Problem with connecting Spektrum receiver to pixhawk 4


Hello everyone! I’m newbie in drone using and I trying to set everything up.
I’ve got pixhawk 4 flight controller and Spektrum AR9030T telemetry receiver.
The problem is that when i connect my whole receiver to pixhawk through DSM\SBUS port (as you may see in the picture)

I have some lags. The receiver connected, but in qgroundcontrol in Settings\Radio
dots wich represent each chennal are stuttering or flickering or i don’t how to say it. They are just moving inadvertently without me touching any sticks at the TX.

In the same time, when i connect a single Spektrum satellite, everything is just fine, i don’t have any lags.

Maybe the problem is because it shows 16 channels in qgroundcontrol, and my receiver has only 9 channels. I’ve already tried reducing rc_chan_cnt parameter to 9, but nothing happens.
Any help is appreciated.

P/S I apologize for my English. It’s not my first language.


As far as I know Spektrum does have only few Receivers that have SBUS/PPM (like AR7700), most are all single PWM Signal Receivers, despite the Satellites themselves have the signal towards the main receiver. In order to use it with Pixhawk you need a PPM Encoder where you connect all your PWM Channels to a small board that encodes them together in one PPM Signal that goes to the Pixhawk PPM Input.


It is written, that my receiver support DSMX technology. As I’ve understood, this is a digital protocol, which is similar to SBUS. And it is written that pixhawk understand this DSMX technology as well.
Maybe I was not correctly at the post before. For example, when i moving THR stick, the throttle dot movse on the screen, but simultaneously other dots are chaotically moving to. What i wanted to say is that it works but with a big lags. I can’t even make a calibration because of this flickering.


DSMX is a Radio Protocol invented by Spectrum. Before there was DSM2. However this is not a Signal Protocol that transfers Data from your Receiver to the Pixhawk. Pixhawk is labled DSM2/DSMX compatible since it is able to talk to a Satellite directly and bind it to a Spektrum TX. Sadly most Spektrum Receivers do not expose this signal on the Pins (except some newer ones like AR7700).

This is my knowledge when I left the “Spektrum World” about a year ago. I had a Spektrum 7s System with which I used a PPM Encoder to hook it up to a Pixhawk. But maybe my Information is outdated.


Thank you for the answer. I’ve already ordered PPM encoder, but i heard, that ppm has high latancy and i wanted to have max of performance.


Have you tried connecting just one of the Satellite Rx to the DSM port? I believe that’s what it’s for (or if you have an SBUS Rx like the FrSky X8R) then do your Radio calibration. I have my QuadRanger with a 36" extension and the Rx mounted on top of the vertical fin and works well. I use the unused ports of the Pixhawk 1 for servo output to control the gimbal.

Good luck.


Yes, I have, and everything is just fine. But I want to use the whole receiver with both remote satellite RC receivers for better connction.
I’ve already ordered PPM encoder, but as i said before I want at best latency as possible.
The special output on telemetry receiver called “SRXL”. Does anybody know what that means? Do I have to connect this receiver through this port to pixhawk? Maybe this port is made for something else?


Posted on this the other day QGroundControl: How to Spektrum Bind when connected to Pixhawk

Get an AR7700 if you want an easy install and 22ms default, use the DSMX port and you can get the low-latency (7.5ms) modes from an AR9030 (Spektrum Black).