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

[James Spottiswoode]

Dear Brian,

As it turned out converting the nanoVNA to a tinyPFA was almost effortless.  The only slight hiccup was installing UNIX utility for loading the inlay correctly.  So I have recorded the noise floor of the system and am starting to compare phase of OXCOs.

One question to the group: When you output wrapped phase (logged) from the tinyPFA what are the Units?  Radians, degrees…?  Neither look right when I unlog the numbers. This matters for me as I have written all my own code (in R) for getting ADEV and MADEV and for logging the phase data.  As I mentioned have a very bad relationship with Windows particularly when it comes to using a cheap Windows 10 box for data logging.  I also want to log the phase data continuously as control data and a machine which reboots every few nights for updates is a PITA.  I have spent several hours googling and modifying Windoze settings to no avail.  Basically it behaves like a corporate machine which one can't control.  Off hobbyhorse :-)

73s James

> On Aug 19, 2024, at 2:19 PM, Brian Flynn via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Dear James,
> 
> I am new to this list but have been taking an interest in accurate frequency standards for my ham radio interests. I have just bought a Hugen NanoVNA-H4 from Zeenko on Aliexpress, for conversion to a TinyPFA. I was doing it on a Windoze system but the process went very smoothly for me. I hope that was of use.  I followed the instructions on:
> 
> https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.FW
> 
> and all went well.
> 
> I have various linux systems around the place but have a fairly catholic taste in operating systems but also understand your caution. ;-)
> 
> 73s
> 
> Brian GM8BJF
> 
> On 18/08/2024 18:00, James Spottiswoode via time-nuts wrote:
>> 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
>> Zoom:  https://us06web.zoom.us/j/5657505742?pwd=d1hQUzR5SE8yMXo3ZUliRGwva2RvQT09
>> 
>> 
>> 
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> Brian Flynn, 22A Biggiesknowe, Peebles, EH45 8HS. +44 (0)7969668147
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James Spottiswoode
Applied Mathematics & Statistics
310-270-6220
James.spottiswoode at gmail.com
Zoom:  https://us06web.zoom.us/j/5657505742?pwd=d1hQUzR5SE8yMXo3ZUliRGwva2RvQT09