[RTK] Localization problem as soon as RTK is fixed

[BRNKR]

Hey @Stifael @bkueng
i need a better and stable localization. that's the reason why i jumped from this issue #12105 to RTK.

I have a Drotek TinyRTK Module on my UAV connected to GPS port (has no magnetometer). I have a second normal NEO 8 GPS Module connected to Telem2 and the Magnetometer to I2C. GPS2 is deactivated (i want the magnetometer). I am getting a good normal gps reception. while moving around by hand i see the movement in QGroundcontrol.

I have also a TinyRTK connected to QGroundcontrol which sends RTCM to my UAV. When my UAV is on RTK (float) i can see the movement in QGC. BUT! When it goes to RTK (fix) then nothing happens.

here the log:
1st movement -> just gps
2nd movement -> rtk (float)
3nd "movement" -> rtk (fix)
https://review.px4.io/plot_app?plots=pid_analysis&log=ee5e58a5-2662-441f-9143-c3b348291b9b

i dont know if it is related to this issue:
#11716

[bkueng]

The log shows it never goes into fixed RTK mode, but falls out of RTK for the 3rd movement.
What link do you use for the RTCM data?

[BRNKR]

jep. that is what i have seen today. it goes from 3D RTK (float) to 3D DGPS Lock.
HDOP and VDOP jump from under 1.0 to 100.0

i am using some Hobbyking 915mhz telemetry modules. and i send RTCM over Qgroundcontrol (the autoconf way). Do the PX4 stack and QGroundControl setup the RTK modules correct from every actual config?

[bkueng]

There can be several reasons for dropping out of RTK mode:

• the telemetry bandwidth is too low / link quality decreases when moving. You can monitor gps status to check that the RTCM injection rate stays stable.
• GPS signal is quality is low. You might get RTK when holding still, but as you move you lose it (I've seen this before)

Do the PX4 stack and QGroundControl setup the RTK modules correct from every actual config?

Yes

[BRNKR]

found the problem. it was a faulty cable with loose contact on plug side. strange because it was a retail cable and is looking fine. i think the RX on GPS side was loose and hasnt get the RTCM messages and config.