Patent GB-722178-A (GB)
Title: Improvements in or relating to automatic telephone systems
Inventor: SCOWEN FRANK
IPC: H04Q11/04
Filed: 1950-04-04
Abstract: 722,178. Automatic exchange systems. POSTMASTER GENERAL. Dec. 28, 1951 [April 4, 1950], No. 8477/50. Class 40 (4). A rectifier gate associated with a switch outlet denoted by a multi-digit number is opened to pass a marking signal to the switch outlet only when potential is applied to all digit leads connected to the gate, there being one digit lead for each possible value of each digit and the gate being connected to the digit leads corresponding to the number of the associated outlet. The marking arrangement to the systems described in Specifications 694,092 and 722,172. Each switch consists of a go and return multiplex and a common marking lead. The outlets which are designated by a four-digit number may be single subscriber's lines, PBX groups or groups of junctions and groups of outlets may be scattered over several switches. A group of outlets is marked by the application to the common leads of switches having outlets in the group of a series of equally spaced pulses in time positions corresponding to those of the wanted channels of the multiplexes. The marker X, Fig. 2, has 4 groups often digit leads A0 . . . D1, one group for each digit. In response to the four digit number abcd the marker closes contacts MAa ... MDd and applies a potential of 45 volts to the digit leads Aa . . . Dd. Apparatus Y associated with each outlet has four commoned input leads connected to the appropriate digit leads so that a rectifier W in each apparatus Y corresponding to a called outlet is connected between the 45-volt battery B1 and a 40-volt battery B2 and conducts, whereupon the pulse series characterizing the called outlet is passed from lead F through the rectifier W and the lead G to the common marking lead of the switch. Each of the contacts MAa ... MDd may be replaced by the circuit of Fig. 3. When a lead Aa is to be marked an A.C. is applied to the primary of transformer T1 and a condenser C is charged through a rectifier W1 to cause a tube V to conduct, whereupon a potential clamped by rectifier W2 to 45 volts is induced in the secondary winding of a transformer T2 for a period greater than the short time required for marking a called outlet. To reduce the number of pulse sources required, the F-leads are grouped, each group being commoned to an individual repeated long pulse source, and the G-leads are grouped in cross-sections of the F-lead groups, each G-lead group being connected through a gate controlled by an individual repeated short pulse source to the common marking lead of the switch. Alternatively, if the number of outlets of a switch is N x M where N, M are prime numbers the F-leads may be grouped in N equal groups each commoned to a repeated short pulse source having a repetition time of N units and M groups of G-leads are formed, each being a cross.section of the F-lead groups and being connected through a gate controlled by an individual short pulse source having a repetition time of M units to the common marking lead. Specification 707,373, [Group XL (b)], also is referred to.