Low-cost FSK (Frequency-Shift Keying) modern network for polled communication systems

A frequency-shift keying (FSK) modulator-demodulator (modem) network has een devised for the mine-monitoring systems. This network permits an unlimited number of remote stations to communicate with one central station over the same pair of wires. The network operates at a speed of 4,800 Bd at distances up to 5 miles. The development and operation of the modems are described. The theory of operation, schematic diagrams, and printed circuit board layouts are provided. Although the modems were built for a specific application, a more general use is discussed whereby the network would operate with a typical serial channel format.