[time-nuts] GNSS Disciplined Clock
kb8tq at n1k.org
Sat May 27 19:39:58 EDT 2017
Second to second jitter *could* be another interpretation of the 15 ns. That would be a pretty
loose number. Modern stuff after sawtooth correction gets down to < 1 ns on that basis. Since it’s
a GPSDO, I would guess it’s under 1 ns (1x10^-9) at one second.
Correcting for timing bias to get back to UTC is an involved process. The “easy” way to do it
is to run a dual frequency receiver and run the RINEX data through post processing. That only helps
you for “past history”. It is the most common way to do it. The same dual frequency process also
takes care of the X,Y,Z stuff.
Bottom line - with a single frequency device, you don’t have a lot of options for eliminating the bias
> On May 27, 2017, at 2:56 PM, Ebrahim Roghanizad <e.roghanizad at gmail.com> wrote:
> Dear Bob
> As I understand from your response, 15 ns reflects the jitter, i.e. the
> time difference between successive PPSs is not exactly 1 second and its
> standard deviation (one sigma) is 15 ns. In that case, "precision" is more
> appropriate than "accuracy" to be used in the datasheet. Moreover, how do
> you infer horizontal and vertical position *accuracy*? As well, could you
> please guide me to find its timing bias with respect to GNSS/UTC?
> Thanks a lot
> On Thu, May 25, 2017 at 8:26 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>> I don’t speak for Trimble and their interpretation of all this may be a
>> bit unique. Normally
>> what the 15 ns means is the time out of a simulator compared to the 1 pps
>> out of the module.
>> Put another way, it’s just a measure of the receiver. It does not include
>> any ionosphere / troposphere
>> issues. It assumes a perfect estimate of the location (no bias from
>> antenna multipath). IT also
>> does not take into account any delay in the antenna or coax to the
>> antenna. Time errors between
>> Glonass and GPS are not included (bad broadcast offset estimate etc).
>> Finally there is the
>> fairly important qualifier of “one sigma” on the 15 ns number.
>> All that said, two devices with the same antennas, same cables, close to
>> each other, looking at the
>> same sats, using the same systems, … should track pretty well.
>>> On May 25, 2017, at 9:27 AM, Ebrahim Roghanizad <e.roghanizad at gmail.com>
>>> Dear members
>>> I am a new amateur member in your group. Maybe my question has been
>>> Recently I found Trimble Mini-T GG, whose data sheet is attached, as a
>>> GNSS disciplined time reference. I would like to know if there exists a
>>> more accurate one, since it does not employ dual frequencies to
>>> ionospheric delay, though it handles both GPS and GLONASS. Besides, could
>>> anyone guide me about the presented accuracy in the datasheet? There, it
>>> stated that "When operating in Over Determined Timing Mode, the accuracy
>>> pulse per second (PPS) is within 15 nanoseconds of GNSS/UTC." Does it
>>> that it includes both bias and the noise? In other words, is it true to
>>> that "The time-synchronization error between two of them with a long
>>> distance is less than 2*15 ns"?
>>> Best Regards
>>> <Trimble Mini-T GG.pdf>_______________________________________________
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