The Radyne Corporation DMD2401 and DMD2401 L Satellite Modems (Figure 1-1) are microprocessor-controlled Binary Phase Shift Keyed (BPSK), Quadrature Phase Shift Keyed (QPSK), Offset Quadrature Phase Shift Keyed (OQPSK), or Trellis Coded 8 Phase Shift Keyed (8PSK) Modulators/Demodulators. They are used as part of the transmitting and receiving ground equipment in a satellite communications system. The modem is designed for service in an SCPC system where two modems are set for continuous operation with each other.