GB201564A - Improvements in or relating to the selective transmission of electric waves - Google Patents

Abstract

201,564. Western Electric Co., Ltd., (Assignees of Vennes, H. J.). July 26, 1922, [Convention date]. Wired wireless systems; multiplex signalling; combined transmitting and receiving arrangements.-Receiving and transmitting circuits are associated with a transmission line or medium by inductively coupling the receiving-circuit to the line, and by connecting the transmitting-circuit directly in the line at an electrical mid-point. As shown, the main line ML is connected through a high-pass filter HPF to the primary coil 5 of a transformer, which is divided at its middle point for the connection of the transmission circuit TC. The receiving-circuit RC includes the other coil of the transformer. Low-frequency telephone currents in the line L are transmitted through a balanced transformer 6 to a valve M which modulates the oscillatory current generated by the valve O and transmits the modulated current through a band filter SBF and, if desired, a second filter TGF to the transmitting line TC. The high-frequency currents received from the line ML pass through band filters GF and RBF to a detector D and thence through a voice-frequency filter VF to the low-frequency line L. Several channels employing different frequencies may be associated with the transmitting and receiving lines TC, RC, selection being effected by band filters such as SBF, RBF, while filters TGF and GF may be arranged to pass the whole set of transmitting and receiving frequencies respectively. The first elements of the receiving filters have low impedance at transmitter frequencies, so that the receiving-coil of the transformer is practically short-circuited as regards currents coming in from the line TC. The effect of this is to reduce the impedance of the line coil of the transformer 5 for the transmitter frequencies. The first elements of the transmitter band filters are similarly arranged to have low impedance for receiver frequencies, and thus form practically a short-circuit connection between the two portions of the line coil 5 for carrier currents coming in on the line ML. An earthed electrostatic shield 11 is arranged between the two windings of the transformer 5. The line ML may transmit lowfrequency currents through a low-pass filter LPF to an ordinary telephone line TL. The filters are of the kind described in Specification 142,115.