 
Category: IOO 
Subject: AM modulation mistery 

From the night day before yesterday (Sep 22nd, Thursday night. Sorry for my late update), there are more AM modulations than I measured in the previous post. It is changing a lot, indeed! Looking at the REFL11 I and Q signals on the dataviewer, the signal offset were huge, even after "LSCoffset" script. Probably the modulation index of AM was same order of PM at that time. The level of AM mod index is changing a lot depending on the EOM alingment which is not very stable, and also on the environment such as temperature .

To reduce AM modulations, here I note some suggestions you may want to try :

* Change the SAM connectors between RF resonator and EOM to be a soft but short connector, so that the resonator box doesn't hung from the EOM.

* Change the RF resonator base to be stable posts. Now several black plates are piled to make one base.

* Install a temperature shield

* Also probably you want to change the BNC connector on the RF resonator to be SMA.

* Be careful of the EOM yaw alignment. Pitch seemed to be less sensitive in producing AM than yaw alignment.

 

Quote:

AM modulation will add offset on SRCL signal as well as PRCL signal. About 2% of the signal amplitude with the current AM level. MICH will not be affected very much.

From #5504, as for the AM modulation I checked the MICH and SRCL signals in addition to the last post for PRCL, to see the AM modulation effect on those signals. On the last post, PRCL (REFL11I) was found to have 0.002 while the maximum signal amplitude is 0.15 we use . Here, I did the same simulation for MICH and SRCL.

As a result, MICH signals are not affected very much. The AM modulation slightly changes signal slopes, but doesn't add offsets apparently. SRCL is affected more, for REFL signals. All the REFL channels get about 0.0015 offsets while the signal ampliture varies up to 0.002. AS55I (currently used for SRCL) has 1e-7 offset for 6e-6 amplitude signal (in the last figure) - which is the same offset ratio comparing with the amplitude in the PRCL case -

 

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