GB240954A - Improvements relating to apparatus for supplying high frequency alternating electric current from a low frequency source - Google Patents

Abstract

240,954. Westinghouse Brake & Saxby Signal Co., Ltd., (Union Switch & Signal Co.). July 28, 1924. Thermionic generators for supplying high-frequency currents to a load circuit, such as the track circuit of a railway signalling system, have their plate circuits energized bv a low-frequency supply through a transformer which also serves to transfer the high-frequency currents to the load circuit; and filter devices direct the. two currents into the desired channels. Further valves may be employed for generating a different high frequency, or for amplification. As shown in Fig. 1, the plate circuit of the valve 1 is back-coupled to the grid circuit 7, 11 so as to generate alternating current at the frequency of this circuit. The grid circuit also includes a leak resistance 10 and condenser 6. The plate circuit is supplied from a low-frequency alternator 14 through a transformer 12. The current of higher frequency generated by the valve is taken off by a third coil 23 of the transformer and is supplied to the load 24. A filter or small condenser 25 blocks the supply frequency from the load 24, and a choke 17 blocks the higher frequency from the alternator 14. A separate high-frequency generator 26, Fig. 3, of any suitable type may be connected in the grid circuit instead of employing a back coupling; and a single coil 13, Fig. 3, may be used both as the low-frequency input coil and as high-frequency output coil, the two currents being kept to their proper paths by the choke 17 and condensers 25, 27. Fig. 5 shows a modification in which two separate valves 1<a>, 1<b> are used for generating two different high frequencies, which after amplification are supplied to the track rails C, D of a block section of a railway. A transformer 29 supplies the filament circuits of all the valves in parallel, and their plate circuits are supplied from a transformer 30, the mid-points of the two secondaries being connected together. One end of the secondary coil of the transformer 30 is connected through a filter inductance 17<a> to the plates of one generating valve 1<a>, and one amplifying valve 38<a>. The other end of the secondary coil of the transformer 31 is connected through a similar inductance 17<b> to the plates of the valves 1<b> and 38<b>. Thus for one half cycle of the supply, the plates of valves 1<a>, 38<a> are at a positive potential, and oscillations generated by the valve 1<a> are passed through the coupling 35a to the grid of the amplifier 38<a>, and the amplified currents in the plate circuit are transferred through the coupling 13<a>, 23 to the track rails C, D. During the alternate half-cycles, the other pair of valves are active and current of a different frequency is supplied to the track rails. The intermittent character of the high-frequency currents does not interfere with their employment for signalling. The amplifying valves 38<a>, 38<b> may be omitted.