Patent GB-1052826-A (GB)
IPC: H04J3/20
Abstract: 1,052,826. Automatic exchange systems; pulse modulation systems. SIEMENS & HALSKE A.G. April 29, 1964 [April 29, 1963] No. 17761/64. Headings H4K and H4L. In a time division multiplex exchange utilizing the resonant transfer method of signalling, a common inductor is connected in shunt to the highway and the closing time t 1  of the switch connecting a station to the highway is equal to one quarter of the periodic time of the LC circuit formed by the inductor and a capacitor at the station viz. t 1  = “ (2# #LC). Thus in the system shown in Fig. 1 the values of capacitors C1 and C2 may be chosen independently to match the characteristics of the stations A1 and A2 to which they belong, the closing times of switches S1 and S2 then being adjusted accordingly. In operation switch S1 is closed during one time slot whereby in the first quarter oscillation of the tuned circuit LC1 the charge on C1 falls to zero and the current in L reaches a maximum. In the next time slot S1 is opened and S2 is closed whereby at the end of the first quarter oscillation of the timed circuit LC2, capacitor C2 attains an equal and opposite charge to that originally present on C1. During the second time slot any charge on C2 is transferred to L so that if in a third time slot. Sl is reopened capacitor C1 becomes charged, i.e. two-way transmission between stations A1 and A2 is achieved during three consecutive time slots. In order to allow for slight delays between the opening of one switch and the closing of another, inductor L may be momentarily short-circuited (either directly or by means of a short-circuited secondary winding coupled thereto, Fig. 3, not shown) or it may be shunted by a capacitor (Fig. 4, not shown), in either case the stored energy in the inductor is retained until the next switch S1 or S2 operates. Any residual charge on L may be removed by periodically breaking the earth connection thereto (Fig. 5. not shown). In a system having 4-wire substations (Fig. 8, not shown) the Go wire of one station and the Return wire of the other station are consecutively connected to the highway as described above following which (but not necessarily immediately) the Go wire of the other station and the Return wire of the one station are similarly connected to the highway. In a somewhat similar arrangement (Fig. 9) which however has a Go and a Return highway, Ms and Me respectively, the inductor L is switched from one highway to the other during consecutive time slots. With this arrangement however it is only necessary that the two switches Szs and Sze should be closed for an accurate period of time t 1 , the closing time of the line switches Sa and Sb is then not critical provided that it is longer than t 1 . If switches Szs and Sze are connected to opposite ends of the inductor L and a further switch is connected between each of its ends and earth (Fig. 11. not shown) the charge transfer can be made to take place without any change of sign. In the system of Fig. 12, the stations are connected to a " calling" " and a " called " highway, Mab and Man, respectively. In the case when Al is the calling station, its capacitor C1 is connected to L1 via Sa1 and A2 is connected to L2 via Sb2 during a first time slot and in the next following time slot L1 is connected to C2 via Sb2 and L2 is connected to C1 via Sal so that a complete exchange of information is then accomplished in only two time slots. Again the common switches Sz are the only ones that require to be closed for an accurate period of time. The inductor may be replaced by a parametric amplifier.