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Message ID: 2357     Entry time: Mon Jun 17 18:05:20 2019
Author: anchal 
Type: DailyProgress 
Category: BEAT 
Subject: Moku Frequency Noise Measurement 

I thought, why not just measure Moku's own synthesized frequency output with itself. Attached plot shows the frequency noise measured this way. The measured noise is divided by the square root of 2 to get individual input referred noise of the phase meter.

Then I thought, maybe the phase noises in the synthesized frequency and phase noise of phase meter could be potentially canceling each other as they are coming through the same source. So I inserted a very long cable between output of Moku and it's phasemeter input so that the two things are time separated by at least 1 cycle of 27.34 MHz. I didn't want to open up and measure the length of these neatly packed SMA cables but they are surely more than 6.58 m (wavelength of 27.34 MHz in these cables) long together.


Conclusions:

  • I do not see any reason why this measurement would not be correct unless the correlation length of phase noise in time is really long and I need a cable which separates the input and output of Moku by many cycles of 27.34 MHz.
  • So under the above assumption, Moku's phasemeter input referred frequency noise is less than 1mHz/rtHz up to 4 kHz and is less than 0.1 mHz/rtHz up to ~250 Hz.
  • If these numbers are correct, we should be good to go with using Moku as our phasemeter instead of our clunky PLL.
Attachment 2: MokuSelfFreqNoiseAnalysis.pdf  36 kB  Uploaded Mon Jun 17 19:28:40 2019  | Hide | Hide all
MokuSelfFreqNoiseAnalysis.pdf
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