GB769125A - Improvements in or relating to devices for indicating the presence of a particular pulse group having preselected time intervals between the pulses thereof - Google Patents

Abstract

769,125. Pulse selecting circuits. TELEFONAKTIEBOLAGET L. M. ERICSSON. Feb. 23, 1955 [Feb. 26, 1954], No. 5488/55. Class 40(6) In a circuit for indicating the presence in a pulse train of a particular group of pulses having predetermined time intervals between them, the pulses are applied to a delay network from the tapping points of which connections are made to a cascaded connection of electric discharge tubes so that only when the required pulse group is applied are all the tubes simultaneously actuated to pass an output pulse and thus give an indication of the required pulse group. Fig. 1a shows a pulse train in which it is required to indicate the presence of the three pulses 1, 2 and 3 in the first group of the train. These are applied as shown in Fig. 2 to the input terminals of a terminated delay network 6, the tapping poirits 7, 11 and 10 of which are such that the delay between 7 and 11 and between 11 and 10 respectively are equal to the intervals between pulses 1 and 2 and 2 and 3 respectively. The discharge tubes 12, 13 and 14 are normally biased to be non-conductive. It will be seen from Fig. 1b and c that only during the occurrence of the pulse 3 of the required group are all the tubes 12, 13 and 14 simultaneously conductive so that a pulse from generator 32 will pass to the output 30. In a modification shown in Fig. 3 the tubes are replaced by biased semiconductor diodes 37. 41 which are normally conductive and thus normally form with resistors 34 and 38 an impedance network between the input terminals 7, 8 and the output 30 which has a very high attenuation. When the required pulse group is present at the input 7, 8 of the delay line 6 the diodes 37, 41 are rendered non-conductive and an output signal appears at terminal 30.