GB544144A - Electrical filters - Google Patents

Abstract

544,144. Protective arrangements; inductors. STANDARD TELEPHONES & CABLES, Ltd. Sept 25, 1940, No. 14558. Convention date, Sept. 29, 1939. [Classes 38 (ii) and 38 (iv)] [Also in Groups XL, XXXVI and XXXIX] A high frequency filter for suppressing radio interference, e.g. by telephone impulse-senders, comprises a coiled conductor wound upon a permalloy core to form an inductance element and a second conductor coiled in parallel with a continuation of the first conductor to form a capacity element, which may surround the inductance element. The filter may comprise a lamination 18 of permalloy, metal foil conductors, 10, 11 such as tin foil or aluminium foil, and paper di-electric 13, 14, the sheet 10 being of greater length than sheet 11. The combined elements 18, 13, 10, 14, 11 are wound in a single operation commencing from the left, so that the core 18 is first covered several turns of paper 13 only, then by foil 10 and paper 13, 14, then after the point a by both foils 10, 11 and paper 13, 14, and finally by the rest of the paper 14. The inner part of the filter comprising the core and left-hand part of foil 10 up to the point a constitutes the inductance element, and the outer part comprising foil 11 and the rest of the foil 10 constitutes the capacity element. Terminals 15, 16, 17 are attached to the foil at the points shown. The complete unit is placed in a V-shaped cardboard holder 25 within a collapsible lead tube 20, which may be compressed to the shape shown in Fig. 4. The unit is mounted within the casing of the impulse-sender Fig. 5 (not shown), the capacity element being connected across the impulse-contact and the inductance element in series therewith, Fig. 6 (not shown). The Specification as open to inspection under Sect. 91 also describes a modification in which the capacity element forms the inner part of the unit, a third metal foil on the outside forming a shield for the inductance element. This subject-matter does not appear in the Specification as accepted.