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H04M1/00—Substation equipment, e.g. for use by subscribers
H04M1/02—Constructional features of telephone sets
H04M1/19—Arrangements of transmitters, receivers, or complete sets to prevent eavesdropping, to attenuate local noise or to prevent undesired transmission; Mouthpieces or receivers specially adapted therefor
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FR782809D1934-12-181934-12-18Obturateur de micro d'appareil téléphonique, assurant l'inviolabilité des conversations avec des tiers
ExpiredFR782809A
(fr)
Dispositif pour réaliser l'accouplement, avec un écouteur téléphonique, d'un microphone tel, notamment, que celui d'un appareil électroacoustique pour sourds