Electronics > Metrology

Low phase noise 10Mhz refrence for the Lab

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Zenwizard:
I am looking to add a 10 Mhz reference for the lab I currently have a Leo Bodnar GPSDO in the lab and I love it, It has served me from some time. But my needs have continued to go and I need a sine wave output with low phase noise. I am going to be adding some spec and to the lab and need a reference that I can clock them with in the hopes to improve their performance and stability over the long run. From what I have been able to tell so far I am looking for a 10 Mhz oscillator that has both good close in phase noise and long term drift specs. But I have nothing in the lab currently that I can measure or quantify phase noise parameters nor access to a lab that would let me make some quick measurements so I cant at the moment build something and test it. Does anyone have experience with the Endrun Meridan II unit. The phase noise specs of the US-OCXO seem excellent. Even better then rubidium or is there something I am missing something?

https://endruntechnologies.com/products/time-frequency/low-phase-noise

Zen

tkamiya:
I've been down this road.

I don't know what your budget is like, but if it's going to be a typical hobby budget these things new will be well outside of it.  Also, the phase noise graph looks too good.  It's probably idealized graph meaning reality will be a bit different.  Before you go far in thinking process, it might be better to give them a call and get a rough price quote.

Typically, GPS or anything that pushs and pulls OCXO will have much worse phase noise than same OCXO without.  Some of us use OCXO based GPSDO and disconnect the GPS side to make measurement.

Zenwizard:
Thanks Tkamiya.

Where I am at the moment is I am at the beginning of a long path down the rabbit hole, and I am setting up the lab and trying to future proof it with in reason. I am been thinking about pulling the trigger on the SRS rubidium unit but I do not have yet a way to generate 1PPS output to lock it to the GPS in the lab. So in terms of price I know where the ball park is. To start and hope to generate the 1PPS signal I have ordered one of the Samsung modules that I am hoping to hook up to lady heather when on arrives on extended shipping time. But I might just use SRS as they are the known quality. In terms of budget rubidium is not out of reach, cesium beam yea… uh NOPE. But in learning I want my tools to be better then I am so when something is messed up I KNOW it is my fault and not the tools.

Zen

nctnico:
Be aware that the phase noise of a Rubidium clock is horrible short term. You'll need to put a so called 'cleanup oscillator' behind it to have a signal which has a low phase noise both short and long term. I second tkamiya's suggestion to use a GPSDO in holdover mode to have a clean 10MHz.

tkamiya:
I've actually tried that....

PRS-10 can follow a reference such as GPS by 1 pps and adjust itself.  It's handy for calibration purpose, but Adev measurement (stability) showed having PRS-10 alone is better than such combination by 10 fold.  I'd suggest you try it and see for yourself.  If nothing else, it's curious and interesting.

Rubidium's long term stability is such that training via GPS continuously make little sense.  As I understand it, making this work will take vast amount of knowledge and experience to a level someone who can design these things from scratch.  That is not me!  Instead, I have both as separate unit. 

I like PRS-10.  SRS has put 10 times the amount of rubidium in it that usual mode of failure, depleted Rb doesn't usually happen.  One thing to note that Adev has this weird hump around tau = 1 second mark. 

I know of several experts in this area.  They don't depend on one type of unit for their needs.  They do things like using OCXO alone for 100 seconds, and rest with Rb or Cs.  Take both graph and merge them. 

For my lab reference, I have both GPSDO and Rb, and they are switchable.  For measurement reference purpose, I have all of above.  After fighting with all these stuff for 3 years, I come to realize everything is a compromise.  I must accept something that is good enough.  It's far more important that my lab equipment are all based on the same clock.  For this, GPSDO is more than sufficient.  If I lose GPS, then switch over to Rb.  I calibrate Rb with GPS every 6 months.

Just get what you want and try it yourself.  If nothing else, it's fun.
 

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