[ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"

unruh unruh at invalid.ca
Tue Jan 10 22:28:19 UTC 2012


On 2012-01-10, E-Mail Sent to this address will be added to the BlackLists <Null at BlackList.Anitech-Systems.invalid> wrote:
> unruh wrote:
>> David J Taylor wrote:
>>> "David Woolley" wrote:
>>> pulse over the length of line he talks about should be no
>>>  problem at all (but a microsecond-wide pulse might).
>>>  The timing PPS I've seen are in the tens of milliseconds wide.
>>>  If there is overshoot, perhaps a capacitor to ...
>>
>> Did you mean 10s of ns? The Sure width is about 5-10ns.
>>  at the card without any line attached.
>> The line could certainly broaden that up to about 1us, but ms?
>> Even the Garmin 18 is less than a usec.
>
> Really?  I must missed something.
>
> 20ms to 980ms for the Garmin 18 & 18x LVC PPS?
>
><http://static.garmincdn.com/pumac/GPS_18x_Tech_Specs.pdf>
><http://static.garmincdn.com/pumac/425_TechnicalSpecification.pdf>
>
> Perhaps you are talking about how close the rising or falling edge
>  is to the actual GPS second?   The Garmin 18 LVC says 1us for that.

No, I was talking about the width of the edge transition. Neither the
accuracy of that transition, nor the width of the pulse. the former one
cannot know unless one has another gps whose accuracy one knows, and the
latter is irrelevant to timekeeping. However the post I was replying to
almost certainly was talking about the width of the pulse, not the width
of the transition. Note that the gamin has a pulse width that is quite a
bit less than 1usec. What its accuracy is I do not know. 

>



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