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 (circuit arrangements for preventing eavesdropping H04M1/68; telephone cabinets E04H1/14)

Full Title

Substation equipment, e.g. for use by subscribers (subscriber services or facilities provided at exchanges H04M3/00; prepayment telephone coin boxes H04M17/00; current supply arrangements H04M19/08) > Constructional features of telephone sets > 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 (circuit arrangements for preventing eavesdropping H04M1/68; telephone cabinets E04H1/14)