Telemetering system for multi-channel data over voice grade telephone lines

Claim 1

A telemetering system for multi-channel data where the transmission medium is a single voice quality communications channel said system comprising: frequency modulation means for receiving said multi-channel data such means including in each channel a single inductor coupled with capacitor means forming a resonant circuit and tuned for providing a unique carrier frequency for each data channel said modulation means being frequency modulated by said data and also including a transistor for each channel with said resonant circuit being connected across its emitter and collector and tuned to a carrier frequency, such circuit including fixed d.c. biasing means for said base and including said single inductor which responds to a change of d.c. current through it to change its inductance value, said base of said transistor being responsive to data from a channel and being direct coupled to said channel to change said d.c. current in accordance with the signal magnitude of said data whereby said carrier frequency is frequency modulated by said data, means for coupling said frequency modulation means to said communications channel, phase detector means adapted for being coupled to said communications channel for demodulating said signal transmitted by said channel said phase detector means including a plurality of circuits resonant at each of said carrier frequencies each resonant circuit having an inductor identical with respect to electrical characteristics to said inductor in the corresponding cannel of said frequency modulation means.