TinyRTK: no FIX solution, only FLOAT availalbe


we have major problems getting a RTK FIX with the TinyRTK Modules. Here our Setup:

Working properly, survey in and “successfully finised”. 7 GPS satellites, 6 GLONASS satellites
db looking good, no flucutations, very stable.
PDOP < 1.2
Antenna: aktiv
Radio 433Mhz

same satellites as in Base available. (20m away from base)
Antenna: Helix L1/L2 aktive, db strength constantly at good values
Receiving RTCM data via radio, after a few seconds, Rover switches into 3D/DGNSS/FLOAT
Waiting, waiting, waiting - but no attempt to switch in FIX mode.

What I did so far:

  • test to disable SBAS satellites (there are issues if you use Neo-8P in PPK mode)
  • checking configuration of Base and Rover in U-center (twice)
  • checking RTCM messages
  • checking STATUS and SVINFO messages in UCenter-> messageview>UBX>NAV … seem ok, GPS satellites are used for correction.

Please, any ideas or a solution for the problem? Thank you, regards

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Did you update the M8P firmware to latest version as Ublox suggest ?

Yes, updated both (rover and base) with latest *.bin files: u-blox M8 Flash Firmware 3.01 HPG 1.30


  • Can you provide roughly Signal to Noise Ratios for base and rover?
  • Do you have another RF equipment nearby?
  • Are you using a ground plane? (I think the Helix antennas do not need any ground plane, but at least for the base)
  • What antenna are you using for the base?

Hello Kevin,

enclosed a screenshot for SNR levels of Base. Rover looking similar.
We do not use any RF equipment nearby, furthermore the 433MHZ radio is shielded with coper to reduce influence on reception.
Yes we use a ground plane on base, ca. 8x8cm. rover not, as for Helix antenna there is no need for.
We use the TW2405 from Tallysman for base, but tried others (TW3710 as far as I remember)

Thank you, regards! Hans

SNR looks good, although you should see more satellites.

  • Have you tried with using on rover an antenna similar to base’s one?
  • What is the maximum observation time you have conducted? (If ephemeris are not present inside the module, you can wait up to 12 min before they are)
  • What does deviation map look like when you have Float solution?

Hello Kevin,

  • I’ve tried several types of antennas (even survey antennas) but none of them gave me good results.
  • The number of satellites will not increase in Austria, as mountain ridges are too high. But: I have tested the ImageVector close to Munich last Week, with same (FLOAT only) result.
  • I build a complete new set with new TinyRTK modules (same settings) and after 40min of observation I got a FIX for 5 min+. But as soon as I moved the Rover (antenna still in perfect receipt conditions) the mode switched back to FLOAT and didn’t get back to FIX.
  • Now something strange: I disconnected the radio power supply from Rover and reconnected the radio again. After a few minutes, the FIX was there again. (Tested 2 times!) Nevertheless, as soon as I move the Rover a few meters, FLOAT was again the only solution.
  • Deviation map looks realistic in FLOAT mode. Approx. 40cm movement.

Thank you for your kind assistance!
regards, Hans

1 Like

Interesting! Some further questions :

  • how is your telemetry antenna placed in relation to your GPS antenna?
  • how powerful are your 433 MHz radios?

Interesting, indeed.

  • at the Base, the telemetry antenna is placed ~ 8cm away from the GNSS antenna an the radio itself is shielded with copper. Already thought that there might be scattered and second radiation on telemetry and therefore tried to put it 50cm away. But no improvement on the behavior of the system or even on SNR.
  • at rover side, the telemetry is more than 1 meter away from the Helix antenna - so I guess no bad influences.
  • for all the testing, we run the radios with 10mW or less.

thx, regards, Hans

Hello Hans,

u-blox has released a new firmware for the M8P, have you tried it by chance?

Hello Kevin,
I already tried it, but with the same behavior as before. My expectations were not that high for this firmware upgrade, as it mainly (only) is for a moving base setup.

In the meanwhile, we enhanced our Datalogger (from our ImageVector Product) to use the TinyRTK in PPK mode :slight_smile: … working perfect.
It’s an upgrade from our existing datalogger, so we can record any kind of data from the ublox chip, any trigger information, combine it with IMU data and, and and… :slight_smile:

But RTK improvement is still on our to to list… So if you, or anyone has any suggestion, I would be glad.

regards, Hans

Great, I’ll keep you posted if we have something new.

Hello Hans
I tried some solutions but I still cannot use tiny RTK in PPK mode.

Could you please explain us how do you use tiny RTK in PPK mode if you don’t mind?

Thanks in advance for helping us out


Hi Dan,

1st, you have to set the UBX messages to be outputted. This can be done using u-center > Configuration > Messages > RAWX, ???X , ???X to be turned on at UART and USB.

2nd: you need a kind of logger (an external for UART or a PC for USB). For PC, start u-center, an press the record button. This will create an *.ubx file from the datastream derived from TinyRTK. If you need a UART GNSS Logger, contact me. Our company REDcatch is producing one and will shortly ship them.

3rd: You need step 2 at both, Rover and Base. So two *.ubx files at the same time period + 12minutes

4th: Use RTKconv.exe from RTKlib to convert *.ubx to rinex *.obs

5th: Use RTKpost.exe from RTKlib to postprocess the Rover positions with the one from the Base. (Use Kinematic mode, and “Fix and Hold” on both, GPS and GLONASS.)

6th: Eventually you have Trigger events, from UAV? You also have to geotag the images… For this, we will provide a software with the logger mentioned above.

Everything a bit tricky, but working very well. Keep us up to date, if you are able to manage the steps in this short guide.

best regards,

Hello Hans

Thanks a lot for your answer. I do know why I didn’t see it before !

Please send me more information about your REDcatch logger, we are interested.

best regards