JPH0331396B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a coaxial cable system simulation circuit,
In particular, the cable closest to the coaxial cable failure point (hereinafter referred to as
It is said to be close to the point of failure. ) It relates to a simulation circuit that simulates the impedance at the connection point between a repeater and the cable, as well as the failure point.

Prior Art Since group-based two-wire bidirectional relay coaxial cable systems provide a large number of lines over long distances,
A high degree of reliability is required, and even in the event of a cable failure, the point of failure must be quickly located, the cable pulled up and repaired as necessary, and operation resumed in a short time. For this reason, various fault point locating methods have been proposed. For example, in Japanese Patent Publication No. 56-44387, as shown in FIG. is sent to the coaxial cable system 3 through the system, and only a specific burst is extracted from a burst train consisting of a folded signal of repeater distortion output of a high group frequency generated in the same system and measured by a sampling level meter 4. A synchronizing means 5 synchronizes the burst oscillator 1 with the sampling level meter 4. Among the repeaters 6 of the coaxial cable system, the impedance Z _i when looking at the fault point 7 from the connection point C between the repeater 6a closest to the fault point 7 and the coaxial cable 3 where the fault point is located is given by the following equation.

Z _i =Z _p 1+M(ω)・D(ω)/1−M(ω)・D
(ω)…(1) To simplify the description, assuming |D(ω)| is sufficiently small compared to 1, Z _i ≒Z _p {1+2M(ω)e ^-2 〓 ^l-j2 〓 ^l }...(1a) where, Z _p : Characteristic impedance of the coaxial cable M(ω) : Reflection coefficient at the fault point D(ω) : Round-trip propagation characteristic of the coaxial cable from the connection point to the fault point (D(ω)= e ^-2 〓 ^l-j2 〓 ^l ) α: Attenuation constant of coaxial cable (Naper/Km) β: Phase constant of coaxial cable (rad/Km) l: Distance from connection point to fault (Km) (1a) Formula As is clear from the above, the impedance Z _i seen from the repeater 6a closest to the fault point to the fault point 7 has a periodic characteristic of 2βl on the frequency axis. The distortion output exhibits a frequency characteristic in which a periodic characteristic of 2βl due to load impedance is superimposed on a gentle frequency characteristic. An example of this is shown in curve _C1 in FIG. Therefore, if the repeater 6a closest to the fault point is appropriately detected, and the frequency characteristics of the distortion output of the repeater 6a near the fault point are measured, the above fluctuation period 2βl can be obtained.
From this cycle 2βl and the phase constant β of the cable, calculate the distance l between the repeater 6a nearest the fault point and the fault point 7, and calculate the distance l between the repeater 6a nearest the known fault point and the distance l
The fault point 7 can be located from the point.

However, the accurate and quick operation of this type of fault locating device requires training of its personnel. However, it is impossible to use cables that are in operation for training purposes, and it is also uneconomical to prepare coaxial cables that are suitable for relay point spacing of several kilometers or more just for training purposes. On the other hand, if a simulated circuit is constructed using the prior art, the following drawbacks are inevitable. (b) The transmission loss due to the loss of the inductance element is too large, causing errors; (b) the impedance element itself has frequency characteristics, which may complicate the simulation circuit; and (c) the inductance of the coaxial cable is small. (d) The size of the simulation circuit becomes too large to simulate the signal delay in the repeater spacing, which can reach more than 10 km. For example, in actual equipment
If there is a delay of about 5μs, use a commercially available
To simulate using a combination of 0.05 μs elements, 100 such elements are required, which increases the size of the simulated circuit.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned drawbacks of the prior art by providing a circuit for simulating the impedance frequency characteristics of a coaxial cable, which has a simple structure and is easy to operate.

Composition of the Invention In order to achieve this object, a simulation circuit according to the present invention locates a fault point position in a group-based two-wire bidirectional relay coaxial cable system by using periodic changes in the input impedance of the faulty cable with respect to frequency. A simulated circuit is connected to the device in place of a faulty cable to train how to use the device, and its configuration includes a unidirectional element that conducts current in only one direction, a delay element, a reflection coefficient multiplier, and a hybrid coil. It comprises a simulated line connected in series and an input/output line connected to the hybrid coil, and the hybrid coil couples the measurement signal of the device from the input/output line only to the one direction of the simulated line, and The output of the simulated line is coupled only to the input/output line as a reflected component of the measurement signal.

Embodiment Referring to FIG. 3, which illustrates the principle of the invention, an input/output line 11 is coupled to a simulated line via a hybrid coil 12. The simulated line includes a unidirectional element 13 that conducts current in only one direction, such as an amplifier, and a delay element 1.
4 and a reflection coefficient multiplication element 15 are connected in series. The hybrid coil 12 is connected to the terminal 11
The input e _io applied from T to the input/output line 11 is coupled to the simulated line only in the one direction, and the output e _r from the simulated line is coupled only to the input/output line 11.

Assuming that the transmission loss in the hybrid coil 12 is canceled by the multiplier by the unidirectional element 13,
If the multiplier corresponding to the delay of the delay element 14 is set as D'(ω), and the multiplier corresponding to the reflection coefficient of the reflection coefficient multiplier 15 is set as M'(ω), the following equation holds true.

e _r = −D′(ω)・M′(ω)・e _io (2) The output e _r from the simulated circuit is the output from the entire line side when the input e _io is added from the input/output line 11 to the simulated line. It can also be treated as reflected voltage. Input/output line 1
Since the impedance seen as a whole from the input/output line 11 to the terminal 11T side can be set equal to the characteristic impedance Z _p of the coaxial cable, if the impedance seen as a whole from the input/output line 11 to the simulated line side is Z _io , then
From the theory of traveling wave reflection, the relationship between the output e _r as a reflected voltage and the input e _io is given by the following equation.

e _r =(Z _io −Z _p /Z _io +Z _p )e _io (3) By rearranging equations (2) and (3), the following equation is obtained.

Z _io = Z _p (e _io +e _r /e _io −e _r ) Z _io = Z _p 1−D′(ω)・M′(ω)/1+D′(ω)・M
′(ω)(4) The right-hand side of equation (4) and the right-hand side of equation (1) have the same form.

Since the reflection coefficient M(ω) in equation (1) indicates the ratio of the amplitude of the reflected wave to the incident wave, the reflection coefficient multiplier circuit 15 of the simulation circuit in FIG. A corresponding coefficient can be realized as a coefficient M'(ω), for example, by a combination circuit of a transformer with the required turns ratio and a resistive attenuator.

In addition, the propagation characteristic D(ω) of equation (1) is D(ω)=
It is given by e ^-2 〓 ^l-j2 〓 ^l , where −2αl indicates the amplitude attenuation −
Since j2βl indicates a delay, the delay element 14 in FIG. ) can be realized as Therefore, equation (4) is expressed as follows:
This shows that the impedance seen can be simulated by the circuit configuration shown in FIG.

FIG. 4 shows a preferred embodiment of the simulating circuit according to the present invention. In this embodiment, the amplifier 16 compensates for the loss of the simulated circuit element and ensures the unidirectional characteristic of the simulated circuit. In addition, the ultrasonic delay line 17
A transformer is used as the reflection coefficient multiplier 15 and its polarity is inverted to obtain the reflection coefficient. The ultrasonic delay element 17 converts an electric signal into a harmonic wave signal, gives a required delay, and then converts it back into an electric signal and inputs it into a simulated circuit for measurement. can be provided by a small element.

FIG. 5 shows an embodiment in which, when the band of the delay element is limited to the low frequency side, a simulated circuit is provided at the terminal stations at both ends of a two-wire bidirectional repeating system by switch. In the same figure, the line impedance for the low group transmission band frequency is the circuit 18.
The frequency of the high group transmission band is converted to the low group transmission band by the high group transmission circuit 19 consisting of appropriate elements, and the frequency that has passed through the delay element is returned to the high group transmission band. The low group circuit 18 and the high group circuit 19 are connected to the switch 20.
Switch to use.

As explained in detail above, the simulation circuit according to the present invention is a circuit with a simple configuration, and is a function of the impedance of a faulty coaxial cable system, especially the distance l between the fault point and its nearest repeater. Since the periodic impedance frequency characteristic is simulated, this can be used in combination with a measuring device as appropriate for training in fault location.

Effects of the Invention Since the simulating circuit according to the present invention uses unidirectional simulating wires connected by a hybrid coil, it has the following effects.

(a) Since a unidirectional simulated wire is used, the influence of reflection in circuit elements can be excluded.

(b) By using an amplifier as a unidirectional element, it is possible to compensate for the loss of the simulation circuit element and accurately simulate the actual equipment.

(c) Since loss compensation is possible, small elements such as ultrasonic delay lines with large delay times can be used.

(d) A single simulation circuit can perform both simulation at high group transmission band frequencies and simulation at low group transmission band frequencies.

(e) Since the structure is simple, it can be manufactured at low cost and can be easily miniaturized.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of a conventional device, FIG. 3 is a diagram showing the principle of the present invention, and FIGS. 4 and 5 are schematic circuit diagrams of an embodiment of the present invention. 3... Coaxial cable, 6... Repeater, 7... Fault point, 11... Input/output line, 12... Hybrid coil, 13... One-way element, 14... Delay element, 15... Reflection coefficient multiplication element.

Claims (1)

[Claims] 1. In order to train how to use a device that locates the location of a fault point in a group-based two-wire bidirectional relay coaxial cable system using periodic changes in the input impedance of the faulty cable with respect to frequency, the device is used in place of the faulty cable. The connected simulated circuit includes a simulated line in which a unidirectional element that conducts current in only one direction, a delay element, a reflection coefficient multiplier element, and a hybrid coil are connected in series, and an input/output line connected to the hybrid coil, The hybrid coil couples the measurement signal of the device from the input/output line only to the one direction of the simulated line, and couples the output of the simulated line as a reflected component of the measurement signal only to the input/output line. A simulation circuit of a coaxial cable system.