Patent GB-984913-A (GB)
Title: Improvements in or relating to time division multiplex signal transmission systems
IPC: H04Q11/04
Filed: 1962-09-26
Abstract: 984,913. Automatic exchange systems; transmission systems. SIEMENS & HALSKE A.G. Sept. 26, 1962 [Sept. 26, 1961 (2)], No. 36485/62. Headings H4K and H4R. In a time division multiplex system in which an attenuation compensator is included in the highway of the system, the attenuation provided by the compensator is varied by a control signal which at any instant is dependent on the attenuation of the particular transmission line connected at that instant to the highway. The compensator is of particular use in a system which includes a plurality of transmission lines, e.g. subscribers' lines, of varying attenuation, whereby signals between these lines may be attenuated or amplified in order to maintain a uniform response for the system. Both 2-wire and 4-wire systems utilizing the " resonant transfer " technique are described. Each subscriber Tn1 (Fig. 1) is connected, in the time slot allocated to him for the call, to his associated compensator al whereby energy stored in his capacitor C1 is transferred via highway P(1) to a storage device in a1 and at the same time a control signal, which is a function of the D.C. line current flowing, is passed via control highway PC to a1, whereby the attenuation of a1 is adjusted accordingly. During a later time slot, viz. half a channel repetition period later, the stored energy in a1 is passed to a coupling network KF from whence it is transferred by a similar process to the wanted subscriber. A single compensator may replace the individual compensators a1 to am. The above-mentioned storage device may comprise a parallel-tuned LC circuit which is shunted by a " resistor " whose value is altered (positive, infinite or negative) by the control signal in order to vary the time constant of the LC circuit and hence determine whether the energy stored therein is attenuated or amplified (Fig. 2, not shown). The " resistor " may comprise a transistor amplifier whose working point is varied by the control signal (Fig. 4, not shown). In an alternative embodiment the compensator comprises a pair of diodes D1, D2 (Fig. 6) which are biased in accordance with the line current flowing in a control winding T of transformer U in order to vary the attenuation of the signals applied to transistor amplifier V (Fig. 10, not shown). The control signal may be applied to a plurality of amplitude filters whereby the output from one of which selects a corresponding tapping point in a potential divider connected to the highway in order to vary the attenuation of the signal before it is amplified (Fig. 7, not shown). The control signal may be " translated " into a binary code whereby various combinations of resistive T-filters may be placed in series with the highway and an amplifier (Fig. 8, not shown). The control signal may be an audio-frequency signal which is transmitted by each subscribed station at the beginning of a call and which is stored in a circulating memory (magnetostrictive delay line) in the compensator whereby at each time slot appertaining to the subscriber, the appropriate sections of a plurality of resistive T filters are inserted in the signal path (Fig. 9, not shown).