JPS5814100B2 - Crosstalk attenuation measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crosstalk attenuation measurement method for detecting the worst value of crosstalk attenuation with respect to a crosstalk standard in a certain frequency band.

Crosstalk that occurs in transmission equipment and lines when transmitting signals causes oscillation in repeaters, and signal crosstalk causes many problems, such as color flicker noise in the case of color television signals.

Therefore, in the case of transmission using a cable or the like in which sufficient crosstalk attenuation cannot be obtained, it is necessary to measure the crosstalk attenuation.

Conventional crosstalk attenuation measurement uses an oscillator and a level meter, and when the output of the oscillator is applied to one signal path, the level of the signal generated in the signal path in the other direction is measured with the level meter, and both signals are measured using the level meter. The amount of attenuation between the paths was measured for each frequency.

However, when the frequency characteristics change in a complicated manner, such as near-end crosstalk attenuation, even if the required crosstalk attenuation is satisfied at the measurement frequency, the measurement points other than those indicated by the X mark as shown in Figure 1 are Frequencies marked with a circle may break the standard.

In FIG. 1, curve 11 is the crosstalk characteristic, and curve 12 is the standard characteristic.

For this reason, there is a drawback that measurement must be performed at a large number of frequencies with sufficiently narrow frequency intervals.

In order to avoid this problem, measurement is conventionally performed by frequency sweep.

However, in the case of frequency characteristics with complex standard characteristics, this measurement method requires a relatively long time to check the swept waveform on a cathode ray tube, requires expensive measuring equipment, is large, and requires a manhole. However, there were drawbacks such as difficulty in making measurements in confined spaces.

Disturbances due to near-end crosstalk include repeater oscillations in bidirectional broadband transmission over balanced pair cables.

FIG. 2 is a diagram for explaining oscillation of the repeater due to near-end crosstalk, in which line pairs 14 and 15 in the main cable 13 are branched into a stub cable 16 and introduced into the repeater housing 17. It is connected to the input side of downstream repeaters 18 and 19.

The output side of the repeater 18 , 19 is connected to a line pair 21 , 22 which is introduced into the main cable 13 through the stub cable 16 .

On the other hand, the line pair 23 and 24 in the main cable 13 is branched into a stub cable 16 and connected to an uplink repeater 25 in the housing 17.
．． 26, respectively connected to the input sides of the repeaters 25 and 26.
Line pairs 27 and 28 connected to the output side of the stub cable 16 are introduced into the main cable 13.

The output of the repeater 18 is the near-end crosstalk between the line pairs 21 and 23, which is added to the input of the repeater 25, and after being amplified, the output is sent to the line pair 27.
and 14 to the input of repeater 18,
The stage crosstalk forms a feedback loop.

Therefore, if the near-end crosstalk attenuation is less than the repeater gain, oscillation occurs.

The output of the repeater 18 is line pair 21, line pair 24, and repeater 2.
Since the signal is also fed back to the input via the route 6, one line pair 28, one line pair 14, consideration must be given to multi-stage crosstalk.

For this reason, when bidirectional multi-repeat transmission is performed using a cable that does not have sufficient crosstalk attenuation, line pairs are selected and housed at a distance from each other.

However, the repeater is housed in a housing 17, and the housing 11 is connected to the main cable 13 by a stub cable 16.

A dog cable with sufficient crosstalk attenuation can be used as the stub cable 16, but if the connection point with the main cable 13 is not sufficiently treated, crosstalk may deteriorate at that connection point.

To avoid this, it is necessary to measure crosstalk when the housing 17 is connected to the cable.

However, conventional measurement methods require a long time and are difficult to implement.

This is because the repeater housing 17 is usually installed inside a manhole or on a pole, and work is often limited to late at night, and in the case of a two-way P system, there are two P repeaters (in the case of P = 50, This is because the measurement of the near-end crosstalk visceral attenuation frequency characteristics for 2,500 combinations is very time-consuming and labor-intensive.

For this reason, in the past, crosstalk attenuation was not measured, and the cable jacket was connected immediately after connection to make it waterproof.

Afterwards, the line was tested for commissioning, and if problems such as crosstalk occurred, measurements were taken and connection points were dealt with.

Connecting the cable sheath requires a lead worker and the like, so even an experienced worker will need an overnight job, which increases the construction period and cost.

In addition, because of this construction method, when increasing the number of circuits, the repeater in use may oscillate due to being connected to a core wire that has not been used before, resulting in drawbacks in terms of construction and maintenance. there were.

In order to solve these drawbacks, the present invention provides a crosstalk attenuation measuring method that can instantly detect whether or not required crosstalk standards are satisfied.

FIG. 3 shows an example of a measuring instrument used in the measuring method according to the present invention, in which an amplifier section 31 is housed in the measuring instrument 29, and the input side and output side of the amplifier section 31 are connected to the crosstalk measurement connection of the measuring instrument 29. They are connected to terminals 32 and 33, respectively, and a level meter 34 is connected to the output side.

The gain of the amplifier section 31 can be adjusted by a signal from a gain adjustment terminal 35 or manually.

The amplifying section 31 of the measuring instrument 29 is connected through terminals 32 and 33 to a crosstalk-generating object, that is, a section of the object to be measured, such as a section of a railway line, where it is measured whether the amount of crosstalk attenuation satisfies a predetermined standard value set in advance. and use it.

With such a configuration, when the Nyquist diagram of the sum of the gain characteristics of the amplifier 31 and the crosstalk attenuation surrounds (i, o), oscillation occurs, and an output appears on the level meter 34 (1.
0), no oscillation occurs and only thermal noise is displayed on the level meter 34.

Generally, the phase of near-end crosstalk attenuation is random, so if the absolute value exceeds 1, oscillation occurs.

Therefore, if the gain characteristics of the amplifier section 31 are made equal to the required crosstalk attenuation characteristics corresponding to each standard characteristic, the crosstalk attenuation in the section of the measured object will satisfy the standard depending on the presence or absence of oscillation detected by the measuring instrument 29. You can immediately know whether or not to do so.

For example, in the case shown in Fig. 1, if the gain characteristic of the amplifier section 31 is set to the standard characteristic of curve 12, even when the frequency width that divides the standard is very narrow as in the case of the frequency marked with ○, the It is possible to reliably detect that the amount of crosstalk attenuation in the section is below a predetermined standard value.

The level meter 34 may be of any type as long as it can display oscillations, so instead of using a pointer-type level meter, it may be used to indicate whether the standards are met by turning on or off a light emitting element, or by making a sound such as a buzzer. .

Further, if the configuration is such that the oscillation display point is determined by changing the gain of the amplifying section 31 manually or by an input signal from the terminal 35, the absolute value of the crosstalk attenuation amount can be known.

It is also possible to obtain the difference from the standard value.

For example, a gain frequency characteristic as shown by a curve 36 in FIG. 4 is given to the amplifier section 31.

This characteristic is the cable near-end crosstalk standard characteristic during baseband transmission of color television signals, and the repeater gain characteristic shown by the dotted line 37 includes multiple relays, accumulation due to multiple crosstalk, oscillation margin, luminance crosstalk standard, and chromaticity crosstalk standard. It has added characteristics.

Therefore, when crosstalk is measured with a measuring instrument having this characteristic, if no oscillation is displayed, not only oscillation due to near-end crosstalk but also luminance crosstalk interference and chromaticity crosstalk interference will not occur.

In this case, if the amplifying section 31 is configured with a multi-stage variable equalizer to obtain an arbitrary gain characteristic, a desired standard characteristic can be detected as necessary.

Next, a case will be described in which the present invention is used to detect multistage and multiple crosstalk.

In this case, for example, in FIG. 2, the repeaters 18, 19,
25 and 26, the measuring instruments 29 shown in FIG. 3 are inserted into the repeater housing 17, respectively.

At this time, the gain characteristic of the amplifying section 31 of the measuring instrument 29 inserted is set in advance to a characteristic obtained by adding an increase due to multiple repeats and the accumulation of multiple crosstalk and an oscillation margin to the repeater gain characteristic.

In this case, if the measuring device 29 connected instead of the repeaters 18 and 19 displays an oscillation, then the line pair 14 and 15
It can be instantly detected that one or both of the crosstalk between the line pairs 22 and 21 does not meet the standards.

Therefore, by measuring using the measuring device 29 when connecting the housing stub cable 16 to the main cable 13, it is possible to find out the necessary processing points before connecting the cable jacket, and avoid duplicating the work.

Although the above description has been made regarding the case of two systems in both directions, it goes without saying that the same applies even if the number of systems increases.

In this case, it is possible to reduce the amount of work required by connecting the gain control external terminals 35 of each measuring instrument according to the transmission direction and simultaneously controlling and checking the gains of the measuring instrument amplifiers 31 in the same transmission direction. Needless to say.

Further, a plurality of amplification units 31 may be housed in one measuring instrument housing so that the worst value of multiple multi-stage crosstalk can be detected by simultaneously using a plurality of amplification units 31 in this manner.

Furthermore, even if lines are opened sequentially in a multi-system case, measuring crosstalk for the entire case when connecting the cases does not increase the work time, so crosstalk attenuation for lines that are opened later cannot be measured. Interference with other lines can be avoided.

The present invention also allows measurement of far-end crosstalk attenuation.

If, for example, both ends of a cable drum are connected between the crosstalk measurement connection terminals 32 and 33 in FIG. 3 with different core wires, the amount of far-end crosstalk attenuation is indicated by an oscillating display.

In this case, if the phases between the input and output of the amplifying section 31 are equal, oscillation may not be displayed, but by changing the phase, an attenuation characteristic with an absolute value equal to the gain characteristic of the amplifying section 31 is connected. oscillates.

As explained above, according to the present invention, the worst value of crosstalk attenuation for any standard characteristic over the entire required band can be easily detected by simply connecting a measuring instrument, thereby reducing work time and construction costs. It is possible to reduce the amount of noise and improve the quality of the line.

[Brief explanation of the drawing]

Fig. 1 is a crosstalk attenuation frequency characteristic curve diagram, Fig. 2 is a diagram showing the connection state between the cable and the repeater, Fig. 3 is a block diagram showing the measuring instrument used in the measuring method of the present invention, 4
The figure is a curve diagram showing an example of the gain frequency characteristic of the amplifier section 31. 31: Amplification section, 32, 33: Crosstalk measurement terminal, 34: Level meter, 35: Amplification section gain variable control signal input terminal.

Claims (1)

[Claims] 1. Set the gain and frequency characteristics of the amplifier section of the measuring device equal to the predetermined crosstalk attenuation and frequency characteristics in the measurement frequency band, and connect the crosstalk measurement connection terminal of the measuring device to the crosstalk attenuation amount and frequency characteristics in the measurement frequency band. is inserted into the measurement section of the object to be measured, and by detecting oscillation in the amplifying section of the measuring device, which is inserted into the measurement section of the object to be measured. Crosstalk attenuation characterized by detecting that the crosstalk attenuation and frequency characteristics in the measurement section of the measuring object are worse than the predetermined crosstalk attenuation and frequency characteristics corresponding to the gain and frequency characteristics preset in the amplification section. Quantity measurement method.