A full duplex repeater can be made by connecting two RT9080 E&M radios back to back using a repeater cable, part no: 119-47-348.
Transmit 4W audio is on pins 4 and 12 of the DB-15 connector
Receive 4W audio is on pins 3 and 10. The Rx and Tx audio levels in the cable between the radios are 1VPP at 3.5 kHz deviation.
Receive COR of one radio activates the M relay which places a ground on pin 2 of the DB15 of the other radio (Tx key).