GB643981A - Improvements in or relating to electromechanical wave-guide modulators or switches - Google Patents

Abstract

643,981. Wave-guides. SPERRY GYROSCOPE CO., Inc. Aug. 28, 1946, No. 25867. Convention date, Aug. 30, 1947. [Class 40 (viii)] [Also in Group XL (c)] A wave-guide switching or amplitude modulating apparatus comprises a wave-guide with an open end spaced from the open end of another wave-guide, abrupt constriction at the end of one guide to reduce the effective crosssection of the guide, and a member of variable reflectivity rotating between the wave-guide ends. In a distributer system, Fig. 1, particularly for use in aircraft instrument landing transmitters, the output of a generator 11 is modulated at one of two audio frequencies, and fed to loads 12, 13, 14 and 15 in succession. A wave-guide 16, coupled to generator 11, forms a shunt T-join with wave-guides 17, 18, each of which is bent through a quarter circle. Waveguides 19, 21 and 23, 22, arranged side-by-side, form series T-junctions with wave-guides 17. and 18 respectively. Load circuits 12, 14, 15 and 13 are coupled to wave-guides 24, 27, 25 and 26, the open ends of these wave-guides being opposite and adjacent to but spaced from the open ends of wave-guides 19, 23, 21 and 22, respectively. A metal disc 28, driven by a motor 32, rotates in the air gaps 34, 37 coupling guides 19 and 23 to guides 24 and 27 respectively. A similar disc 29, also driven by motor 32, rotates in the air-gaps 35, 36, coupling guides 21, 22 to guides 25, 26 respectively. Each wave-guide 24, 25, 26 and 27 is terminated by a diaphragm 42, Fig. 3, provided with a resonant slot 43, thus reducing the effective cross-section of the wave-guide and the size of discs 28, 29. Each air-gap, such as 34, is provided with a wave-trap, Fig. 4, comprising annularly slotted members 38, 39, on ends of the coupled waveguides 19, 24. The annular slot 41 is made i-wavelength deep at the operating frequency and “-wavelength from the wave-guide opening. The discs 28, 29 have five and eight notches respectively spaced over a quarter of their circumference, and are arranged to permit energy to flow to each load 12-15 in turn. If motor 32 runs at 1800 r.p.m., the energy passed by disc 28 to loads 12 and 14 is modulated at 600 c/s., while the energy passed by disc 29 to loads 13, 15 is modulated at 900 c/s. Specifications 582,768 and 608,839 are referred to.