[time-nuts] Re: Question about ADEV for tau < 1000s

[Bob Camp]

HI

Keep in mind that a “good” OCXO likely costs > $1K when new. Shopping on eBay at pennies on the dollar spoils all of us. 

A low ADEV at 1 second would be below 2x10^-13. That "very good" OCXO probably would cost you $5K or more, even on eBay. You might spend a couple years shopping for something like that. It probably would involve buying multiple candidates that don’t quite make the cut. 

Measurement wise, you would want something that comes in well below 1x10^-13 ADEV at 1 second. Something in the < 2x10^-14 would be the target. There are devices out there that do that sort of thing. I’d budget $20K for one of them. 

This is all based on your “lowest possible” criteria. If something less than best of the best is acceptable, then the budget changes. Buying a hundred $50 10811’s and sorting them all out should get you multiple candidates below 5x10^-13. The trick is to only buy ones that have not already been sorted by somebody else …

Fun !!!

Bob

> On Aug 16, 2024, at 5:00 PM, James Spottiswoode via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi Time-nuts Experts,
> 
> I’ve found the time-nuts archive to be incredibly useful over the last year - thank you all!  I have an unusual question.  
> 
> I’m interested in getting the lowest possible ADEV at tau’s ~< 1000s and am not concerned about longer term drifts.  The protocol I’m using is based on comparing phase or frequency between two 10 MHz frequency standards a few meters apart in the lab.   Currently I am comparing a pair of OSC5A2BO2 OXCOs using an Agilent 53230A running with a 1 sec gate time and using the undocumented RCON command.  I am seeing a short term ADEV of 3e-11 at tau = 100s. I would like to get an order of magnitude or more better than this if possible without breaking the bank!
> 
> From the research I’ve done it looks like high end OCXOs are the best bet for lowest ADEV but many are designed for high acceleration environments, which I do not need for static references. The best I’ve found so far is the Connor-Winfield OH320-LA.  Does anyone here have a better suggestion? Are double oven controlled oscillators a better way to go?
> 
> For frequency or phase comparisons between the pair of OCXOs an SDR looks like a better option than the 53230. This paper: "High-Precision Measurement of Sine and Pulse Reference Signals using Software-Defined Radio” which can be found here: https://arxiv.org/pdf/1803.01438 states in the abstract:   “… The measurement system is implemented and verified using the Universal Software Radio Peripheral (USRP) N210 by Ettus Research LLC. Applying standard 10MHz and 1PPS reference signals for testing, a measurement precision (standard deviation) of 0.36ps and 16.6 ps is obtained, respectively.”  This is considerably better than is achievable with the 53230A.
> 
> So I have two asks:  Advice on the lowest ADEV OCXO for tau < 1000s and your thoughts on the SDR based method described above for high precision phase measurements.
> 
> With many thanks in advance,
> 
> James
> 
> James Spottiswoode  KG6SMH
> 
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