JPH0563593A - Signal level display device - Google Patents

Abstract

PURPOSE:To display it as a change in a signal level when either of a level of an input RF signal or the C/N is at least changed. CONSTITUTION:A 1st intermediate frequency signal is converted into a prescribed 2nd intermediate frequency signal by a frequency down-converter 2 and the band is limited by a band pass filter 3 and the signal is a signal of a prescribed level by an AGC circuit 4 and demodulated into a base band signal by an FM demodulator 13. A band pass filter 14 extracts a noise level component from a base band signal and a level detection circuit 15 obtains a noise level detection voltage and a level detection circuit 4c of the AGC circuit 4 obtains a level detection voltage and an adder circuit 16 adds the voltages. The sum voltage is converted into a digital data by an A/D converter 6 and the result is fed to a CPU 7, which generates a signal level display data, and the signal level of the input RF signal is displayed accurately on a display circuit 8 based on the data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal level display device for displaying the received power of a tuner in a satellite broadcast receiving system, and more particularly to a signal level display device for displaying stable received power under various signal conditions. Regarding

[0002]

2. Description of the Related Art In satellite broadcasting, image services are provided using FM-modulated signals.
Since the receiving state greatly depends on the direction of the receiving antenna such as a parabola, it is necessary to control the receiving antenna so that the receiving antenna is always accurately directed to the broadcasting satellite. Therefore, the receiver for satellite broadcasting generally has a function of displaying the signal level of the received signal.

As a conventional device of this type, as shown in FIG. 5, a signal level display device described in JP-A-63-191072 is known. SHF from broadcasting satellite
When an RF signal in the band (3 GHz to 30 GHz) is frequency-converted by an outdoor converter (not shown) to be a first intermediate frequency signal and supplied to the input terminal 1, this signal is selected by the frequency down converter 2 and then the second signal is selected. After being frequency-converted to an intermediate frequency signal, it is supplied to an automatic gain control circuit (AGC circuit) 4 via a bandpass filter 3.

The AGC circuit 4 includes a variable gain amplifier 4a,
4b and a level detection circuit 4c that controls these with voltage. The level detection voltage according to the level change of the second intermediate frequency signal is negatively fed back to perform gain control, and the output terminal 5 always outputs a constant level signal. The second intermediate frequency signal is output, supplied to an FM demodulator (not shown), and demodulated into a baseband video signal.

Further, the level detection voltage of the AGC circuit 4 is supplied to the analog-digital converter 6, where it is converted into digital data and then supplied to the CPU 7. The CPU
A display circuit 8 for displaying signal level display data, a RAM 9 for storing the digital data from the analog-digital converter 6, a signal meter switching circuit 10 for switching the processing mode of the CPU 7, and a selection circuit 7 are provided. An external input circuit 12 for interrupting signal level display in response to an instruction from the station circuit 11 is connected. The tuning circuit 11 is connected to the frequency down converter 2, supplies tuning data to the frequency down converter 2 to select a desired station, and outputs a predetermined second intermediate frequency signal from the frequency down converter 2. Is output.

The signal level displayed by the above configuration is displayed based on the signal obtained by further detecting the signal obtained by frequency-reducing the input RF signal to the second intermediate frequency signal. The larger the received power of the antenna system, the larger the signal level display. Further, the cable length, the conversion gain of the frequency down converter 2, and the gain of the AGC circuit 4 also affect the magnitude of the display level. Therefore, it is impossible to distinguish whether the display level of the signal level is different between the systems or whether the difference of the display level depending on the receiving channel is caused by the magnitude of the input level.

In addition, the display of the signal level at that time is
Strictly speaking, it is a channel selection signal, that is, a signal of the sum of a carrier signal and an in-band noise signal, and therefore the signal level is displayed including the in-band noise component level. However, in this type of receiving system, the signal-to-noise ratio (S /
Since the N ratio) is determined by the ratio of the carrier signal to the noise signal (C / N ratio), the input level to the frequency down converter 2 proportional to the received power of the antenna system must be within the dynamic range. For example, it does not affect the signal level display.

Therefore, in consideration of the above matters, the error in the display level between the systems and between the channels due to the gain deviation of the antenna system is not a problem as long as it is not affected by the total noise temperature of the system, and rather the antenna system is concerned. The deviation of noise temperature between channels is a problem. But,
As a countermeasure against this, a general antenna system is designed to minimize and flatten the noise temperature in the band.

As described above, the true reception state in the satellite broadcasting receiving system is determined by the C / N ratio. Normally, the noise figure which determines the noise level is peculiar to the antenna system and should not be changed. To be designed, the total power of the carrier signal and the noise signal is displayed as the received power level. However, this is because it is misunderstood that the receiving condition can be improved by lengthening the cable or inserting a booster between the antenna and the receiver, or the C / N ratio is constant. It is easy to misunderstand that the display of the signal level changes due to an error between channels.

Further, the variable gain amplifiers 4a and 4b in the AGC circuit 4 often have large gain fluctuations due to temperature changes, and the level detection circuit 4c controls the voltage so as to compensate for them, so that the output voltage is controlled by the temperature. Change and cause a temperature drift of the display level. This temperature drift becomes a particular problem when adjusting the pointing of the antenna, and in order to prevent the temperature drift, it is necessary to add a temperature compensation circuit using a thermistor or the like.

As described above, in the related art, many display the voltage according to the input level based on the level detection voltage of the AGC circuit 4 which makes the change of the input level constant. However, the voltage proportional to the input level is displayed. Indicates only the signal level, not the C / N ratio important for satellite broadcast reception. Therefore, the sensitivity is extremely low with respect to changes in the C / N ratio that do not cause large level changes due to clouds and ambient temperature.

When the input C / N ratio is sufficiently good and the S / N ratio of the demodulated signal is not saturated, it does not operate. On the contrary, when the input C / N ratio is extremely bad and approaches the FM threshold region, Impulse noise is generated in the demodulated signal, and unstable fluctuation occurs due to energy over the entire frequency band.

[0013]

As described above, the conventional signal level display device has the AGC that is proportional to the input level.
The output voltage of the level detection circuit in the circuit indicates the level of the signal power including the noise signal, not the C / N ratio important for satellite broadcast reception. Therefore, there is an inconvenience that the sensitivity is extremely low with respect to a change in the C / N ratio without a large level change.
The present invention has been made to solve the above conventional problems, and always performs stable display, and displays as a change in signal level when at least one of the input signal level or the C / N ratio changes. It is an object of the present invention to provide such a signal level display device.

[0014]

In order to achieve the above object, the present invention provides a means for converting an input radio wave from a broadcasting satellite whose frequency is converted by an outdoor converter into an intermediate frequency signal by a frequency down converter, and the intermediate means. A variable gain amplifier for amplifying a frequency signal, a level detection circuit for generating a first voltage according to a level change of the intermediate frequency signal, and controlling the gain of the variable gain amplifier with the first voltage, An FM demodulator that demodulates the output signal from the gain amplifier to output a baseband signal, an extracting unit that extracts a noise component outside the signal band from the baseband signal, and an output signal of the extracting unit according to the noise level. And a signal for indicating the reception level of the input radio wave from the added voltage, the level detecting means for generating a second voltage, and the first voltage and the second voltage being added. A display data generating means for generating a bell display data is obtained by and a display means for displaying the reception level of the input electromagnetic wave based on the signal level display data outputted from said display data producing means.

[0015]

The noise level component of the baseband signal from the FM demodulator is taken out by the extracting means, and the noise level detecting voltage (the second voltage) is obtained by the level detecting means, and at the same time the level is detected by the level detecting circuit of the AGC circuit. The detection voltage (the first voltage) is obtained, and these two detection voltages are supplied to the display data creating means. Then, in the display data creating means, the noise level detection voltage is added to the level detection voltage, signal level display data is created from the added voltage, and display means is displayed according to the signal level display data. By this, the error component due to the noise signal is compensated and the signal level of the input radio wave is accurately displayed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a signal level display device according to the present invention. SH from broadcasting satellite
The RF signal in the F band is frequency-converted by an outdoor converter (not shown) and becomes a first intermediate frequency signal, which is supplied to the input terminal 1. This signal is selected by the frequency down converter 2, frequency-converted into the second intermediate frequency signal, and then supplied to the automatic gain control circuit (AGC circuit) 4 via the bandpass filter 3.

The output signal of the AGC circuit 4 is supplied to an FM demodulator 13 to be demodulated into a baseband signal, and after passing through a bandpass filter 14 set to a higher band than the signal band of this baseband signal, a level detection circuit. Demodulation noise is detected at 15, and the noise level detection voltage is supplied to the adding circuit 16. The AGC circuit 4 is composed of two variable gain amplifiers (not shown), and a level detection circuit 4c for controlling these amplifiers by voltage is connected to the AGC circuit 4 to respond to the level change of the second intermediate frequency signal. The level detection voltage is negatively fed back to perform gain control, and the AGC circuit 4 always outputs the second intermediate frequency signal of a constant level and supplies the level detection voltage to the adding circuit 16.

The level detection voltage from the level detection circuit 4c and the noise level detection voltage from the level detection circuit 15 are added, and the added voltage is converted to digital data by the analog-digital converter 6. It is supplied to the CPU 7. The CPU 7 performs arithmetic processing on the digital signal, and a display circuit 8 for displaying signal level display data obtained by the arithmetic processing, and a RAM 9 for storing the digital data from the analog-digital converter 6. Then, a tuning circuit 11 for tuning and controlling the frequency down converter 2 and an external input circuit 12 for setting a signal level display processing mode according to an instruction from the tuning circuit 11 are connected. The tuning circuit 11 automatically fine-tunes the frequency down converter 2 according to the tuning data, and the CPU 7 updates the signal level at a predetermined timing in accordance with this operation.

FIG. 2 is a circuit diagram showing an example of the adder circuit 16. The input terminal 21 is connected to the inverting input terminal (−) of the operational amplifier 23 via the resistor R22, and the connection point A between the resistor R22 and the inverting input terminal (−) is the resistor R24.
Is connected to the output side of the operational amplifier 23 via. on the other hand,
The input terminal 25 is connected to the non-inverting input terminal (+) of the operational amplifier 23 via the resistor R26, and the connection point B between the resistor R26 and the non-inverting input terminal (+) is connected to the reference potential point via the resistor R27. Connected. The output side of the operational amplifier 23 has an output terminal 29 through a resistor R28 for protecting the output.
Are connected. Here, the resistors R22 and R24 set the gain of the adder circuit 16.
26 and R27 are dividing resistors.

In the adder circuit 16 thus constructed, the level detection voltage from the level detection circuit 4c is supplied to the input terminal 21, and the noise level detection signal from the level detection circuit 15 is supplied to the input terminal 25. When a voltage is supplied, when the noise signal increases in the input signal which is the sum of the channel selection signal and the in-band noise signal, the noise level detection voltage corresponding to this noise signal is the output signal of the AGC circuit 4. Is added to the level detection voltage based on
A voltage corrected by the noise signal is output from the output terminal 29 of the output terminal 29, and an accurate input level can be displayed in the display circuit 8 as described later.

Next, the operation of the above embodiment will be described with reference to FIGS. When the tuning circuit 11 automatically tunes the frequency down converter 2 by tuning data and tunes in,
The first intermediate frequency signal is converted into a predetermined second intermediate frequency signal by the down converter 2, band-limited by the band filter 3 at the next stage, then becomes a constant level signal by the AGC circuit 4, and the FM demodulator 13 Is demodulated to a baseband signal.

Bandpass filter 1 from the baseband signal
At 4, the components in the higher band than the signal band of the baseband signal are taken out, the demodulation noise is detected at the level detection circuit 15, and the noise level detection voltage is supplied to the addition circuit 16. Of the two variable gain amplifiers (not shown) of the AGC circuit 4, the output signal of the variable gain amplifier of the latter stage is detected by the level detection circuit 4c, and the level detection voltage is negatively fed back to the two variable gain amplifiers. It controls the gain of the amplifier,
The level detection voltage is also supplied to the adder circuit 16.

As shown in FIG. 2, the adder circuit 16 is supplied with the level detection voltage and the noise level detection voltage at its input terminals 21 and 25, respectively. When the noise level detection voltage is constant, the level detection voltage is changed. When it increases, the potential at the point A increases, so that the voltage output from the output terminal 29 decreases. That is, as the signal level of the input RF signal increases, the output from the adder circuit 16 decreases in inverse proportion, and this output signal is converted into digital data by the analog-digital converter 6 and then processed by the CPU 7 to be displayed. The data is supplied to the display circuit 8 to display a signal level proportional to the signal level of the input RF signal.

By the way, when the noise level detection voltage is not constant and increases, in the conventional signal level display device, the increased noise signal is added to the input RF signal,
The signal level of the input RF signal is displayed larger than the actual level. However, in this example,
When the noise level detection voltage increases, the potential at the point B in FIG. 2 increases, and the potential at the point A decreases, so that the voltage output from the output terminal 29 increases.

That is, the higher the signal level of the noise signal,
Since the output voltage from the adder 6 is increased, by adding the noise level detection voltage from the level detection circuit 15 to the level detection voltage of the level detection circuit 4c, the noise level component of the noise signal is corrected. The voltage is supplied to the analog-digital converter 6. Here, after being converted into digital data, it is arithmetically processed by the CPU 7 and becomes display data which is supplied to the display circuit 8 to display a signal level proportional to the true RF input signal level of the input RF signal. In this way, according to this embodiment, when the noise signal increases, the level detection voltage based on the output signal from the AGC circuit is added with the noise level detection voltage due to the noise component of the demodulated signal to compensate. By preventing an inaccurate signal level display due to a noise signal, the signal level of the true input RF signal can be displayed.

As an effective utilization method of this embodiment, CS
(Communication satellite) Polarization plane adjustment for broadcast reception will be described.
In order to make effective use of the frequency spectrum, signals for CS broadcasting are generally arranged alternately on the frequency axis using two orthogonal polarized waves as shown in FIG. In FIG. 4, horizontal polarization is allocated to even channels and vertical polarization is allocated to odd channels.

Here, when the angle of the plane of polarization is adjusted, the (b) signal and the (c) signal appear according to the deviation of the angle.
There is no significant difference in the input level between the case of the optimum angle of the signal (a) and the case of the optimum angle of the signals (b) and (c) which are deviated by 90 degrees. However, if the angles are misaligned, for example,
The signals (b) and (c) are added to the signal (a), resulting in interference of a plurality of channels, resulting in a poor C / N ratio. Therefore, in the present embodiment, which can be displayed as a change in the signal level when either the level of the input RF signal or the C / N ratio changes, the polarization plane can be adjusted with higher accuracy.

FIG. 3 shows a modification of the embodiment of FIG. 1 described above. In the embodiment of FIG. 1, the level detection voltage of each of the level detection circuits 4c and 15 or the noise level detection voltage is added by the adder circuit 16. Then, the added voltage is converted into digital data by the analog-digital converter 6 and supplied to the CPU 7 for arithmetic processing. In this modified example, the detected voltages of the level detection circuits 4c and 15 are converted into analog-digital data, respectively. Bowl 6
The difference is that the data is converted to digital data by a and 6b and then supplied to the CPU 7 for arithmetic processing. Since other configurations are similar to those of the above-described embodiment, corresponding elements and parts are designated by the same reference numerals, and description thereof will be omitted. According to this embodiment, the same effect as that of the above embodiment can be obtained.

[0029]

As described in detail above, according to the present invention, the extraction means and the level detection means are provided, and the noise level detection voltage of the noise signal component is obtained from the demodulated signal by these means,
This noise level detection voltage is added to the level detection voltage based on the output signal of the AGC circuit before FM demodulation by the display data creating means to create the signal level display data, thereby displaying the signal level. , At least when one of the input RF signal level and the C / N ratio changes, it can be displayed as a signal level change, and the sensitivity is improved even for a small level change of the input RF signal, and a more accurate signal level display It has an excellent effect that

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a signal level display device according to the present invention.

FIG. 2 is a circuit diagram showing an example of an adder circuit shown in FIG.

FIG. 3 is a block diagram showing a modification of the signal level display device of FIG.

FIG. 4 is an explanatory diagram showing a channel arrangement of signals in which orthogonal polarization is assigned as a channel signal.

FIG. 5 is a block diagram of a conventional signal level display device.

[Explanation of symbols]

 4 ... AGC circuit, 4c ... Level detection circuit, 6, 6a, 6b ... Analog-digital converter, 7 ... CPU, 8 ... Display circuit, 15 ... Level detection circuit, 16 ... Addition circuit.

Claims (1)

[Claims] 1. A means for converting an input radio wave from a broadcasting satellite whose frequency is converted by an outdoor converter into an intermediate frequency signal by a frequency down converter, a variable gain amplifier for amplifying the intermediate frequency signal, and a level of the intermediate frequency signal. A level detection circuit that generates a first voltage according to the change and controls the gain of the variable gain amplifier with the first voltage, and demodulates an output signal from the variable gain amplifier to output a baseband signal. An FM demodulator, an extraction means for extracting a noise component outside the signal band from the baseband signal, and a second output signal of the extraction means according to a noise level
And a display data creating unit that adds the first voltage and the second voltage and creates signal level display data indicating the reception level of the input radio wave from the added voltage. A signal level display device in a satellite broadcast receiver, comprising: a display unit that displays the reception level of an input radio wave based on the signal level display data output from the display data creation unit.