The COMMS 300 and the openGear version, Intercom units provides a means to interface between two channels of 2-wire party-line intercom audio and two channels of 4-Wire analog line-level signals. The unit is capable of performing auto nulling for each channel with the push of a button. In addition, each of the 4-Wire input and output channel levels are monitored and displayed on easy to understand front panel VU meters. With the flip of a switch the unit can be a +28VDC party-line voltage power source while providing the 200 ohm intercom audio termination on both channels. If so desired, the party-line source and termination can be removed by just flipping the switch back. The unit can also be configured to work with either RTS party-line or Clear Com party-line equipment with the flip of a front panel control switch. This switch adjusts the output gain between the party line circuitry and the 4 Wire line level circuitry depending on which type of units one is interfacing with Auto nulling is done to achieve maximum return loss between the 4 Wire input and the 4 Wire output channels.