[ntp:questions] Frequency Offset

David Lord snews at lordynet.org
Fri Feb 24 21:23:30 UTC 2012

unruh wrote:
> On 2012-02-24, David Lord <snews at lordynet.org> wrote:
>> unruh wrote:
>>> On 2012-02-23, Alby VA <albyva at empire.org> wrote:
>>>> On Feb 23, 4:29?pm, unruh <un... at invalid.ca> wrote:
>>>>> No, that is a very typical figure for the frequency offset. Remember
>>>>> that the crystals used to control the timing in computers are not
>>>>> supposed to be terribly accurate. (They are chosen to be cheap, not
>>>>> great).
>>>>> It is because such frequency offsets exist that ntp was invented to
>>>>> correct.
>>>>   When you say "crystals used to control the timing in computers",
>>>> are you referring to the parts that make up my actual FreeBSD
>>>> Server (ie: Motherboard)?  Or Parts in the GPS Device (ie: Sure Elec.
>>>> GPS)?
>>> On your motherboard. 
>>>> Or in the Satellites receiving the GPS signal?
>>>>  I'm just trying to gauge, what hardware should be looking to obtain
>>>> to
>>>> improve that frequency offset. Or is it a moot point unless I'm going
>>>> to
>>>> invest in some high dollar atomic clock?
>>> An atomic clock.
>>>>  Or better yet, can I buy quality crystals from DigiKey and do some
>>>> soldering in whatever devices that need crystal upgrading?
>>> No.
>>> And why do you care? As I said this is waht ntp was invented for. It is
>>> doing its job. 
>> When I started using ntpd it didn't work with some of my
>> systems as the clocks were too far out, >> 50ppm, and/or
> Do you mean >500PPM? 
> If you were running linux, you could use the adjtimex program and the -t
> or --tick adjustment to change the tick value of your system clock. 
> each value of 1 adjustment speeds up or slows down the clock by about 100PPM. 
> You can use that to get the clock within the +- 500PPM range that ntpd
> can adjust. chrony uses it automatically. 
>> too temperature sensitive. Some of my motherboards had a
>> 3-pin jumper already fitted so that an external clock
>> source could be connected.
> Temperature sensitivity is usually in the "less than 1PPM per degree C"
> so you would have had to be expriencing quite a heat wave (500 degrees
> C) to have temperture be a factor. I suspect other things might have
> been more urgent worries then.

If you're correct there is a charred cinder replying.


>> One of my desktop systems, p4-2667, has just taken two
>> days to get to an offset of under 2 ms after a kernel
> ntpd is slow, but not that slow. Since for greater than 128ms offset it
> does a step, and since it fixes things by about 1/2 per hour, half a day
> is more like it to get it down to microsecond, not millisecond ranges.
>> change. I suspect because that coincided with the hottest
>> day in February since 1998. All my pcs were affected
>> except the one connected to PPS from a Sure GPS. The one
>> with an MSF source, no PPS, was also fighting to keep sync.
> It sounds to me like network problems and ntp server problems were
> playing a role. 
>> David
>>> Note that even all of the time standard labs around the world use
>>> programs like ntp to track their frequency offsets.
>>> And all atomic clocks have them.

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