Patent GB-778714-A (GB)
Title: Improvements relating to code telegraphy
Inventor: WHEELER LEONARD KEITH
IPC: H03M13/51
Filed: 1952-12-29
Abstract: 778,714. Code telegraphy. POSTMASTER GENERAL. Dec. 14, 1953 [Dec. 29, 1952], No. 32908/52. Class 40 (3). In a telegraph system employing a code comprising a fixed number of elements of one or the other of two conditions, a transmitter translates the code into an error-detecting code by adding further elements of one or the other condition which are determined by counting the number of elements of one kind as the elements of a character are being transmitted. In the arrangement described, signals with 0 marks and 1 mark have marks added to bring the total number of marks to two, whilst signals with 3 and 4 marks have marks added to bring the total number of marks to five. The elements added to the combinations with 1 mark or 4 marks may be mark and space, or space and mark, bringing the total number of marks to two or five. If, in the case of character combination with one or four marks, mark precedes space, similar combinations with the addition of space followed by mark can be used for service signals, such as tape out, circuit disengaged, request of repetition and other facilities up to a total of ten, if required. In the transmitting arrangement, Fig. 1, signal elements from a tape transmitter are passed via gate C1 and selectively closed contacts TR1 ... TR5 to gates G1 ... G5 to which pulses are sequentially applied by a distributer D. The gates G1 ... G5 which are opened by mark elements pass pulses to a counter C which has three positions corresponding to 0 or 3 marks, 1 or 4 marks and 2 or 5 marks. If there are 0 or 3 marks gates G6, G7 are opened by the 6th and 7th pulses from the distributer and pass pulses to the trigger T2. If the five-unit combination includes 1 or 4 marks G6 is opened, but G7 is not opened so that the added units are mark, space. If the counter C is in the third position neither G6 nor G7 is opened and the two added elements are both spaces. The pulses P which step the distributer D are also passed to a gate G10 which opens to provide a pulse inhibiting the output trigger T2 if a space is applied by a gate G1 ... G7. When the output from any gate G1 ... G7 is a mark, the gate G10 is inhibited and the trigger T2 is operated to send a marking signal to the line until a pulse P is able to pass through G10 due to absence of a pulse on the output of the gates G1 ... G7. A pulse from the fifth element of the distributer is passed through a delay device L2 to operate a normally uninhibited trigger T1 to provide a pulse for the magnet M to step the tape for the next character to be transmitted. A pulse from the seventh element of the distributer D is passed through a delay device L1 to reset the counter C. Modification for transmission of service signals. If, during transmission, the tape becomes torn or is exhausted, the closure of contacts TR6 apply a pulse to a trigger T3 and a pulse applied from the fifth element of the distributer D operates the trigger to provide a pulse inhibiting the gate G11 so that pulses cannot be passed from TR1 ... TR5 to the gates G1 ... G5 and the trigger T1 is also prevented from operating the magnet M to step the tape. A pulse from the seventh element of the distributer is applied, with a delay L4 relative to the counter resetting pulse, to a trigger T6 which produces a pulse. The trigger T3 passes a pulse to the gate C5 which is opened by the fifth pulse from the distributer and the counter C is stepped to position 1. The pulse from T6 inhibits gate G8 so that gate G6 cannot be operated by the sixth element of the distributer D, but gate G9 is opened by the pulse from T6 and the second position of the counter so that the seventh pulse from the distributer cycle opens gate G7 to send a mark and the added elements are space and mark in lieu of mark and space for the corresponding character signal with one mark. The trigger T3 is inhibited by the fifth pulse from the distributer, after the contacts TR6 have been opened. Similar action results from the closure of the contacts PB1 to transmit the disengage or clearing-down signal, the output of trigger T4 opening gate G1 for the transmission of the first element of the signal as a mark. In the receiving arrangement, Fig. 2, the pulses P controlling the distributer D<SP>1</SP> are passed through a delay device #S and the resulting pulses P are brought into phase with the incoming signals by the aid of a phase comparator #C which may be of the type described in Specification 670,760, [Group XXXV]. When marking elements on the line coincide with the pulses from the distributer D<SP>1</SP>, the corresponding triggers R1<SP>1</SP> ... R7<SP>1</SP> are operated and pulses pass through delay devices L1<SP>1</SP> ... L5<SP>1</SP> to storage triggers S1 ... S5. Also, the pulses resulting from the response of the triggers R1<SP>1</SP> ... R7<SP>1</SP> to marking elements are passed to the counter C<SP>1</SP> which is invariably operated to the third position (2 or 5 marks) if the signal has been correctly received, in which case the gate G1<SP>1</SP> is opened and the mark elements of the five-unit signal operate the appropriate triggers S1 ... S5. Impulses from elements 2 ... 6 of the distributer D<SP>1</SP> are passed to the gates G3<SP>1</SP> ... G7<SP>1</SP> which are selectively operated. The pulses P<SP>1</SP> applied to a gate G9<SP>1</SP>, normally uninhibited, operate an output trigger OT to send spacing elements to the line O. After the transmission of the spacing start element, the trigger OT will be selectively operated by the marking elements and a gate G8<SP>1</SP> opened by the seventh element of the distributer D<SP>1</SP> will operate the trigger OT to send the marking polarity as the stop element. The triggers R1<SP>1</SP> . . . R7<SP>1</SP> are reset by a pulse from D<SP>1</SP>7 with a delay effected by L6<SP>1</SP> and the counter C<SP>1</SP> is reset by the same pulse delayed by a further device L7<SP>1</SP>. The triggers S1 ... S5 are reset by a pulse from the element D'6 with a delay effected by the device L8<SP>1</SP>. If the counter C<SP>1</SP> is not moved to the position 2/5, the gate G1<SP>1</SP> is not opened and an all spacing signal is sent to the teleprinter to print an error-indicating symbol. If one of the service signals is received, the 6th and 7th elements will be space-mark and a trigger S6 will be operated to provide an output to a trigger SC1 which with the pulse on L5<SP>1</SP> and the removal of the inhibiting controls on L1<SP>1</SP> ... L4<SP>1</SP> will pass a pulse to gate G9<SP>1</SP> which will be prevented from passing the pulses P<SP>1</SP> to operate the trigger OT to the spacing condition and an all marking signal will result. In the case of the engaged signal in which the first code element is marking, the trigger S6 is operated by the space mark combination and the trigger SC2 operates to provide a pulse which inhibits G8<SP>1</SP> so that a continuous spacing signal is sent out. The triggers SC1, SC2 are reset once in every cycle of the distributer D<SP>1</SP> by a pulse over the lead L6<SP>1</SP>. In a modified transmitter, Fig. 3 (not shown), if the counter is in the 0/3 position the gate opened by the 6th pulse from the distributer steps the counter to the position 1/4 so that a second gate is opened by the 7th pulse from the distributer. In this arrangement, the special service signals are terminated by mark space instead of space mark, and the receiving arrangement, Fig. 4 (not shown), is modified so that the trigger corresponding to S6 of Fig. 2 is fired by this combination. Figs. 7, 8 (not shown) show arrangements in which two transmitters as modified by Fig. 3 (not shown) and two receivers as shown in Fig. 2, as modified by Fig. 4 (not shown), have alternate use of a single transmission channel. The successive signals are stored on two sets of triggers corresponding to S1 ... S5, Fig. 2, and are passed to the appropriate teleprinter channels by two distributers stepped by alternate pulses P<SP>1</SP> and operating at one half of the speed of the distributer D<SP>1</SP> which deals with the signals arriving from the line.