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Recently, several experiments have been reported on utilization of commercial power distribution line for data transmission purpose in realizing local FA /HA system. The power line, have been constructed not for the communication purpose, exhibits very poor transmission charctreistics; high attenuation rate with severe selective fading, extremely low line impedance and persistent line noise etc, usually deny the application to the communication field unless cumbersome measures are taken, which cannot normally be allowed to local FA/HA system. This paper first studies general characteristics of local power distribution line and determines 100 KHz to 200 KHz band as most suitable for carrier transmission and the fact that, in order to compete severe selective fading phenomenon in the line, spectrum technique with appropriate modification be applied. Based on the study, the author introduces highly versatile yet simple MODEM unit which can transmit and receive 8 bit ASC I I data of 2400 bps through local power distribution line with the error rate less than 10^(-4) when SNR is 5dB. The MODEM, composed of a simply constructed spectrum spreader/correlator, carrier modulator and a PN generator triggered from fixed phase of power line voltage. A carefully designed matching transformer is used in order to assure perfact matching to power line impedence which drops sometimes down to less than 10 ohms. To insure efficient transmission via the transmission method is choosed and it’s frequency of 113 KHz-137 KHz range is selected based on the result of surveys conducted on various commercial lines. In order to eliminate synchronization problem of carrier demodulation process, the system utilizes two carrier frequencies each represent mark and space signal of spreaded signal, which operates as conventional FSK system. The process gain of SS system, 5dB to 8dB, in conjunction with the improving factor of FSK, some 3 dB to 4 dB, effectively overcome the deficiencies of power line and insures successful data communication. A series of measurements have been conducted on dummy line as well as on actual commercial lines with the results fairly matched to the analytical values.
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