I have a fully working telemetry-setup with Pixhawk 2.1 and a plane with standard 3DR 100mW 433MHz-radios.
The radio on the ground connected to USB.
The radio in the plane with the cable that came with the Pixhawk 2.1-kit between the Pixhawk 2.1 and the radio with 6 wires (GND, Vcc, Rx, Tx, CTS, RTS).
But when using another radio in the plane that only have 4 wires (GND, Vcc, Rx, Tx) i dont get it to work. I cant get it tto work if I connect Tx from Pixhawk 2.1 to RX on the radio and Tx from radio to Rx on the Pixhawk 2.1. The radios works if I for example connect them using USB to set NetID.
CTS and RTS are used when flashing the unit but not for telemetry.
I assume both are on the same netid.
Have you set the ports speed and communication type to Mavlink.
I don’t know about that setting as I have never seen it before in Arducopter, but perhaps it’s in a newer version and I am unfamiliar with it.
For telemetry ports used for MAVLink communication you may select to use MAVLink1 by setting the SERIALx_PROTOCOL to “1” or MAVLink2 by setting SERIALx_PROTOCOL to “2”.
Well, it works now. What I did? I dont know. I used three other SiK-radios and then back to the ones I tested first which are meant for the plane. All same NetID and other settings. I do not like when I dont do anything and the results differ. Thanks anyway. I have learned a lot anyhow.