To upgrade a transmitter without an optical network connection (LBB 4502 range) to a transmitter with an optical network connection (INT-TX range) a Transmitter Upgrade Kit (INT-TXK) is required. The upgrade kit comprises the main PCB of the transmitter, a rear panel, a glue stud and a screw for mounting the main PCB in the housing of the LBB 4502 transmitter.