Patent GB-299855-A (GB)
IPC: H04B1/46
Filed: 1928-11-02
Abstract: 299,855. Telefunken Ges. f³r Drahtlose Telegraphie. Nov. 2, 1927, [Convention date]. Void [Published under Sect. 91 of the Acts]. Combined transmitting and receiving arrangements; duplex signalling. - High-frequency telephone systems arranged for two-way working between a low-frequency telephone line and a high-frequency line (or transmitting and receiving aerials), are provided with automatic opening and blocking devices by which speech currents from the active telephone transmitter are caused to connect the high-frequency transmitter and/or to block the receiver; or the activity of the highfrequency receiver is caused to complete its' connection to the lowfrequency line and/or to block the highfrequency transmitter; or both systems may be combined. As shown in Fig. 1, the telephone line La, Lb is balanced by a network N and is coupled by a balanced transformer D to the outgoing amplifier V1 which supplies the amplified speech currents to a high-frequency transmitter S for energizing the outgoing aerial As. The incoming waves are received on an aerial Ae and after passing the detector E and low-frequency amplifier V2 are applied to the telephone line La, Lb at conjugate points. Speech currents when present in the amplifier V1 are partially shunted to a further amplifier V which feeds a rectifier r and creates a direct current voltage across the resistance X. This voltage is used to establish an effective connection of the transmitter S to the aerial As. As shown this is effected by a relay Xo closing a series switch x<1>; but the relay may open a shorting-switch x<2> or may increase a short resistance x preferably of the liquid or electronictype; or the voltage across the resistance X may be applied to the grid of an amplifier. Alternatively the relays may be energized by alternating current, the rectifier r being omitted. In all cases, the effect is that the presence of speech currents originating in the line La, Lb sets the transmitter S into effective connection with the aerial As, whilst as soon as these speech currents cease, the effective connection is broken. The voltage across resistance X due to the presence of speech currents in V1 may be utilized to block the receiver path by opening contact xI<SP>1>, by closing contact x2<SP>1>, by reducing the resistance x<1>, or by other suitable means. The connection of the transmitter S and the blocking of the receiver E may be simultaneously effected. In another form of the invention which may be used separately or in combination with that already described, the amplifier V feeding the rectifier r and resistance x, is connected across the receiver path between the detector E and amplifier V2 and operates when the receiver is active, to connect the receiver to the line La, Lb, and/or to disconnect the transmitter S from the aerial As. If a high-frequency system of the carriersuppression type is employed, the amplifier V and rectifier r may be fed with high-frequency received current. Instead of using aerials for transmission and reception, the output from the transmitter S and the input to the receiver E may be conjugately connected to a high-frequency line, which is balanced by a network, in a manner similar to that shown for the low-frequencv line La, Lb.