GB545690A - A system for changing the frequency of electric oscillations - Google Patents

Abstract

545,690. Valve modulating and generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 5, 1940, No. 17330. Convention date, Dec. 6, 1939. [Class 40 (v)] A system for changing the frequency of an electric oscillation comprises a line in which travelling waves are set up from a source and to spaced points on which valves are connected and have their impedances cyclically varied by out of phase voltages from a second source so that the valves successively feed the output at a frequency equal to the sum or difference of the sources. Fig. 2, shows a line comprising a pair of co-axial conductors with valves having a common output spaced #/4 apart. The modulating potentials frequency modulated on a carrier-wave as by a thermionic reactance in parallel with an oscillator circuit, Fig. 5 (not shown) are applied to terminals X, X and produce two-phase energy in the stator of phase shifter 7. Phase displaced voltages are applied to the valve pairs from the rotor through chokes 6 to render the valve pairs cyclically operative. Blocking condensers BC prevent the line short-circuiting the modulating voltages. In this way the frequency of the master oscillator fed to the output is increased or decreased. Instead of twophase operation polyphase operation may be employed. The valves are neutralized by condensers NC and with an even number of elements their effects on the line cancel out and do not cause reflections or standing waves. Saturation excitation is preferably used so that the output amplitude is constant. In a modification, Fig. 3, single valve stages are used and the line instead of being terminated by a matching impedance Z0 is backcoupled to the oscillator output circuit 45. In this arrangement the capacities imposed on the line by the valves are tuned out by reactances TR and the oscillator 41 is stabilized by a line 42. The line instead of being back-coupled may be terminated by a matching impedance, Fig. 4 (not shown). Fig. 6 shows a relay station in which a receiver 80 and amplifier 82 feed the input to a converter 90 as previously described and in which frequency from a local source 95 is added before retransmission. Specification 413,647 is referred to.