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Message ID: 1590     Entry time: Wed Oct 14 20:30:27 2015
Author: Antonio 
Type: DailyProgress 
Category: BEAT 
Subject: PLL noise  

Summary

========

 

New PLL noise measurements have been made with  Fdev=1KHz and Fdev=10kHz at the input range of the Marconi.

There is an improvement of a factor ~10 for frequencies above 200Hz. However the two set of measurement show

the same noise in Hz/sqrt(Hz) between them. The lock of the PLL has been done keeping the same gain; when Fdev = 10KHz

the sr560 gain is 50, and when Fdev = 1kHz the SR560 gain is 500. The latter setting provokes an increase of the noise in V/sqrt(Hz)

which compensate for the reduction in the input range when Fdev goes from 10kHz to 1kHz. It is not clear to me what is happening.

 

Additionally it is not clear what is the “extra” noise that we see in the following noise budget as the sum does not match with the measurement.

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Plots:

=====

1. The first plot shows the noise budget with the measurement taken in September 12 (2015). We see that the PLL noise is dominated by the

Marconi and photo thermal noise;

 

2. The second plot shows the noise budget with the PLL noise measured today with Fdev=1kHz; Here I do not understand

what is happening above ~200Hz; the total noise is off from what has been measured. I also should check the power on the photodiode and

see if it matches the level (2dB) I have used for the Marconi noise measurement.

 

3. The same as in point 2. but here we have Fdev=10kHz; here the total noise is closer to match the measurement,

 

4. The last plot is just the comparison between the PLL noise taken in the past September and the one measured today.

 

Please note:  ISS is off

 

Data

====

Data are stored in TCN lab computer: controlfb2/data/20151014_PLL_noise

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