Patent GB-744274-A (GB)
Title: Improvements in or relating to start-stop telegraph regenerators
Inventor: TERRY VICTOR JOHN
IPC: H04L25/24
Filed: 1953-08-17
Abstract: 744,274. Telegraph regenerative repeaters. STANDARD TELEPHONES & CABLES, Ltd. Aug. 13, 1954 [Aug. 17, 1953], No. 22655/53. Class 40 (3). In an electronic regenerative repeater for start-stop codes employing a time scale synchronized by incoming signals, means are provided for examining the condition of the incoming line during the nominal stop element, when the line condition should be mark, and if the condition is found to be space, the time scale after being restored to zero is not restarted until a subsequent mark to space transition occurs. The invention has the effect of quickly restoring the repeater to correct operation in the event of lack of synchronism since under such conditions there is an even chance that space will occur during the stop interval. The invention does not assist in regaining synchronism when a space does not occur, but its use is found in practice to effect a substantial reduction in the number of characters wrongly repeated. The invention is described as a modification of the repeater described in Specification 692,411 and includes also facilities for forced stop insertion and long space transmission. In the Figure, gate circuits are denoted by a circle and two position switches by double rectangles. Output conductors from the switches are indicated by corresponding lower-case reference letter. TC denotes the time scale (a counting chain) potentials from which appear on leads T at times (in milliseconds) as indicated. The incoming line controls a modulator (not shown) to which 5 Kc/s. pulses are applied from a source P and appear on mark and space output leads M and S. The pulse source also drives the time scale. A speed of signalling of 50 Bauds is assumed with equal length five unit start-stop code combinations each lasting 140 ms. Operation. Switch 1F is initially in position SZ and switch 2F in position 1. Receipt of a start space element opens gate G1 and operates switch IF to ST whereupon the time scale is reset to zero through gate G3, if not already in that condition, and gate G2 opened to allow pulses from P to operate the time scale. The condition of the mark and space leads are examined at 10, 30, 50, 70, 90 and 110 ms. by gates G7 and G8 and the conditions found repeated to the outgoing line by switch 4F. If forced stop insertion is not provided, the condition of the leads is also examined at 130 ms. At 140 ms. gate G4 is operated to change over switch IF and reset the time scale. The examination of the incoming line during the stop interval is effected at 130 ms. by gate G3 to which the space lead S is connected. The gate is also controlled by switch 3F (see below) which is assumed at present to be in position 0. Switch 2F is set to 1 whenever a mark appears but is changed to 0 is space is detected at 130 ms. With switch 2F in condition 0 gate G1 cannot be opened and therefore the time scale cannot be restarted. When mark subsequently appears on the incoming line, switch 2F is reversed to 1 and gate G1 reconditioned to accept the next space transition. The mark condition is also repeated to the outgoing line by driving switch 4F over gate G10. Forced stop insertion. Gate G10 is omitted together with the examination by gates G7 and G8 at 130 ms. and replaced by a gate G9 opened by the time scale at 130 ms. Long space transmission. This is controlled by a switch 3F which is set to condition 1 at 1 ms. and is controlled to position 0 by the mark lead which is examined at 30, 50, 70, 90 and 110 ms. by gate G6. Switch 3F controls gates G3 and G9 over conductor 3fo and accordingly prevents both switch 2F from being operated by the stop condition test at 130 ms. and switch 4F from being forcibly set to mark over gate G9 in the event of a long space signal. Specifications 653,867, 692,456, 692,457 are referred to.