Patent GB-366273-A (GB)
Title: Improvements in or relating to a method and apparatus for wireless tuning circuits
IPC: H03H7/01
Filed: 1931-01-26
Abstract: 366,273. Impedance networks. BRANCH, L. E. T., 15, The Crescent, Ilford, Essex. Jan. 26, 1931, No. 2485. [Class 40 (iii).] An arrangement of inductances for a multiwave-range band-pass filter comprises pairs or sets of coils, one pair or set for each wave range, so disposed on a common supporting structure that the coils of each pair or set have a mutual inductance such that, when they form parts of separate tuned circuits, the circuits can be tuned substantially independently, the mutual inductance providing the requisite inductive coupling for the combined circuits to have a band-pass characteristic. In one arrangement for a dualrange filter a pair of coils for the lower range is mounted near the ends of a tubular former with a band of metal, or one or more short-circuited turns of wire arranged midway between them, to reduce the inductive coupling. A second pair of coils for the long range are mounted on flanged rings arranged coaxially on each side of the former with their axes at right-angles to the axis of the former. In a preferred arrangement, Fig. 2, the medium range coils G, G<1>, and the long range coils H, H<1>, are arranged coaxially on a tubular former F, the coils H, H<1>, being wound on a tube J which can be fixed on the former before one or both of the coils G, G<1> are wound. A short-circuited metal band K is arranged midway between the coil H, H<1>, and a switch L is placed inside the former, and provided with an operating rod L<1> extending through the former and tube J. The dimensions of the arrangement suitable for a medium range of 200-600 metres and a long range of 1000-2000 metres are given. The connections for a dualrange band-pass filter used in a wireless receiving circuit and comprising two circuits tuned to substantially the same frequency, with an inductive coupling provided by the coils, and a capacitative coupling provided by a fixed condenser 0, are shown in Fig. 3. The aerial P may be connected directly to the outer end of the coil G, but is preferably connected to one end of a small coil P<1> mounted on the former between the coils G, H. The other end of the coil P<1> is connected to a point on the coil H so as to obtain aperiodic coupling to the coils G or H or to both these coils. The inner ends of the coils H, H<1> are connected together and to earth. The switch L carries movable contacts L<4> adapted to short-circuit the coils H, H<1>, and to connect the coil P<1> to earth, when the filter is operating on the lower range. The outer end of the coil G<1> may be connected to the control electrode or grid of the first valve R of the receiver. If regenerative effects are desired, the outer end of the coil G may be connected through a variable condenser S to the anode circuit of the first or second valve following the coils, according as the mutual inductance is negative or positive. If desired, the coils of a pair may be mounted with their axes parallel instead of coaxial, or the two pairs of coils may be mounted so that the coils of one pair are coaxial while the axes of the coils of the other pair are parallel. For a three-waverange filter, six coils may be arranged coaxially on the former, or three pairs of coils may be arranged with their axes at right-angles.