on the PCB are
1x optocoupler serial interface RS232 (+/- 12V level) 1x Icom CIV Cat interface

The optocoupler serial interface is on the internal serial interface of the Raspi. It is additionally protected with overvoltage diodes and is suitable for all applications, especially with long cables that can carry overvoltage.

The Icom-CIV interface uses a USB / serial converter that is already provided on the board. If it is to be used, a connection (4 wires) must be made to a USB connector on the Raspi.

As usual, further serial interfaces can be provided via normal USB / serial converter cables.

see labeling in the circuit diagram.

JP1: Connection for a very short USB cable
Pin1 … + USB 5V
Pin2 + 3 … USB signal lines
Pin4 … GND

If no optocouplers are needed, do not equip them. Instead, close the solder bridges below the optocouplers and at the dc/dc converter DC1, which is also not required.