JPH0556434A - Satellite broadcast receiver - Google Patents

Abstract

PURPOSE:To always detect a C/N value, and execute noise reduction processing as occasion demands. CONSTITUTION:After installing a BS antenna, when a power switch SW3 is turned on and a desired channel is selected, a system controller 17 outputs a PLL control signal, and a tuner 5 outputs the broadcast signal of the desired channel. Then, the broadcast signal is given AGC at the time of passing through an amplifier 8, and AGC voltage is inputted to a comparison circuit 16 through a waveform shaper circuit 13 and an ADD-converter 14. The noise level of the selected current channel read out of a memory 18 is inputted to the circuit, and the circuit 16 outputs the C/N value at present. This C/N value is inputted to a discrimination circuit 19, and the circuit 19 controls change-over switches SW1. SW2 so that a noise reduction circuit 12 is bypassed if it is layer than a certain value, and the circuit 12 is passed through if the C/N value is smaller than the certain value. Then, the noise level is stored in the memory 18, and since a carrier level is detected always during the reception, and the C/N value is always detected, the noise reduction processing is executed automatically as occasion demands.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiving apparatus for performing noise reduction processing when the C / N value (reception carrier power to noise ratio) is lowered.

[0002]

2. Description of the Related Art The reception power of satellite broadcasting greatly depends on the orientation of the BS antenna, the antenna diameter, and weather conditions (rain, snow, etc.). Therefore, some existing satellite broadcast receivers are provided with means for detecting a C / N value and perform noise reduction processing when the C / N value is lowered.

Specifically, the C / N value detection utilizes the fact that the electric field strength is proportional to the AGC voltage of the tuner unit as shown in FIG. 3, the noise level is detected by the AGC voltage value of the empty channel, and this noise level is detected. The noise level of the currently selected channel is calculated, and this noise level is compared with the AGC voltage (carrier level) of the currently selected channel.

[0004]

However, since the conventional C / N value detection temporarily mutes the channel because an empty channel is temporarily tuned, the C / N value display button (antenna level button) is selected by the user. I could only do it when I chose. Therefore, under the present circumstances, it cannot be said that the noise reduction circuit cannot be effectively used because the noise reduction process cannot be automatically performed according to the change of the C / N value.

Therefore, it is an object of the present invention to provide a satellite broadcast receiving apparatus that always detects the C / N value and automatically performs noise reduction processing as needed.

[0006]

A satellite broadcast receiving apparatus of the present invention for achieving the above object includes a tuner unit for tuning a broadcast signal of a desired channel from a received signal of a BS antenna, and the tuner when an empty channel is selected. An arithmetic circuit that calculates the noise level of each channel based on the AGC voltage of the unit, a memory that stores the arithmetic result of this arithmetic circuit, the noise level of the currently selected channel stored in this memory, and the AG of the tuner unit.
It is composed of a comparison circuit for comparing with the C voltage and a discrimination circuit for discriminating whether or not to perform the noise reduction processing based on the C / N value which is the comparison result of the comparison circuit.

[0007]

In order to detect the C / N value by previously storing the noise level of each channel station in the memory and comparing the noise level in the memory of the selected channel station with the current AGC voltage, that is, the carrier level. It is possible to always perform processing according to the C / N value.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show one embodiment of the present invention.

FIG. 1 shows a circuit block diagram of the satellite broadcast receiving apparatus. In FIG. 1, S of about 12 GHz
The HF broadcast wave is received by the BS antenna 1, and the SHF band signal received by the BS antenna 1 is the first intermediate frequency signal by the converter 2 (UHF band signal of about 1 GHz).
The frequency is converted to. The first intermediate frequency signal of the converter 2 is supplied to the tuner 5 of the indoor tuner unit 4 via the coaxial cable 3.

The tuner 5 constitutes a PLL loop together with an oscillator 6 whose oscillation frequency can be varied, and the oscillation frequency of the oscillator 6 is varied by a PLL control signal by a viewer's tuning operation. Then, the tuner 5 obtains the broadcast signal (UHF signal) of the selected channel station by converting it into the second intermediate frequency signal. The second intermediate frequency signal of the tuner 5 is supplied to the amplifier 8 via the bandpass filter 7.

The output of the amplifier 8 is supplied to the AGC voltage detection circuit 9 to form an AGC voltage, and the AGC voltage is fed back to the amplifier 8 and AGC is applied so that the output of the amplifier 8 becomes constant. The output of the amplifier 8 is FM demodulated by the FM demodulation circuit 10, and the FM demodulated signal is supplied to the video signal processing circuit 11. The video signal processing circuit 11 is subjected to de-emphasis processing, energy diffusion processing, etc., and the output of the video signal processing circuit 11 is output from the noise reduction circuit 12 by the _two changeover switches SW ₁ and SW ₂ .
Is selected.

On the other hand, the AGC of the AGC voltage detection circuit 9
The voltage is also guided to the waveform shaping circuit 13, and the waveform shaping circuit 13
Performs waveform shaping by emphasizing changes in the AGC voltage so that the changed state can be clearly recognized. This waveform shaping circuit 13
The AGC voltage whose waveform has been shaped in (1) is led to the arithmetic circuit 15 and one input terminal of the comparison circuit 16 via the A / D converter 14, respectively.

The operation circuit 15 includes a system controller 1
The AGC voltage of two empty channels (-0.5 ch and 16.5 ch) is input by the drive control signal from 7. Since this AGC voltage is for an empty channel, it indicates a noise level, and the arithmetic circuit 15 obtains the noise level of each channel by linear approximation calculation. That is, as shown in FIG. 2, the AGC voltage point of −0.5 ch and 16.5
The AGC voltage of each channel on the straight line connecting the AGC voltage points of ch is obtained by calculation, and written in the memory 18 as the noise level of each channel. This memory 1
The write / read control of 8 is performed by the system controller 17, and the read data of the memory 18 is compared circuit 1
6 is output to the other input terminal.

The comparison circuit 16 compares two input signals,
The difference data (C / N value) is output to the discrimination circuit 19.
The discrimination circuit 19 allows the video signal to pass through the noise reduction circuit 12 when the input data (C / N value) is less than a certain value, and the video signal is noise reduction when the input data (C / N value) is more than the certain value. A switching control signal is output to the two switching switches SW ₁ and SW ₂ so as to pass through the circuit 12.

The system controller 17 controls the arithmetic circuit 15 and the memory 18 as described above, and outputs a PLL control signal (tuning signal) to the oscillator 6 based on the tuning operation by the viewer. Further, the detection output of the power ON / OFF detection circuit 20 is guided to the system controller 17, and whether the power ON / OFF detection circuit 20 is supplying power to the power supply circuit 21 by turning on / off the power switch SW ₃ . Detect whether or not. Then, when the power-off is selected in the power-on state, the noise level in the memory 18 is rewritten as will be described below. Further, the output of the C / N value display (antenna level) button 21 is guided to the system controller 17, and when the C / N value display button 21 is pressed, the noise level in the memory 18 is rewritten and updated. The C / N value based on the noise level is displayed on the screen.

The operation of the above configuration will be described below.

First, when the BS antenna 1 is set, the C / N value display button 22 is pressed. Then, the system controller 17 outputs a PLL control signal to select an empty channel (-0.5 ch and 16.5 ch) and the AGC voltage (noise level) at that time is input to the arithmetic circuit 15. Then, the noise level of each channel is calculated by the arithmetic circuit 15, and the calculation result is written in the memory 18.

On the other hand, after the empty channel is selected, the channel having the broadcast wave is selected, and the carrier level which is the AGC voltage at this time is input to the comparison circuit 16. Then,
The noise level of the selected channel is read from the memory 18 to the comparison circuit 16, the C / N value is output from the comparison circuit 16, and the C / N value is displayed on the screen. And C / N
When the value display button 22 is pressed, the above operation is repeated, and the BS antenna 1 is installed at the position where the C / N value is the best.

When the power switch SW ₃ is turned on and the desired channel is selected after the BS antenna is installed, the system controller 17 outputs the PLL control signal and the tuner 5 outputs the broadcast signal of the desired channel (second intermediate frequency). Signal) is output. And the broadcast signal is the amplifier 8
When passing, AGC is applied, and the AGC voltage (carrier level) is input to the comparison circuit 16 via the waveform shaping circuit 13 and the A / D converter 14. The comparison circuit 16 has a memory 18
The noise level of the currently selected channel thus read is input, and the comparison circuit 16 outputs the current C / N value. This C / N value is input to the discriminating circuit 19, and the discriminating circuit 19 allows the noise reduction circuit 12 to pass through if the C / N value is a certain value or more, and if the C / N value is less than the certain value. The changeover switches SW ₁ and SW ₂ are controlled so as to pass through the noise reduction circuit 12. The noise level is stored in the memory 18, the carrier level is constantly detected during reception, and the C / N value is always detected. Therefore, noise reduction processing is automatically performed as necessary.

When the power switch SW ₃ is turned off, the power ON / OFF detection circuit 20 outputs to the system controller 17 that power off has been selected. Then, the system controller 17 causes the empty channel (-0.5) as in the case where the C / N value display button 22 is pressed.
ch and 16.5 ch) are sequentially selected and the AGC voltage indicating the noise level is fetched into the arithmetic circuit 15 to execute the arithmetic operation. Then, the data of the memory 18 is updated by writing the calculated noise level of each channel in the memory 18.

Therefore, in the next reception, the C / N value is calculated by the updated noise level, so that a considerably accurate C / N value can be obtained. Since the noise level depends on the characteristics of the converter 2 and the coaxial cable 3, the noise level does not change significantly after the satellite broadcast receiving device is installed, but it may change due to deterioration of the characteristics of the converter 2 or the like.

Further, in this embodiment, since the memory 18 is updated in association with the power off, the memory 18 is updated without the screen being in the mute state for a moment.

[0023]

As described above, according to the present invention, the noise level of each channel is stored in the memory, and the noise level of the selected channel is compared with the AGC voltage indicating the current carrier level. Since the C / N value is detected and the noise reduction process is performed based on the C / N value, the C / N value can be always detected, and the noise reduction process is automatically performed when necessary. ..

Further, since the noise level in the memory is updated when the power is turned off, there is an effect that an accurate C / N value can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a satellite broadcast receiving device (embodiment).

FIG. 2 is a diagram showing characteristics of a noise level and a carrier level (Example).

FIG. 3 is a characteristic diagram of AGC voltage with respect to electric field strength.

[Explanation of symbols]

1 ... BS antenna, 4 ... Tuner unit, 15 ... Arithmetic circuit, 16 ... Comparison circuit, 18 ... Memory, 19 ... Discrimination circuit.

Claims (2)

[Claims] 1. A tuner unit for tuning a broadcast signal of a desired channel station from a received signal of a BS antenna, and an AG of the tuner unit when an empty channel is selected.
An arithmetic circuit that calculates the noise level of each channel based on the C voltage, a memory that stores the calculation result of this arithmetic circuit, the noise level of the currently selected channel stored in this memory, and the AGC voltage of the tuner unit. And a comparison result of this comparison circuit, C /
A satellite broadcast receiving device, comprising: a discriminating circuit for discriminating whether or not to perform noise reduction processing based on an N value. 2. The satellite broadcast receiving apparatus according to claim 1, wherein the noise level of each channel stored in the memory is rewritten by a channel selection operation to an empty channel when the power is off.