Telemetry issues on Matek F405 CTR

I’m trying to set up two telemetry connections on a Matek F405 CTR running copter 4.0.3, but I’m having luck with neither.

Telem1 is wired to a V2 SiK telemetry radio from an old pixhawk 1 kit. I’ve connected the radio to the tx/rx1 on the Matek, which should be Serial1 = Telemetry 1 in Arducopter. I verified that my Serial1_Protocol is set to Mavlink1, and changed it to Mavlink2 since I plan to use some features not in the older protocol. The radio powers on and quickly establishes a link with the GS radio (steady green LED), but QGroundControl doesn’t connect (tried on Windows and Mac). Same system connected instantly with Pixhawk.

Telem2 is going to a raspberry pi with mavproxy configured (for wifi control of the FC). I’ve wired tx/rx2 to the Pi’s GPIO 15/14 (making sure to cross the tx->rx and vice versa) and verified that Serial2_Protocol is mavlink2. Again this worked great with my pixhawk. The raspi gets power and boots, but no connection to the FC can be found.

I can connect via QGroundControl over USB just fine.

What am I missing?

You could double check with Matek or just try it, I tested by bridging the resistor with tweezers, but it could be the same issue I had with the F405-STD.

I’ll try to contact Matek. I’m setting up for SiK not FrSky and my board doesn’t have a similar resistor array to the F405-STD in that thread.

I think my mistake was really simple. The Tx/Rx numbers correspond to the UART number, not the serial port number. There’s a mapping on Matek’s product page. I just didn’t get that UART3 means Tx3/Rx3.

My mistake was twofold. 1: I should have used Tx3/Rx3 = Serial1 in ArduCopter, and 2. The Tx and Rx pins on my V2 SiK radio are flipped! See this helpful Amazon review here