The 4-wire/2-way radio interface connects two external 4-wire circuits to matrix. Camera intercoms, 2-way radios, microwave, satellite links, IFBs and program audio inputs and outputs are candidates for the FOR-22. The module provides proper impedance matching, transformer isolation and level adjustments between systems. It also supports external relay activation and call-sense circuitry. The relays can be controlled separately to add to the frame relay complement.