[time-nuts] u-blox LEAH M8F

[Bob Camp]

Hi

There are a couple of issues in multi GNSS timing. One is the basic time offset 
between systems (maybe a few ns, maybe a lot more). The next is the accuracy
of the estimate of that offset (again maybe a few ns, maybe …). After that you 
get into things like survey accuracy. Position hold is a single fixed location that
gets applied to all systems. If the “right”survey is here for this system and there
for that system, there will be an error one way or the other. Do they agree to CM or M
or 10’s of M? Some places they agree very well. Other places not so much ….

Lots of messy details.

Bob


> On Dec 22, 2016, at 12:23 PM, Scott Stobbe <scott.j.stobbe at gmail.com> wrote:
> 
> There was an interesting comment in the Lea-m8f datasheet,
> "In strong signal clear-sky applications the best time pulse consistency
> between neighbouring receivers is
> achieved when using a single GNSS because of the small time offsets between
> different GNSS systems. "
> 
> 
> On Thu, Dec 22, 2016 at 8:01 AM John Haine <john.haine at haine-online.net>
> wrote:
> 
>> I was slightly imprecise in my previous posting about ubx timing modules
>> 
>> and a few people have raised queries in the list or by email.
>> 
>> 
>> 
>> What I should have said is that this module is designed as a precise
>> 
>> low-noise /frequency /reference so it directly generates the 30.72 MHz
>> 
>> needed in LTE infrastructure from a GPS disciplined VCTCXO.  As I
>> 
>> understand it, the usual 10 MHz output is digitally generated and
>> 
>> jitters, so can't be used as a reference in high performance radio
>> 
>> systems.  One could use a phase-locked synth to multiply up from the 1
>> 
>> PPS signal but given the large ratio needed this is prone to generating
>> 
>> its own noise.  The M8F does it all internally and is therefore
>> 
>> preferred if what you want is a low noise frequency reference, though
>> 
>> its frequency may not be ideal if for example you wanted 10 MHz - you
>> 
>> could get 10.24 MHz by dividing by 3 but 10 MHz is trickier.
>> 
>> 
>> 
>> --
>> 
>> John Haine
>> 
>> 9 Parkway
>> 
>> Shudy Camps
>> 
>> Cambridge
>> 
>> CB21 4RQ
>> 
>> 
>> 
>> 01799 584773 (T)
>> 
>> 07841 322831 (M)
>> 
>> 
>> 
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