[ntp:questions] GPS_NEMA, but high offset and jitter?

David Lord snews at lordynet.org
Mon Mar 1 10:46:06 UTC 2010


unruh wrote:
> On 2010-03-01, Kelsey Cummings <kgc at microshaft.org> wrote:
>> David J Taylor wrote:
>> ...
>>> I would knock something up if there were enough interest, but it would
>>> be a Windows program so of limited interest to the OP.
>> That's the idea anyway.  At the time, I was convinced the PPS signal was
>> showing clearly and it was but with the led transistor in backwards the
>> PPS line was getting pulled down to 1.4v or thereabouts.  Not enough for
> 
> Hard to know how it would do that. 

Transistor inserted with reversed C/E have low Vce breakdown,
very low gain and possibly higher Vce_sat. They still operate
as transistors and long time ago I've used in that mode but I
can't remember what that was for (not so long after red spot
or white spot transistors were sold in a box of one which cost
a quid = eight weeks pocket money).

David


> 
>> the serial port to register it.  It would have been useful to have
>> something that just watched for the DCD pulse rather than trying to
>> figure out what nptd was or was not seeing.
>>
>> With that fixed, everything synced right up.  Seems reasonably stable
>> with jitter at 4ms and offset fluctuating from -4ms to 4ms.  More than
>> good enough for our needs.
> 
> 4ms??? PPS from GPS should be 4usec, a thousand times better! (Or was
> that what you meant). 
> You could set up whatever was reading the pps to record to syslog every
> time it received a pulse. 
> 
>> -K




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