GB595934A - Improvements in or relating to electric attenuating devices - Google Patents

Abstract

595,934. Attenuators. STANDARD TELEPHONES & CABLES, Ltd., and SECKER, B. July 10, 1945, No. 17561. [Class 40 (iii)] An attenuator for very high frequencies comprises a coaxial transmission line 1, 2, whose outer conductor 2 has a helical slot 3 in consequence of which the skin current flows outside and around the conductor. Outside the conductor are one or more tubes 7, 9 made of magnetic material of high permeability, each having a straight longitudinal slot whereby the circumferential currents induced in their inner surfaces bv the currents in the outer surfaces of the enclosed conductors are forced into outer return paths, the final current path being on the inside surfaces of the cylinders 6, 10, which are not slotted. In this way energy is dissipated, the attenuation at any frequency bearing a constant ratio to that of the coaxial line, while the characteristic impedance is substantially that of the line. The attenuation is varied by shifting the assembly longitudinally or by stretching the helical part of the conductor 2. The latter may alternatively comprise helically-wound copper tape. A fixed attenuator with micrometer adjustment, Fig. 6 (not shown) may be used instead of the variable attenuator. The device described may be used as an equalizer in an amplifier having negative feedback.