Patent GB-777695-A (GB)
Title: Type printing telegraph system with error correction
Inventor: DUUREN HENDRIK CORNELIS ANTHON
IPC: H04L1/18
Filed: 1952-05-13
Abstract: 777,695. Code telegraphy. STAATSBEDRIJF DER POSTERIJEN TELEGRAFIE EN TELEFONIE. May 12, 1953 [May 13, 1952], No. 12124/52. Class 40 (3). A two-way radio-telegraph system of the kind in which information signals comprise a constant number of signal elements of two kinds having a given constant ratio of elements of one kind to those of the other kind, and in which mutilationdetecting means is provided at a receiving station for signalling to a transmitting station that a signal has been received in a mutilated condition not having the given constant ratio of elements and for calling on the transmitting station to repeat the said signal is characterized by the provision of a simplified mutilationdetecting means brought into operation when a special signal indicating that the transmitting station is not transmitting information signals is received, said simplified mutilation-detecting means examining only a predetermined group of elements and calling for repetition only if an element of said predetermined group in said special signal is mutilated. This reduces the number of repetition requests interrupting traffic in the other direction; it is particularly useful when information traffic in the first direction has ceased due to bad conditions wherein the special idle-time signal may be frequently mutilated. Fig. 1 shows the elements of the repetition request signal I, the special idle-time signal α, and idle-time signal # which is used to indicate that a station previously transmitting signals α is about to transmit traffic signals, and to cause the receiving station to switch back to its normal mutilation detector. Fig. 2 shows the means at a receiving station for switching between normal and simplified mutilation detectors. A repetition request is initiated by operation of relay SX whose circuit is connected, via contacts be<SP>2</SP> of switching relay BE, either to the normal mutilation detector (not shown) over conductor C, or to the simplified mutilation detector which comprises relay contacts d<SP>1</SP>, el, f<SP>1</SP> and d<SP>2</SP>, e<SP>2</SP>,f<SP>2</SP>. The simplified mutilation detector therefore examines signal elements d, e and f only, and it will be seen that all combinations of these elements other than those shown (Fig. 1) for signals α and # will provide an earth for relay SX. Thus when the simplified mutilation detector is in use a repetition request will result from mutilation of signal α or signal #. Should the station transmitting idle-time signals α require a repetition of traffic in the other direction it sends signal I which operates apparatus to instigate the necessary repetition but also opens relay contact rq in the circuit of relay SX so that the simplified mutilation detector does not energize relay SX in this instance. The only combination of signal elements d, e, f which operates relay BE is that shown for signal #. Reception of signal #, therefore, operates relay BE, which holds over its contacts be<SP>1</SP>, and switches relay SX to the normal mutilation detector by contacts be<SP>2</SP>. Normal traffic working may then proceed. Relay BE is released only if contacts b, d4 and f<SP>4</SP> are simultaneously opened. This is brought about by reception of idle-time signal α which thereby causes contacts bc<SP>2</SP> to change over and brings the simplified mutilation detector into use. Accidental release of relay BE by a mutilated signal is prevented by closure of contacts xc<SP>1</SP> when SX operates to request repetition. Specifications 632,795, 666,316, 693,211 and 710,700 are referred to.