Patent classifications
H
ELECTRICITY
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H04
ELECTRIC COMMUNICATION TECHNIQUE
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H04Q
SELECTING
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1/00
Details of selecting apparatus or arrangements
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H04Q1/30
Signalling arrangements; Manipulation of signalling currents
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H04Q1/444
with voice-band signalling frequencies
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H04Q1/46
comprising means for distinguishing between a signalling current of predetermined frequency and a complex current containing that frequency, e.g. speech current
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