I have one connected to a 3dr telem radio. Could I connect a blue tooth to the other one at the same time? Why is there two port? Thanks
yes you can.
There is two ports, because history tells us we “never” get enough I/O ports
You can for example run one at 57600 for radio telemetry, or 9600baud for satellite modem, with one sparse set of mavlink messages and message frequency, while the other port can run 921600 baud for communication to an onboard computer with very high message rate.