Patent GB-774509-A (GB)
Title: System for transmitting telegraph signals
Inventor: DUUREN HENDRIK CORNELIS ANTHON
IPC: H04L27/02
Filed: 1952-01-15
Abstract: 774,509. Telegraph systems. STAATSBEDRIJF DER POSTERIJEN TELEGRAFIE EN TELEFONIE. Dec. 29, 1952 [Jan. 15, 1952], No. 1185/52. Class 40 (3). In a telegraph system the signals, which are transmitted over a route incorporating a carrier frequency link, are converted into a balanced form, i.e. the number of marking elements is made equal to the number of spacing elements, and are utilized to modulate a carrier frequency, and the information is transmitted by one of the side-bands of the modulated carrier, with or without carrier suppression. The balanced signal is formed by converting the usual five-unit code into an eight-unit code having an equal number of marks and spaces, or each element of the signal is transformed to two half elements of opposite polarities, the first half element having the polarity of the element which is converted, i.e. a mark element being represented by a mark half element followed by a space half element, and a space element represented by spacing and marking half elements respectively. Transmitting-arrangement. The signals to be converted into the balanced form by the method of dividing the code elements are fed to a trigger Tr1 which passes outputs corresponding to the signal in its original and inverted form to points A, B of rectifier networks c, d having outputs C, D connected to a trigger Tr2 passing the converted signal to a modulating device for radio transmission. The terminals E, F and G, H of the networks c, d are fed at S, R with biasing voltages comprising a square waveform (curve 2, Fig. 7b) of a frequency corresponding to the time of the incoming elements (i.e. the baud frequency), and positive pulses (curve 3, Fig. 7b) at a frequency twice that of the waveform 2, and at 100 c.p.s., if the baud frequency is 50 c.p.s. The 50 cycle waveform acts as a switching voltage for the networks c, d and the pulses, curve 3, operate the respective network to pass the voltage existing at A or B to the input of the trigger Tr2. At instant t1, positive voltage is passed from A to C and to the trigger Tr2, and at instant t3, the network d being biased, the voltage at the lower output of Tr1, which is reversed in relation to that shown in curve 1, Fig. 7b, is passed from terminal D to the trigger Tr2. At instant t5, the network c is effective and the voltage at the upper output of Tr1 is passed to terminal C and the input of trigger Tr2. At the instant t7 the lower network d is made operative and the voltage, now positive, at the lower output of Tr1, is passed via the network d to the input of Tr2. Receiving-arrangement. The received signals are passed as pulses of short duration to a double trigger arrangement Tr1, Tr2, Fig. 9, a start element W being received as a positive pulse on W1 followed 10 ms. later by a positive pulse on R1. A stop element R is received as a positive pulse on R1, followed by a positive pulse on W1 after an interval of 10 ms. The receiving relay A has its winding W energized and tube d conductive for the reproduction of the start polarity elements, whilst tube a is conductive and winding R of relay A energized for the reproduction of the elements of stop polarity. The tubes b, c are cut off immediately when tubes a, b conduct, and the anodegrid interconnections of the tubes a, d have delay circuits t<SP>1</SP>, c<SP>1</SP> and t<SP>2</SP>, c<SP>2</SP> such that the voltages at the plates of tubes a, d are applied respectively to the grids of tubes d, a with a delay greater than the duration of the received pulses, but less than 10 ms. Assuming that the circuit, Fig. 9, is in the start condition with the tubes b, d conducting and winding W energized when the first pulse of the start element has been received, the reception after 10 ms. of the pulse on R1 will make c conductive and cut-off valve d, but owing to the delay circuit c<SP>1</SP>, t<SP>1</SP> valve a is not made conductive. Fig. 10 shows diagrammatically the reception of a signal with divided code elements, the valves which are in a conductive state being indicated by the shaded squares. When the first impulse of the stop element is received the positive pulse on R1 makes valve a conductive cutting off valve b, and valve c remains conductive. The next impulse, positive on W1, makes valve b conductive, thus cutting off the valve a, but d is 'not made conductive so that the winding W is not energized. At the instant t4 corresponding to the beginning of two positive (start polarity) elements, the positive pulse on W1 makes d conductive, operating relay A to the start condition. At the instant t5 the next pulse on R1 makes c conducting, and at t6 the positive pulse on W1 again makes the valve d conductive so that the relay A remains in the start polarity condition. At the instant t7 the positive pulse on R1 operates the valve c cutting off the valve d, and at t8 the pulse on R1 makes valves a, c conductive so that the relay A moves to the stop polarity condition. At t9, the pulse on W1 makes valve b conducting, cutting off the valve a, but owing to the delay circuit c<SP>2</SP>, t<SP>2</SP> the valve d is not made conductive. Detection of mutilated signals. If at the instant t7, the signal is mutilated and as indicated by the dotted line, a positive pulse is received on R1, the valve a is made conductive, valve b non-conductive and valve c is held in its conductive condition. As a result, the positive pulses on R1 and at the anode of valve b apply a positive potential to rectifiers 7, 8 and point e so that a positive pulse is applied at g to operate a signal alarm, indicating that mutilation has occurred, and preferably operating a device requesting signal repetition. In the example described, the erroneous element at the instant t9 does not cause mutilation of the signal received by the relay A. A further example described in connection with Fig. 11 (not shown) shows the operation of the above arrangement in response to a mutilated element which causes incorrect reproduction of the received signal.