systems.

For many years, the search continued for a cheap bi-directional technology suitable for applications such as remote meter reading. French electric power Électricité de France (EDF) prototyped and standardized a system called spread frequency shift keying or S-FSK. (See IEC 61334) It is now a simple, low-cost system with a long history, however it has a very slow transmission rate. In the 1970s, the Tokyo Electric Power Company