The inductive communication system was developed under this contract for use in the hoist of deep mines. This program was a four-phase program with experimental dual frequency equipment resulting from Phase I, emergency single frequency equipment developed under Phase II, and equipment documentation required under Phase III. An additional emergency system was provided under Phase IV. The inductive communication system is designed to provide reliable voice communications between the hoist operator and the hoist cage at all levels down to 10,000 feet. Dual frequency, fm transceivers, operating at 35 and 52 hz, were developed as experimental units under Phase I. The two signals are transmitted simultaneously and received by the dual frequency receiver which has decision circuitry to select the strongest signal. The communication system consists of two sets of transceivers, power supplies, station controls, and rope couplers, with one set used in the cage and the other in the hoist room.