To provide an SS compound packet data communication system in which signals of various data are modulated by spectrum spreading and can be transmitted/received using a wired communication line.

Transmitting terminals 6, 8 are connected through SAW devices 5, 7 to a twist pair or coaxial communication line 4 connected to a communication exchange system for a packet data communication system. On the other hand, receiving terminals are connected through SAW devices to the communication line, signals are modulated and sent out onto the communication line by performing spectrum spreading processing using a SAW convolver system in the transmitting terminals. On the other hand, the modulated signal is received via the SAW devices and demodulated also at the receiving terminals so that data can be transmitted/received. Thus, an economical communication system using an existent private communication system can be newly constructed and communication system layout construction costs of industrial plants, in particular, can be reduced.

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