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

[Jim Lux]

A decided "maybe"

Yes, the differential corrections can be used to estimate the ionospheric component (and if differential position over short distance, things like solid earth tides) all of which are important when it comes to getting "better than a meter".

If you have a dual frequency receiver *that* alone helps you with the ionospheric corrections (because the delay is frequency dependent).

But as for the actual 1pps output from the receiver?  That typically has other issues (e.g. it's synchronous with some internal clock, which may or may not be locked to the GPS time epoch).

On applications where time and position are important typically it's done with post processing.  For instance, the SunRISE payloads in space will process the raw observables (L1 and L2) through a precision orbit determination process (GIPSYx) which produces a pos-goa file for position (and uncertainty) and a tdp (time dependent parameter) file which gives clock bias and rate (and uncertainties) for the receiver's clock. 

Getting to sub-ns and sub-meter is certainly possible. 


 


On Sun, 27 Apr 2025 08:52:12 +0000, drew wollin via time-nuts <time-nuts at lists.febo.com> wrote:

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]
Introduction - SparkFun LG290P Quadband GNSS RTK Breakout Hookup Guide
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]
Geoscience Australia Portal
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.
portal.ga.gov.au

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