Toko, Inc.

Toko Kabushiki Kaisha

Masami Osawa

Noboru Takada

Shigeru Hatada

A radio-frequency tuning circuit includes an input tuning transformer, and an output tuning transformer. The input tuning transformer comprises a primary coil adapted to serve as input coil, and a secondary coil to which a pair of variable-capacitance diodes having cathodes thereof connected together are connected in parallel therewith to form a first tuning circuit. The output tuning transformer comprises a primary coil to which a variable-capacitance element is connected to form a second tuning circuit, and a secondary coil adapted to serve as output coil. The input and output tuning transformers are connected in such a manner as to form a double-tuning circuit. Q-factor of the output tuning transformer is made to be twice as high as that of the input tuning transformer, and resonant impedance of the first tuning circuit and that of the second tuning circuit are made to be substantially equal to each other.

Electronic-tuning type radio-frequency tuning circuit

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.

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Tsurugashima, Japan

Masami Osawa