Using the LRS back channel for APM Telemetry


I would like to use a 433 LRS system with an FPV plane (X8) but the alternative 3DR 900 Mhz telemetry hardware is not permitted in Germany even if you have an Amateur Radio Licence as I do. The 800-1000 Mhz band is widely used by mobile phones and 3G/4G systems.

Has anyone had any success using the 2 way link on 433 LRS systems like, for example, the ImmersionRC system for APM telemetry. Thinking about it, even if the software could be made to work for the telemetry downlink, the uplink would still have to time share with the RC control signals so I am not sure how effective it would be.

Or alternatively, is there any way to allow the 3DR 433 telemetry hardware to be in use with 433 LRS without massive adjacent channel interference? I have tried a very short experiment with a HK openLRS system but without much success.

In Germany, large parts of the 430-440 Mhz/70Cm amateur band are available for use by telemetry but any solution would need to be legal.

I expect someone has already tried this but I cannot find anything in a forum search. Any help or pointers gratefully received.



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  • Hi, I've made a custom firmware in order to make OpenLRS work well with APM, so far I've gone 10 km away with full APM telemetry. No need to modify anything on APM, no need to ctrl-T, all parameters are sent correctly, everything can be modified even during the flight, such as changing PID parameters or sending a new mission. Full 19200 bauds for APM, and of course RC is sent as well.

    Described here :

    Discussed here :

  • Checkout my fork of OpenLRSng:

    It has been specifically developed to convert your OpenLRS device to a combined RC / Telemetry system.

    The thing it does primarily is to enable you to specify transparent serial bandwidth (bytes per packet dedicated to serial transmission), and it also enables the OpenLRS device to talk back to the APM for dynamic stream rate adjustments (improves link quality).

    openLRSng (with extended telemetry support). Contribute to gitsly/openLRSng development by creating an account on GitHub.
    • My setup consists of Futaba 9C with Deluxe TX and Hawkeye 6 channel RX. APM en-route. I also ordered the 900 radio's as well just in case I couldn't get this to work.

      So, after reading a ton of info, I'm not having any luck uploading to my Hawkeye Deluxe TX. Is it possible at all? What gitsly version are you using? link? I did however (i think) successfully uploaded to the RX. When I choose option 6 for the Deluxe TX and Board type Leonardo I get errors. If I change the board type to the pro or pro mini, the sketch will verify but then says sketch too big.

      Help please.


  • At the moment i am working on getting the APM Mavlink to run smoothly over OpenLRS. It works but needs some tweaking because the datarate cannot be as high as mavlink needs. If you set the OpenLRS telemetry to 9600 baud and the telemety in the APM also to 9600 you can connect with mission planner using CTRL + T. This way it won't load all the parameters.

    Also look at the SR0 / SR3 (if you use UART2) settings 

  • Jay,

    Thanks for the reply. it is true that LRS do not speak Mavlink natively but I am not certain what is purpose of the two-way function of LRS systems - I am assuming telemetry. I will have to look into that.



  • Mhhh no specialist here.. simple look.. how you make the LRS run with the MavLink Protocol... same frequency doesnt mean they speak the same language.. i never looked into LRS.. so I might state complete bogus... but I think the LRS can only transmit PWM/PPM signals.. and thats why they dont interconnect




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