GB765171A - Means for reducing leakage inductance in magnetic antennas - Google Patents

Abstract

765,171. Aerials; radio direction-finding. BENDIX AVIATION CORPORATION. Feb. 17, 1955 '[March 22, 1954], No. 4821/55. Class 40(7) The invention relates to magnetic aerial systems comprising a rotor consisting of a pick-up coil 2 wound on a high permeability core 1 which is surrounded by a plurality of high permeability pole pieces 3 separated from each other by equally dimensioned air gaps 5. Each pole piece is symmetrical about a respective vertical plane and is in low reluctance relationship with a bar (6, 7, 8 or 9) of high permeability material extending radially from the rotor. Such an aerial system may be used for direction-finding by the null method or may be aligned for maximum signal strength for communication purposes. It is a limitation of this type of aerial system that the leakage flux 15 through the pole-pieces of the bars in minimum pick-up relationship to the rotor increases the inductance of the coil and im pairs the match between the coil and its associated timed circuit in the transducer. The increase in inductance is not constant but depends on the rotor position relative to the air gaps 5. It's variation masks the direction finding null by rendering its sides less steep and may cause error in bearing determination. According to the present invention means are provided increasing the reluctance of the pole pieces to the leakage flux in order to reduce possible error to an unobjectionable level. One such means comprises a short conductive turn 16 arranged round each pole piece in its plane of symmetry. Preferably the 'turn 16 is formed of flat copper strip let into a recess or groove 17 formed in the pole piece. It is stated that a single turn 16 is usually sufficient but that more than one turn on each pole piece may be used provided that the distances between turns and the distances between the outside turns and the air gaps 5 are made equal. Means are shown in Fig. 4 for holding the inner ends of the bars in close relationship with the pole pieces. Each bar is provided with a U-shaped spring 13 attached to its lower surface and mounted to pivot on a pin 18 below collar 20. The pin 18 extends upwards into a bore 19 in the lower part of the bar. Thus the bar is capable of angular adjustment about pin 18 while its overhanging face 12 is maintained in close contact with the horizontal part 11 of the outer end of the pole piece 3. Specifications 719,526 and 765,172 are referred to.