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How an Atomic Clock Really Works, Zeeman Alignment
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BrianHG:

--- Quote from: ejeffrey on December 02, 2022, 07:35:39 pm ---I was able to measure this.

Yellow: This is from a SRS FS725 that warmed up for ~10 minutes before starting the test.  The locked light was on, but it might improve stability if it is on for a few hours/days.  It is also coming from a distribution amplifier that doesn't have the cleanest waveform

Green: this is from a separate SRS FS725 that has been powered up for probably a few weeks.  The output is taken directly from one of the instruments 10 MHz output.

There is no perceptible drift or jitter, the waveforms look completely stable on the scope.  I took two photos 8 minutes apart to show the slow drift: In that time, the green trace has slewed approximately 30 ns, or about 62 ppt.  That is well within spec, the accuracy at shipment is supposed to be +/- 50 ppt, and aging increases that further.

Since there is some definite offset, I don't think there can be injection locking, this is the real stability.  I will try again after the first source warms up for a few hours.

--- End quote ---

Thank you ejeffrey.  At least now I know my claim of the Rubidium VS the properly aligned Cesium don't even come close to comparison.  They're truly in 2 completely different worlds.  (@36 minutes in the video.)

The video I pasted by CuriousMarc shows us there is a lot more involved in attaining the true Cesium precision via the 'Zeeman Alignment' and how to extrapolate a 5MHz reference from it.  Those 20 minutes of a dead perfect cross alignment between the Cesium clocks, the second one turned on and aligned separately, all together shows how difficult and still amazingly unbelievable how 2 free running oscillator references can achieve such a perfect reference of time.
ejeffrey:
I came back a few hours later and the frequency difference  between the two had stabilized at very close to 5 ns/ minute.  The stability is considerably better than that and they could be recallibrated for better accuracy but it's nothing like a cesium clock.
BrianHG:
Here is the Cesium difference after 20 minutes: (*seen at 36min in the video)



It looks to be 1/5 of a horizontal time base.
Now, if I could only make out the H-time base dial setting on the scope and H-zoom settings shown a minute later in the video.  The we could calculate the ppt drift.
BrianHG:
Here are the 2 images separate...
The second trace slanted like this: ' \ ' has moved ever so slightly to the right after 20 minutes.


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