Patent GB-441727-A (GB)
Title: Improvements in intermediate frequency transformers
IPC: H03H7/01
Filed: 1934-10-27
Abstract: 441,727. Transformers; inductances ; wireless receiving-apparatus. JOHNSON LABORATORIES, Inc., 609, West Lake Street, Chicago, U.S.A.-(Assignees of Neighbors, C. C.; 11, North Long Avenue, and Meinema, H. E. ; 2312, West 108th Place, both in Chicago, U.S.A.) Oct. 27, 1934, No. 30892. Convention date, Nov. 11, 1933. [Class 38 (ii)] [See also Groups XXXVI and XL] A high-frequency coupling device for use in carrier wave signalling systems comprises two inductances having powdered iron cores and disposed mutually at right angles, one of the inductances being disposed approximately in line with the magnetic axis of the other and being adjustable in a direction transverse to said axis to permit variation of the electromagnetic coupling. Fig. 2 shows two coupled coils 10 and 11 forming an intermediate frequency transformer for a superheterodyne radio receiver. The coils 10 and 11 are arranged respectively on the hollow cylindrical powdered iron cores 12 and 13 and are carried by an insulating frame 9 carried on an insulating disc 8 which is supported by terminal bars 7 connected to the condensers 34 from a base 1 of ceramic or other insulating material. The condensers, which are arranged respectively on the lower and upper sides of the base, are connected one across the winding 10 and the other across the winding 11 and their capacities are capable of slight adjustment, by screw 5 or nut 6, so that the condensers and their associated windings form resonant circuits. Adjustment of the coupling between the coils 10 and 11 is obtained by moving the coil 10 along its core 12. The coil 10 may be attached to a U-shaped insulating member movable by means of a screw to alter the coupling. Fig. 8 shows an alternative type of frame for carrying the coils 10 and 11 and adapted to be attached to the insulating base by screws 40. The cross-bar 38 is arranged to pass through the hollow cylindrical core 12 carrying the coil 10 while the core 13 carrying the coil 11 is placed on the stud 33a. The coupling between the coils may then be adjusted by moving the core 12 and coil 10 along the cross-bar 38. The core 12 may be fixed to the bar 38 which will then be capable of sliding. The various leads of the apparatus may be cemented in the grooves 34 in the frame. The whole arrangement of coils and casing &c. in either of the constructions described is enclosed by a cylindrical metallic screening casing 21. The coupling between the coils 10 and 11 may be capacitative as shown in Fig. 4a in which case the coils are arranged so that there is zero magnetic coupling. The capacitative coupling is then produced between coils, leads or terminals and by a condenser 30 may be used additionally. A combination of capacitative and magnetic coupling may be employed. Fig. 9 shows a circuit arrangement in which the influence of stray electrostatic field on the coupling of the transformer is reduced by placing each of the single high potential plates of the condensers 3a and 4a between two low potential plates. The condenser 45b is employed as a byepass for radio frequency across the H.T. battery.