GB836091A - Improvements in or relating to arrangements for correcting distortion in start-stop telecommunication systems - Google Patents

Abstract

836,091. Telegraph regenerative repeaters. SIEMENS & HALSKE A.G. April 3, 1958 [April 3, 1957], No. 10900/58. Class 40 (3). The invention relates to a distortion correcting arrangement for start-stop code combinations in which the condition of an input circuit St1 is transferred to an output circuit St2 by means of switching elements K5, K6 which are actuated by sampling pulses occurring at the theoretical centres of received signal elements, i.e. at 10, 30, 50, &c. milliseconds in the example considered. The sampling pulses are derived from a counter Z1 responsive to high-frequency pulses from a source Tb, the pulses being applied to the counter to initiate a cycle of operation in response to the reception of a start (mark) signal which causes the triggering of a cycling switch US and the consequent closure of a gate K2. Counter Z1 also produces pulses at 20, 40, 60, &c. milliseconds which are applied to a further counter Z2 which operates after seven pulses, i.e. at 140 milliseconds at the end of a code combination comprising a start element, five permutable code elements and a stop element, to reset cycling switch US and terminate the operation until a new start signal is received. The resetting of switch US also closes a gate K3 which causes a pulse to be applied from source Tb to switches K5, K6 via a switching device D and a mixer M7. This operation ensures that the output circuit St2 is positively aligned with the condition of input circuit St1 at the termination of each code combination. In accordance with the invention, a gate K4 is included between counter Z2 and cycling switch US and is controlled by the output circuit St2 so that the resetting of switch US only takes place if the output has been set to a normal stop (space) condition for the last signal element. If a mark condition exists, gate K2 remains open, a new cycle of operation is immediately started and the output and input circuits are not positively aligned at 140 milliseconds. The arrangement according to the invention allows the apparatus to repeat a long mark switching signal, e.g. a dialling signal. In the event of such a signal which terminates in the interval between 130 and 140 milliseconds the invention prevents distortion, since, in the absence of gate K4, the positive alignment of the output circuit at 140 milliseconds would cause the signal to be reduced in duration to 130 milliseconds. Triggering of switch US by a start signal is effected by an input switch ES which is actuated by the start signal transition via a differentiation circuit Di and closes a gate circuit K1 whereby pulses from a source Ta are applied to the switch US. A pulse from the differentiating circuit is also applied to close switching device D for a period sufficiently long to prevent a pulse from source Tb passing through gate K3 (which is open until switch US is triggered) to mixer M7 and gates K5, K6. The pulses from Ta are 180 degrees out of phase with those from Tb.