[time-nuts] Re: GNSS-disciplining a Ball FRS-C Rubidium Oscillator

[John Miller]

Great feedback, thanks guys!

John

> On Jan 16, 2023, at 10:59 PM, Francis Grosz via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi, John,
> 
>     Bob's suggestion is exactly on point, but if you have the right toys
> you can automate much of the process.  As Bob says, get a GPS/GNSS module
> that has a PPS output.  Then feed the 10 MHz from the Rb into one of TvB's
> picDIV chips to get a 1 PPS (more or less) by dividing the Rb output by 10
> million.  If you have a counter with the Time Interval function (e.g., HP
> 5334B), feed the two 1 PPS signals into that and it will output the time
> between the two pulses every second.  Then, if the counter has a GPIB (IEEE
> 488) interface, you can feed that into a computer and collect the data into
> a file for as long as you want and process it to get the frequency offset
> between the Rb and the GPS, and other statistics if you want that.  Doing
> it this way makes it easy to collect very long data sets and the resolution
> of the counter is more accurate than eyeballing a 'scope.  Anyway, it works
> for me.  Have fun!
> 
>                    Francis Grosz
> 
> -----------------------------------------------------------------------------
> Original Message:
> 
> Message: 2
> Date: Sat, 14 Jan 2023 19:47:14 -0500
> From: Bob  Camp <kb8tq at n1k.org>
> Subject: [time-nuts] Re: GNSS-disciplining a Ball FRS-C Rubidium
>        Oscillator
> To: Discussion of precise time and frequency measurement
>        <time-nuts at lists.febo.com>
> Message-ID: <69E2DAAB-2BF7-4FFC-9EA2-0400384FCCE9 at n1k.org>
> Content-Type: text/plain;       charset=utf-8
> 
> Hi
> 
> Turns out that getting one set on frequency is not as insane as you might
> think:
> 
> Grab a fairly cheap GPS module that puts out a PPS output.
> 
> Feed one channel of a scope with it ( or at least trigger the scope with
> it).
> 
> Watch the 10 MHz sine wave move relative to the trigger
> 
> You can (eventually) adjust the Rb to the point that the 10 MHz does not
> move.
> 
> Simple math:
> 
> The Rb is likely to already be within 1x10^-8 of the correct frequency.
> 
> If it’s that far off, it will move 1/10th of a cycle per second ( 10 MHz
> period is
> 100 NS and 10 ns would be 1x10^-8 ….).
> 
> Watch it for 10 seconds and you can be reasonably sure it’s within 1x10^-8
> 
> Watch for 100 seconds and you are pretty sure of 1x10^-9 ….
> 
> Since your GPS will have some jitter, things get exciting if you start to
> try to
> go below 1/10th of a cycle. This isn’t a process that you can speed up a
> lot.
> 
> At a bit over a day ( if you keep at it ) you get to 100,000 seconds and a
> cycle is
> going to be 1x10^-12. For most folks, that is into the “good enough” range.
> For
> the insane, you can keep at it for days / weeks / months. At the month
> level, the
> resolution of your adjustment pot will become a pretty big issue….. Yes,
> there are
> ways to attack that problem … :) :)
> 
> Bob
> 
>> On Jan 14, 2023, at 4:49 PM, John Miller via time-nuts <
> time-nuts at lists.febo.com> wrote:
>> 
>> Hello Everyone!
>> A while back, a friend of mine who knows I'm into this hobby found a Ball
> FRS-C RuXO at an electronics surplus shop local to him. It works great, and
> outputs 10MHz with as many zeros as the best frequency counterI have access
> to can measure. I don't really know what to do with it, but I have thought
> about building a system to discipline it with a GNSS receiver. Any
> recommendations, thoughts, etc.? I suspect this thing may be out of my
> scope and I should find a new home for it.
>> 
>> Here are photos of the unit:
> https://photos.millerjs.org/?f=Ball+Efratom+FRS-C
>> 
>> Thanks,
>> John
>> KC1QLN
>> _________
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