GB287048A - Improvements in duplex signalling systems - Google Patents

Abstract

287,048. Siemens & Halske Akt.- Ges. March 12, 1927, [Convention date]. Duplex signalling. - Relates to duplex telegraphy in which currents of different ranges of frequencies are used for the two directions, the sending circuit zl for frequencies f1 - - f2 and the receiving circuit z2 for frequencies #3 - - #4 being connected to the line l by a balanced repeater a, u1. According to the invention, the circuits z1 or z2, or both, are connected to the repeater a, u1 by a bridge arrangement selective as to frequency so as to reduce the passage of currents from circuit z1 to circuit z2, or viceversa, due, for example, to imperfect balance of the bridge at all frequencies. Thus the alternating-current resistances r1, w1 of the 'bridge b1 associated with the sending circuit z1 are so dimensioned as to stop all frequencies above f2, whilst the bridge b2 stops all frequencies below f3. Amplifiers are shown at v1, v2. Fig. 2 shows the invention applied to a system using a four-wire connection, currents from line l1 passing through the repeater a1, selective bridge b1 and amplifiers v1 to line l2, while currents from line l2 pass via b2, v2, a1 to line l1. Specification 222,852 is referred to.