These are small adapter boards to adapt the pinout of the RLS-1000B to the pinout of the RLC-Club. The RLS-1000B only directly supports logic high PL mode. This includes a small logic inverter to accept logic low signals, and also allows for the COR and PL signals to be tied together for receivers where they are already tied together. For a combined logic low COR and PL system, jumper pins 2-4 and 5-6. The 4 pin header is a provision for the connection of an external PL decoder board, signals as labeled. The companion breakout for the DB25 is here: https://oshpark.com/shared_projects/YJuL8J8m