Patent GB-733070-A (GB)
Title: Improvements in or relating to apparatus for receiving electric telegraph signals
IPC: H04L17/30
Filed: 1952-03-06
Abstract: 733,070. Printing telegraphy receivers. GENERAL ELECTRIC CO., Ltd., BAYLISS, A. J., and PEDDLE, E. A. R. March 6, 1953 [March 6, 1952], No. 5866/52. Class 40 (3). Apparatus for receiving electric telegraph signals and decoding them electrically comprises a plurality of storage means which are arranged respectively to store the several elements of a code which corresponds to a character and'which is reprerented by a pulse or pulses in the signal applied to the apparatus, counting means adapted to determine the number (or numbers) of a particular element (or elements) in such a code, and a plurality of means adapted to be operated by electric signals supplied by both the storage means and the counting means such that each of this plurality of means is responsive to pulses in an applied signal representing a particular respective code. The embodiment utilizes electronic valves of the cold cathode type to form the receiving system of a teleprinter, the rest of which may be constituted by the apparatus described in Specification 733,071. Valves 27 ... 31 comprise the storage means for the five-element code and are arranged to be conducting for a mark element and non-conducting for a space element. Valves 61 ... 67 form the counting means and are adapted to count the mark elements in each signalled character by being fired in sequence by the mark elements only. Valves 46 ... 50 are typical of the operating means and have type-setting electromagnets (such as 41 ... 45) in their anode circuits, each of the thirty-one codes that may be signalled having an associated valve and electromagnet. The telegraph signal is applied over a pair of lines 1 to a high-speed relay L whose contact L1 is shown unoperated but in the normal rest (mark) condition would be in the other position. Valves 2 and 3 are arranged in a bi-stable circuit with valve 2 conducting (as described below) during rest periods. Valve 6 is arranged as a relaxation oscillator at the frequency (50 c/s.) at which code elements occur in the applied signal. On receipt of a " start " signal contact L1 applies a positive pulse to trigger valve 3 which fires, operating relay E and extinguishing valve 2. Contacts El apply H.T. to valves 11 ... 16, 27 ... 31 and 61 . . . 67, and also remove the positive bias from the cathode of valve 6 which starts oscillating. Contact L1 also gives a positive pulse to the grid of valve 6 each time a " space " element is received and serve to keep the oscillations synchronized with the code elements of a character. Valves 11 . . . 16 are arranged in cascade and fire in sequence on successive positive half-cycles of the oscillations from valve 6. The cathodes of valves 11 ... 15 are respectively coupled to valves 19 ... 23 to supply positive pulses to their grids in turn when the former valves fire. The anodes of valves 19 ... 23 are fed by contact LI during "mark" elements only; so these valves fire if the pulse from the appropriate distribution valve 1<SP>1</SP> . . . 15 coincides with a " mark " element, and extinguish at the end of such mark element. The cathodes of valves 19 . . . 23 are coupled to the grids of storage valves 27 . . . 31 respectively so'that when the former valves fire the latter are triggered and remain conducting till the apparatus as a whole is re-set in readiness for the next character as described later. The cathodes of valves 27 ... 31 are connected respectively to bus-bars 35 . . . 39 which thus represent the code elements of a signalled character, a mark element being represented by a positive voltage on the corresponding bus-bar. To determine what character has been signalled and to operate the appropriate electromagnet, each valve such as 46 ... 50 has its grid connected via rectifiers to those bus-bars which should be positive when the character the particular valve is associated with is signalled. Thus if all the said bus-bars are positive the valve has a positive bias on its grid and fires as soon as contacts P1 close. If one of the connected bus-bars is not raised to a positive voltage (due to its associated storage valve being non-conducting) then the rectifier connected to that bus-bar will form a relatively low impedance and the valve grid will not receive sufficient positive bias to fire. To remove ambiguity (such as the valve 46 firing for any character for which bus-bar 36 is made positive), a cascade counter (valves 61 ... 67) is provided to count the number of mark elements in a code signalled and supply positive priming bias to those operating valves associated with characters containing that number of mark elements in their codes. For this purpose the valves 46 ... 50 &c. are segregated into five groups according to the number of mark elements required to fire them and each of the groups is biased from valves 63 ... 67 respectively. The anode of a valve 68 is supplied via contact L1 and its grid is fed direct from the oscillator 6 so that valve 68 fires each time a mark element is received. The cathode of valve 68 is coupled to the grids of valves 62 ... 67. Valve 61 fires immediately relay contacts El supply H.T. and thus valve 62 fires on the first mark element. As the "stop" signal is a mark element valve 63 will be conducting finally if the code signalled contained only one mark, whilst only valve 67 will be conducting if the code contained five marks-preceding valves being extinguished as successive valves fire. Thus only that group of operating valves dealing with the specific number of mark elements signalled will receive a positive priming bias. A transitional ambiguity still exists, since, for example, during the signalling of the code to operate valve 49 the first two mark elements would bias the grid of valve 47 and the third mark element would act as a " stop " signal to fire valve 64 and hence prime and fire valve 47 incorrectly. This is avoided by the provision of contacts P1 which close only on the completion of a seven-element code signal. Contacts P1 are operated by a relay P in the circuit of a valve 74 forming a mono-stable pair with a normally conducting valve 75. The seventh positive half-cycle from oscillator 6 fires a valve 16 on the end of the distributer chain 11 ... 15 and this triggers valve 74 to temporarily operate relay P. The firing of valve 16 also triggers valve 2 which fires and extinguishes valve 3 which releases relay E. Contacts E1 remove the H.T. supply from valves 11 ... 16, 27 . . . 31 and 61 ... 67 and put an extinguishing positive bias on the cathode of oscillator 6 and the apparatus is then ready to receive the next character code.