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Entry  Mon Mar 29 21:43:27 2010, Alberto, Configuration, PSL, Reference Cavity PD Noise Spectrum 2010-03-29_FSS_PD_shotnoise_and_darknoise.png2010-03-29_FSS_PD_shotnoise_and_darknoise.png
    Reply  Tue Mar 30 06:37:32 2010, rana, Configuration, PSL, Reference Cavity PD Noise Spectrum rc.png
       Reply  Wed Mar 31 15:31:53 2010, steve, Update, PSL, Reference Cavity RF PD base upgraded brspdbs.JPG
    Reply  Sat Apr 3 11:35:47 2010, rana, Configuration, PSL, Reference Cavity PD Noise Spectrum 
       Reply  Sat Apr 3 16:07:40 2010, Alberto, Configuration, PSL, Reference Cavity PD Noise Spectrum 2010-03-29_FSS_PD_shotnoise_and_darknoise.png
          Reply  Tue Apr 6 11:27:11 2010, Alberto, Update, Computer Scripts / Programs, Data formats in the Agilent AG4395a Spectrum Analyzer 
             Reply  Tue Apr 6 16:55:28 2010, Alberto, Update, Computer Scripts / Programs, Data formats in the Agilent AG4395a Spectrum Analyzer 
Message ID: 2760     Entry time: Sat Apr 3 16:07:40 2010     In reply to: 2759     Reply to this: 2775
Author: Alberto 
Type: Configuration 
Category: PSL 
Subject: Reference Cavity PD Noise Spectrum 

 I was aware of a problem on those units since I acquired the data. Then it wasn't totally clear to me which were the units of the data as downloaded from the Agilent 4395A, and, in part, still isn't.

It's clear that the data was in units of spectrum, an not spectral density: in between the two there is a division by the bandwidth (100KHz, in this case). Correcting for that, one gets the following plot for the FSS PD:

2010-03-29_FSS_PD_shotnoise_and_darknoise.png

Although the reason why I was hesitating to elog this other plot is that it looks like there's still a discrepancy of about 0.5dBm between what one reads on the display of the spectrum analyzer and the data values downloaded from it.

However I well know that, I should have just posted it, including my reserves about that possible offset (as I'm doing now).

Quote:

The units on this plot are completely bogus - we know that the thermal noise from the resonant part of the circuit is just V = sqrt(4*k*T*Z) ~ 3nV/rHz. Then the gain of the MAX4107 stage is 10. The output resistor is 50 Ohms, which forms a divide by 2 with the input impedance of the spectrum analyzer and so the bump in the dark noise should only be 15 nV/rHz and not microVolts.

Quote:

[Rana, Alberto]

This evening we measured the noise spectrum of the reference cavity PD used in the FSS loop. From that we estimated the transimpedance and found that the PD is shot-noise limited. We also found a big AM oscillation in correspondence of the FSS modulation sideband which we later attenuated at least in part.

This plot shows the spectrum noise from the RF output of the photodetector.

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