SPM4651T with SRXL2

Actually I am using the Spektrum DX7 as a transmitter with an original Satelite Receiver (SPM9646). The receiver is connected directly to my Pixhawk 1. This runs perfectly.

Now I want to use the Telemetry Functions on the Spektrum DX7 with the Remote Serial Receiver with Telemetry (SPM4651T). In the AduCopter Documentation I found that the SRXL2 Protocol is compatible.

But my question is if the Telemtrie function is also supported by the pixhawk? Does anybody has experience?


Here’s one I prepared earlier

Since you are the only person I know of apart from me with an SRXL2 device I’d be happy to do you a firmware build with the support to test if you want.

1 Like

That sounds very nice!
But before, my question is where I can connect the Receiver? Today my SPM4651T has arrived.
It is not possible to use the the DSM connector on the pixhawk?

I need this adapter ?


No it’s not possible to use the DSM port. SRXL2 is a half-duplex serial protocol only. It will only work on a UART (e.g. Telem1)

Okay thank you.
I have tried to use a Smart Port Converter & used Telem1.

Baudrate: 57
Serial_Options: 4 (half_duplex)
Protokoll, 4,10,23

But without success. There is no communication beetween SPM4651T & Pixhawk 1.

Without a firmware build using my PR it will not work

Okay, thanks for sharing your know-how.

And how can I make a firmware build with your PR? Or do you share a firmware with me? What does PR stand for?
Sorry for my questions, but I have no knowledge of the subject.


I can build you the firmware if you tell me what board you have. Note that the firmware build would be against master (the current development branch in github) with the usual possibility of bugs and issues, so if this is for a machine that is especially valuable or you don’t like risk then I would wait until this makes it into a released version (probably several months from now).

Okay, I understand the risk.

Please make me a build. I have a Pixhawk 1.

Perfect, Thank you!
Is there a special configuration necessary?

COM Options, Baud, Protokoll?


You need to configure

SERIALn_OPTIONS=8 (for Half-duplex)

You need to connect the signal pin of the receiver to the TX pin of the serial port (not the RX pin)

Perfect! It runs! :grimacing: :slightly_smiling_face:

Thank you so much for this solution.
I´ll test it and give feedback if I find problems.


Would you be willing to build a firmware for a pixhawk cube blue with the SRXL2 capabilities? I would greatly appreciate it!

What receiver do you have? If it’s one that operates in remote mode then you can just pull the latest master firmware from https://firmware.ardupilot.org/Copter/latest/ as SRXL2 is already in master. It’s only this weird bootstrap version that is not.

We’re going to be using the 4651T satellite receiver. We’re trying to find a way to get RSSI data from the Spektrum receivers.

Do you have a link - I don’t see that on the spektrum site

My apologies. Typo



I would expect that to work with the existing support - so just download a build of master and try it out