Station Selecting Device

The present invention relates to a station selecting device in which the tuning voltage is selectively supplied to an electronic tuner to tune in the desired station.

In the conventional device --for example, CATV in the United States--a number of variable resistors with respective fixed resistors connected to each end thereof are grouped into three bands as shown in FIG. 1, i.e., 2nd to 13th channels, A- to L-channels, and M- to W-channels. Each variable resistor produces a tuning voltage that corresponds to a certain channel. Assigned to the 2nd to 13th channels are variable resistors 7a . . . 7n with resistors 1a . . . 1n and 2a . . . 2n connected to respective ends. For A- to L-channels are used a group of variable resistors 8a . . . 8n having resistors 3a . . . 3n and 4a . . . 4n connected to their respective ends. For M- to W-channels, variable resistors 9a . . . 9n with resistors 5a . . . 5n and 6a . . . 6n connected at their ends are used. The resistors of each band are connected in parallel with each other. The resistors 1a . . . 1n, 3a . . . 3n and 5a . . . 5n are connected at one end to the terminal 15 which in turn is connected to the power source. The resistors 2a . . . 2n, 4a . . . 4n, and 6a . . . 6n are connected at one end to the terminal 16 which is grounded. The variable resistors 7a . . . 9n are connected through their sliders to channel selection switches 10a . . . 12n which in turn are connected to a band selection switch 13. The movable contact of the band selection switch 13 is connected to the output terminal 14.

To tune in a desired channel, the band selection switch 13 is changed over to the band containing the resistor that produces the tuning voltage corresponding to the desired channel and at the same time one of the channel selection switches 10a . . . 12n which corresponds to the desired channel is closed. This supplies the tuning voltage to the electronic tuner through the terminal 14, thereby tuning in the desired channel. The channel selection switches 10a, 11a, 12a are linked with the corresponding channel selection switches 10b, 11b, 12b, . . . , and 10n, 11n, 12n so that each group of corresponding switches move simultaneously.

Since it is necessary to provide a channel selection switch for each variable resistor, the conventional device is complex in construction and large in size and requires a large number of component parts pushing up the production cost.

An object of this invention is to provide a station selecting device which eliminates the above drawbacks and in which the number of the channel selection switches are greatly reduced to make the construction simple and compact.

To achieve this objective a station selecting device of this invention comprises: a plurality of variable resistors, grouped into several reception bands, the variable resistors in each group being connected in parallel; band selection switches for selectively supplying voltage to the variable resistors of the desired band; and channel selection switches for picking up the tuning voltage across the selected variable resistor, said each channel selection switch being connected to one of variable resistors of each band.

FIG. 1 is a circuit of the conventional station selecting device; and

FIG. 2 is a circuit of one embodiment of the station selecting device according to this invention.

The present invention will now be described with reference to the accompanying drawings. Referring to FIG. 2, a rheostat or variable resistor 7a is connected at both ends with respective resistors 1a, 2a to form a resistor unit that produces a voltage corresponding to a given channel. A number of resistor units are divided, for example in the case of CATV in the United States, into three bands; from 2nd to 13th channels, from A- to L-channels, and from M- to W-channels. Used for the 2nd to 13th channels are a group of resistor units consisting of variable resistors 7a . . . 7n fitted at both ends with respective resistors 1a . . . 1n and 2a . . . 2n. For the A- to L-channels, a group of variable resistors 8a . . . 8n having resistors 3a . . . 3n and 4a . . . 4n connected to their respective ends are used. Assigned to the M- to W-channels are a group of resistor units consisting of variable resistors 9a . . . 9n having resistors 5a . . . 5n and 6a . . . 6n connected to their respective ends. For each band, a group of resistor units are connected in parallel with each other. Each group of resistors 1a . . . 1n, 3a . . . 3n, and 5a . . . 5n are connected at one end to one of the three stationary contacts of a band selection switch 18 that selectively feeds the supply voltage to any group of the resistors. And each group of resistors 2a . . . 2n, 4a . . . 4n, and 6a . . . 6n are connected at one end to one of the three stationary contacts of another band selection switch 19 that selectively connects any group of resistors to the ground. The two band selection switches 18, 19 are linked with each other for simultaneous movement, and the movable contacts of these switches 18, 19 are connected to the power supply and the ground respectively so that when the supply voltage is applied to one end of the group of resistors in the band selected the other end of that group of resistors is grounded.

The variable resistors 7a, 8a, 9a are connected through their sliders to the channel selection switch 17a, the variable resistors 7b, 8b, 9b to the channel selection switch 17b, and so on. Likewise variable resistors 7n, 8n, 9n are connected to the channel selection switch 17n. The movable contacts of the channel selection switches 17a . . . 17n are connected to the output terminal 14.

To tune in a certain station, the band selection switches 18, 19 are changed over to the desired band to supply voltage to the group of resistors of the band, and one of the channel selection switches 17a . . . 17n is operated to select the variable resistor which provides a tuning voltage corresponding to the desired station. If, for example, the channel selection switch 17a, to which the sliders of the variable resistors 7a, 8a, 9a are connected, is closed, the voltage across the variable resistor 7a is applied to the electronic tuner through the terminal 14 because in the case shown in FIG. 2 only the group of variable resistors 7a . . . 7n are supplied with power. This tunes in the station corresponding to the tuning voltage obtained from that variable resistor 7a.

As can be seen in the foregoing, since each of the channel selection switches is connected to one of the variable resistors of each band, the number of channel selection switches required is greatly reduced (to about one third as compared with the conventional device) resulting in a simpler construction, smaller size and reduced cost. Furthermore, this invention has another advantage that the current is passed through a group of resistors of the selected band only, instead of supplying current to all the resistors as in the conventional device, and the load on the power supply is reduced.