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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: 5502     Entry time: Wed Sep 21 16:44:18 2011     In reply to: 5491     Reply to this: 5503
Author: Keiko 
Type: Update 
Category: IOO 
Subject: AM modulation mistery 

AM modulation depths are found to be 50 times smaller than PM modulation depths.

m(AM,f1) ~ m(AM, f2) = 0.003 while m(PM, f1)=0.17 and m(PM, f2)=0.19.

Measured values;

* DC power = 5.2V which is assumed to be 0.74mW according to the PDA255 manual.

*AM_f1 and AM_f2 power = -55.9 dBm = 2.5 * 10^(-9) W.

P92101381.jpg

AM f2 power is assumed to be the similar value of f1. I can't measure f2 (55MHz) level properly because the PD (PDA255) is 50MHz bandwidth. From the (P_SB/P_CR) = (m/2) ^2 relation where P_SB and P_CR are the sideband and carrier power, respectively, I estimated the rough the AM modulation depths. Although DC power include the AM SB powers, I assumed that SB powers are enough small and the DC power can be considered as the carrier power, P_CR. The resulting modulation depth is about 0.003.

On the other hand, from the OSA, today's PM mod depths are 0.17 and 0.19 for f1 and f2, respectively. Please note that these numbers contains (small) AM sidebands components too. Comparing with the PM and AM sideband depths, AM sidebands seems to be enough small.

Quote:

Keiko, Suresh

AM modulations are still there ... the mechanical design for the stages, RF cables, and connections are not good and affecting the alignment. 

 

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