[ntp:questions] Loop Frequency and Offset

Richard B. Gilbert rgilbert88 at comcast.net
Mon Sep 26 21:39:09 UTC 2011


On 9/26/2011 9:41 AM, Miguel Gonçalves wrote:
> 2011/9/26 Dave Hart<hart at ntp.org>
>
>> 2011/9/25 Dave Hart<hart at ntp.org>:
>>> 2011/9/25 Miguel Gonçalves<mail at miguelgoncalves.com>:
>>>
>>>> tick# tail -10 /var/log/ntp/loopstats
>>>> 55829 66927.314 0.000011263 185.398 0.000000620 0.001452 4
>>>> 55829 66942.315 0.000011355 185.398 0.000000402 0.001358 4
>>>> 55829 66957.315 0.000010197 185.398 0.000001026 0.001270 4
>> Nice theory, Dave, but you overlooked that all those offsets are
>> within 500 usec of zero (in fact within +10 to +12 usec), which would
>> trigger the end of initial offset convergence and unclamping the
>> frequency compensation.
>>
>
> What is a typical offset of the loop without using special oscillators? Is
> less than 1 us achievable?
>

I don't believe that accuracy of 1 microsecond , or less, is obtainable 
without without installing a GPS Timing Receiver or an atomic clock of 
some sort.

Your chances of obtaining 1 microsecond accuracy using clocks on the 
internet is just about nil!  OTOH very few people actually need
microsecond accuracy for anything other than "bragging rights"!

Would you really care if you missed the first 75 microseconds of your 
favorite TV program?  I didn't think so!

The telephone companies, wired or wireless, rely on extremely precise 
timing.  Radio astronomers really care about nanoseconds.  I'm sure that 
a few others care about the nanoseconds.  Those who do need the 
nanoseconds generally have the specialized equipment and know how 
required.





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