Toko Kabushiki Kaisha

Noboru Takada

Koichi Sakai

Yukio Suzuki

Masami Osawa

Ken Kasahara

Hajime Yokoyama

An electronic tuning circuit for an AM radio receiver in which a signal of a specific frequency is selected from the input signal from an antenna is provided, this tuning circuit having a tuning transformer with a first winding and a second winding, the number of turns on the first winding being greater than the number of turns on said second winding, the input from the antenna being applied to the second winding of the tuning transformer, and further having two varactor diodes, each of which is connected in series with a DC-blocking capacitor, these series-connected varactor-capacitor combinations being connected in parallel with the first winding of the tuning transformer such that the polarities of the varactor diodes are mutually opposing.

Electronic tuning circuit for an AM receiver

A helical filter is provided which includes a plurality of coupled helical coils each wound around one of a plurality of substantially parallel elongated bobbins having first and second end portions. Each of the coils has an open end at a first end thereof and a grounded end at a second end thereof. A moving member for adjusting the resonance frequency of the filter is provided at the first end portion of one of the bobbins, and a bandwidth-adjusting screw is provided in the hollow interior region of one of the bobbins at the second side thereof. The screw is accessible from the second end portiion of the bobbin so as to be rotated for adjustment of the bandwidth of the filter. The bandwidth-adjusting screw is disposed at the grounded second end of the helical coil wound around the hollow bobbin.

Helical filter

The construction of cores in an electric-current-controlled type variable inductor used in radio receivers is disclosed. The inductors have three or four cores. In the case of the variable inductors of the type having three cores, the winding portion of a first core is formed with a hollow portion, a second core is inserted into the hollow portion in such a way that the winding portion of the second core can be maintained in parallel with the winding portion of the first core, the first core is inserted into a pot-shaped third core in such a way that the winding portion of the first core can be maintained perpendicular to the bottom of the third core and the magnetic path established by a control coil mounted on the first core and the magnetic path established by a tuning coil mounted on the second core are superimposed one upon another around the winding portion of the second core. According to the present invention, the second core through which is extended the magnetic path established by the tuning coil and a part or means for substantially covering the second core are made of a high-frequency material (or a material best adapted to operate at a high frequency) while the remaining parts through which is extended the magnetic path established by the control coil is made of a low-frequency material (or a material best adapted to operate at a low frequency). Furthermore, in the case of variable conductors each having four cores, a fourth core is made of a high-frequency material, confines the magnetic path established by the tuning coil and is so disposed as to cover the second core in the hollow portion.

Electric current control type variable inductor

An inductor is configured so as to wind a control coil on one of winding portions of first and second cores and to wind a tuning coil on the other winding portion to insert the second core into a hollow portion provided inside the first core, thereafter accommodating the first and second cores thus assembled into a pot-shaped core, wherein both winding portions of the first and second cores are arranged in parallel with each other and the winding portion of the first core is arranged perpendicular to a bottom surface of the pot-shaped third core. The control coil and the tuning coil are arranged so that their magnetic paths overlap with each other at the winding portion of the second core, thereby to control a current flowing through the control coil when energized to vary effective permeability of the core on which the tuning coil is wound, thus producing changes in inductance.

Growing community of inventors

Tsurugashima, Japan

Noboru Takada