A low cost communications device such as a modem reduces electrical interference or noise of signals received from a power line and transmitted to electrical devices. The modem forwards messages and commands between electrical devices and an external computer device. That is, the modem communicates over a power line without the use of a controller such as a microprocessor or microcomputer. The modem can reduce electrical interference of signals received from a power line through the use of an adjustable automatic gain (AGC) circuit.