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H04M1/00—Substation equipment, e.g. for use by subscribers
H04M1/60—Substation equipment, e.g. for use by subscribers including speech amplifiers
H04M1/6033—Substation equipment, e.g. for use by subscribers including speech amplifiers for providing handsfree use or a loudspeaker mode in telephone sets
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Signal Processing
(AREA)
FR780267D1934-01-091934-01-09
Improvements to telephone devices
ExpiredFR780267A
(en)