JPH0937178A - Reception level display device - Google Patents

Abstract

(57) [Abstract] [Problem] The C is accurately measured regardless of the input signal level.
/ Enable to display the reception level according to the N value. An AGC voltage obtained by an AGC circuit,
AFC voltage obtained by the FM demodulation unit 16, noise detection voltage obtained by the BPF 18 and the detection circuit 19, video signal detection results obtained by the video signal detection units 20 and 21, and audio signal detection obtained by the audio signal detection units 22 and 23 The result is input to the display control unit 24. Then, in the display control unit 24,
The input signal level of the receiver is detected based on the AGC voltage, and the noise detection voltage is corrected according to the input signal level,
Based on the noise detection voltage with this correction, C / of the input signal
N is obtained, and the display level is displayed on the display unit 25 according to the input signal C / N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception level display device used in a satellite broadcast receiver or the like, and more particularly to the power of a main carrier signal input to the receiver and the frequency band occupied by the main carrier signal. Ratio of noise power (hereinafter C /
C) of the signal input to the receiver
It relates to the one that can be displayed accurately.

[0002]

2. Description of the Related Art Conventionally, in television broadcasting using a satellite, a signal is frequency-modulated and transmitted. However, the C / N of the frequency-modulated signal and the signal and noise after demodulating the signal are generated. The voltage amplitude ratio (hereinafter referred to as S / N) is (1)
There is an expression relationship.

[0003]

[Equation 1] In the equation (1), IFM and IEMP are the FM improvement degree and the emphasis improvement degree, respectively.

From equation (1), it can be seen that C / N and S / N are in a proportional relationship, and if both C / N and S / N are plotted on the logarithmic axis, the locus becomes a straight line with a slope of 1. . However, when the C / N deteriorates, the so-called threshold phenomenon causes a sudden increase in medaka-like noise, and the S / N of the demodulated signal largely deviates from the straight line having the slope 1.

This point is an input signal condition in which the noise amplitude and the FM signal amplitude are the same, and the C / N at that time is
Is about 9 dB. FIG. 6 shows the input signal C / N and the demodulated signal S.
The relationship of / N is shown.

From the above contents, it is understood that in order to receive a high S / N video signal, it is necessary to increase the C / N of the signal input to the receiver, but the C / N of the input signal is required. Is determined by the equation (2).

[0007]

[Equation 2]

EIRP: Equivalent isotropic radiated power of satellite Lf: Free space propagation loss Gr: Antenna gain β: Antenna pointing loss R: Rain attenuation Gc: Converter gain Lk: Cable attenuation k: Boltzmann constant T: Receiver system Total noise temperature B: Reception bandwidth Note that parameters other than rain attenuation R are constants unique to the reception system. However, the antenna pointing loss β depends on the installation accuracy of the antenna and can be set to 0 by adjusting the best angle of the antenna directional characteristics to the arrival direction of the radio wave.

As an antenna for receiving a satellite broadcast, a parabola or an offset type having a directivity with a half-value angle of about 2 degrees and a very sharp directivity is generally used. Fine adjustment of the antenna is required while checking the C / N of the output signal.

Further, the rainfall attenuation R is a parameter which fluctuates due to weather conditions and the like and which greatly fluctuates the C / N of the received signal. For example, C / N of about 16 dB during fine weather (at this time, a video signal S / N of about 40 dB (no evaluation) can be obtained)
Therefore, the image cannot be received at all during a thunderstorm.
Fluctuates up to / N. Therefore, if the C / N can be confirmed at any time when the broadcast is received, it becomes an effective means for grasping the reception state.

Therefore, conventionally, a reception level display device configured as shown in FIG. 7 is used. In FIG.
1 transmitted by a coaxial cable from an antenna (not shown)
The first intermediate frequency signal in the GHz band is connected to the input terminal 1 of the receiver, the channel selection circuit 2 extracts only a specific channel signal, and is converted into the second intermediate frequency signal in the 400 MHz band. This second intermediate frequency signal is demodulated by the FM demodulation circuit 3 and passes through the amplification circuit 4 to the bandpass filter 5,
It is supplied to the video signal processing circuit 8 and the QPSK demodulation unit 10.

The bandpass filter 5 is a frequency band other than the video signal band of 4.5 MHz or less and the audio signal band of 5.73 ± 0.5 MHz in the FM demodulated signal having a band of about 12 MHz. The noise component of is extracted and output to the detection circuit 6. The detection circuit 6 detects the noise component extracted by the bandpass filter 5 and generates a DC voltage (hereinafter referred to as a noise detection voltage) that varies according to the amplitude of the noise. This noise detection voltage is displayed by the display control unit 7
Is supplied to.

On the other hand, the video signal processing circuit 8 takes out a video signal of 4.5 MHz or less from the FM demodulated signal, performs processing such as de-emphasis and dispersal removal, and generates a video signal connectable to the television receiver. Let Since the amplitude of the video signal obtained here is adjusted to 1 V (pp) by changing the amplification degree of the amplifier circuit 4, the noise detection voltage becomes a value proportional to the S / N of the FM demodulated signal, The relationship between the C / N of the receiver input signal and the noise detection voltage can also be expressed by the relationship shown in FIG.

The video signal obtained by the video signal processing circuit 8 is supplied to the synchronization detection circuit 9. The sync detection circuit 9 detects a sync signal from the input video signal. This synchronization signal is supplied to the display controller 7.

On the other hand, the QPSK demodulator 10 demodulates an FM demodulated signal into a voice signal by PCM modulation. This PCM
The modulated audio signal is decoded by the PCM decoding unit 11 and supplied to the display control unit 7.

Here, the input control signal C is input to the display controller 7 in advance.
/ N and the relationship between the noise detection voltage are stored and the input signal C / N is input signal C at any one point of 9 dB or more.
By taking the correlation between / N and the noise detection voltage, the input signal C / N can be obtained thereafter based on the noise detection voltage.

The display control unit 7 displays the reception level on the display unit 12 according to the obtained input signal C / N. Display methods include display on the front panel of the receiver, on-screen display in which the display content is superimposed on the video signal output from the receiver and displayed on the screen of the television receiver, and the like. As for the display content, numerical display according to the magnitude of noise, or bar graph graphic display is generally used.

Since the noise power that determines the C / N of the receiver input signal is determined by the atmospheric noise received by the antenna and the thermal noise generated inside the antenna, when no signal is input to the receiver. In the case (including the case where the antenna is not connected to the input terminal), the noise input to the FM demodulation circuit 3 is only the noise generated inside the receiver, and the noise level of the demodulated signal is extremely low.

The noise detection voltage obtained at this time is C /
The value of N is the same as that when it is good, and if the reception level is displayed as it is, the display is contrary to the original purpose of the reception level display, which is to confirm the image quality.

In order to solve this problem, the display controller 7
Controls the reception level display to the minimum value when there is no signal based on the detection result of the presence or absence of the video signal and the audio signal. The video signal is detected by the synchronization detection circuit 9, and the audio signal is detected by the PCM decoding unit 11.

That is, in the audio transmission system of satellite broadcasting, a PCM subcarrier in which a pulse code modulated (PCM) digital signal and other additional data are multiplexed and four-phase phase modulation (QPSK) is performed with a 5.727272 MHz subcarrier. The method is often used.

The bit stream at the output of the QPSK demodulation circuit 10 is composed of a 2,048-bit 1 ms frame as shown in FIG. In addition, one frame consists of frame synchronization data, control code, as shown in FIG.
It consists of range bits, voice data, independent data, and error correction code. Of these, the frame synchronization data is shown in FIG.
It is a 16-bit fixed pattern as shown in.

The PCM decoding unit 11 detects the frame synchronization data from the bit stream of the input signal (this operation is hereinafter referred to as "frame synchronization"), and uses the control code and range bits following the data. Audio data is decoded into PCM data having a sampling frequency of 48 kHz (B mode) or 32 kHz (A mode). The PCM decoding unit 11 outputs an identification signal indicating whether or not frame synchronization is established, and by detecting this signal, the presence / absence of an audio signal can be known.

However, in the conventional reception level display device having the above-mentioned configuration, the video signal is a signal that does not include a synchronization signal, and the audio signal uses a transmission method different from the above-described method. When a signal is received (for example, MUSE signal), the detection result is that there is no signal for both video and audio, and the display control unit displays the C / N of the input signal.
Regardless of the above, there is a problem that the display value is set to the minimum value and the normal reception level cannot be displayed.

In addition, according to the report of the satellite broadcasting reception technology study group by the Radio Technical Association, the input signal level of the receiver is −
It is determined to be 28 dB (mW) to -61 dB (mW), and if the input signal level is within this range, it is common to design the receiver so that the fluctuation does not affect the quality of video and audio signals. Target.

However, when the input signal level falls below the above range, the demodulated signal S / N deteriorates as the input signal level decreases. Fig. 9 shows the input signal C
/ N is constant, input signal level and demodulated signal S /
The relationship of N is shown. That is, in this input signal level region, the display value obtained from the reception level display device of FIG. 7 has a problem that it is a value greatly deviated from the input signal C / N.

[0027]

As described above, in the conventional reception level display device, when the video signal does not include the synchronization signal and the audio signal receives the signal of the transmission method which is out of the standard, the normal reception level display device does not operate normally. There was a problem that the reception level could not be displayed. Further, when the input signal level falls below the specified range, the demodulated signal S / N deteriorates with a decrease in the input signal level, and a value greatly deviated from the input signal C / N is displayed. there were.

An object of the present invention is to solve the above-mentioned problems and to accurately display the reception level according to the C / N value even when the input signal level is low, and to input the signal to the receiver. An object of the present invention is to provide a reception level display device which can display an appropriate reception level even in a situation where the satellite broadcasting reception antenna is not installed, and is particularly effective as means for adjusting the direction and confirming the image quality when a satellite broadcasting receiving antenna is installed.

[0029]

A reception level display device of the present invention for solving the above problems adjusts the level of an FM-modulated television signal of an intermediate frequency to a constant level, and a gain control required for the adjustment. From an automatic gain control unit that outputs information, an FM demodulation unit that FM demodulates an intermediate frequency signal output from this automatic gain control circuit to reproduce a television signal, and a television signal output from this FM demodulation unit. Noise detection means for removing the video and audio signals, extracting only the noise component and detecting it to obtain noise detection information proportional to the noise level, and a reception signal level based on the gain control information, and depending on this reception signal level And a display control unit that corrects the noise detection information to generate reception level display information, and displays the reception level display information obtained by this display control unit. Constituted by and a that the display unit.

In particular, the display control unit is further provided with the F
It is characterized in that the presence or absence of an input signal is discriminated from the frequency control information required for demodulation by the M demodulation section, and the reception level display information is corrected according to the discrimination result.

Further, a video signal detection unit for detecting the presence or absence of a video signal component from the television signal obtained by the FM demodulation unit is provided, and the display control unit responds to the detection result of the video signal detection unit. Then, the reception level display information is corrected.

Alternatively, it further comprises an audio signal detection unit for detecting the presence or absence of an audio signal component from the television signal obtained by the FM demodulation unit, and the display control unit responds to the detection result of the audio signal detection unit. Then, the reception level display information is corrected.

Further, the display control section approximately obtains and stores a relational expression between the known reception level and the noise detection information in advance, and stores the relational expression from the noise detection information using this relational expression. It is characterized in that display information is obtained.

That is, in the reception level display device having the above configuration, the fact that the input signal level of the receiver in a very wide range can be detected from the gain control information obtained by the automatic gain control section is utilized, and the display control section is made By correcting the noise detection information obtained by the detection means with the gain control information, an accurate C / N of the input signal can be obtained, and an appropriate reception level can be displayed on the display section.

Further, the state in which no received signal is input can be detected from the frequency control information obtained by the FM demodulation section and the video / audio detection information obtained by the video signal / audio signal detection section, and the reception level display at that time can be properly detected. Can be controlled.

Further, in the display control section, a relational expression between the known reception level and the noise detection information is approximately obtained and stored in advance, and the reception level is displayed from the noise detection information by using this relational expression. By obtaining the information, it is possible to more accurately display the reception level corresponding to the input signal C / N.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. FIG. 1 shows the configuration of an embodiment of a reception level display device according to the present invention used in a satellite broadcast receiver. In FIG.
Reference numeral 13 is a first intermediate frequency input terminal of the receiver to which a coaxial cable from the antenna is connected, and the first intermediate frequency signal input from this input terminal 13 is supplied to the channel selection circuit 14.

The tuning circuit 14 converts only a desired channel signal from a plurality of channel signals included in the first intermediate frequency signal into a second intermediate frequency signal. The second intermediate frequency signal is AGC (automatic). The gain control circuit 15 is supplied.

The AGC circuit 15 amplifies the selected second intermediate frequency signal up to the operating region of the limiter built in the FM demodulation unit 16 at the subsequent stage, and outputs a signal (AGC voltage) for controlling the amplification degree. Therefore, the amplified second intermediate frequency signal is supplied to the FM demodulation unit 16, and the AGC voltage is supplied to the display control unit 24.

The bandpass filter 18 extracts only a noise component which does not include video and audio signals from the amplified FM demodulated signal, and its output is the detection circuit 1.
9. The detection circuit 19 detects the noise extracted by the bandpass filter 18 and outputs a DC voltage (noise detection voltage) corresponding to the level of the noise. The noise detection voltage is supplied to the display controller 24.

The video signal processing circuit 20 extracts only the video signal from the amplified FM demodulated signal.
This video signal is supplied to the synchronization detection circuit 21. The synchronization detection circuit 21 detects the synchronization signal from the video signal and determines the presence or absence of the video signal, and the determination result is supplied to the display control unit 24.

The QPSK demodulation section 22 uses the amplified F
The QPSK signal is extracted from the M demodulated signal to demodulate the bit stream, and this demodulated signal is supplied to the PCM decoding unit 23. The PCM decoding unit 23
A 16-bit frame synchronization pattern is detected from the bit stream output from the QPSK demodulation unit 22 and P
The presence or absence of a CM audio signal is detected, and the detection result is supplied to the display control unit 24.

The display control section 24 outputs the AGC voltage output from the AGC circuit 15, the noise detection voltage output from the detection circuit 19, the video signal detection result output from the synchronization detection circuit 21, and the PCM decoding section 23. The detection result of the output audio signal is input, the C / N of the receiver input signal is calculated from these values, and the result is displayed on the display unit 2.
5, the display control is performed.

In the above configuration, the AGC voltage output from the AGC circuit 15 will be described first. The level of the signal input to the receiver varies depending on the amplification factor of the antenna and the length of the coaxial cable that connects the antenna and the receiver, but as described above, in a general satellite receiving system, -28 dB (mW). ) To -61 dB (mW).

On the other hand, when demodulating the FM signal, the FM demodulator 16 has a limiter for limiting the demodulated signal to a certain level in order to prevent the AM noise of the intermediate frequency signal from becoming the noise of the demodulated signal. Even if the input signal level fluctuates, the AGC circuit 15 operates so as to amplify the signal to a certain level so that the output signal level of the AGC circuit 15 always falls within the limiter operating region.

FIG. 2 shows the input / output characteristics of the AGC circuit 15. The output level is kept constant with respect to the input signal level regulation of -28 dB (mW) to -61 dB (mW).
The GC operating range is −80 dB (mW) to −28 dB (m
It is a general design that the range is set to (W) and a margin at the time of a low input signal level is taken. Therefore, the input signal level of the receiver in a very wide range can be detected from the AGC voltage.

It is also possible to detect from the AGC voltage whether or not the input signal level is about -80 dB (mW) or less, and the video signal and the audio signal after FM demodulation in this range are both noise. However, there is no problem as it is judged that there is no input signal at once.

The display controller 24 obtains the receiver input signal level from the AGC voltage, and the level is about -61 dB (m
If it is less than W), the noise detection voltage is corrected and the input signal C / N is obtained based on the corrected noise detection voltage. This enables accurate reception level display.

Further, since the state where no signal is input to the receiver can be detected based on the video signal detection result and the audio signal detection result, the reception level display at that time can be properly controlled.

By storing the relational expression of the noise detection voltage peculiar to the receiver and the input signal C / N in each receiver, and calculating the input signal C / N from the noise detection voltage using this relational expression. , The reception level display corresponding to the input signal C / N can be performed more accurately.

In the reception level display device described above,
A first operation example will be described. Conventional satellite broadcasting reception until the noise detection voltage, the video signal synchronization detection result, and the PCM decoding section frame synchronization detection result are obtained after selecting one channel from the signal input to the receiver and performing FM demodulation. It is the same operation as the machine.

As described above, the relationship between the output signal S / N of the FM demodulator 16 and the receiver input signal level when the input signal C / N is constant is as shown in FIG.
That is, when the input signal level is -61 dB (mW) or more, the power of noise input to the receiver is the tuning circuit 14
, And the C / N of the signal at the input of the FM demodulation unit 16 is constant without being affected by the fluctuation of the input signal level because the thermal noise generated by the AGC circuit 15 is sufficiently large.
/ N is also constant.

However, the input signal level is -61d.
In the region of B (mW) or less, the thermal noise generated by the tuning circuit 14 and the AGC circuit 15 cannot be ignored as compared with the noise power included in the first intermediate frequency signal input to the receiver. Therefore, the decrease in the input signal level of the receiver directly decreases the C / N of the input signal of the FM demodulation unit 16,
As a result, the S / N of the demodulated signal is lowered.

The degree of deterioration of the demodulated signal S / N at this time can be represented by a straight line having a slope of 1 when both the input signal level and the demodulated signal S / N are represented by logarithmic axes. Also, demodulated signal S / N
The noise detection voltage output from the detection circuit 19 is proportional to the entire demodulated signal S / N.

Based on the above properties, the display control unit 24 is shown in FIG.
It operates based on the flowchart shown in. A non-volatile memory is built in the display controller 24, and
Function f (LI = f (VAGC)) for obtaining receiver input signal level (LI) from C voltage (VAGC), input signal level (L) when receiver input signal level is -61 dB (mW) or less
I) change ratio (A) of noise detection voltage (VN) and noise detection voltage (VI) to obtain receiver input signal C / N (CN) function g (CN = g (VN
)) Is stored in advance.

Here, regarding the function g, the deterioration of the demodulated signal S / N due to the threshold phenomenon shown in FIG. 2 is taken into consideration, and when the input signal C / N (CN) is larger than 9 dB and below 9 dB. In some cases the slope of the function is changed.

First, the display controller 24 reads the AGC voltage (VAGC) output from the AGC circuit 15 (step S1), and obtains the input signal level (LI) from the relational expression: LI = f (VAGC) ( Step S2).

Next, the noise detection voltage (VN) output from the detection circuit 19 is read (step S3), and it is judged whether or not the input signal level (LI) obtained above is -61 dB (mW) or less (step S3). S4). Here, when the input signal level (LI) is larger than -61 dB (mW) (NO), the input signal C / N (CN) is obtained using the relational expression: CN = g (VN) (step S5). .

In the processing of step S4, when the input signal level (LI) is -61 dB (mW) or less, (Y
ES), and whether or not it is -80 dB (mW) or less (step S6). Where input signal level (LI)
When is less than -80 dB (mW) (YES), the input signal C / N (CN) is set to 0 (step S7). When the input signal level (LI) is higher than -80 dB (mW) (NO), the noise detection voltage (VN) is corrected using the constant A and the corrected noise detection voltage (V
Find N ′). However, the relational expression for correction is VN
'= VN + A (-61-LI) is used (step S
8). Then, the receiver input signal C / N is obtained from the corrected noise detection voltage (VN ') using the relational expression: CN = g (VN') (step S9).

Finally, display data is generated from the value CN obtained in steps S5, S7 and S9 (step S10), and the display unit 25 is controlled to input signal C / N.
The reception level is displayed according to (step S11).

In the above operation example, the input signal C / N can be accurately detected even when the input signal level is low, and the no-signal state at the input of the receiver can be accurately discriminated. The level can be displayed.

Next, the second operation example will be described. In the first operation example, the noise detection voltage and the input signal C /
The relationship of N is expressed by using the same function g for all the receivers, but in the second operation example, the function g ′ peculiar to the receiver is used.

In the first place, the noise detection voltage and the input signal C / N
The reason why the relationship of can be expressed by using a specific function is that the input signal C / N and the demodulated signal S / N have the relationship shown in FIG. 6 as described above, and the demodulated signal S / N and the noise detection voltage are proportional. Because there is a relationship. However, the relationship between the input signal C / N and the demodulated signal S / N and the relationship between the demodulated signal S / N and the noise detection voltage have slight deviations due to characteristic variations unique to the receiver. The purpose of this operational example is to absorb this deviation.

The operation of the display control unit 24 based on this embodiment is shown in the flowchart of FIG. Here, in the manufacturing process of the receiver, four types of signals whose C / Ns are known in advance and whose C / N values are different are prepared.
However, the C / N of the two kinds of signals is C / N (CN1, CN2) larger than 9 dB, and the C / N of the other two kinds of signals is C / N smaller than 9 dB (CN3, CN4).
And

First, C / N inputs signals of CN1 and CN2 to the receiver, and noise detection voltages (VN1, VN) at that time are inputted.
2) is read (steps S21 and S22). From the above results, when the C / N is larger than 9 dB, the noise detection voltage (V
The linear function g'U (CNU = g'U (VNU)) for obtaining the input signal C / N (CNU) is obtained from NU) and stored in the non-volatile memory (step S23).

Next, the C / N inputs the signals of CN3 and CN4 to the receiver, and the noise detection voltage (VN3, VN) at that time is input.
4) is read (steps S24 and S25). From the above results, noise detection voltage (VNL) when C / N is 9 dB or less
Input signal C / N (CNL) from the straight line function g'L
(CNL = gL '(VNL)) is obtained and stored in the nonvolatile memory (step S26).

Further, the intersection of the straight line CNU = g'U (VNU) and the straight line CNL = g'L (VNL) is obtained, and the noise detection voltage (VNTH) at that point is stored as the noise detection voltage at the threshold point. Yes (step S27).

The steps up to this point are performed in the manufacturing process of the receiver, and thereafter, the operation of the display control section 24 in the general use state of the receiver such as when the antenna is installed and when the image quality is confirmed. First, the noise detection voltage (VN) is read (step S2
8) Then, the stored VNTH is compared (step S29). When the noise detection voltage (VN) is larger than VNTH (YES), the input signal C / N (CN) is obtained from the noise detection voltage (VN) using the function g'U (step S30), and the noise detection voltage (VN) ) Is less than or equal to VNTH (NO), the input signal C / N (CN) is obtained from the noise detection voltage (VN) using the function g'L (step S31). Finally, display data corresponding to the input signal C / N (CN) is generated (step S32), and the display unit 2
5 is controlled and displayed (step S33).

Here, the functions g'U and g'L stored in the receiver in the manufacturing process represent the relationship between the noise detection voltage and the input signal C / N including the characteristic variations of the receiver. . Therefore, by calculating the input signal S / N from the noise detection voltage using this function, when the input signal level is higher than -61 dB (mW), the input signal with higher accuracy is obtained as compared with the first operation example. Can display C / N.

However, the input signal level is -61 dB (m
In the case of W) or less, the influence on the noise detection voltage due to the decrease of the input signal level cannot be corrected, so that the display value and the input signal C / N deviate from each other. As a measure against this problem, it is also effective to use a combination of the first operation example and the second operation example.

As described above, the voltage obtained by detecting the noise of the FM demodulated signal is used as the control voltage of the second intermediate frequency AGC circuit, and the FM demodulated signal is used as the video signal detection result and the audio signal detection result. The input signal C / N is calculated from the noise detection voltage by applying the correction and using the relational expression between the input signal C / N and the noise detection voltage peculiar to each receiver stored in the manufacturing process of the receiver. By displaying the value, the input signal C / N can be accurately grasped, and by displaying the reception level according to the C / N, it becomes a very effective function when the antenna is installed and the image quality is confirmed.

[0072]

As described above, according to the present invention, even when the input signal level is low, the reception level can be accurately displayed according to the C / N value, and the signal is input to the receiver. It is possible to provide a reception level display device that can perform an appropriate reception level display even in a situation where the satellite broadcasting reception antenna is not installed, and is particularly effective as means for adjusting direction and confirming image quality when a satellite broadcasting receiving antenna is installed.

[Brief description of drawings]

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

FIG. 2 is a second intermediate frequency stage AGC in the same embodiment;
The figure which shows the input-output characteristic of a circuit.

FIG. 3 is a diagram showing input / output characteristics of the FM demodulation unit in the same embodiment.

FIG. 4 is a flowchart showing an operation of a display control unit in the first operation example of the same embodiment.

FIG. 5 is a flowchart showing the operation of the display control unit in the second operation example of the same embodiment.

FIG. 6 is a diagram showing a relationship between an input signal C / N and a demodulated signal S / N of a satellite broadcast receiver.

FIG. 7 is a block diagram showing a configuration of a conventional reception level display device used in a satellite broadcast receiver.

FIG. 8 is a diagram showing a configuration of a bit stream of a QPSK demodulated signal in a satellite broadcast received signal.

FIG. 9 is a diagram showing the relationship between the input signal level and the demodulated signal S / N when the C / N of the satellite broadcast reception signal is constant.

[Explanation of symbols]

 1 ... Receiver input terminal 2 ... Channel selection circuit 3 ... FM demodulation unit 4 ... Amplification circuit 5 ... Band pass filter (BPF) 6 ... Detection circuit 7 ... Display control unit 8 ... Video signal processing circuit 9 ... Sync detection circuit 10 ... QPSK demodulation unit 11 ... PCM decoding unit 12 ... Display unit 13 ... Receiver input terminal 14 ... Channel selection circuit 15 ... Second intermediate frequency stage AGC circuit 16 ... FM demodulation unit 17 ... Amplification circuit 18 ... Bandpass filter (BPF) 19 ... detection circuit 20 ... video signal processing circuit 21 ... synchronization detection circuit 22 ... QPSK demodulation unit 23 ... PCM decoding unit 24 ... display control unit 25 ... display unit

Claims (5)

[Claims] 1. An automatic gain control section for adjusting the level of an FM-modulated intermediate frequency television signal to a constant level and outputting gain control information required for the adjustment, and an automatic gain control circuit for outputting the gain control information. The intermediate frequency signal
An FM demodulation unit for M-demodulating and reproducing a television signal, and a noise detection proportional to the noise level by removing the video and audio signals from the television signal output from the FM demodulation unit and extracting and extracting only the noise component. A noise detection means for obtaining information, a display control section for obtaining a reception signal level based on the gain control information, and correcting the noise detection information according to the reception signal level to generate reception level display information, A reception level display device, comprising: a display unit for displaying the reception level display information obtained by the control unit. 2. The display control section further identifies the presence or absence of an input signal from the frequency control information required for demodulation by the FM demodulation section, and corrects the reception level display information according to the identification result. The reception level display device according to claim 1, wherein 3. A video signal detection section for detecting the presence or absence of a video signal component from the television signal obtained by the FM demodulation section, wherein the display control section responds to the detection result of the video signal detection section. The reception level display device according to claim 1, wherein the reception level display information is corrected. 4. An audio signal detection unit for detecting the presence or absence of an audio signal component from the television signal obtained by the FM demodulation unit, wherein the display control unit is responsive to the detection result of the audio signal detection unit. The reception level display device according to claim 1, wherein the reception level display information is corrected. 5. The display control unit approximates and stores a relational expression between a known reception level and noise detection information in advance, and uses this relational expression to calculate the reception level from the noise detection information. 2. The reception level display device according to claim 1, wherein display information is obtained.