1. Field of the Invention
The present invention relates to satellite-broadcasting receiving converters with a plurality of output terminals, connected to satellite-TV-broadcasting receivers (hereinafter just called receivers).
2. Description of the Related Art
Satellite TV broadcasting uses, for example, a frequency band ranging from 10.7 GHz to 12.75 GHz, with 10.7 GHz to 11.7 GHz for analog broadcasting and 11.7 GHz to 12.75 GHz for digital broadcasting. A horizontal-polarization wave and a vertical-polarization wave are used for both analog broadcasting and digital broadcasting. In other words, four types of satellite TV broadcasting are used in combinations of analog broadcasting and digital broadcasting, and a horizontal-polarization wave and a vertical-polarization wave.
Satellite-broadcasting receiving converters receive satellite TV broadcasting signals sent from broadcasting satellites and convert a received frequency to a lower frequency.
When a satellite-broadcasting receiving antenna (not shown) receives a signal, the signal is divided into a horizontal-polarization wave and a vertical-polarization wave by a waveguide (not shown) and input to a satellite-broadcasting receiving converter.
FIG. 2 shows a conventional satellite-broadcasting receiving converter. The conventional satellite-broadcasting receiving converter includes a received-signal amplifier circuit section 51 for separately amplifying a horizontal-polarization wave and a vertical-polarization wave, a demultiplexer circuit section 52 for demultiplexing each amplified received signal into two signals with a boundary frequency of 11.7 GHz, a filter section 53 for attenuating the image signal of each demultiplexed received signal, a frequency-conversion section 54 for converting the frequency of each received signal output from the filter section 53, an amplifier circuit section 55 for amplifying each frequency-converted received signal, signal selection means 56 for selecting a received signal of one type from the received signals output from the amplifier circuit section 55, and two regulators 57 and 58 for supplying power-source voltages to the received-signal amplifier circuit section 51 to the signal selection means 56.
The received-signal amplifier circuit section 51 has two amplifiers 59 and 60. The horizontal-polarization wave is input to the amplifier 59 through an input end 51a and is amplified, and the vertical-polarization wave is input to the amplifier 60 through an input end 51b and is amplified.
The demultiplexer circuit section 52 has two demultiplexers 61 and 62, and demultiplexes the polarized waves amplified by the received-signal amplifier circuit section 51 into analog received signals A1 and A2 having a frequency of 11.7 GHz or less and digital received signals D1 and D2 having a frequency of 11.7 GHz or more. With this demultiplexing, the received signals are demultiplexed into the four received signals and output from the demultiplexer circuit section 52.
The filter section 53 has four band-elimination filters (BEFs) 63 to 66. The received signals A1, A2, D1, and D2 output from the demultiplexer circuit section 52 are input to the BEFs 63 to 66, respectively.
Among these BEFs, the BEFs 63 and 64 attenuate signals having frequencies of 7.8 GHz to 8.8 GHz, which correspond to the frequency band of the image signals of the analog received signals A1 and A2, and the BEFs 65 and 66 attenuate signals having frequencies of 8.45 GHz to 9.5 GHz, which correspond to the frequency band of the image signals of the digital received signals D1 and D2.
The received signals whose image signals are attenuated by the BEFs 63 to 66 are input to the frequency converter section 54.
The frequency converter section 54 has four mixers 67 to 70 and two oscillators 71 and 72. The received signals A1, A2, D1, and D2 are input to the mixers 67 to 70 provided correspondingly to the BEFs 63 to 66, respectively.
The oscillator 71 inputs an oscillation signal having a frequency of 9.75 GHz into the mixers 67 and 68, and the oscillator 72 inputs an oscillation signal having a frequency of 10.6 GHz into the mixers 69 and 70. The frequencies of the analog received signals A1 and A2 input into the mixers 67 and 68 are converted to those in a range from 950 MHz to 1950 MHz, and the frequencies of the digital received signals D1 and D2 input into the mixers 69 and 70 are converted to those in a range from 1100 MHz to 2150 MHz. The frequency-converted received signals a1, a2, d1, and d2 are input to the amplifier circuit section 55.
The amplifier circuit section 55 has four amplifiers 73 to 76. The frequency-converted received signals a1, a2, d1, and d2 are input to the amplifiers 73 to 76 provided correspondingly to the mixers 67 to 70, respectively. The received signals amplified by the amplifiers 73 to 76 are input to the signal selection means 56.
The signal selection means 56 has a signal switching circuit 77, two switching control circuits 78 and 79, and two output terminals 56a and 56b. The signal switching circuit 77 selects one of the outputs of the amplifiers 73 to 76 according to the control of the switching control circuit 78 and connects it to one terminal 56a, and selects one of the outputs of the amplifiers 73 to 76 according to the control of the switching control circuit 79 and connects it to the other output terminal 56b. 
The output terminals 56a and 56b are connected to different receivers (not shown). Each receiver sends a selection control voltage used for operating each circuit section of the satellite-broadcasting receiving converter and for controlling the signal selection means 56. This selection control voltage is set to a first DC voltage of, for example, 18 V to select a horizontal-polarization wave, and is set to a second DC voltage of, for example, 14 V to select a vertical-polarization wave. To select a digital received signal d1 or d2, a 22-kHz high-frequency voltage is superposed on the corresponding DC voltage.
More specifically, to select the horizontal-polarization analog broadcasting signal a1, the first DC voltage is sent; to select the vertical-polarization analog broadcasting signal a2, the second DC voltage is sent; to select the horizontal-polarization digital broadcasting signal d1, the first DC voltage on which the high-frequency voltage is superposed is sent; and to select the vertical-polarization digital broadcasting signal d2, the second DC voltage on which the high-frequency voltage is superposed is sent to the corresponding output terminal 56a or 56b as a selection control signal.
A selection control voltage sent to the output terminal 56a is input to the switching control circuit 78 and the regulator 57 through a high-frequency choke coil 80. In the same way, a selection control voltage sent to the output terminal 56b is input to the switching control circuit 79 and the regulator 58 through a high-frequency choke coil 81.
The regulators 57 and 58 supply a power-source voltage of, for example, 8 V to the circuit sections 51 to 56. These two regulators 57 and 58 have the same structure and each have a voltage stabilizer circuit formed of an integrated circuit. The output ends of the regulators 57 and 58 are connected to a power-source-voltage output terminal 84 through reverse-current-prevention diodes 82 and 83, respectively. Therefore, even if one receiver is stopped, this satellite-broadcasting receiving converter is ready to operate since the power-source voltage is supplied to the circuit sections 51 to 56. Since the two regulators 57 and 58 are connected in series between the two output terminals 56a and 56b, the switching control circuits 78 and 79 operate only by the switching control voltage sent from one of the output terminals 56a and 56b. 
As described above, since the conventional satellite-broadcasting receiving converter is provided with the two regulators 57 and 58 so as to be ready to operate even if one of two receivers connected to the two output terminals 56a and 56b is stopped, the converter is expensive.
Accordingly, it is an object of the present invention to provide an inexpensive satellite-broadcasting receiving converter.
The foregoing object is achieved according to the present invention through the provision of a satellite-broadcasting receiving converter including a plurality of output terminals each of which can be connected to an external receiver, to each of which any one of four types of selection control voltages specified according to the combinations of high and low DC voltages and whether a high-frequency voltage having a predetermined frequency is superposed is separately sent from the external receiver, and from each of which a satellite-broadcasting receiving signal of a type selected according to the selection control voltage is separately output to the external receiver; signal selection means for selecting one type of a receiving signal according to the selection control voltage from four types of satellite-broadcasting receiving signals different in modulation-signal form and polarization direction from each other for each output terminal to output it; a regulator for receiving the selection control voltage sent from each output terminal in common and for converting the selection control voltage to a predetermined power-source voltage to output it; and a plurality of high-frequency attenuation means each connected in series between each output terminal and an input end of the regulator.
Since each of the high-frequency attenuation means is connected in series between each output terminal and the input end of the regulator, the selection control voltage sent to each output terminal reaches the input end of the regulator with its superposed high-frequency voltage being sufficiently attenuated by the high-frequency attenuation means. The selection control voltage does not flow reversely into other output terminals from the input end of the regulator. A type of a receiving signal is separately selected and output to each output terminal. Therefore, only one regulator is required for a plurality of types of selection control voltages sent from a plurality of output terminals.
The satellite-broadcasting receiving converter may be configured such that each of the plurality of high-frequency attenuation means includes a transistor and a low-pass filter having a cutoff frequency lower than the frequency of the high-frequency voltage.
In this case, the high-frequency voltage is attenuated by a simple circuit.
The satellite-broadcasting receiving converter may be configured such that the low-pass filter is formed of a resistor and a capacitor which determine the cutoff frequency; and the selection control voltage is input to the collector of the transistor, the resistor is connected between the collector and the base, the base is grounded through the capacitor, and the emitter is connected to the input end of the regulator.
In this case, a ripple-voltage attenuation effect is great and the signal selection means is positively operated with its erroneous operation being prevented.
Alternatively, the satellite-broadcasting receiving converter may be configured such that a high-frequency choke coil and a reverse-current-prevention diode are connected to each other in series between the output terminal and the collector of the transistor.
In this case, even if a high reverse voltage is applied to the high-frequency attenuation means, the transistor is not destroyed by the reverse voltage.