JP5712116B2 - Strain measuring method and strain measuring apparatus - Google Patents

Description

  The present invention relates to a technique for measuring distortion characteristics of a transmission line.

  Measurement of the quality of a coaxial transmission line that transmits an RF video signal, such as television broadcasting, is not the direct measurement of the quality of the coaxial transmission line, but the quality of the signal flowing through the transmission line. In the case of analog broadcasting, noise was confirmed as a separate phenomenon such as white noise and distortion was a striped pattern. However, in digital broadcasting, both the characteristics (noise and distortion) of the coaxial transmission line are the same. Rate), it is difficult to identify the cause of the failure.

  In the laboratory, it is possible to measure the noise and distortion of a coaxial transmission line by using a multi-channel signal generator (apparatus that transmits CW signals for the number and frequency of broadcast signals) and using a spectrum analyzer as a receiver. .

  Patent Document 1 discloses an invention that uses white noise to measure the frequency characteristics of a transmission line of a CATV system.

JP-A-6-37676

  However, multi-channel signal generators are expensive and large, and are difficult to use to measure coaxial cable sections in a user's home.

  The present invention has been made in view of the above, and an object thereof is to measure the distortion of a coaxial transmission line by a simple method.

  A distortion measurement method according to a first aspect of the present invention is a distortion measurement method for measuring distortion of a transmission line connected by a coaxial cable for transmitting a television broadcast signal, and generates white noise and inputs the white noise to the transmission line. Measuring the output signal level of the white noise transmitted through the transmission line; changing the input signal level of white noise input to the transmission line; and after changing the input signal level, Measuring the output signal level, and determining that distortion has occurred when the change in the output signal level with respect to the change in the input signal level follows non-linearly.

  In the above distortion measurement method, for each measurement result obtained by measuring the output signal level with respect to the input signal level, the output for each measurement result from a reference straight line passing through the measurement result having the low input signal level among the measurement results. A step of obtaining a compression level in which the signal level is compressed, and a measurement result obtained by referring to a backoff table in which a compression level is associated with a backoff indicating a margin of an input signal level in which distortion occurs at the compression level. Calculating the input signal level at which the distortion of the transmission path has occurred by obtaining the back-off from each degree of compression.

  A distortion measuring apparatus according to a second aspect of the present invention is a distortion measuring apparatus that measures distortion of a transmission line connected by a coaxial cable that transmits a television broadcast signal, and generates white noise and inputs the generated noise to the transmission line. White noise generating means, measuring means for measuring the output signal level of the white noise transmitted through the transmission line, and the input signal level when the white noise generating means changes the input signal level of the white noise. Distortion determining means for determining that distortion has occurred when the change in the output signal level with respect to the change follows non-linearly.

  In the distortion measurement apparatus, for each measurement result obtained by measuring the output signal level relative to the input signal level, the output signal for each measurement result from a reference straight line passing through the measurement result having the low input signal level among the measurement results. The level of compression is obtained, and the compression of each of the measurement results is referred to by referring to a backoff table that associates the degree of compression with a backoff indicating a margin of the input signal level at which the distortion occurs at the degree of compression. It has an input determining means for calculating the input signal level where the transmission path distortion occurs by obtaining the back-off from the degree.

  According to the present invention, the distortion of the coaxial transmission line can be measured by a simple method.

1 is an overall configuration diagram including a strain measuring device in the present embodiment. It is a schematic diagram which shows the white noise utilized in this Embodiment. It is a figure which shows a mode that the signal loss of a white noise is changed and the passage loss of a coaxial area is measured. 4 is a saturation characteristic graph in which the measurement results of FIG. 3 are plotted with the input power on the horizontal axis and the output on the vertical axis. It is a figure which shows a mode that a reference | standard straight line is plotted and the compression degree is calculated | required. It is a figure which shows the example of the measurement result of the compression degree in each input power. It is a figure which shows the example which drawn the back-off on the saturation characteristic graph. It is a figure which shows the example of the back-off table which calculates | requires the back-off of each measurement point. It is a figure which shows the example of a measurement result. It is a figure which shows the example of a display of the distortion | strain measuring apparatus in this Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram including a strain measuring apparatus according to the present embodiment. The distortion measuring apparatus in the present embodiment includes a white noise generator 11 and a measuring instrument 12.

  The white noise generator 11 generates white noise having substantially the same signal level at all frequencies, and inputs the white noise to a coaxial section 100 that is a transmission path connected by a coaxial cable that transmits a television broadcast signal. The coaxial section 100 includes devices such as a booster and a distributor.

  The measuring instrument 12 is a spectrum analyzer, and measures the output signal level of white noise transmitted through the coaxial section 100 in the frequency domain to measure distortion and determine a normal input level.

  As shown in FIG. 2, the distortion is measured by generating white noise including the frequency band of the digital broadcast RF signal with the white noise generator 11, and changing the input signal level of the generated white noise, thereby measuring the instrument 12. This is done by following the change in the output signal level. When the change in the output signal level measured by the measuring instrument 12 with respect to the change in the input signal level of white noise input to the coaxial section 100 follows non-linearly, it is determined that distortion has occurred. When the coaxial section 100 has perfect linearity, the output signal level of white noise measured by the measuring instrument 12 increases in proportion to the input signal level raised by the white noise generator 11. When the booster is included in the coaxial section 100, when the input signal level of white noise is increased, the output of the booster reaches a limit and is saturated, and the output of white noise measured by the measuring instrument 12 compared to the increased input signal level. The increase in signal level is reduced. It is determined that distortion has occurred when the reduced amount reaches a predetermined value (for example, 1 dB). For example, when the input signal level of white noise is increased by 3 dB, it is determined that distortion has occurred when the output signal level of the measuring instrument 12 is only increased by 2 dB.

  Next, a procedure for determining a normal input signal level from the distortion amount will be described. When the degree of compression of the increase amount of white noise measured by the measuring instrument 12 exceeds a predetermined value, the normal input signal level to the booster may already be exceeded. This is because fine compression cannot be detected by simple measurement using white noise. In order to compensate for this, the input signal level at which a predetermined compression level is observed is subtracted from the input signal level at which compression is generated by subtracting a predetermined margin (backoff) from the input signal level at which the predetermined compression level is observed. judge. In order to make the determination more accurate, an average of the input signal levels obtained from a plurality of input signal levels capable of detecting the degree of compression is calculated. Hereinafter, the flow of processing will be described.

  First, the input signal level of white noise is changed, and the passage loss of the coaxial section 100 is sequentially measured from the low level side. In the example shown in FIG. 3, white noise is input with input power of −30, −20, −10, 0, +10, and +20 dB with respect to the standard input (0 dBm / 2.1 GHz), and the pass characteristic of the standard input is obtained. Find the standardized normalized output.

  Subsequently, the normalized output of the band to be measured is averaged for each input power, and a saturation characteristic graph is drawn. In the example shown in FIG. 4, the normalized output in the UHF band (470-770 MHz) is averaged for each input power, the input power is plotted on the horizontal axis, and the normalized output is plotted on the vertical axis, and the measurement points are plotted on a saturation characteristic graph. .

  Subsequently, a reference line passing through a measurement point with low input power is drawn on the saturation characteristic graph, and the degree of compression from the reference line is inspected for each measurement point. FIG. 5 shows a state in which a reference straight line is drawn on the saturation characteristic graph. In the present embodiment, a fixed point called a pivot is selected from the measurement points, and a straight line having an inclination of 1 passing through the pivot is drawn as a reference straight line. The point used as a pivot can be set arbitrarily. In FIG. 5, a measurement point (● in FIG. 5) where the input power is −20 dB is defined as a pivot. Then, the degree of compression from the reference straight line is inspected for measurement points that exceed the input power of the pivot. In the example shown in FIG. 5, the degree of compression was obtained for measurement points of −10, 0, +10, +20 dB exceeding the input power (−20 dB) of the measurement point as a pivot. FIG. 6 shows the measurement results.

  Then, the input signal level Y at which distortion occurs from the degree of compression is obtained and drawn on the saturation characteristic graph. FIG. 7 shows an example in which the input signal level Y at which distortion occurs in the saturation characteristic graph is drawn. The input signal level Y is calculated by averaging the value obtained by subtracting the back-off corresponding to the degree of compression at the measurement point from the input signal level at each measurement point. At this time, a compression degree within a predetermined range is excluded from the backoff calculation target as a measurement error. The backoff corresponding to the degree of compression is obtained from a backoff table in which the degree of compression is associated with the backoff. FIG. 9 shows an example of the back-off table.

  Here, the calculation process of the input signal level Y in which distortion occurs will be specifically described. In the present embodiment, since the compression level within 1 dB is excluded from the backoff calculation target as a measurement error, the measurement point with the input power of −10, 0 dB is excluded from the backoff calculation target. Since the compression degree when the input power is 10 dB is -1.4 dB, the back-off is X2 from the back-off table. Since the compression degree when the input power is 20 dB is -2.6 dB, the back-off is X5. Then, an input signal level Y at which distortion occurs is obtained by averaging values obtained by subtracting back-off from the input power at each measurement point. That is, Y = average (10−X2, 20−X5) is calculated to obtain the input signal level Y.

  Then, the input signal level Y and the determination reference value S are compared to determine whether the input level is normal. For example, if the determination reference value S is 0 dB, the determination result is NG because the example shown in FIG. 8 has the input signal level Y lower than 0 dB.

  Next, an example in which distortion measurement is performed at the user's home will be described.

  At the user's house, the digital broadcast signal is received by an antenna installed on a roof or the like, transmitted to the RF terminal of each room by a distributor via a booster, and input to the television. When an IP retransmission service using an optical network is used, a digital broadcast signal is transmitted as an optical signal to an ONU (Optical Network Unit) in the user's house and converted into an electric signal by the ONU. The digital broadcast signal converted into an electric signal is transmitted to the RF terminal of each room by a distributor via a booster.

  First, the white noise generator 11 is connected to an antenna or an ONU output destination, and the measuring device 12 is connected to a coaxial cable input to the television.

  Then, white noise is generated from the white noise generator 11 and input to the coaxial section in the user's home, and the white noise input to the coaxial section is detected by the measuring device 12.

  After that, after changing the white noise input signal level, the measuring device 12 measures the white noise output signal level transmitted through the coaxial section, and the change in the output signal level with respect to the change in the input signal level follows non-linearly. It is determined that distortion has occurred.

  FIG. 9 shows an example of a normal measurement result and an abnormal measurement result with the frequency (MHz) on the horizontal axis and the gain compression (dB) on the vertical axis. Here, it is determined that distortion has occurred when the gain compression reaches 1 dB in the frequency band of cable television or terrestrial digital broadcasting (about 90 to 770 MHz) and the frequency band of BS / CS digital broadcasting (about 1 to 2 GHz). .

  In the normal measurement result in FIG. 9A, distortion occurs when the total input level is 110 dBuV, whereas in the abnormal measurement result in FIG. 9B, distortion occurs at 90 dBuV where the total input level is smaller. It has occurred. In FIG. 9B, it is considered that the booster installed in the coaxial section 100 is saturated early or oscillates.

  FIG. 10 is a diagram showing a display example of the measuring instrument 12 in the present embodiment.

  In the display example shown in FIG. 10, the frequency bands used for television broadcasting are classified into eight, and distortion characteristics are measured and displayed for each of the eight frequency bands.

  As described above, according to the present embodiment, white noise is generated by the white noise generator 11 and input to the coaxial section 100 in the user's home, and the input signal level of the white noise is changed. Measure the distortion of the coaxial transmission line by a simple method by measuring the change in the output signal level of the white noise transmitted through the coaxial section 100 and determining that distortion has occurred when the change follows non-linearly. be able to.

11 ... White noise generator 12 ... Measuring instrument 100 ... Coaxial section

Claims (4)

A distortion measurement method for measuring distortion of a transmission line connected by a coaxial cable for transmitting a television broadcast signal,
Generating white noise and inputting it into the transmission line;
Measuring an output signal level of the white noise transmitted through the transmission path;
Changing an input signal level of white noise input to the transmission path;
Measuring the output signal level after changing the input signal level and determining that distortion has occurred when the change in the output signal level with respect to the change in the input signal level follows non-linearly;
A strain measurement method comprising: For each measurement result obtained by measuring the output signal level relative to the input signal level, the output signal level is compressed for each measurement result from a reference line passing through the measurement result having the low input signal level among the measurement results. Determining the degree of compression;
Refer to a back-off table in which a compression level and a back-off indicating a margin of an input signal level in which distortion occurs at the compression level are associated with each other. Calculating the input signal level at which distortion of
The strain measuring method according to claim 1, wherein: A distortion measuring device that measures distortion of a transmission line connected by a coaxial cable that transmits a television broadcast signal,
White noise generating means for generating white noise and inputting it into the transmission line;
Measuring means for measuring an output signal level of the white noise transmitted through the transmission line;
Distortion determining means for determining that distortion has occurred when the change in the output signal level with respect to the change in the input signal level follows non-linearly when the white noise generating means changes the input signal level of the white noise When,
A strain measuring apparatus comprising:   For each measurement result obtained by measuring the output signal level relative to the input signal level, the output signal level is compressed for each measurement result from a reference line passing through the measurement result having the low input signal level among the measurement results. A compression level is obtained, and a back-off table in which a compression level and a back-off indicating a margin of an input signal level in which distortion occurs at the compression level is referred to, and the back-off is calculated based on the compression level of each measurement result. 4. The distortion measuring apparatus according to claim 3, further comprising an input determination unit that calculates and calculates an input signal level at which the distortion of the transmission path has occurred.

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