[time-nuts] Frequency Ensemble

[Bob kb8tq]

Hi

You can access an “NTRIP stream” from various free sites. There is some 
mumbo jumbo on some of them to get an account. There are streams dedicated
to “clock and orbit correction”. CLK11 and CLK93 are two fairly common ones.

Since NTRIP is a real time product (as in < 30 seconds delay) it can be used for 
“right now” sort of correction. RTKLIB is probably the most common way to get
the local receiver and an NTRIP stream combined. 

If you just want to play with it ntrip.itsware.net <http://ntrip.itsware.net/> port 2101 is a free / no registration source
of the CLK11 stream. They also have various other “correction product” streams
you can play with. 

In theory (though I can in no way prove it yet) you should be able to reduce the 
timing errors associated with the broadcast clock and orbit estimates by about an order
of magnitude. It is *abundantly* unclear what that translates into in nanoseconds due
to a whole lot of layers everything goes through….. 

The NTRIP products are all aimed at surveying applications so there is a lot of translation 
involved to get to the sort of time numbers we like to deal with. It should help, the big
question is how much (10 is unlikely …. sqrt(10) maybe …. sqrt(10) / 2 … who knows ….). 

Bob

> On Mar 18, 2019, at 1:32 PM, Anders Wallin <anders.e.e.wallin at gmail.com> wrote:
> 
> If you search for "GNSS time transfer" you will find a lot of papers etc.
> For example these might get you started:
> https://www.bipm.org/ws/CCTF/TAI_TRAINING/Allowed/Fundamentals/Training-2012-GNSS-Defraigne.pdf
> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7909843
> 
> I tried to collect some tools for PPP post-processing on github:
> https://github.com/aewallin/ppp-tools
> I am not sure what (open) software exists for common-view analysis...
> PPP uses satellite clock-corrections and orbit-corrections from an IGS
> data-centre. They have "ultra rapid" and "rapid" products (=downloadable
> files) that are available with some days or hours of delay.
> The "final" products can have up to two weeks (?) of delay.
> With a dual-frequency receiver the ionosphere delay can be removed
> ('ionosphere-free L1/L2 linear combination') and my understanding is the
> troposphere-delay (water content) is one of the larger remaining
> uncertainties.
> 
> AW
> 
> 
> On Mon, Mar 18, 2019 at 5:03 PM Rodger via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> 
>> Regarding your comments on collecting raw time data from GPS and post
>> processing it.  Can you provide any reference info, links, etc. with more
>> detail on that topic?
>> Clearly I'd need a GPS that outputs the proper raw messaging and the
>> software for processing it.  I'm somewhat familiar with the techniques
>> involved to improve GPS position data, but hadn't thought about it as much
>> for timing.
>> 
>> Thanks,
>> 
>> Rodger
>> 
>> 
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