[time-nuts] Advantages of GNSS ???

[Bob kb8tq]

Hi

On the F9P you have the specific issue of L1 / L2 with older GPS satellites. The device
only does L2C. That cuts the “population” roughly in half. This is not a great thing for a 
“GPS only” setup with that device. 

BIPM does not directly control or feed timing into the various GNSS systems. They do 
use highly specialized gear to do time transfer. Some of that is via GNSS sats. What they
do is a bit different than what a typical timing user would do. 

Frequency of any GNSS output on the F9P is limited by the accuracy of the time pulse. 
Correction is only done once a second. The same “fraction of a nanosecond” sort of wobble
you see in time gets you a “fraction of a PPB” frequency wobble. You will need a local 
standard to discipline in order to do very well. A commercial GPSDO is one way to do this.
There are other approaches. 

Indeed this is just the first layer or two of the list of fun you are going to have :)

Bob


> On Jul 5, 2019, at 11:19 PM, Luiz Paulo Damaceno <luizpauloeletrico42 at gmail.com> wrote:
> 
> Hey Graham,
> 
> I'm gonna start a project soon to evaluate a F9P as a Time Transfer GNSS
> receiver. For now i haven't too much answers for you but only i know is:
> the BIPM uses all labs that participate from UTC to make corrections of
> GNSS satellites frequency, also for the TAI use. I think GNNS T&F is a good
> and reliable source for many projects. Here in my lab with Septentrio's
> Pola RX 3 Tr we have a very low Time Dilution Of Precision when the Glonass
> and all anothers becomes enabled, so our frequency if compared to all GNSS
> constallations is good, i think the same logic can be applied for frequency
> generation / distribution. What i want to say is: with more satellites of
> different constellations you can have a better end signal (more stable and
> reliable). Tests should be done. I hope can help more in the future.
> 
> Best regards,
> 
> Luiz
> 
> Em sex, 5 de jul de 2019 às 23:00, Graham / KE9H <ke9h.graham at gmail.com>
> escreveu:
> 
>> I have several questions for the group, since there are several members
>> that have been able to start evaluating the uBlox F9P and perhaps the F9T
>> GNSS receivers.
>> 
>> For the purposes of time and frequency determination, is there an advantage
>> to using the GNSS receivers, relative to just the US GPS?
>> 
>> It appears that a really good GPS (only) based GPSDO can get into the 1e-11
>> and perhaps the 1e-12 accuracy range.
>> 
>> Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou
>> (China), and plus Galileo (Europe), actually provide any improvement in
>> time/frequency accuracy?
>> 
>> Is that what the F9P actually does, or only some sub-combinations of the
>> above?
>> 
>> Down at that level of accuracy, do the four systems agree within 1 e-12,
>> anyway?
>> 
>> Is there any advantage to using the GNSS for time/frequency?
>> 
>> Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning
>> accuracy also improve time/frequency accuracy?
>> 
>> The underlying question I am trying to get at is: Will a GNSS based GPSDO
>> have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO?
>> 
>> Thanks,
>> --- Graham
>> 
>> ==
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.