A device used to transmit and receive signals from a satellite transponder. For transmission, it modulates digital data signals from a multiplexing device into a carrier frequency for delivery to an upconverter, amplifier and antenna. For receiving, it converts the frequencies from the downconverter into digital pulses for the multiplexor. Commercial telecom providers use stand-alone satellite modems; however, the satellite receivers and large dishes that were used before DSS became popular contained the demodulator part of the modem. See earth station.