[ntp:questions] NTP absolute accuracy?
Todd Glassey
tglassey at earthlink.net
Mon Nov 2 17:33:33 UTC 2009
RedGrittyBrick wrote:
> Unruh wrote:
>
>> "David J Taylor" <david-taylor at blueyonder.not-this-bit.nor-this.co.uk.invalid> writes:
>>
>>
>>> At source, it's recently been within about 10 microseconds:
>>>
>> Sorry, at 10usec, the distance away of the transmitter must be less than 3 km.
>>
>
> At *source*, the distance to the transmitter must surely be a lot less
> than 3 km :-)
>
> According to the National Physics Laboratory "Every UTC second is marked
> by an 'off' preceded by at least 500 ms of carrier, and this second
> marker is transmitted with an accuracy better than ±1 ms." from which I
> conclude it's never going to to be more accurate than a few ms at
> *receiver*.
>
Yea - every TAI second is what they mean. UTC is a calculated value
which is published after the fact and sets the TOD at a particular
instant some 25 to 30 days previous. From that point onward until the
next UTC fixing per schedule T the time is measured in incremental TAI
seconds per the convention of the Meter's definition of the Second.
Todd
> Someone has compared a KHz radio time signal from DCF with the GHz radio
> time signals from GPS: http://www.hopf-time.com/en/dcf-gps.htm. I
> imagine MSF accuracy is similar to DCF.
>
>
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