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

[James Spottiswoode]

Erik,

Many thanks indeed for your comments.  I note that in the last link you sent:  https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Examples the instrument used is listed in the results is a tinyDMTD - is this the same device as the tinyPFA?   I happen to already have a nanoVNA-H4 so it looks like I can load the SW and convert it to a tinyPFA.  Are there any gotchas in this process?  I try to maintain a Windows free zone here :-) but it looks like dfu-util will run under BSD on a Mac which is my preferred OS. This may a quick and cheap way to get a Dual Mixer Time Difference going but I suspect that for publication purposes I’ll eventually have to get a N210.  

Many thanks - James


> On Aug 16, 2024, at 10:36 PM, Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Jim,
> 
> For accurate phase comparison without much effort and cost you may have a look at the tinyPFA : https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.HomePage
> An example of the expected performance when connected to Timelab: https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.TimeLab
> Some measurements use the name tinyDMTD instead of tinyPFA but its the same device.
> Here is are some examples measuring OCXO/DOCXO and Rb: https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Examples
> You can search this list for more info
> 
> Erik.
> 
> 
> On 16-8-2024 23:00, James Spottiswoode via time-nuts 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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James Spottiswoode
Applied Mathematics & Statistics
310-270-6220
James.spottiswoode at gmail.com
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