M8P Rover change to 3D/DGNSS/FLOAT only for seconds but mostly stay in 3D/DGNSS

0 votes

Hi friends,

i have already read 5 "related questions", the most problem is receiving RTCM messages. 

i am using Wifi to transport RTCM messages via TCP. (str2str application) as follow screenshot 


through Message-UBX-RXM-RTCM(RTCM input status) i can see the RTCM messages have been received by Rover 

But beyond that, I have made a aluminum-plate for Base Antenna and put both station on the empty ground under a good weather condition.

what could be wrong?

thanks in advance! 

update   05/04/2018 



detail for Message-UBX-RXM



Base Survey-in successfully finished


but through Message-RTCM3, RTCM3 messages can not be seen.




by Ya-SA asked Apr 3
by Ya-SA edited Apr 5
+1 vote
I assume you are using NEO-M8P.

Check that all required messages (per datasheet) are being sent.

Check that there is no interruption in correction flow.

Make sure you are testing under unobstructed view (no trees, buildings above 10 deg elevation).

Make sure you have latest FW (from u-blox website).

If you have C94-M8P then use included radio link to send correction data from one C94 to the other to see if performance is better.  If C94 approach works correctly then the issue with your correction data or transport mechanism.
by grumpy answered Apr 3
thanks for your answer!

1. exactly as you said, I am using two NEO-M8P (Tiny RTK module) with two BeagleboneBlack board.

2. through UBX-RXM-RTCM i can only see 1005, 1077,1087,1127. Does hier message 1130  matters?

3. in correction flow i did not find any interruption. or can you give me some advice how can i check that?

4. i tested under unobstructed view, but got the same problem

5.i have update the latest FW : u-blox M8 Flash Firmware 3.01 HPG 1.40

6. i don't have C94
+1 vote
The images are unreadable, u-Blox shrinks/sizes them, please host on an external site and link to them

I think I see an * in front of the messages, which means whatever you are sending is "unsupported"
by clive1 answered Apr 3
thank you clive1 !
1. sorry for the images, i will try to make it readable.
2.indeed there is an * in front of the messages, so I tried another place, which has less trees. And this time * disappear.
Hi clive1, I have updated my questions.  I've been stuck with this problem for a long time, please help me. thx
For GLONASS you want 1230, and you also need 1005 to provide antenna location. Both these could probably suffice with a 0.1 Hz period. With clean data you should be able to get to RTK FIXED in 7-10 mins.
I'd drop BEIDOU. I'd enable UBX-NAV-PVT
Do a reasonable survey, 2.5m is not that, shoot for 0.5m. Getting 30 mins of raw measurements and post-processing should give you an indication if you have workable data, and a position good to a few cm.
according your advice I did survey again, 0.5m and observation time 1800s.
measurement Frequency for base 1Hz, for Rover 2Hz.
still can not get to Float and Fixed.
In Rover Message-RXM-RTCM3 still Message 1230 can not be received.in base I already enable message 1230. My questions are:
1. should I set both base and rover Measurement Frequency 0.1Hz?
2.what is the reason that i can not receive Message 1230?
1) No, the 0.1 Hz selection refers to messages with static content, ie 1005 and 1230, where the transmission serves only to eat radio bandwidth, but are needed when a new remote node comes on-line. Only the Base transmits RTCM3, the rover merely receives and acts upon that data, effectively solving for position twice.

2) Don't know, the Base is not transmitting it, or it is getting lost on the radio link? You'd need to observed the data at the Base's NEO-M8P UART TX pin.

You could also try with a simplified GPS ONLY configurations, using UBX-CFG-GNSS and only 1005 and 1077 messages.
Is receiving Message 1230 a prerequisite for entering Float/fix mode?