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Entry  Thu Mar 4 19:44:08 2010, Tara Chalermsongsak, Laser, RC noise, Noise from VCO Noise20100304.jpg
    Reply  Fri Mar 5 00:34:09 2010, Frank, Laser, RC noise, Noise from VCO 
       Reply  Fri Mar 5 14:40:21 2010, Frank, Laser, RC noise, Noise from VCO irf2023_@80Mhz.png
Message ID: 87     Entry time: Fri Mar 5 00:34:09 2010     In reply to: 86     Reply to this: 88
Author: Frank 
Type: Laser 
Category: RC noise 
Subject: Noise from VCO 

Quote:

VCO frequency noise is measured. V input is 4.7 Volt. The signal output from the VCO (which controls the AOM) is mixed with signal from ifr2023 at ~80MHz. The demodulated signal

is then fed to SR560. Gain setting is 5 x10^3, low pass at 1Hz. The output signal is split into two. One is sent back to ifr2023 for freq modulation, another one is fed to the spectrum analyzer. The voltage output is

then converted to frequency by calibration from last week (0.714 MHz/V).

The plot shows frequncy noise from:

1: function generator (ifr2023) in brown

2: VCO,  in pink

3&4 Frank's RC noise data from FEB09, in red and blue

5:  RCnoise from beat measurment, in green

6: estimated noise

 

VCO seems to limit our noise at f=100Hz and higher/

 you have to measure a new calibration coeff. If you change the center frequency of the marconi the maximum FM modulation range changes too and so the coeff. If i remember right your range was 500kHz compared to 1Mhz last week, right? So it should change about a factor of 2 or so, so the actual measured noise is a little bit less but nevertheless much to high

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