using alternate current (H04Q1/50 takes precedence)

Full Title

Details of selecting apparatus or arrangements > Electrical details > Signalling arrangements; Manipulation of signalling currents (multiplex systems providing for calling or supervisory signals H04J1/14, H04J3/12) > using alternate current (H04Q1/50 takes precedence)

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• H04Q 1/442 with out-of-voice band signalling frequencies
• H04Q 1/444 with voice-band signalling frequencies