GB246195A - Improved method and apparatus suitable for receiving cable and like signals - Google Patents

Abstract

246,195. Telegraph Construction & Maintenance Co., Ltd., and Stevenson, G. E. Oct. 4, 1924. Thermionic receivers for line telegraphy.- Current impulses received over a cable are amplified by causing them to modulate a locallyproduced alternating current of audio-frequency which is then amplified and rectified and finally acts upon a D.C. relay or marker. Modulator system. The cable core 1 and earth 2 are connected respectively to the grids of the valves 3, 3<1> and (by way of impedances 4. 4<1> and a potentiometer 5) to the valve filaments. A Wheatstone bridge is formed as follows : One pair of arms comprises the filament-plate paths of the valves 3, 3' and another the impedances 6, 6'; one diagonal comprises the audio-frequency generator 8 and plate battery 7 in parallel, together with impedances 9, 10; and the conjugate diagonal comprises an output coil 11 shunted if necessary by a filter 12. Impulses received from the cable 1 upset the balance of the bridge and permit alternating current to pass to the output coil 11. Alternatively, the coil 11 may be omitted and the impedances 6, 6' replaced by the primaries of two transformers as described below. In the arrangement shown in Fig. 2, the impulses are applied to the outer grid 40 of a tetrode valve 13, and in this case the first pair of arms of the Wheatstone bridge comprises the space between the filament and inner grid 41 and between the filament and plate 42 respec. tively of the valve, while the second pair comprises the condensers 14, 14<1>; one diagonal contains the A.C. source 8 and the other the output coil 11 shunted by the filter 12. Rectifying system. The alternating potential released as described above under the control of the received impulses is after one or more stages of amplification applied to the grid of a triode rectifier, the plate circuit of which contains a telegraphic relay or recorder shunted by a condenser and by a battery which is arranged to prevent current from normally flowing in the instrument. In the modification shown in Fig. 4, the bridge at the left-hand side is similar to that shown in Fig. 1, but the output coil 11 of that Figure is replaced by a telephone 31 employed for testing the balance of the bridge, while the impedances 6, 6<1> constitute the primary coils of transformers. The output currents, after amplification at 25, 25<1>, are communicated respectively to the grids of the rectifying valves 15, 15'; and as these currents are normally equal there is normally a balance in the bridge at the right-hand side of Fig. 4. The four arms of this bridge comprises the filament-plate paths of the two valves 15. 15<1> and the resistances 29, 29<1>, while one diagonal comprises the battery 19 and the other diagonal comprises the telegraphic receiver 20. On receipt of an impulse from the cable 1 the currents in the coils 6, 6' become unequal, the balance of the valves 15,15' is upset, and direct current flows in the instrument 20.