Improvements in or relating to high frequency resistances

Abstract

Abstract 554,630. Resistances; power measurements. MULLARD RADIO VALVE CO., Ltd., and LATIMER, K. E. Jan. 9, 1942, No. 380. [Class 37] A resistor is so constructed as to have a constant value, apart from skin effects, up to a frequency such that the wave-length may be considerably shorter than the dimensions of the resistor. The resistor shown comprises a cylindrical core 10 of dielectric material such as porcelain, glass, ceramic material, polystyrene &c. On the surface of the core is a resistance element 11 consisting of a coating of resistance material such as a sprayed or adhesively-bonded coating of carbon, or a metal coating of tungsten, platinum applied by sublimation, sputtering, or sintering, or of coppernickel alloy produced by electrodepositing copper and nickel separately and heating to a temperature below the melting point of the alloy or its constituents. Electrical connection with the ends of the resistance element 11 is effected by bands 12, 13 consisting of a coating of silver or other low resistance metal. Surrounding the resistance element is a metal sleeve 14 in the shape of a logarithmic horn. This sleeve is of brass which is electrolytically silver plated and rhodium flashed. The sleeve itself may form part of the resistance element, in which case it may consist of a thin shell of metal or a moulded matrix of carbon suspended in a binder. The throat of the sleeve is soldered or brazed to the terminal band 13, external connections being made to the band 12 and the flared end of the sleeve 14. For connection to a concentric transmission line the dimensions of the sleeve 14 and the element 10, 11 are so chosen that the connecting portions coincide with the outer and inner conductor. High-frequency power may be measured by the temperature produced in the resistance element, as by filling the tube 10 with a fluid such as monostyrene or benzine and measuring its thermal expansion by a pressure-measuring instrument calibrated in watts. Alternatively a thermocouple may be positioned within the resistance element and connected to a voltmeter calibrated in watts. Instead of a coated core the resistance element may be formed of a number of thin wires braided together.

Inventors

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