Nokia E71 + Qstarz BT-Q818X: non-consistent datalog frequency

Hello from Greece!

I use racechrono for the last two years, and I never had any problems. Since I upgraded to RC 1.43, I experience major problems with the datalog frequency and accuracy. Despite the fact that I set the receiver to 5Hz, the data looks like it was logged at 1Hz. Specificly, the traveled route line appears very harsh, and the logged channel curves are very spiky. The problem is not appearing every time. For example, the first session can be logged normally, and the problem can appear at the very next session.

This characteristic NMEA file is from 3 sessions, where the first two seem to be logged normally, and the problem appears in the third session:
And the corresponding vbo file. If you open this file with performancetools, you will be able to see the obviousdifference between the laps of the first two sessions, and the laps of the third session:

I wonder if there is a correlation with the problem reported here: Maybe, setting the GPS baud rate manually will solve the problem. Has anyone else experienced the same problems? Any help will be appreciated.


  • Did you change anything on the configuration? Is the GPS and phone attached similar as before? Is the GPS fully charged? Has something changed on the vehicle (new interference)?
  • Everything is the same, the GPS and the phone is always attached in the exact same position, and the GPS receiver is always charged before the trackday. The vehicle is also the same.
  • The problems seems quite odd to me, as you say it does not happen always. Maybe the GPS receiver has broken somehow, and cannot work reliably anymore.
  • Hello papdoc. I cheched the data from your vbo file. The frequency of your gps receiver is quite well fixed on 5HZ. I also compared each laps using RaceChrono graphs. It is quite evident that during the first two sessions the GPS receiver was able to send more precise data to RC. In fact, even if the 3D precision, the coordinate precision and the number of fixed satellites are quite similar among the three sessions, during the first two sessions these values look more stable than over the third session. The final results is a more precise tracking during the first two sessions. I placed the start/finish line on the straight portion of track in front of the pit and I noticed that during the first two sessions about all the laps start and finish in very close positions. On the third sessions, most laps start and finish on very different position. Finally, the path tracked during the 3rd session seems evenly out of phase compared to the average path of the 1st and 2nd sessions. In my opinion, it seems that the precision of your GPS receiver changed during the day. It could be caused by the satellites positions (which affect the value and stability of the DOP) and/or by some interferences. I have a BT-Q818XT GPS receiver (10HZ) and I noticed that many factors interfere with the quality of the received signal. I know that you have not changed anything on your equipment but I suggest you to carry out a test, putting the GPS receiver in a safe seat out of the car cab, as far as possible from the engine and with the upper surface of the receiver fully open to the sky (no cover, so find a safe way to fix the receiver to the seat avoiding its detachment during the run). I experienced very good results with a similar solution. Bye
  • edited August 2011
    Aol, thank you for your answers, and also I thank vinpippo for his effort ! I will buy a new GPS receiver, and I hope that this will solve the problems.
  • Hello again!
    The problem appeared again! :(
    Me and a friend bought two new BT-Q818XT receivers, and raced on 10/11-12-2011 for the last Greek Track Club Championship race of the year. The problem appeared on both of us, on different time periods. My friend had problems on Saturday's free practice, and I had problems the next day during my second race run.
    My conclusions are:
    1. It doesn't seem to be hardware related, since it happened on two different setups (Nokia E71 and Nokia N-something phones), both with brand new receivers.
    2. It doesn't seem to be satellite related, since I was right behind my friend when his data got messed up, and my data was correct.
    3. The OBDII data on my setup were recorded correctly during the problematic run, and were usable ( see the second part of the onboard video )
    Any help will be appreciated! :)
  • Hello papdoc. On the video it is clear that just ODBII data were available. Did RC record any gps data during the race? It is not clear if the data collected when the system was not working were inconsistent (for instance when the route is not well drawn) or if RC did not recorded any gps data during the run.
  • Hello vinpippo and Happy New Year!
    Yes GPS data were recorded, but they were inconsistent so I didn't used them on the video. With Trackvision I can choose which data to use, so I left the crappy GPS data out.
  • aolaol
    edited January 2012
    Have you tried without OBD-II, if it the GPS works better? Also I've noticed the XT receiver works much better when the 1/10 Hz switch is in 1 Hz. (Don't worry RaceChrono will use it in 5 Hz when the switch is 1 Hz).
  • Hi aol!
    No I haven't tried it, because if I wanted GPS only Data, I have a PerformanceBox rusting in my closet.
    I would like to downgrade and test RaceChrono v.1.30 again, because I strongly believe that this is a software problem. With 1.30 I have NEVER experienced any problems, and it was extensively tested in 5 different tracks (Athens Circuit, Tripoli Airport, Nurburgring Nordschleife, Dijon, Magny-Cours). Is it possible for you to send me v.1.30?
    Thank you in advance!
  • aolaol
    edited January 2012
    Unfortunately I don't think the v1.30 will work anymore because of the expiration. But I'm not 100% sure, so you can try it:

    I don't think it is a software problem as I didn't change anything like this from 1.30 to 1.40... this is why I asked you to test without OBD-II. You could do changes to the setup to see what is causing the problems, or at least what eliminates it. Anyway, I hope you find a good solution to the problem!
  • Thank you aol! I installed 1.30, I set the phone's date on year 2010, and it works. I will test it on my next race on February and I will report the results.
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