JP2002022787A - C/n ratio measuring device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To learn a limit value for a C/N ratio required for well picturing an image with digital broadcasting signals. SOLUTION: Noise signals from a noise signal generation part 10 with their level controlled by a variable gain amplifier 12 are mixed with the digital broadcasting signals input from an input terminal 4 by a mixer 8. This mixed signals are supplied from an output terminal 14 to a digital adaptive TV receiver. With the gain of the variable gain amplifier 12 gradually increased until no image is pictured with the TV receiver, the C/N ratio is measured by a signal measurement processing circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a C / N ratio of a digital broadcast signal such as a BS digital broadcast signal, a CS digital broadcast signal, and a terrestrial digital broadcast signal, and a C / N ratio measuring method.

[0002]

2. Description of the Related Art Conventionally, when measuring the C / N ratio of a television broadcast signal, a television broadcast signal received by an antenna is input to an electric field intensity measuring instrument, and the received television broadcasting signal is stored in the electric field intensity measuring instrument. Tuned by the tuner, frequency-converts the tuned television broadcast signal into an intermediate frequency signal in a predetermined frequency band, and supplies it to a signal measurement processing circuit in the electric field strength measuring instrument. In some cases, the intensity level is measured and the C / N ratio is measured, and these measured values are displayed on a display unit provided in the electric field intensity measuring device.

[0003]

Conventionally, analog signals have been mainly used as television broadcast signals. In this case, the projected image gradually deteriorates as the reception level decreases or the C / N ratio deteriorates, and the image does not suddenly disappear at all. However, in recent years, digitized television broadcast signals are increasing. In the case of a digital broadcast signal, when the C / N ratio falls below a certain value due to its characteristics, no image is suddenly displayed at all. Therefore, at present, even if an image is displayed, the image may not be displayed even if the C / N ratio is slightly reduced. Therefore, in order to maintain a state in which an image is projected, it is necessary to know how much margin the C / N ratio has. If the margin is small, it is necessary to take measures to reduce noise. That is, it is necessary to know the limit value of the C / N ratio. However, the above-described C / N ratio measurement technique can only know the current C / N ratio, and cannot respond to the above demand.

[0004] It is an object of the present invention to provide a C / N ratio measuring apparatus and method capable of knowing a limit value of a C / N ratio for favorably displaying an image by a digital broadcast signal. Other objects of the present invention will become apparent from the following description.

[0005]

A C / N ratio measuring apparatus according to the present invention comprises: an input terminal to which a digital broadcast signal is input;
Noise signal generating means, level adjusting means for adjusting the level of the noise signal, mixing means for mixing the level-adjusted noise signal and the digital television broadcast signal, and outputting a mixed signal; An output terminal for outputting a mixed signal from the means and a C / N ratio measuring means for measuring a C / N ratio of the mixed signal are provided. This C
The / N ratio measuring device is desirably housed in a portable housing, and it is also desirable that the electric field strength can be measured together with the noise signal generating means in a non-operating state. As the digital broadcast signal supplied to the input terminal, for example, a signal received by an antenna is used. As the level adjusting means, various means can be used as long as the level of the noise signal can be changed. For example, a variable gain amplifier or a variable attenuator can be used.

In such a C / N ratio measuring apparatus, a digital broadcast signal is supplied to an input terminal from an antenna or the like, and an output terminal is connected to, for example, a digital television receiver. Assuming that an image is displayed on the television receiver in this state, the noise signal generating means is operated. The noise signal and the digital television broadcast signal are mixed by the mixing means, and the mixed signal is supplied to the television receiver from an output terminal. Therefore, the television receiver is supplied with a digital broadcast signal to which the noise signal generated by the noise generating means is added. At the same time, the digital broadcast signal to which the noise signal has been added is supplied to the C / N ratio measuring means, and the C / N ratio is measured.

[0007] In this state, the level of the noise signal is adjusted by the level adjusting means to increase the level of the noise signal added to the digital broadcast signal. Causes the image not to be displayed. By measuring the C / N ratio at this time, it is possible to know the limit value of the C / N ratio for projecting an image on a television receiver. For example, by measuring the C / N ratio before adding a noise signal, it is possible to know how much the C / N ratio has a margin.

The above-mentioned input terminal, noise signal generating means, level adjusting means, mixing means, output terminal and C / N
The ratio measuring means can be provided in one housing. In this case, the C / N ratio measurement device can be easily carried,
The time required for preparing the operation for measuring the / N ratio can be shortened, and the operation for measuring the C / N ratio can be facilitated.

Further, instead of providing an output terminal, an image display means for displaying an image based on a mixed signal from the mixing means may be provided in the C / N ratio measuring apparatus. In this case, it is possible to save the trouble of connecting the C / N ratio measuring device to the television receiver, and the operation of measuring the C / N ratio is simplified.

[0010] The C / N ratio measuring method according to the present invention uses the C / N ratio.
Inputting a digital broadcast signal to an input terminal of the ratio measuring device; and mixing the digital broadcast signal with a variable-level noise signal in the C / N ratio measuring device, and transmitting the mixed signal from the C / N ratio measuring device. Supplying the digital signal to a digital television receiver, and changing the level of the noise signal in the C / N ratio measuring device so that the C / N ratio of the mixed signal when the digital television receiver becomes unreceivable. Is measured in a C / N ratio measuring device.

According to this C / N ratio measuring method, a digital broadcast signal is input to an input terminal of a C / N ratio measuring device, a noise signal is mixed with the digital broadcast signal, and the mixed signal is used as a digital television receiver. To change the level of the noise signal, and measure the C / N ratio when reception becomes impossible in the digital television receiver.

In the above C / N ratio measuring method, a C / N ratio measuring device may be directly connected to the digital television receiver, but the C / N ratio measuring device may be directly connected to the digital television receiver via a transmission line of a joint receiving system. The mixed signal can be supplied from an N ratio measuring device. In this case, the noise signal supplied to the digital television receiver includes, in addition to the noise generated by the noise signal generating means, a noise signal added during transmission of the digital television broadcast signal through the transmission path. ing. Therefore, it is possible to know the C / N ratio necessary for the digital broadcast signal before being transmitted through the transmission path to be transmitted through the transmission path and display an image on the television receiver.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric field strength measuring instrument 1 according to a first embodiment of the present invention has a housing 2 as shown in FIG. The housing 2 is configured to be portable. The housing 2 is provided with an input terminal 4. This input terminal 4
Is supplied with a digital broadcast signal, for example, a BS digital broadcast signal, a CS digital broadcast signal, or a terrestrial digital broadcast signal. This digital broadcast signal is supplied to one input terminal of a mixing means, for example, a mixer 8 via a DC blocking capacitor 6.

At the other input terminal of the mixer 8, a noise signal, for example, a noise signal generated by the noise generating unit 10, for example, a white noise signal, is adjusted in level by a level adjusting unit, for example, a variable gain amplifier 12. Are supplied. The mixed output signal of the mixer 8 is supplied to an output terminal 14 provided on the housing 2.

The mixed signal of the mixer 8 is supplied to frequency conversion means, for example, a tuner 16. Tuner 16
Then, the mixed signal is frequency-converted into an intermediate frequency signal of a predetermined frequency. This intermediate frequency signal is supplied to extraction means, for example, a bandpass filter 18 having a pass band for passing the intermediate frequency signal.

The output signal of the band pass filter 18 is supplied to a signal measuring circuit 20. As shown in FIG. 2, the signal measuring circuit 20 includes a level measuring device 20a and a C / C
And an N ratio measuring device 20b. Level measuring device 20a
Measures the output level (electric field strength) from the bandpass filter 18. Further, the C / N ratio measuring device 20b measures the C / N ratio of the output from the band pass filter 18. When these measurements are performed, the level measurement device 2
0a, the C / N ratio measuring device 20b includes a changeover switch 20c.
Connects the dummy resistor 20d. The level measurement signals and the C / N ratio measurement signals from the level measurement device 20a and the C / N ratio measurement device 20b are changed over by a changeover switch 20c.
Is supplied to the demodulator 20e via the
It is supplied to the CPU 24. When measuring the level and the C / N ratio, the dummy resistor 20d is connected to the level measuring devices 20a and 20c.
/ N ratio measuring device 20b is connected to these measuring devices 20b.
This is because a and 20b are separated from the demodulator 20e during measurement, so that impedance matching is achieved.

The CPU 24 digitally displays the level represented by the level measurement signal and the C / N ratio represented by the C / N ratio measurement signal on the digital display section 26. Also, the CPU 24
Controls the start and stop of the operation of the noise generator 10, adjusts the gain of the variable gain amplifier 12, controls the tuning operation of the tuner 16, measures the level by the signal measurement circuit 20, For example, it controls the C / N ratio measurement. Note that the level of the noise signal is adjusted by the CPU 24, for example, according to the operation of the operation knob 27 shown in FIG.

A power supply unit 28 is provided in the housing 2 of the electric field intensity measuring device 1.
And a DC power supply to the input terminal 4 via the high-frequency blocking coil 30. When the digital broadcast signal is, for example, a BS digital broadcast signal or a CS digital broadcast signal, the DC power is supplied to a converter attached to a BS or CS receiving antenna for receiving the digital broadcast signal and operates the converter.

This electric field strength measuring instrument 1 is used, for example, as shown in FIG. The BS digital broadcast signal from the converter 32 attached to the BS digital broadcast receiving antenna 31 and the CS digital broadcast receiving antenna 3
4 and a CS digital broadcast signal from a converter 36 attached thereto. This mixed signal is supplied to the input terminal 4 of the electric field strength measuring instrument 1. Also, the output terminal 14 of the electric field strength measuring instrument 1 is connected to a digital television receiver 40. Then, when the television receiver 40 is receiving the BS digital broadcast or the CS digital broadcast, the operation of the operation knob 27 causes the noise signal generator 1 as shown in FIG.
In a state where no noise signal is generated by 0, the C / N ratio is measured. Next, from the state shown in FIG. 5A to the state in which the noise level is slightly increased as shown in FIG. 5C, through the state in which the noise level is slightly increased as shown in FIG. , And gradually increase the noise level. In such a process, when no image is displayed on the television receiver 40, C
The / N ratio is read from the display unit 26 of the electric field strength measuring instrument 1. By comparing the C / N ratio when no image is generated with the state where no noise is generated, the C / N ratio is calculated.
It is possible to know how much the N ratio has a margin.

In some cases, only the BS digital broadcast signal from the converter 32 attached to the BS digital broadcast receiving antenna 31 is supplied to the input terminal 4, or the converter 36 attached to the CS digital broadcast receiving antenna 34.
May be supplied to the input terminal 4 only. Alternatively, a terrestrial digital broadcast signal received by a terrestrial digital broadcast receiving antenna (not shown) may be supplied to the input terminal 4.

Alternatively, as shown in FIG. 4, a BS digital broadcast signal from a converter 32 attached to a BS digital broadcast receiving antenna 31 and a CS digital broadcast signal from a converter 36 attached to a CS digital broadcast receiving antenna 34 are output. The broadcast signal is supplied to the head end 42 of the joint receiving system. A terrestrial digital broadcast signal from a terrestrial digital broadcast signal receiving antenna 44 is also supplied to the head end 42. The output signal of the head end 42 is supplied to the input terminal 4 of the electric field strength measuring instrument 1.

An output signal from the output terminal 14 of the electric field strength measuring instrument 1 is supplied to a transmission line of the joint receiving system. For example, the output terminal 14 of the electric field strength measuring instrument 1 is
It is connected to the. The distribution side of the four distributor 46 is connected to terminal terminals 48a to 48d via, for example, coaxial cables 50a to 50d. Terminal terminals 48a to 48d
The digital television receiver 40 is connected to one of the terminals, for example, the terminal terminal 48a. That is, the output terminal 14 of the electric field strength measuring instrument 1 is connected to the television receiver 40 via the transmission path of the joint receiving system.

Also in this case, the C / N ratio is read by the display unit 26 in a state where noise is not generated while receiving the digital broadcast in the television receiver 40. Thereafter, the level of the noise signal generated in the electric field strength measuring device 1 is gradually increased, and the C / N ratio when the television receiver 40 cannot receive the signal is displayed on the display unit 2.
Read by 6.

In this case, the television receiver 40 includes:
In addition to the noise signal from the electric field strength measuring instrument 1, a noise signal generated during transmission through the coaxial cable 50a is also added. Therefore, the margin of the C / N ratio of the digital broadcast signal transmitted from the head end 42 can be known in consideration of the noise generated during the transmission.

When the electric field intensity is measured by the electric field intensity measuring device 1, the CPU 24 stops the noise signal generating section 10 so that the noise signal is not superimposed on the digital broadcast signal. Avoid the effects of noise.

It should be noted that the electric field intensity measuring device 1 can be used to determine which modulation system the digital broadcast signal is. For example, FIG. 6 shows 64QAM, 16QA
It shows the relationship between the C / N ratio and the bit error rate (BER) in different modulation schemes of M, DQPSK, and QPSK. It is known that when the bit error rate is greater than 1.00 * 10 ^-4 , reception becomes impossible. This bit error rate is 1.0
The C / N ratio when it becomes 0 * 10 ^-4 is different as shown by reference numerals a to d in FIG. Therefore, these C
Storage means attached to the CPU 24 in advance for / N ratios a to d,
For example, it is stored in a memory (not shown), and when the C / N ratio when the image is no longer displayed is within a predetermined allowable range before and after a, 64QAM, and a predetermined allowable range before and after b. By determining that 16QAM is within the predetermined range, DPSK is within the predetermined allowable range before and after c, and QPSK is within the predetermined allowable range before and after d. It can be determined whether the digital broadcast signal is a modulation type digital broadcast signal.

FIG. 7 shows an electric field strength measuring instrument 1a according to a second embodiment of the present invention. In the electric field strength measuring device 1a, a U / V tuner 16a, a CS tuner 16
b, three types of BS tuners 16c are provided. Accordingly, the band pass filters 18a, 18b and 18c are provided for each tuner. The output signal of the mixer 8 is supplied to a U / V tuner 16a, C selected by a selection means, for example, a changeover switch 56.
It is supplied to one of the S tuner 16b and the BS tuner 16c. The changeover switch 56 is switched by the CPU 24. The other configuration is the same as that of the electric field strength measuring instrument 1 of the first embodiment, and therefore, the same parts are denoted by the same reference numerals and description thereof will be omitted.

This electric field measuring device 1a can be used similarly to the electric field intensity measuring device 1 shown in FIGS.
Therefore, it is possible to know the limit value and the margin of the C / N ratio when the image of the digital broadcast is projected on the digital television receiver.

When used as shown in FIGS. 3 and 4, the U / V tuner 16a, CS tuner 16b,
One of the BS tuners 16c has a changeover switch 56
, The digital broadcast signal input to the input terminal 4 is supplied.

Further, in the memory attached to the CPU 24, 6
The bit error rate in each of the different modulation schemes of 4QAM, 16QAM, DQPSK, and QPSK is 1.0
By storing a C / N ratio larger than 0 * 10 ^-4 and comparing the actual C / N ratio when an image is no longer displayed with each C / N ratio stored in the memory, , It is possible to determine which modulation scheme the digital broadcast signal is.

In the above two embodiments, the output terminal 1
4 is provided, but it may be removed and an image display means may be provided in the housing of the electric field strength measuring instrument 1 or 1a. As this image display means, for example, the tuner 16 or 16
What is necessary is just to have a demodulation means for demodulating the intermediate frequency signals from the signals a, 16b, and 16c, and a monitor for displaying a digital broadcast image based on the demodulated output. It is desirable that the monitor be small enough to fit in the housing 2. Alternatively, a signal measuring device having a noise signal generator, a mixer, and a C / N ratio measuring device is provided inside a digital television receiver, and a tuner and a band-pass filter of the digital television receiver are used. Thus, a C / N ratio measuring device can be configured. In this case, a monitor included in a digital-compatible television receiver can be used as the display unit. Further, in the above two embodiments, the variable gain amplifier 12 is used as the level adjusting means, but a variable attenuator may be used. Further, in the above embodiment, the electric field strength of the digital broadcast signal is measured and the measured value is displayed. However, when only the measurement of the C / N ratio is required, this measurement is unnecessary, and FIG. Level meter 20b shown
Is unnecessary.

[0032]

As described above, according to the present invention, C / N
A noise generating means is provided inside the ratio measuring device, and the noise signal is mixed with the input digital broadcast signal, and the level of the noise signal is made variable, so that an image is displayed while watching the actual screen. C / when gone
Since the N ratio is measured, the value of the C / N ratio required to display digital broadcast images and the current
It is possible to know whether or not the N ratio has a margin, and it is possible to easily determine whether or not it is necessary to take noise reduction measures.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electric field strength measuring device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a signal measuring circuit of the electric field strength measuring device of FIG.

FIG. 3 is a diagram showing a first use state of the electric field strength measuring device of FIG. 1;

FIG. 4 is a diagram showing a second use state of the electric field strength measuring device of FIG. 1;

FIG. 5 is a diagram showing a state where a noise level is gradually changed in the electric field strength measuring device of FIG. 1;

FIG. 6 is a diagram illustrating a relationship between a bit error rate of a digital broadcast signal of a different modulation scheme and a C / N ratio.

FIG. 7 is a block diagram of an electric field strength measuring device according to a second embodiment of the present invention.

[Explanation of symbols]

 11a Electric field strength measuring instrument. 2 housing 4 input terminal 8 mixer (mixing means) 10 noise generator (noise generating means) 12 variable gain amplifier (level adjusting means) 14 output terminal 20c C / N ratio measuring circuit (C / N ratio measuring means)

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshiyuki Itasaka 2-15, Hamasaki-dori, Hyogo-ku, Kobe-shi, Hyogo F-term (reference) 5C061 BB03 5K042 BA10 CA02 CA23 DA13 DA19 EA14 FA06 FA15 FA22 HA01

Claims (5)

[Claims] An input terminal to which a digital broadcast signal is input; a noise signal generating means; a level adjusting means for adjusting the level of the noise signal; and mixing the level-adjusted noise signal with the digital broadcast signal. And a mixing means for outputting a mixed signal, an output terminal for outputting a mixed signal from the mixing means, and a C / N ratio measuring means for measuring a C / N ratio of the mixed signal. N ratio measurement device. 2. The C / N ratio measuring apparatus according to claim 1, wherein said input terminal, said noise signal generating means, said level adjusting means, said mixing means, said output terminal and said C terminal are provided.
A C / N ratio measuring device in which the / N ratio measuring means is provided in one housing. 3. An input terminal to which a digital broadcast signal is input, a noise signal generating means, a level adjusting means for adjusting the level of the noise signal, and mixing the level-adjusted noise signal with the digital broadcast signal. A mixing means for outputting a mixed signal; a video display means for displaying an image based on the mixed signal from the mixing means; and a C / N ratio measuring means for measuring a C / N ratio of the mixed signal. A C / N ratio measurement device provided in one housing. 4. A step of inputting a digital broadcast signal to an input terminal of a C / N ratio measuring apparatus, and mixing a variable level noise signal with the digital broadcast signal in the C / N ratio measuring apparatus. To C
Supplying the digital television receiver from the C / N ratio measurement device to the digital television receiver; and changing the level of the noise signal in the C / N ratio measurement device so that the digital television receiver becomes unreceivable. The signal C / N ratio is C / N
Measuring in an N ratio measuring device.
N ratio measurement method. 5. The C / N ratio measuring method according to claim 4, wherein the mixed signal is supplied to the digital television receiver from the C / N ratio measuring device via a transmission path of a joint receiving system. C / N ratio measurement method.