[ntp:questions] Thunderbolt at NTP ref clock.

unruh unruh at invalid.ca
Thu Aug 1 19:55:15 UTC 2013

On 2013-08-01, DaveB <spam.goes at nowhere.com> wrote:
> In article <ktcujr$vpc$1 at dont-email.me>, david-
> taylor at blueyonder.co.uk.invalid says...
>> On 31/07/2013 20:36, DaveB wrote:
>> []
>> > The server is using 5 'net based servers at this time (my original GPS
>> > RX died) and is only just stable enough for what I'm doing.  Sometimes
>> > due to asymetric ping times, it "wanders a bit" for an hour or three.
>> []
>> > Oh...  Though the time server is FreeBSD based, other boxes in my empire
>> > are a mixture of Windows and Linux, various versions types and
>> > requirements.
>> >
>> > Cheers All.
>> >
>> > Dave. (G0WBX/G8KBV)
>> Dave,
>> A small GPS with PPS I can recommend to you is this one:
>>    http://www.adafruit.com/products/746
>> At least here, on the top floor of a two-storey house in Scotland, it 
>> gets enough signal to lock consistently.  Not too expensive, and 
>> available from a UK stockist.
>> http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/
>> A few hundred microseconds should be enough for your pulse, although 
>> GPSs tend to use either 100 ms or 200 ms by default.  Easier to see on a 
>> non-storage 'scope as well!  I'm pondering on making a driver and having 
>> a terminated line running around the shack here (at pseudo RS-232 
>> levels) for feeding PPS into all my PCs which have COM ports to get the 
>> best time synchronisation.  AT the moment, those PCs which aren't 
>> stratum-1 have the poll interval set to 32 seconds to the local 
>> stratum-1 servers.
>> I'm sure you know about the information on my site for FreeBSD, Windows 
>> and Linux, but others may not:
>>   http://www.satsignal.eu/ntp/index.html
> Yes, well aware of your wonderful resource pages.  And thanks for the 
> link to the adafruit site, I'd forgotten about them.
> I now have a new-old-stock GPS-16 (with unmolested full length lead and 
> original connector) should I need, but I may end up using that for 
> similar needs in a mobile setting, hence my interest in using the TB to 
> drive the shack NTP box.
> Took a look at the TB's PPS signal last night, & yes, 20ns duration, and 
> though it can be turned -ve (as in 0 to -5V) or off, the width can't be 
> changed.

nanoseconds? That could easily get washed out by inappropriate
termination or a cable with too high a load for the output drivers on
the trimble (ev, 50 ohm cable, would require a steady state current of
100mA which is a lot I suspect that the voltages getting through are
just too low to trigger the interrupt because of current saturation of
the output. 

> Too many toys, so little time. :)
> 73.
> Dave G0WBX/G8KBV.

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