Patent GB-1170061-A (GB)
Title: Improvements in or relating to Signalling Systems
Inventor: HEPTINSTALL DENNIS LEONARD
IPC: H04Q3/42
Filed: 1965-11-08
Abstract: 1,170,061. Selective signalling systems. H.M. POSTMASTER GENERAL. 4 Nov., 1966 [8 Nov., 1965], No. 47338/65. Headings G4H and G4J. [Also in Division H4] An operator's manual board 10, Fig. 1, has a keysender 14 by which signals are sent via the outgoing relay set 13 and a sender hunter 18 to a sender 102. The signals from the keysender are sent as a combination of two-outof-five D.C. levels on two wires and the sender 102 converts the D.C. level code into a two-outof-six voice frequency code on the outgoing line 17. Fig. 2 shows the operator's key sender in which, after depression of a start key to operate relay KS, the depression of any key KXA to KXP produces a unique combination of voltage levels on the lines T and R, the voltage levels available being Œ50V, from the supplies and - 20, - 6-2, and + 10V from Zener diodes MRF, MRE and MRD. In the sender, Figs. 3, 4 and 5, the voltages on the lines T and R cause one of the transistors VT6 to 10 and one of the transistors VT16 to 20 to be rendered conductive to operate two of the relays RA to RF to cause the connection of the appropriate v.f. signals to the outgoing circuit over the contacts RA1 to RF1. Circuit operation is such that the incoming potential on lines T and R causes the conduction of those of transistors VT1 to VT5 and VT11 to VT15 whose emitter bias is of the same sign but of smaller magnitude than the input signal applied to the base. A network of diodes MR1 to MR4, and the corresponding diodes associated with transistors VT11 to VT15, then ensure that only one of the transistors VT6 to VT10 and one of the transistors VT16 to VT20 conducts to operate the appropriate combination of relays RA to RF corresponding to the D.C. levels received. In order to prevent false operation of the sender during transient conditions at the beginning or end of a keying operation the D.C. receiver is inhibited, by potentials on line N and P of the receiver, until the signals have been maintained for a predetermined period, e.g. 15 m.sec., and then is only enabled for a further predetermined period, e.g. 15 m. sec., being then inhibited until the signal is removed. Inhibiting circuit. Fig. 7, comprises a start relay ST which is operated by the start signal from the operator. In the absence of signals on lines R and T both coils of relay GD are shunted by transistors VT22 and VT23, GDR is operated by the current through VT29, and transistors VT25 and VT28 are operated to put an inhibiting potential on lines N and P. When the signalling potential appear on lines T and R one or both of transistors VT21 and VT24 is caused to conduct to discharge capacitor C1 and/or C2, so that, a predetermined time after the signals appear, VT22 and/or VT3 is cut off so that relay GD operates. Operation of contacts GD1 completes the circuit between the bases of transistors VT26 and VT27 causing them to conduct to cut off transistors VT25 and VT28 so as to remove the inhibiting potentials from lines N and P so allowing the sender, Figs. 3, 4 and 5, to receive and interpret the D.C. signals. Operation of relay GD also causes transistor VT29 to be cut off so that C3 commences to discharge through relay GDR holding it operated for a predetermined time, e.g. 15 m.sec. After this time GDR releases, opening contacts GDR1, causing VT26 and VT27 to turn off, and therefore causing VT25 and VT28 to conduct again and restore the inhibiting potential to the lines N and P. When the signals on lines T and R cease, transistors VT21 and VT24 are turned off to allow capacitors C1 and C2 to charge up, transistors VT22 and VT23 to conduct to release relay GD and restore the circuit to a waiting condition ready for the next D.C. signals on lines T and R.