Patent GB-979614-A (GB)
Title: Improvements in or relating to electromagnetic wave switching systems
Inventor: WALSH ARTHUR STEPHEN
IPC: H01P1/10
Filed: 1960-01-14
Abstract: 979,614. Keying carrier frequencies; transistor switching circuits. GENERAL ELECTRIC CO. Ltd. Jan. 11, 1961 [Jan. 14, 1960], No. 1470/60. Headings H3R and H3T. [Also in Division H1] An on-off carrier switching system comprises a magic-T or 3 db coupler 3 feeding two waveguide branches equally but with 90 degrees phase difference produced by a 90 degrees phase shifter in one branch (unnecessary with a 3 db coupler) and each including variable phase shifters producing alternately and respectively 0 degrees and 90 degrees phase shift when ferrite components are energized by an input 14 or 16. The two branch outputs are then combined in a 3 db coupler 9 so that its outputs are substantially equal and in phase or anti-phase, and then pass to the collinear arms of a magic-T 4 so that an output is derived from guide 2 when the inputs are in phase or diverted to a dummy load 8 when in anti-phase. To bias the system to a condition in which input 16 is normally energized, and input 14 de-energized, rectifiers 24, 25 through directional couplers 17, 18 detect unequal small portions of the two inputs to magic-T 4 so that a differential output is obtained and after amplifying applied to energize one only (16) of coils 14, 16. Moreover, due to the coupler 9, no energization or equal energization of the phase shifters causes a 90 degrees phase difference such that all energy is directed to the rectifier 24 and produces the same stable condition of only coil 16 being energized. Signalling is produced by a D.C. or pulse input over a transistor switching circuit and a system of diodes, reversing the control action of the rectifiers 24, 25 on the phase-shifting coils 14, 16, i.e. control is exercised by the rectifiers in both the on and off signalling periods. Alternatively, control may apply only during one signal condition. The waveguide portions between couplers 3, 9 may be slightly unequal to increase the system bandwidth, e.g. by making unequal the radii of curvature connecting coupler 3 with the parallel lengths of waveguide. In a modification the coupler 9 is omitted and as in Specification 957,713 one or each of phase shifters 12, 15 further energized by an auxiliary modulating current, and the directional couplers 17, 18 and rectifiers connected to the non-collinear arms of the magic-T 4. The output of one rectifier is then compared in phase with the modulating current in a phasesensitive rectifier whose output controls the phase shifters 12, 15 so that they produce exactly 0 degrees and 90 degrees phase shift respectively. Signalling, as before, is made by reversing the action of the two rectifiers. Transistor switching circuit. The slightly unequal outputs of rectifiers 24, 25 are applied over a differential amplifier to a further differential amplifier having two NPN transistors with a pair of output circuits connected to each collector of the two transistors. The output of the transistor switching circuit (to which the signal pulses are applied) renders over series diodes one of the two collectors circuits of the differential amplifier inoperative and as each actuates through a transistor a respective one of the two coils 14, 16, a reversal of the monostable circuit due to a signal reverses the energization of the two coils. Also a reversal of the outputs of rectifiers 24, 25 reverses the sense of conducton of the differential amplifier and therefore also determines the particular coil energized.