[time-nuts] Re: Does cm accurate GPS via RTK give more accurate time?

[David Cureton]

Hi Drew, 
  As you probably aware the posittion accurace is largely dependent on time accuracy.  The largest error for domestic GPS recievers has been ionspheric variation in path from satellites to receiver as I understand.   The new crop of cm accurate GPS's achive this step up in accuracy by using a second L5 Band and with the two frequencies in use, the ionsespheric variation can largely be modeled and compensated for by the reciever.  Therefore you would also expect a similar step up in the performance of the timekeeping of these GPS's.   I did have a quick loook at the ZED-F9P from ublox and the datasheets were devoid of ANY characterisation of the TIMEPULSE signal accuracy.  However the receiver will also  be limited by the internal reference clocks  their timebase and the stability/phasen noise of the PLLs.  I think there is a version of the Ublox devices that you can actually provide the recever with a timebase that is much better that the tiny little TCXO that is on the devices.    


Look forward to hearing of your results. 


Regards,

David VK3DCU

----- Original Message -----
From: "drew wollin via time-nuts" <time-nuts at lists.febo.com>
To: "time-nuts" <time-nuts at lists.febo.com>
Cc: "drew wollin" <drew_wollin at hotmail.com>
Sent: Sunday, 27 April, 2025 6:52:12 PM
Subject: [time-nuts] Does cm accurate GPS via RTK give more accurate time?

Hi All

I have a long-term interest in GPS/GNSS for accurate position, frequency and time.

Conventional GNSS receivers are accurate to a few metres and about 10 nanoseconds.

The accuracy can be improved by using correction information via RTK over the internet. The receiver needs to be within about 20 km of an RTK base station. The RTK base stations are linked and available as government or private correction networks, some of which are free. See the link for the Australian RTK network.

The RTK corrections are based on local space weather and the ionosphere's effect on the received satellite signal.

It is relatively inexpensive and easy to use these networks to get cm accuracy positioning. U-blox and Quectel make RTK-capable receivers, which are available from SparkFun and AliExpress. The receiver boards from AliExpress cost around US$50.

The receivers can be used with software from the respective manufacturers

With centimetre position accuracy, presumably, time pulse accuracy also improves. Does anyone know if that is the case? I looked on the web without success

The Quectel LG290P has a 1 PPS output that could be connected to other timing equipment.

I have an SRS PRS10 GPSDO cesium clock with an early single-satellite GPS receiver. I was thinking of replacing it with a 1 PPS signal from an RTK-corrected LG290P.

The other question, of course, is how do I measure if the time is better?

Regards Drew VK4ZXI

https://portal.ga.gov.au/persona/pa

https://docs.sparkfun.com/SparkFun_LG290P_Quadband_GNSS_RTK_Breakout/print_view/
[https://docs.sparkfun.com/SparkFun_LG290P_Quadband_GNSS_RTK_Breakout/print_view/%22https://i.ytimg.com/vi/a-aU4-Yodzg/default.jpg%22]<https://docs.sparkfun.com/SparkFun_LG290P_Quadband_GNSS_RTK_Breakout/print_view/>
Introduction - SparkFun LG290P Quadband GNSS RTK Breakout Hookup Guide<https://docs.sparkfun.com/SparkFun_LG290P_Quadband_GNSS_RTK_Breakout/print_view/>
The SparkFun Quadband GNSS RTK Breakout - LG290P (Qwiic) features the Quectel LG290P GNSS module. The board's dimensions, pin layout, and connectors are exactly the same as our vary popular SparkFun GPS-RTK-SMA Breakout - ZED-F9P (Qwiic); and can be used as a drop-in replacement.The board also accommodates users with a diverse choice of interfaces including UART, SPI 1, and I 2 C 1.
docs.sparkfun.com

[https://nonprod.portal.ga.gov.au/cache/images/portal_ga.png]<https://portal.ga.gov.au/persona/pa>
Geoscience Australia Portal<https://portal.ga.gov.au/persona/pa>
This portal (Geoscience Australia Portal Core) provides full access to Geoscience Australia data and other publically available data sources as well as suite of analytical and multi-criteria assessment tools to maximise the value of the data. A series of personas have been created on the Geoscience Australia Portal Core technology to meet specific stakeholder and project requirements.
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