Patent GB-666974-A (GB)
Title: Improvements in telegraph distributors
Inventor: DAIN GORDON TAYLOR
IPC: H04L13/14
Filed: 1948-06-14
Abstract: 666,974. Type-printing telegraphy. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 19, 1949 [June 14, 1948], No. 16003/48. Class 40 (iii). In a telegraph distributer having a plurality of electrical switching circuits to which code potentials are applied simultaneously said circuits are adapted to be rendered effective in turn and each at any predetermined instant during a corresponding code element transmission period. The Specification describes start-stop telegraph electronic transmitting arrangements. An assymetric multi-vibrator V1 has a voltage waveform at its right-hand grid as shown in Fig. 3, and this is applied via a cathode follower V9 (connected as a triode) to the left-hand grids of trigger pairs V2-V7. The right-hand valves of these pairs are normally conducting and the cathode bias resistors R2 ... R13 are so graded in value that after 20 ms. the sweep voltage (Fig. 3) transposes the first trigger pair V2, and after each further 20 ms. transposes a further additional trigger pair. When V2 is transposed it extinguishes a control valve V10 over C2, R15 and applies positive bias to the control grid of the next control valve V11. When the valve V10 was conducting it applied a negative bias from the common anode resistor R20 to the left-hand grid of a transmitting trigger V8, the right-hand half of which therefore conducted to cause the relay T to transmit a starting space condition. If tape contacts associated with the lead 1 are in the spacing position lead 1 will be disconnected and the screen voltage of V11 will be positive. This valve will therefore conduct since its control grid is now also positive and the consequent fall in potential at the common anode resistor R20 retains the trigger V8 and relay T in their spacing condition. If the tape contacts are in their marking position, lead 1 will be earthed, thus earthing the screen grid of V11 which cannot therefore conduct, causing the common anode resistor R20 to bias V8 positively and transmit a mark. As the sweep voltage increases the triggers V2 ... V7 are transposed in turn at 20 ms. intervals and the control valves V11 ... V15 conduct or not according to the code set up on the tape contact leads 1 ... 5, each control valve V11 ... V15 being extinguished when its following trigger pair V3 ... V7 is transposed. V7 is transposed after 120 ms. and for the remaining 30 ms. of the sweep cycle no control valve is conducting and a marking or stop condition is transmitted. When the sweep voltage returns to zero again all the trigger pairs V2 ... V7 are restored simultaneously and V2 makes V10 conducting over C2, R15 to transmit a fresh start condition. When V7 was first transposed it made V16 conducting to operate tape relay P and step on the tape one character. As the sweep now continues the new code elements, and stop condition, follow the start signal in sequence as before. In an alternative embodiment (Figs. 4 and 5, not shown), the control valves are replaced by metal rectifier pairs, one rectifier of a pair being by-passed to earth when a marking condition is present on the associated tape-contact lead. The other rectifier then transmits a positive pulse from its associated trigger valve to the marking triode of the transmitting trigger. When the tape contacts are spacing both rectifiers of the pair pass a positive pulse, one to the spacing and the other to the marking valve, both pulses being applied over time-constant circuits of which the spacing circuit has the longer delay. The spacing pulse therefore persists longer than the marking pulse and triggers the transmitting valves to the required spacing condition. Testing. By making the bias resistor values of the trigger pairs V2 ... V7 variable the lengths of the individual signal elements can be varied to produce artificial distortion for test purposes.