Patent GB-655728-A (GB)
Title: Improvements in or relating to regenerative telegraph repeaters
Inventor: DAIN GORDON TAYLOR
IPC: H04L25/04
Filed: 1948-06-14
Abstract: 655,728. Telegraphy. BRITISH TELE-COMMUNICATIONS RESEARCH, Ltd. June, 14, 1948, Nos. 16002 and 31091. [Class 40 (iii)] In an electronic startstop telegraph regenerative repeater the regenerated signals are produced with a pre-determined delay after an incoming start signal is received, but only if the start signal persists throughout the delay period. All the valves used are double-triodes and the letters L and R will be used to denote the left or right valve respectively of each pair in the Figure, e.g. V1L, V1R. In the normal state with marking current on the line IN the following valves are conducting, V1R, V2R, V3R, V4L and V5R. When a spacing start element is received it operates a line relay RL over its left-hand coil and at contact RL1 removes the short-circuit from a condenser C1 which changes over resistors R2, RV1. After a time (10 ms.), determined by the resistor RV1, valve V1L conducts, but if the start signal is spurious and the marking condition returns before 10 ms. the condenser C1 discharges rapidly and the circuit returns to normal. When V1L conducts it extinguishes V1R and the consequent positive anode pulse causes V2L and V3L to conduct, extinguishing in turn V2R and V3R. The anode pulse from V2R fires a neon or other discharge tube V7 and the consequent current in resistor R32 biasses the valve V5R, connected as a diode, to cut-off. The valve therefore presents a high impedance to current over the path R25, RV4, R34 and this current rapidly charges a condenser C10 instead, causing the multi-vibrator V4L, V4R to generate pulses at a frequency, 50 c.p.s., determined by the resistor RV4. When V4L is non-conducting a positive pulse is applied to the grids of valves V6L and V6R, both of which are normally biassed nearly to cut-off. If a space is being received, contact RL1 short-circuits the grid resistor R36 to earth and no pulse reaches V6L, V6R conducting and operating the transmit relay S to space. If a mark is being received, the grid potential derived from resistor R36 is arranged to be greater than that derived from resistor R40 and V6L conducts, causing relay S to send on a mark. After 120 ms. the flip-flop valve V3L is again extinguished, causing V5L to conduct and so operate the line relay RL to mark. This ensures that a stop element is transmitted whether or not one is received. After a further 10 ms. the flip-flop valve V2R again conducts and its negative anode pulse extinguishes the neon tube V7, allowing V5R to conduct again. This therefore presents a low impedance and holds the grid of V4R near earth potential, thus locking the multi-vibrator V4. All circuits are now normal, ready to receive a further character signal. In the first Provisional Specification the automatic provision of a stop element and the suppression of spurious (short) start elements is accomplished by a somewhat different circuit arrangement. The minimum length of a " correct" start element is determined by the pre-determined delay between the operation of two electromagnetic relays, which in turn is dependent upon a time-constant circuit in a valve biassing arrangement.