Patent GB-779370-A (GB)
Title: Improvements in or relating to regenerative repeaters comprising a double memory forsignals in a start-stop-code
Inventor: OBERMAN ROELOF MAARTEN MARIE
IPC: H04L25/24
Filed: 1955-02-08
Abstract: 779,370. Regenerative telegraph repeaters. STAATSBEDRIJF DER POSTERIJEN, TELEGRAFIE EN TELEFONIE. Feb. 8, 1955 [Feb. 11, 1954], No. 3779/55. Class 40 (3). In a regenerative repeater for telegraph start-stop code combinations, the received signal elements are stored successively in a common memory device, each for the duration of one element, and are read off and retransmitted under the control of a timing means operating independently of the timing means controlling the reception. The invention reduces the risk of misreading in the event of signal distortion where a number of repeaters are operated in tandem. The Specification describes both a mechanical and an electronic repeater, each employing conventional midpoint sampling. In the mechanical repeater, the memory device is a capacitor or polarized relay. In the electronic repeater, a valve trigger circuit is used. Mechanical repeater, Fig. 7. The repeater comprises two distributers which are driven by a common shaft via slip couplings or differential gears. For signals in the 5-unit code at a transmission speed of 50 Bauds, the receiving distributer R has a duration of revolution of 130 m. sec., whilst the transmitting distributer '1' has a duration of either 138 or 140 m. sec., depending whether 7 or 7¢-unit transmissions are employed with minimum stop elements of 18 and 20 m. sec. respectively. The received signals operate relay OR, the start signal energizing the decoupling magnet of the receiving distributer R to lift the pawl and release the distributer arm. The received intelligence elements are thereafter sampled briefly by contacts c-g and stored in a common memory device in the form of capacitor C or a polarized relay. Immediately after release of the receiving distributer arm, auxiliary contacts a, b are bridged to release the transmitting distributer T. This then takes up in turn at contacts i-m the potentials on capacitor C to control the transmitting polarized relay ZR and adds the invariable start and stop elements by means of permanent negative and positive potentials applied to the auxiliary segments hand n. In systems having calling and closure signalling, the incoming stop elements must be sampled as for the intelligence elements, and the distributers are modified appropriately. If due to mistiming of a received signal, the receiving distributer is restarted for a subsequent signal before the transmitting distributer has returned to its initial position, the transmitting distributer must continue its rotation without stopping (its duration of revolution ensuring the minimum length of stop signal), and to effect this the auxiliary contacts a, b on the receiving distributer are arranged so that the transmitting distributer decoupling magnet is energized to lift the pawl for a period up to a maximum of 10 m. secs. .. Electronic repeater, Fig. 5, illustrates the circuit and Figs. 6 and 6a waveforms throughout the circuit at the points indicated. Received signals in the 5-unit code at a transmission speed of 50 Bauds are received on relay OR, the start element causing contact or to apply a positive potential through rectifier G1 1 to trigger a start-stop device B1, B2 of which valve B1 is non-conducting in the rest condition. The rise in anode potential of valve B2 then allows a first 50 c/s pulse generator to start operating, the first pulse appearing after 10 m. secs and being applied from terminal 6 via rectifier G3 to trigger a first timing circuit B5, B6 which applies back a positive holding potential through rectifier G2 to the grid of B1 to maintain the generator in operation. Timing circuit B5, B6 has an approximate holding time of 120 m. sees. and is triggered off positively at 130 m. secs. from start by the seventh generator impulse. Positive and negative pulses are obtained from the generator by differentiation at terminal 6 and 5 respectively and these are applied to a rectifier gating network G10-G15 to sample the incoming signal conditions and set a trigger stage B13, B14 accordingly. This trigger stage constitutes the memory device. The positive holding potential applied from the first timing circuit at 10 m. secs. is also applied over rectifier G6 to trigger a second start-stop circuit B7, B8. This circuit is associated with a second 50 c/s pulse generator B9, B10 and functions in a manner similar to the first to start the generator. The first pulse under normal conditions appears after 10 m. secs., corresponding to 20 m. secs. from start, and triggers a second timing circuit B11, B12 which in like manner applies back a holding potential via rectifier G9 to the grid of B7 in the start-stop circuit. In this instance, the timing circuit has a holding time of approximately 110 m. secs. and is positively reset after this time by a pulse from generator B9, B10. To ensure the production of a minimum length of stop signal, the second timing circuit also applies a potential to the start-stop circuit via rectifier G7 and a delay network C8, R41. This arrangement becomes effective when the timing circuit is reset and applies a negative potential to the grid of B7 for a period to delay the retriggering of the circuit over rectifier G6. The regenerated signals are transmitted by trigger circuit B15, B16 controlling output relay ZR and condition of the memory device B13, B14 is read off and transferred to the trigger circuit by rectifier gating network G17-G22. This network receives the oppositely-phased square waveforms from terminals 7 and 8 of the first pulse generator B3, B4 and also the corresponding, but 10 m. sec. delayed waveforms from terminals 9 and 10 of the second pulse generator B9, B10. The network functions to transfer the memory condition only when the corresponding waveforms from the two generators are of like polarity. The second generator normally starts 10 m. secs. after the first. Thus the read-off period corresponds to the rest period and further evenly numbered halfcycles of the second generator in so far as they coincide with odd numbered half-cycles of the first generator. During normal operations, therefore, the read-off and transmission coincides with the sampling and storage by the reception circuit. In the event of mistiming of start-signals, however, the second generator may be started into operation with a delay over the first of more than 10 m. secs. due to maintenance of a minimum length of stop signal by delay circuit C8, R41. The operation then proceeds as indicated in the last three curves of Fig. 6a with delayed read-off times. The readoff periods may decrease to a fraction of a millisecond so that delays between receiving and retransmitting operations of up to 10 m. sees. can be accommodated. In the event of mistiming, it is necessary to ensure that the start signal is not read-off immediately (as will normally occur at the first half-cycle of the first generator and the reset condition of the second generator), and to prevent this the rectifier gating network G17-G20 is rendered ineffective by a positive potential applied from the second start-stop circuit B7, B8 via rectifier G16 during the rest period. Furthermore, in the event of mistiming, it is also necessary to make special provision to read-off the stop signal since, at the read-off time, the first generator will have stopped. Accordingly a second rectifier gating network G23, G24, G25 and G30 is provided in parallel with the first and is supplied with positive and negative pulses from B11, B12 when the circuit resets. The two networks are connected in parallel by rectifiers G26-G29. The circuit may be rearranged so that the gating networks are controlled only by the second generator and to ensure that the read-off action cannot lead with respect to the receiver sampling action, the second generator is arranged to be started with a small, but constant, delay. The receiving and transmitting relays may be replaced by valve trigger circuits.