Due to the Engineering F2F last week, the cross correlation phase noise meauserment was rescheduled for this week.  We measured the phase noise on the 3.125Mhz source located in the CER using the BluePhase 1000 Phase Noise Test System along with Rich Abbott's excellent notes on this measurement to hopefully nail this phase noise.  The first attempt is located in this ALOG 51551.

First step is to measure the mixer slope which I found to be 44.2mV out of the IFR at 100Hz bandwidth.

Second step is to lock the frequency sources to the signal under test and measure the UGF of the system at 100Hz bandwidth which I found to be 34Hz.

Next we measure the PSD using FFT cross correlation.

Finally we adjust the raw FFT with the transform based on the first two steps as follows:

Loop Factor Compensation = ABS((20*LOG10(SQRT(1+(UGF/F)^2))))dB

Mixer Slope = 20LOG10(Vpp/(0.02*PI()))dB

Preamp Gain = 60dB

SSB Correction Factor = 3dB

Transform = FFT + Loop Factor Compensation - Mixer Slope - Preamp Gain - SSB Correction

I have attached the plot which is using a locking bandwidth of of 100Hz.  After playing with the numbers I have found 10kHz locking bandwidth would give us an answer closer to the expected values from the notes.

Here is the link to the 3.125MHz Oscillator for reference:

https://dcc.ligo.org/DocDB/0140/T1700016/001/Wenzel_500_30576.pdf

Here is the link to Rich Abbott's application note for this measurement:

https://dcc.ligo.org/DocDB/0161/T1900434/003/iLigoVcoPhaseNoiseAnalysis_v3.pdf