JP2013187840A - Signal level measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal level measuring device capable of accurately measuring a signal level of one-segment broadcast performed with ordinary television broadcast and a signal level of area one-segment for performing only the one-segment broadcast respectively in digital television broadcast using terrestrial waves.SOLUTION: A signal level measuring device: selects the one-segment broadcast of a measurement channel and detects signal level thereof (S120); selects the other segment of the measurement channel and detects signal level thereof (S130); determines whether the measurement channel is a channel of full-segment broadcast or a channel dedicated to the one-segment broadcast depending on whether or not the signal level of the one-segment broadcast is higher than the signal level of the other segment by not less than a threshold value (S140); removes a signal component of an adjacent segment by subtracting a correction value A from the signal level obtained in S120 when the measurement channel is the full-segment broadcast (S150); and corrects a loss during channel selection by adding a correction value B to the signal level obtained in S120 when the measurement channel is not the full-segment broadcast (S160).

Description

  The present invention relates to a signal level measuring apparatus that measures the signal level of one-segment broadcasting performed using one segment of digital television broadcasting.

  Conventionally, in a digital television broadcast distributed to a receiving terminal using a radio wave transmitted from a ground station, 13 segments with a frequency bandwidth of about 428 kHz are included in a 6 MHz frequency band assigned to each channel of the television broadcast. Allocate and use one segment in the center to perform one-segment broadcasting that can stably receive video and audio while moving to portable receivers such as in-vehicle TVs and mobile phones, and use the remaining 12 segments to fix TV broadcasting for receivers.

  For this reason, in such an apparatus for measuring the signal level of the broadcast radio wave of digital television broadcasting, not only the signal level of the broadcast signal for one channel of the television broadcast but also the signal level of the broadcast signal of a specific segment in which one-segment broadcasting is performed. It is necessary to be able to measure.

  Here, the signal level of the one-segment broadcasting is obtained by measuring the signal level (specifically, power or electric field strength) of the broadcasting signal for one channel of the television broadcasting and calculating the measurement result to 1/13. Also good.

  However, the signal level of the one-segment broadcasting calculated in this way deviates from the normal signal level when the signal level changes within a band corresponding to one channel of the television broadcasting due to the influence of multipath or the like on the broadcast radio wave. .

  Therefore, in order to prevent such a problem, the signal level for one segment corresponding to the one-segment broadcasting is measured, and the difference between the measured value and the theoretical value obtained by 1/13 of the measurement result for one channel of the television broadcasting is measured. Has been proposed (see, for example, Patent Document 1).

  According to the proposed apparatus, the user can determine whether or not the broadcast signal is affected by the multipath or the like as well as the signal level (actual measurement value) of the one-segment broadcasting by viewing the display result. Can do.

JP 2007-198936 A

  As described above, when measuring the signal level of one-segment broadcasting, a specific segment in which one-segment broadcasting is being performed on the measurement target broadcast channel from the received signals from the receiving antenna that receives the broadcast radio waves of digital television broadcasting It is necessary to tune in.

  For the channel selection, a band pass filter that selectively passes only the signal of a specific segment is used. The bandwidth of this band pass fill is matched to the frequency band for one segment used for one-segment broadcasting. , About 428 kHz.

  By the way, the bandpass filter cannot abruptly change the attenuation characteristics near the cutoff frequency even when the upper and lower cutoff frequencies are appropriate. Instead, a part of the signal of the adjacent segment adjacent to the specific segment is output.

For this reason, when a signal of a specific segment is selected using a band pass filter and the signal level is measured, the signal component of the adjacent segment is included in the measurement result.
On the other hand, in order to prevent this problem, the correction value corresponding to the signal component of the adjacent segment that has passed through the band pass filter may be subtracted from the measurement result of the signal level of the specific segment.

  However, in this way, there is a problem that in the digital television broadcasting that performs only one-segment broadcasting, the signal level of the one-segment broadcasting cannot be measured normally, and an error occurs in the measurement result.

  In other words, in digital television broadcasting, so-called area one seg that restricts the broadcasting area and performs one seg broadcasting has been proposed, but in the area where this area one seg is implemented, it is necessary to measure the signal level of that area one seg is there.

  However, in digital television broadcasting that uses area one segment, there is no segment adjacent to the segment for area one segment, so select a specific segment signal as described above, measure its signal level, and then measure it. If the correction value corresponding to the signal component of the adjacent segment is subtracted from the result, the measurement result of the signal level becomes lower than the actual signal level.

  The present invention has been made in view of these problems. In digital television broadcasting using terrestrial waves, the signal level of one-segment broadcasting performed together with normal television broadcasting and the signal of area one-segment broadcasting in which only one-segment broadcasting is performed. An object of the present invention is to provide a signal level measuring device capable of measuring each level with high accuracy.

The signal level measuring apparatus according to claim 1, which has been made to achieve the object,
A frequency conversion means for acquiring a received signal from a receiving antenna that receives a broadcast wave of digital television broadcasting, and converting the frequency of the received signal so that a signal of a specific frequency in a broadcast channel to be measured becomes a reference frequency;
A band-pass filter that selectively passes a signal component in a frequency band for one segment centered on the reference frequency, out of the received signal frequency-converted by the frequency converting means;
Detection means for detecting a signal in a frequency band for one segment that has passed through the bandpass filter;
The frequency conversion means causes the received signal to be frequency-converted so that a center frequency of a specific segment used for one-segment broadcasting in the broadcast channel to be measured becomes the reference frequency, and after the frequency conversion, the detection means passes through the detection means. First level detecting means for detecting the detected voltage obtained as a signal level of the specific segment;
The frequency conversion means is configured to frequency-convert the received signal so that a center frequency of a comparison segment that is a segment different from the specific segment in the broadcast channel to be measured becomes the reference frequency, and after the frequency conversion, Second level detection means for detecting a detection voltage obtained via the detection means as a signal level of the comparison segment;
It is determined whether or not the signal level of the specific segment detected by the first level detection means is higher than a signal level of the comparison segment detected by the second level detection means. Determination means to perform,
When the determination means determines that the signal level of the specific segment is not higher than the threshold value compared to the signal level of the comparison segment, a first correction is made from the signal level detected by the first level detection means. First correction means for removing a signal component of an adjacent segment adjacent to the specific segment by reducing the value;
It is provided with.

  According to a second aspect of the present invention, in the signal level measuring apparatus according to the first aspect, the determination unit determines that the signal level of the specific segment is higher than the threshold value compared to the signal level of the comparison segment. Then, a second correction means for correcting a measurement error due to the attenuation characteristic of the bandpass filter by adding a second correction value to the signal level detected by the first level detection means is provided. Features.

  According to the signal level measuring apparatus of the first aspect, the first level detecting unit is configured such that the center frequency of the specific segment used for the one-segment broadcasting in the broadcasting channel to be measured becomes the reference frequency with respect to the frequency converting unit. The received signal is frequency-converted. Then, the first level detection means detects the detection voltage obtained via the detection means after frequency conversion of the received signal by the frequency conversion means as the signal level of the specific segment.

  The second level detection means causes the frequency conversion means to frequency-convert the received signal so that the center frequency of the comparison segment that is a segment different from the specific segment in the broadcast channel to be measured becomes the reference frequency. The second level detection means detects the detection voltage obtained through the detection means after the frequency conversion by the frequency conversion means as the signal level of the comparison segment.

  Further, when the signal level of the specific segment and the comparison segment is detected by the first level detection unit and the second level detection unit in this way, the determination unit determines the signal level of the specific segment based on the detection result. It is determined whether or not the signal level of the comparison segment is higher than a predetermined threshold value.

  When the determination unit determines that the signal level of the specific segment is not higher than the threshold value compared to the signal level of the comparison segment, the first correction unit determines from the signal level detected by the first level detection unit, By subtracting the first correction value, the signal component of the adjacent segment adjacent to the specific segment is removed.

  In other words, when the signal level of the specific segment is higher than the threshold value compared with the signal level of the comparison segment, the determination means uses a broadcast channel for measurement as a broadcast channel dedicated to one-segment broadcasting (for example, the above-described area one-segment broadcasting channel). ).

  In this case, since the received signal passing through the so-called band-pass filter for channel selection is a received signal for one segment of one-segment broadcasting, the signal level of the specific segment detected by the first level detecting means is It is not affected by the adjacent segment adjacent to the specific segment.

  However, if the signal level of a specific segment is not higher than the threshold level compared to the signal level of the comparative segment (that is, when each of these signal levels is substantially the same level), the broadcast channel to be measured is a normal channel including one-segment broadcasting. It can be determined that this is a broadcast channel for performing television broadcasting (so-called full segment broadcasting).

  In this broadcast channel, the received signal that passes through the tuning band-pass filter is a signal obtained by adding the signal component of the adjacent segment to the received signal for one segment of the one-segment broadcasting.

  Therefore, in the present invention, the determination means determines that the signal level of the specific segment is not higher than the threshold value compared to the signal level of the comparison segment (that is, the broadcast channel to be measured is a broadcast channel for performing normal full segment broadcasting). Only when it is determined, the first correction means is operated.

  As a result, according to the signal level measuring apparatus of the present invention, even if the broadcasting channel to be measured is a broadcasting channel dedicated to one-segment broadcasting such as area one-segment broadcasting, or one-segment broadcasting and normal television broadcasting are performed. Even for a full-segment broadcasting channel, the signal level of one-segment broadcasting can be accurately measured.

  By the way, the band-pass filter used for the one-segment broadcasting channel selection cannot eliminate the passage loss within the frequency band for one segment, and the passage loss is particularly large near the upper and lower cutoff frequencies.

  For this reason, when the broadcast channel to be measured is a broadcast channel dedicated to one-segment broadcasting (for example, the above-described area one-segment broadcasting channel), the received signal for one segment of the one-segment broadcasting that passes through the bandpass filter is A part of the signal is attenuated when passing through the band-pass filter, and the signal level of the specific segment detected by the first level detection means may be lower than the actual signal level.

  Therefore, in the signal level measurement device of the present invention, as described in claim 2, when the determination means determines that the signal level of the specific segment is higher than the threshold value compared to the signal level of the comparison segment, The second correction unit may correct the measurement error due to the attenuation characteristic of the bandpass filter by adding the second correction value to the signal level detected by the first level detection unit.

  In this way, the signal level of the specific segment can be measured with higher accuracy.

It is a block diagram showing the structure of the level checker of embodiment. It is a flowchart showing the signal level measurement process performed in the control part of FIG. 3 is a time chart for explaining the operation of the signal level measurement process of FIG. 2.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, a signal level measuring apparatus (hereinafter referred to as a level checker) 2 according to the present embodiment uses a digital television broadcast radio wave (UHF band) transmitted from a ground station (specifically, a broadcast station or a relay station). A receivable antenna 4 is provided, and a signal level of one-segment broadcasting of a specific broadcast channel is measured from a received signal from the antenna 4.

  For this reason, the level checker 2 is used to select one-segment broadcasting of a specific broadcast channel from the input terminal 6 for capturing the received signal from the antenna 4 and the received signal input via the input terminal 6. A channel selection unit 10 and a detection unit 20 that detects the signal level of the one-seg broadcast signal selected by the channel selection unit 10 by detecting the envelope are provided.

  The channel selection unit 10 also receives an amplification circuit 12 that amplifies the reception signal, an oscillator 14 that generates a high-frequency signal for frequency-converting the reception signal, and a high-frequency signal from the oscillator 14 and the reception signal. A mixer 16 that converts the frequency of the signal, and a bandpass that passes a signal of a bandwidth (about 428 kHz) corresponding to one segment of the one-segment broadcasting centered on the reference frequency fr among the received signals after frequency conversion output from the mixer 16 And a filter (hereinafter referred to as BPF) 18.

Here, the oscillator 14 is configured by a variable oscillator capable of controlling the oscillation frequency by a control signal (voltage) from the control unit 30.
Then, the control unit 30 outputs a control signal for generating a high frequency signal fb (= fa−fr) necessary for frequency conversion of the signal of the specific frequency fa of the specific broadcast channel to the reference frequency fr to the oscillator 14. .

  As a result, in the mixer 16, the signal of the specific frequency fa is frequency-converted (down-converted) to the reference frequency fr. From the BPF 18, a signal having a bandwidth corresponding to one segment centered on the down-converted reference frequency fr. Will be output.

  Next, the control unit 30 is mainly configured by a microcomputer including a CPU, a ROM, a RAM, and the like, and a broadcast channel to be selected by the channel selection unit 10 (a broadcast channel to be measured, hereinafter also referred to as a measurement channel). Is set according to a command from the operation unit 24.

  The ROM of the control unit 30 stores the center frequency of the segment used for one-segment broadcasting for each UHF band television broadcast channel that can be selected by the channel selection unit 10. CPU), when measuring the signal level of the one-segment broadcast of the specific broadcast channel (measurement channel), reads the center frequency f0 of the one-segment broadcast from the ROM, and the center frequency becomes the reference frequency fr. The oscillation frequency of the oscillator 14 is controlled.

  In addition to the operation unit 24, the control unit 30 is connected to a display unit 22 for displaying the measurement result of the signal level of the one-segment broadcasting. The display unit 22 is configured by a liquid crystal display panel or the like, and is disposed in the vicinity of the operation unit 24.

Next, signal level measurement processing executed when the CPU of the control unit 30 measures the signal level of the one-segment broadcasting will be described with reference to the flowchart shown in FIG.
This signal level measurement process is started when a measurement command for the signal level of one-segment broadcasting in a desired broadcast channel to be measured is input via the operation unit 24.

As shown in FIG. 2, when this signal level measurement process is started, first, in S110 (S represents a step), a measurement channel set via the operation unit 24 is read.
In the next S120, the tuning unit 10 is tuned to the one-segment broadcasting of the measurement channel, and then the detection voltage for one segment of the selected one-seg broadcasting is read from the detecting unit 20.

  As shown in FIG. 3A, in a normal digital television broadcast signal composed of 13 segments, the central segment is used for one-segment broadcasting. Therefore, in S120, the center frequency f0 of the central segment is used. Are read from the ROM as the frequency (specific frequency) of the signal to be frequency-converted to the reference frequency fr.

  Then, by outputting a control signal to the oscillator 14, the oscillator 14 generates a high frequency signal fb (= f0−fr) necessary for frequency conversion of the signal of the specific frequency f0 to the reference frequency fr.

  As a result, in the channel selection unit 10, the received signal is frequency-converted so that the center frequency f0 of the one-segment broadcasting segment becomes the reference frequency fr, and among the frequency-converted received signals, signals for one segment of the one-segment broadcasting are obtained. , And output to the detector 20 via the BPF 18.

  Then, the detection unit 20 outputs a detection voltage indicating the signal level (power) by envelope detection of the signal input via the BPF 18, and in S120, by reading the detection voltage, Detects the signal level of 1Seg broadcasting.

  Next, in S130, as shown in FIG. 3A, the frequency is higher by a predetermined frequency (for example, 1.5 MHz) than the one-segment broadcasting selected in S120 by the channel selection unit 10 in the measurement channel. A signal having a frequency band corresponding to the segment is selected by the tuning unit 10 as a comparison segment, and then the detection voltage of the selected comparison segment is read from the detection unit 20.

  In other words, in S130, the channel selection unit 10 receives a signal having a frequency f1 that is higher than the center frequency f0 of the one-segment broadcasting selected in S120 by a predetermined frequency (for example, 1.5 MHz) as the reference frequency fr. By converting the frequency of the signal, the detection unit 20 is caused to output, as a comparison segment, a received signal having a bandwidth corresponding to one segment centered on the frequency f1 in the measurement channel via the BPF 18. The detection voltage of the segment is read from the detection unit 20.

  Next, in S140, the one-segment broadcasting detection voltage read in S120 is compared with the detection voltage of the comparison segment read in S130, and the detection voltage of the one-segment broadcasting is compared with the detection voltage of the comparison segment. By determining whether or not the threshold is higher than the threshold, the measurement channel is a normal channel (see FIG. 3A) for performing normal digital television broadcasting (so-called full-segment broadcasting) consisting of 13 segments, or only one-segment broadcasting. It is determined whether the channel is a channel dedicated to one-segment broadcasting to be performed (see FIG. 3B).

  In S140, if the detection voltage of the one-segment broadcasting is not higher than the detection voltage of the comparison segment by a threshold or more (that is, if the difference between the detection voltages is small), it is determined that normal full-segment broadcasting is being performed on the measurement channel. Then, the process proceeds to S150.

Then, in S150, the detection voltage for one-segment broadcasting is corrected by subtracting the first correction value A for full-segment broadcasting from the detection voltage for one-segment broadcasting read in S120.
When the measurement channel is full-segment broadcasting, as shown in FIG. 3A, 13 segment broadcast signals (OFDM signals) are arranged in the frequency band (6 MHz) of the measurement channel, and the BPF 18 is used. This is because the signal for one segment of the one-segment broadcasting output to the detection unit 20 includes the signal component of the adjacent segment.

  That is, the upper and lower cut-off frequencies (specifically, the cut-off frequencies on the high frequency side and the low frequency side) of the BPF 18 are set so as to pass a signal for one segment (a signal having a bandwidth of about 428 kHz).

  However, as shown by the dotted line in FIG. 3, in the BPF 18, it is difficult to change the signal pass loss sharply at the upper and lower cut-off frequencies, and in the frequency band outside the pass band where the signal pass loss is small. The passage loss increases gradually.

  For this reason, when the measurement channel is a full-segment broadcast, the signal output to the detection unit 20 via the BPF 18 includes a part of the adjacent segment signal adjacent to the one-segment broadcast segment in addition to the one-segment broadcast signal. Thus, the detection voltage obtained via the detection unit 20 is larger than the normal detection voltage of the one-segment broadcasting alone.

  Therefore, in this embodiment, an error amount of the detection voltage is obtained in advance by experiment / simulation and the like, and this is stored in the ROM as the first correction value A. Is subtracted and corrected using the first correction value A.

  As described above, when the detection voltage measured in S120 is corrected as the detection voltage of the one-segment broadcasting in S150, the process proceeds to S170, and the corrected detection voltage is displayed as the signal level of the one-segment broadcasting on the display unit 22. And the signal level measurement process ends.

  As a result, when the measurement channel is normal full segment broadcasting, the signal level of the one segment broadcasting unit is displayed on the display unit 22 without being affected by the adjacent segment. It is possible to accurately grasp the signal level.

  In S170, when the signal level is displayed on the display unit 22, broadcast type information indicating whether the measurement channel is a normal full-segment broadcast or a broadcast dedicated to one-segment broadcast is also displayed.

  On the other hand, if the detection voltage of the one-segment broadcasting is higher than the detection voltage by the comparison segment, it is determined in S140 that the measurement channel is a channel dedicated to the one-segment broadcasting, and the process of S160 is executed.

  In S160, the detection voltage of the one seg broadcast is corrected by adding the second correction value B dedicated to the one seg broadcast to the detection voltage of the one seg broadcast read in S120, and the process proceeds to S170.

  That is, as shown by the dotted line in FIG. 3, it is difficult to make the signal pass loss constant in the frequency band inside the upper and lower cutoff frequencies in the BPF 18, and the center frequency is near the upper and lower cutoff frequencies. Passing loss is greater than in the vicinity.

  For this reason, as shown in FIG. 3B, when the measurement channel is a channel dedicated to one-segment broadcasting and the signal passing through the BPF 18 is only the signal of the one-segment broadcasting, when a part of the signal passes through the BPF 18 The detection voltage attenuated and obtained via the detection unit 20 is smaller than the normal detection voltage of the one-segment broadcasting alone.

  Therefore, in the present embodiment, an error amount of the detection voltage is obtained in advance by experiment / simulation and the like, and this is stored in the ROM as the second correction value B. Is added and corrected using the second correction value B.

  As a result, when the measurement channel is a channel dedicated to one-segment broadcasting, the display unit 22 is not affected by the signal passing characteristic in the BPF 18 (in other words, the one-segment broadcasting channel selection characteristic in the tuning unit 10), The signal level of one-segment broadcasting alone is displayed, and the user can accurately grasp the signal level of one-segment broadcasting.

  Therefore, according to the level checker 2 of this embodiment, even if the measurement channel is a broadcast channel dedicated to one-segment broadcasting such as area one-segment broadcasting or a broadcasting channel that performs normal full-segment broadcasting, the signal of one-segment broadcasting is used. The level can be measured with high accuracy.

  Here, in this embodiment, the oscillator 14 and the mixer 16 correspond to the frequency conversion means of the present invention, the BPF 18 corresponds to the bandpass filter of the present invention, and the detection unit 20 corresponds to the detection means of the present invention. To do.

  In the present embodiment, the functions of the first level detection means, the second level detection means, the determination means, the first correction means, and the second correction means of the present invention are signals executed by the control unit 30. Realized by level measurement process.

  That is, the function as the first level detection means of the present invention is realized in S120 of FIG. 2, the function as the second level detection means is realized in S130 of FIG. 2, and the function as the determination means is 2, the function as the first correction unit is realized in S150 in FIG. 2, and the function as the second correction unit is realized in S160 in FIG. 2.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.
For example, in the above-described embodiment, the first correction value A and the second correction value B used for correcting the detection voltage in S150 and S160 have been described as being stored in the ROM in advance. The values A and B may be calculated by multiplying the detection voltage of the one-segment broadcasting obtained in S120 by a predetermined ratio.

  DESCRIPTION OF SYMBOLS 2 ... Level checker (signal level measuring apparatus), 4 ... Antenna, 6 ... Input terminal, 10 ... Channel selection part, 12 ... Amplifying circuit, 14 ... Oscillator, 16 ... Mixer, 18 ... PBF (band pass filter), 20 ... Detection Part, 22 ... display part, 24 ... operation part, 30 ... control part.

Claims (2)

A frequency conversion means for acquiring a received signal from a receiving antenna that receives a broadcast wave of digital television broadcasting, and converting the frequency of the received signal so that a signal of a specific frequency in a broadcast channel to be measured becomes a reference frequency;
A band-pass filter that selectively passes a signal component in a frequency band for one segment centered on the reference frequency, out of the received signal frequency-converted by the frequency converting means;
Detection means for detecting a signal in a frequency band for one segment that has passed through the bandpass filter;
The frequency conversion means causes the received signal to be frequency-converted so that a center frequency of a specific segment used for one-segment broadcasting in the broadcast channel to be measured becomes the reference frequency, and after the frequency conversion, the detection means passes through the detection means. First level detecting means for detecting the detected voltage obtained as a signal level of the specific segment;
The frequency conversion means is configured to frequency-convert the received signal so that a center frequency of a comparison segment that is a segment different from the specific segment in the broadcast channel to be measured becomes the reference frequency, and after the frequency conversion, Second level detection means for detecting a detection voltage obtained via the detection means as a signal level of the comparison segment;
It is determined whether or not the signal level of the specific segment detected by the first level detection means is higher than a signal level of the comparison segment detected by the second level detection means. Determination means to perform,
When the determination means determines that the signal level of the specific segment is not higher than the threshold value compared to the signal level of the comparison segment, a first correction is made from the signal level detected by the first level detection means. First correction means for removing a signal component of an adjacent segment adjacent to the specific segment by reducing the value;
A signal level measuring device comprising: If the determination means determines that the signal level of the specific segment is higher than the threshold value compared to the signal level of the comparison segment, a second correction value is added to the signal level detected by the first level detection means. A second correction means for correcting a measurement error due to the attenuation characteristic of the bandpass filter by adding,
The signal level measuring apparatus according to claim 1, further comprising:

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