Patent GB-830440-A (GB)
Title: Improvements in or relating to start-stop telegraph systems
Inventor: MARR ALAN DOUGLAS
IPC: H04L1/00
Filed: 1958-09-11
Abstract: 830,440. Code telegraphy. STANDARD TELEPHONES & CABLES Ltd. Sept. 11, 1958, No. 29111/58. Class 40 (3). A start-stop telegraph transmitter comprising means for transmitting code combinations of signal elements of two kinds together with a start element of a first kind and a stop element of a second kind, includes means operating for transmitting an additional item of information by changing the stop element of a code combination and of each subsequent transmitted code combination to an element of the said first kind and the start element of each said subsequent transmitted code combination to an element of the said second kind, a continuous series of code combinations being automatically transmitted if the transmitter is otherwise idle. In the diagrammatic arrangement, Fig. 1, signals from a teleprinter 5T of station 1 are passed by a transmitter (i over line 3 to a receiving arrangement 10 for the receiver R of a teleprinter 8 of station 2. Similarly signals from teleprinter 8T are passed by transmitter 9 to a receiver 7 and if a fault in transmitter 8T is detected the fault detector 11 modifies the nature of the stop and start signal elements ot the signals transmitted by 9. The receiver 7 detects the reversal start and stop elements and operates the fault indicator 12 to actuate an alarm but restores the correct start and stop elements for the code signal combinations which are passed to the teleprinter receiver 5R. Transmitting arrangement,Fig. 2.-The signal elements are transmitted under control of a timescale counting circuit 13 operated by pulses P from a 5 kc/s. generator 14 to produce positive pulses at 10, 30 ... 130, 138 msecs. from a start instant. The mark and space pulses from the teleprinter transmitter e.g. 8T, are arranged to apply positive pulses on leads 15, 16 respectively connected to gates 22, 23 which receive timing pulses T30 ... T110 and also positive pulses from the T side of trigger 50 with switch 51 in the position shown. The time scale circuit 13 in its zero position in response to a pulse T138 setting trigger 18 to the state SP conducting and providing a restoring pulse through a differentiator 20. With a positive pulse on lead 16 on the occurrence of a normal start element, a P + pulse opens gate 17, changes trigger 18 to the condition 5T conducting, which provides a pulse over conductor 19 to start the time scale circuit 13. The five code elements are passed selectively by gate 22 or 23 to operate the trigger 24 to the mark or space condition to apply the appropriate element to the mark or space outputs 25, 26 respectively. If transmission is normal, i.e. non-occurrence of any fault, the trigger 29 will be in the normal condition with section N conducting, and a pulse supplied to a gate 30 which is opened by a pulse T130 to control the trigger 24 to the M condition if not already in that state. If, however, a fault has been detected the section A of the trigger 29 is conducting and provides a pulse to gate 31 which is opened at T130 and controls trigger 24 to the S condition so that a space element is transmitted as the stop condition. At the commencement of the subsequent signal if the previous stop element was a space a gate 28 is opened by the pulse at T10 and a mark is transmitted as the start element. When the transmitter is idle, the switch 51 is moved to its right-hand position operating section R of the trigger 50 passing a pulse to a gate 52 which is opened when the trigger 29 is operated with fault condition, and passes a pulse to the start section 5T of trigger 18 holding the time scale 13 in operation. Outputs from sections A, R of triggers 29, 50 pass simultaneously to gates 53, 54 of which the former may have positive pulses for marks at, for example, T30, T50, T110 and the latter positive pulses for spaces at T70, T90 to generate MMSSM as the idle signal. Preferably positive pulses for space are applied to the gate 54 at T30 ... T110 to produce the allspacing signal as the idle signal. For a transmission of a fault during the idle period the stop element will be sent as a spacing element and a marking element will be employed for the start element as for fault indication in normal transmission. When the fault has been rectified the change of trigger 29 to the N condition prevents gate 52 from being opened so that the timing circuit 13 is stopped at T138 and restored to normal to respond to the start element when normal transmission is resumed. Receiving arrangements, Fig. 3.-If transmission has been normal, i.e. a fault has not been signalled, the trigger 38 is in the condition N and provides input pulses to gates 34, 37. A normal start element provides a positive pulse to gate 34 which opens on the first P+ pulse and through section 5T of trigger 18 sets the time scale 13 into operation. If the start element is spurious and is not present at 9 msecs. from the initiation of the timing, the incoming line will be at mark and a pulse at T9 will open gate 37 and operate section SP of trigger 18 to stop the timing circuit 13 and restore it to normal. If the start element is genuine, at T10 the output trigger 43 will be changed to S and at T30 ... T110 the gate 44 or 45 will be opened by mark or space received on input 32 or 33 at these instants to operate trigger 43 correspondingly. At T130, the trigger 43 is changed to M to apply mark to the output line 48. If a, fault has been signalled, a space element for the stop condition opens gate 40 at T130 and operates the trigger to the alarm condition A in which a pulse is applied over conductor 42 to a lamp or bell. Also a pulse is applied to gates 35, 36 and the start element of the next signal combination being a mark the first P + pulse will open gate 35 and operate trigger 18 to the condition 5T to start the time input 13. If the start element is spurious, the line will return to space and at T9, gate 36 will open and operate trigger 18 to condition SP to stop and restore the timing circuit 13. If the start element is genuine, the five code elements received will at T30 ...T110 correspondingly operate the trigger 43 to send mark or space to the input lines 48, 49 leading to a teleprinter receiver. When normal transmission has been resumed, a marking element as the stop element will at T130 switch the trigger 38 to its normal condition N. Specification 723,027 is referred to.