[time-nuts] Designing an embedded precision GPS time server

Attila Kinali attila at kinali.ch
Fri Oct 27 21:13:37 UTC 2017

Hoi Leo,

On Fri, 27 Oct 2017 20:27:53 +0100
Leo Bodnar <leo at leobodnar.com> wrote:

> Last year I have designed an NTP server with sub-microsecond turnaround accuracy/jitter at fully saturated 100K+ packets/sec traffic (full 100Mb wire speed) that costs just £250 from stock.
> Its holdover performance on signal loss is in the order of 4-5ms/day.
> https://store.uputronics.com/index.php?route=product/product&path=60_70&product_id=92

Can you tell a little bit how your device looks like on the inside?
What do you use as microprocessor? What as GPS receiver? From the
hold-over spec, I would guess you are using a TCXO, which one is it?
What do you use to get the timing of the PPS pulse? Do you apply
saw-tooth correction?

> If you can come up with a cheaper and higher performance alternative I am
> very interested in licensing your design.

Getting better performance is not that difficult. Getting it cheaper is.
An OCXO (new, not from ebay) and a timing GPS receiver would already cost
something around 100-150€. That's one third to half of the cost of your
complete device already. Using an OCXO from ebay and you can do it quite
> When you come to testing I can highly recommend placing your prototypes in 
> public NTP pool and asking the admins to add it to .ch zone - you are 
> guaranteed to get full 110kpps traffic spikes that will help to flush out bugs.

Why specifically the .ch zone? IIRC you are located in the uk.

I am running an NTP server in the .ch pool and have not yet noticed
any large spikes. (ok, my monitoring is rather crude and if the spike
is very short lived, i wouldnt notice it)

			Attila Kinali

You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

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