[ntp:questions] NTP+ NMEA +GPS +PPS

David Taylor david-taylor at blueyonder.co.uk.invalid
Mon Aug 25 05:43:55 UTC 2014


On 24/08/2014 19:22, Brian Inglis wrote:
[]
> PPS pulse duration is not really any concern - at 115k2bps a bit is only
> 9us wide
> and sampling at 16x bit rate a pulse is only .5us.
> The slew rate limit of 30V/us is the issue for detecting transistions.
> For a typical 3V TTL signal that should take more than 100ns to be
> detectable,
> for 5V 166ns.
> Some high quality timing devices like Trimble Thunderbolts provide very
> short,
> accurate, and precise pulses suitable for locking 10MHz frequency
> standards to
> the UTC second.
> There are solutions like TAPR Fat-PPS to slow down and stretch these pulses
> to be usable with standard computer interfaces instead of RF electronics.

It is indeed the devices you mention which can cause problems, and then 
require fixes such as the add-on you mention.  In this case, as the 
pulse can be seen by the Serial Port LEDs program, they are certainly 
long enough for NTP running on Windows using the serialpps.sys solution.

-- 
Cheers,
David
Web: http://www.satsignal.eu



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