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    Loud-speaking telephone
    12.
    发明授权
    Loud-speaking telephone 失效

    公开(公告)号：US3171901A

    公开(公告)日：1965-03-02

    申请号：US6047660

    申请日：1960-10-04

    Applicant: BELL TELEPHONE LABOR INC

    Inventor： CLEMENCY WILLIAM F ,  GOODALE JR WALTER D

    IPC: H04B1/46 ,  H04M9/08 ,  H04M9/10

    CPC classification number: H04M9/08 ,  H04B1/46 ,  H04M9/10 ,  Y02D70/00 ,  Y02D70/144 ,  Y02D70/40

    Abstract: 916,545. Loud-speaking telephones. WESTERN ELECTRIC CO. Inc. Sept. 21, 1961 [Oct. 4, 1960], No. 33785/61. Class 40 (4). In a loud-speaking telephone set in which the gains of the transmitting and receiving channels are differentially adjusted automatically in accordance with the energy propagating through the channels, the sensitivity of the differential switching device is controlled by the slowly varying ambient noise signal picked up by the transmitter. The Figure shows a loudspeaking telephone set comprising a transmitting channel 1 and a receiving channel 2 connected via a hybrid network 3 to a line 4. The transmitter channel includes a variable impedance device 9 comprising series diodes 12 and 13 which in the absence of D.C. bias current present a high loss to the transmitted signal while the receive channel includes a variable impedance device 23 comprising shunt diodes 28 to 31 which in the absence of D.C. bias present a low loss to the received signal, the two variable impedance networks being differentially switched to their opposite loss conditions by current from the control circuit. This control current is derived from the speech signal in the transmit channel which is conveyed to amplifier 41, via capacitor 50 and resistor 51, rectified at 42 then fed, via diode 45, to the two variable impedance circuits, the diodes of which are connected serially by connection 46. The level at which the switching takes place may be modified in accordance with the ambient noise level picked up by the transmitter microphone by passing the transmitter channel signal through circuit 52 which includes a rectifier circuit which charges capacitors 58 and 72, the charging circuit having a long charge time and a short discharge time, due to diode 59, which thus produces a potential which is dependent on the slowly varying ambient noise level around the transmitter microphone but largely independent of speech signals, this potential produces a current through diode 68 to lower its impedance, therefore a bigger transmitter signal is required to effect the change over from the receive to the transmit condition. A further rectifier circuit is connected to de-energize the control signal by passing a current derived from the received signal fed to the loud-speaker 21 through diode 68 to maintain the apparatus in the receive condition whilst a message is being received. Switch 70 is provided which connects capacitor 72 to a source of positive potential when the loud-speaking facility is not in use, the charge on this capacitor ensuring that the apparatus is not switched to its transmit condition by a high ambient noise level immediately the apparatus is switched on.

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