Patent GB-721191-A (GB)
Title: Improvements in or relating to teleprinter code signal transmission systems
Inventor: COOK ARTHUR
IPC: H03M13/51
Filed: 1949-08-10
Abstract: 721,191. Code telegraphy. POSTMASTER GENERAL. April 13, 1951 [Aug. 10, 1949], No. 20823/49. Class 40 (3). In an error-detecting teleprinter system employing seven unit signals derived from five-unit combinations, the majority of the signals are derived by analysing the five-unit combinations to ascertain the number of either marking or spacing units and then adding to the five-unit combinations further units in accordance with a pre-arranged formula by which the nature of each said further unit is predetermined so that the combination is indicative of one of said numbers, whilst the remaining signal or signals (exception signals) are derived by adding to the standard five-unit combinations additional units not derived in accordance with the formula. In the receiving arrangements, the coded signals are applied via contacts S1 ... S7 to condensers C1 ... C7, the first element of a succeeding signal being applied to a condenser C8 and the signals stored are applied by contacts S9 ... 15 and contact S16 to relays SA/1 ... SG/1 operating contacts SA1 ... SG1 to energize selectively the relays EA/5 . . . EG/5. Contacts EA1 ... EE1, Fig. 3c, normally open, are in series with equal resistors R2 ... R6 in one arm AB of a bridge. In a second arm BC contacts EG1 are in series with a resistor R7 and EF is in series with a resistor R8 having a resistance one half of that of resistors R2 ... R7 and resistor R9 connected in parallel with R8. In the case of a signal having solely one spacing element, only one of the contacts EA1 ... EE1 would be closed and relays EF/1 and EG/1 would be operated by positive (spacing) current so that the adjoining arm R9 would be balanced by one of the resistors R2 ...R6, and the inner relay EI/2 would not be operated. At contact S18, Fig. 3a, a spacing signal is sent out over ET1 and operates relay VD/1 so that its contact VD1 transmits a start spacing signal followed by the five-unit signal via contacts S19 ... S23 and selectively operated contacts SA1 ... SE1. If an error has been detected, relay EI/2 operates when contact S17 is closed and contact EI1 will prevent relay VD/1 being operated, and a second contact is provided to actuate a repetition device. In the case of the exception signals, e.g. letter-shift, the chain EA2 ... EG2 will be closed to operate relay SS/1 and contact SS1 will open the circuit of the error relay EI/2 so that the five-mark signal is passed by relay VD/1. If the five marking signals are not received relay SS1 will not operate and as it is most probable that the signal will not be balanced according to the formula, the error relay EI/2 will operate. Similar conditions apply to the other exception signals-repeat I, repeat II and the all-spacing or " unperforated strip " signal, which control contact chains EA3 ... EG3, EA4 ... EG4, EA5 ... EG5 and associated relays RI/1, RII/1 and SP/1. Transmitting-apparatus. A perforated tape selectively operates contacts L1 ... L5 so that relays ZA/2, ZB/4-ZE/10 are appropriately operated and in addition the corresponding elements are passed by the sequentially operated contacts S24 ... S28 to actuate a transmitting relay 2H/1. At the expiration of about 60 secs. contacts S31, S32, S33, Fig. 4b, are closed and according to the setting of the relays ZA ... ZE, the appropriate circuits of relays ZF/2 and ZG/2 are energized to operate contacts ZF1, ZG1, Fig. 4a, to add the appropriate two units at the end of the code combination. In the case of five marks; none of the relays is operated and relay ZG/2 is operated so that the sixth element is a mark and the seventh unit is a space. For the five space signal, all the relays are operated and ZF/2 is energized so that the sixth unit is a space and the seventh unit is a mark. For the transmission of the " repeat I signal, contact members ZI1-ZI7 are switched over and the seven-unit signal is determined by contacts ZII1 ... ZII7 in the positions shown and these contacts are reversed for the transmission of the " repeat II " signal. In Figs. 5a, 5b (not shown), comprising a modification of Figs. 4a, 4b, impulses are applied to the transmitting relay over contacts connected to the contacts operated by a perforated tape and the five-unit elements are passed in sequence to a sixposition ring counter comprising six pentode valves, the first of which is normally non- conducting and the remainder conducting. After the application of the code combination, the valve in the chain left non-conductive is indicative of the number of spacing impulses in the code combination. The valve left non- conducting operates an associated triode controlling a pair of relays, and the contacts of these relays are connected so that two relays corresponding to the relays ZF, ZG included in Fig. 4b, are selectively operated to add the two final units of the seven-unit code combination. Specification 637,451 is referred to.