Base Stations are connected together via the Base Link Jack and this cable.
Base Link is a method of connecting up to six Base Stations together in order to expand the number of Belt Packs that a system can handle. When two or more Base Stations are linked together, one must be set up as the MASTER and the rest as a SLAVE. The slave Base Station transmitters and wired intercoms will be disabled, but will route wireless Belt Pack audio data to the master unit. In effect, this means that up to 36 Belt Packs can be used in a single wireless two-channel system.