[time-nuts] CSAC Project(was CSAC purchase)

Bob kb8tq kb8tq at n1k.org
Sun Jan 28 21:04:40 EST 2018


As mentioned multiple times in the archives. As you get into the single digit 
milliseconds, the human eye simply can’t keep up. A watch that is 1 ns off 
and one that is 1 ms off are both “good enough” if you are looking at it with a 
normal eyeball. 

From a design standpoint 1 ms / day / week is *way* different that 1 ns over the
same sort of period. Design constraints *do* make a big difference. It’s important
in any project to get them sorted early. 

If you are spending $5K on a CSAC, tossing in another $100 on a GPS isn’t 
going to even get into the roundoff error. You *will* need the GPS gizmo to 
keep the CSAC calibrated. It is only a question of how often the beast gets


> On Jan 28, 2018, at 7:45 PM, Ronald Held <ronaldheld at gmail.com> wrote:
> Bob:
> Right now I own nothing that outputs a GPS PPS. GPS watches I own do
> not have that option.   Maybe for infrequent resets, an independent
> GPS unit is better from a design and construction POV?
>                   Ronald
> Hi
> A GPS PPS output will (most likely) be more accurate than the CSAC
> each time you go back to dock with the charger. A GPS module to do
> everything you would ever want to do is a sub $100 sort of item. You
> would still need a bit of hardware to “glue” things together (but not a lot)
> and some code running on the MCU of your choice to supervise the process.
> Accuracy wise, a GPS PPS is *very* hard to beat.
> Bob
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