JPH0550210B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a coaxial cable that is installed between a coaxial cable that transmits high-frequency signals such as CATV and a signal input section of a television receiver, cuts off abnormal voltage, and transmits high-frequency signals. The present invention relates to a protector that transmits signals without loss and prevents leakage of high-frequency signals.

[Prior Art and Its Disadvantages] Conventional protectors have been designed to block abnormal voltages such as those caused by lightning and to transmit high-frequency signals, but little consideration has been given to the leakage of high-frequency signals. However, in urban CATV and CATV in strong electric field areas, the amplification output has been increased to overcome external damage prevention waves, and high-level high-frequency signals have been transmitted. Conventional protectors have high-pass characteristics, and the outer conductors of the connectors on the input and output sides of the coaxial cable are not installed in the same metal case, but are held through an insulator. Therefore, high-frequency signals leaked from this part, which had the disadvantage of preventing other damage.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and aims to prevent leakage while allowing high frequency signals to pass between the input side plug and the output side plug without passing direct current. The purpose is to provide a safety device that can

[Summary of the Invention] The present invention adds a ferrite element in which two insulated wires are wound between an input side plug and an output side plug, and the primary side of the two wires is inputted via a capacitor. Connect one side of the secondary side to the outer conductor of the input or output side connection via a capacitor, and the other side to the outer conductor of the output or input side connection. Furthermore, a capacitor is also inserted between the external conductor and the metal case.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. Figure 1 shows the circuit configuration of one embodiment.
The input side plug is composed of an inner conductor 1 and an outer conductor 2, and the outer conductor 2 is fixed to a metal case 14 (not shown). Similarly, the output side plug also includes an inner conductor 3 and an outer conductor 4, and the outer conductor 4 is connected to a ground line 15 via a ground capacitor 12. In addition, the left side of the figure shown by the two-dot chain line is the lightning arrester of the protector, which is the same as the conventional configuration, and the right side is the circuit of the present invention. The input connector internal conductor 1 is connected to the primary side of a two-winding ferrite 7 via a fuse 13, and the other primary side of the ferrite 7 is connected to the output connector internal conductor 3 via a coupling capacitor 9. In addition, Chiyoke coil 5
and a lightning arrester 6 are connected to the metal case 14 in parallel. One of the secondary sides of the two-wire-wound ferrite 7 is grounded together with the input side plug external conductor 2, and the other side is connected to the output side plug external conductor 4 via a coupling capacitor 10, and connected to the metal case 1 by a grounding capacitor 8.
4 through an earth line 15. A matching capacitor 1 is installed on the output side of the ferrite 7.
1 is consistent.

As described above, the metal case 14 is grounded via the ground line 15. The input side explained above is a convenient name for the side where abnormal voltage is generated, and is generally connected to the CATV coaxial cable side, while the output side is connected to the TV receiver in the home. It is reversible with respect to high frequency signals.

Next, FIG. 2 shows its cross-sectional configuration. The input side plugs 1 and 2 are directly fixed to the metal case 14 with an input side plug tightening nut 24. Further, the output side plugs 3 and 4 are insulated from the metal case 14 via an insulator 23, and further fixed with an output side plug tightening nut 25 so as not to rotate mechanically. For convenience, the portion 13 shown by the dotted line is called the lightning arrester, and the fuse 13, the lightning coil 5, and the lightning arrester shown in FIG.
A lightning arrester 6, a two-wound ferrite 7, and a grounding capacitor 8 are provided. This lightning arrester 6 is connected to the output side plug internal conductor 3 via a coupling capacitor 9. Further, a matching capacitor 11 is connected between the output-side connector inner conductor 3 and the metal case 14, and a plurality of grounding capacitors 12 are usually connected between the output-side connector outer conductor 4 and the metal case 14. Then, the entire circuit described above is covered with a metal cover 22. Capacitors 8 to 12 used here each have a withstand voltage of 500V.
The capacity of the matching capacitor 11 is
5PF, and the capacity of other capacitors 8 to 10 and 12 is 2200PF.

In the protector configured as above,
A high frequency signal used for CATV is transmitted to the input side plug center conductor 1, and is transmitted to the output side plug inner conductor 3 through a fuse 13, a double-wound ferrite 7, and a coupling capacitor 9. On the other hand, a high frequency signal is conducted between the input-side plug external conductor 2 and the output-side external conductor 4 by means of a grounding capacitor 12.

When an abnormal voltage due to a lightning strike or an electric leak is applied to the input side plug inner conductor 1 and outer conductor 2, it is short-circuited by the chiyoke coil 5 and the voltage drops. The high voltage with a steep waveform at this time causes an arc in the lightning arrester 6 and short-circuits with the external conductor 2, but is blocked by the coupling capacitor 9 and is not transmitted to the output side plug center conductor 3. Particularly when the current due to abnormal voltage is large, the fuse 13 blows and protects the connected coaxial cable. Furthermore, if the above abnormal voltage is applied between the input side connector external conductor 2 and the ground line 15, the output side connector external conductor 4 is cut off by the grounding capacitor 12, so the abnormal voltage is transmitted. The TV receiver connected to the output jack can be protected.

Next, even if an abnormal voltage occurs on the output side, such as a reverse flash during a lightning strike, or if the TV receiver malfunctions and abnormal voltage is applied from the receiver to the output side connectors 3 and 4, DC blocking will occur. Since the grounding capacitor 12 is interposed, abnormal voltage is not applied to the input side plugs 1 and 2, and the CATV circuit can be protected.

Next, the two-wire wound ferrite 7, which is the main part of the present invention, will be explained with reference to FIG. Figure 3a shows the basic circuit of a coupled two-line circuit, with the input on the primary side of two parallel lines. The output terminals are 31 and 33, and the input/output terminals 32 and 34 on the secondary side are respectively grounded. terminal 31
The high frequency signal input to is output to the terminal 33 while maintaining the characteristic impedance of the line. Even if these two wires are wound around the ferrite core 35 as shown in FIG. 3b, the capacitor 35 as shown in FIG.
Even if it is grounded through 6 and 37, its characteristics are all-pass type.

In Figure 3b, when a high frequency signal current flows from the primary side input terminal 31 in the right direction as shown by the solid arrow →, a high frequency signal current in the opposite direction flows to the secondary side as shown by the solid arrow ←. is induced to the left. Due to this current flowing in the opposite direction, ferrite 3
The lines of magnetic force generated within 5 are in opposite directions and cancel each other out, as shown by the broken arrows. Here, the current in the direction of the arrow shown by the solid line is a signal current necessary to connect the protector output to the outer conductor 4 of the coaxial cable. However, the interference currents flowing outside the output connector outer conductor 4 flow in the same direction as indicated by the broken arrows. In this case, magnetic lines of force are generated in the ferrite 35, which acts as a large inductance and works to block the interference wave current indicated by the broken line, thereby preventing leakage of the interference wave to the output side plug outer conductor 4.

FIG. 3c shows a method for floating the two-wire-wound ferrite 7 using direct current, and the capacitors 36, 3
The terminals 32 and 34 are grounded via the terminal 7.

Next, a specific structural example of the ferrite 7 is shown in FIG. Figure 4a shows a short ferrite rod with two axial holes made and two parallel wires wound twice between the two holes.

Fig. 4b shows two parallel wires wound 1.5 times around a ferrite ring core, and Fig. 4c shows two parallel wires wound around the circumference of a ferrite bar.

Ferrite has a large μ at low frequencies and decreases as the frequency increases, so a material with low loss in high frequency bands is suitable. It is desirable to use the same characteristic impedance as the coaxial cable for the two parallel wires. The conducting wires are colored formal wires with a diameter of about 0.3 mm, or wires coated with polyethylene. In order to maintain the withstand voltage between the windings, it is necessary not to damage the insulation and to keep the conductors apart. One or two turns is appropriate in the frequency band used for CATV.

Next, another example of the structure of the above circuit will be explained with reference to FIGS. 5 and 6.

In FIG. 5, one end of the coupling capacitor 8 is grounded, and the other end thereof is connected to the secondary input side of the two-wire wound ferrite 7. The primary output side of this two-wire-wound ferrite 7 is connected to the output side plug internal conductor 3. Further, the secondary output side of the two wire-wound ferrite 7 is directly connected to the output side plug external conductor 4, and the output side plug external conductor 4 is grounded via the grounding capacitor 12. Here, it is assumed that a lightning arrester similar to the one on the left side of the two-dot chain line I in FIG. 1 is connected to the left side of the figure.

The following FIG. 6 shows an example in which the coupling capacitor 9 to the two wire-wound ferrite 7 is connected to both the primary input and output sides, and the secondary side coupling capacitor 10 is connected to the output side. These coupling capacitors 9, 10
Depending on the capacity, one or two may be connected to each of the input and output sides. A feedthrough capacitor, a ceramic capacitor, or the like is used as the ground capacitor 12, and in the case of ceramic capacitors, 2 to 6 capacitors are often used.

As described above, when the double wire-wound ferrite 7 is added, the amount of leakage with respect to the input frequency of the protector becomes as shown by the broken line B in FIG. For reference 2
The same characteristic of a conventional safety device that does not have the main wire-wound ferrite 7 is shown by a solid line A. As shown in the figure, an improvement of approximately 15 dB was obtained in the frequency band used by televisions from 90 to 770 MHz. If the leakage amount is -40dB or more, it will not affect other devices in the vicinity and will not cause interference, so this protector has the necessary and sufficient leakage prevention function. .

In addition, in areas with strong TV signal electric fields, the direct wave of the TV signal is induced in the coaxial cable, enters the TV receiver, and causes interference with the CATV signal.
The so-called front ghost phenomenon may occur, but if the lightning arrester on the left side of the two-dot chain line in Figure 1 is removed, or the circuit on the right side of Figure 1, or Figures 5 and 6,
By using the circuit shown in the figure, the above-mentioned problem can be easily solved.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide a protector that blocks direct current components from passing through and allows only high frequency signals to pass through, while also having the function of preventing leakage of the same high frequency signals. can.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a diagram showing a circuit configuration, FIG. 2 is a vertical cross-sectional view showing a mounting structure, and FIG. 3 is an example of a circuit configuration around a double wire-wound ferrite. Figures 4 and 4 are diagrams showing specific structural examples of the same double wire-wound ferrite, Figures 5 and 6 are diagrams showing other circuit configurations, and Figure 7 is a diagram showing the relationship between frequency and leakage amount in the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1...Input side connector internal conductor, 2...Input side connector outer conductor, 3...Output side connector internal conductor, 4...Output side connector outer conductor, 5...Chiyoke coil, 6...Surge arrester, 7
...Two wire-wound ferrite, 8, 12... Grounding capacitor, 9, 10... Coupling capacitor, 11... Matching capacitor, 13... Fuse, 14... Metal case, 1
5... Earth line, 21... Lightning arrester, 22... Metal cover, 23... Insulator, 24... Input side connector tightening nut, 25... Output side connector tightening nut, 35
...Ferite.

Claims (1)

[Scope of Claims] 1. Direct current is not passed between the input and output of the coaxial cable in which the input side plug is directly fixed to the metal case and the output side plug is fixed via an insulator, but a high frequency signal is passed. In the protector, two insulated wires are wound around a ferrite, the primary side of which is connected to a fuse in series, a lightning arrester and a choke coil in parallel, and connected via a capacitor to the center conductor on the input or output side. On the next side, connect one side to the external conductor of the input side or output side plug via a capacitor, connect it to the metal case via the capacitor, and connect the other side to the external conductor of the output side or input side plug, and A leak-proof protector characterized in that a capacitor is inserted between the outer conductor of the output side plug and the metal case.