JP2003032655A - Two-way catv system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-way CATV system capable of surely preventing the intrusion of any noise from a terminal to a trunk line. SOLUTION: This system is led through a protector 1 to a subscriber house, and a noise removing device 2 equipped with a first coil 34 constituted of a core wire formed by winding a closed magnetic ferrite core 32 with a coaxial cable and a second coil 35 constituted of a jacket conductor is arranged, and a signal distributor 3 having uni-directional terminals with a high pass filter 38 at one of distributing terminals is arranged at the downstream side. In the noise removing device 2, the thickness of the ground side conductor is set so as to be not less than 4 times as long as the skin depth resulted from the skin depth effects of an incoming transmission frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CATV system, and particularly to a bidirectional CTV system effective for reducing ingress noise.
Regarding the ATV system.

[0002]

2. Description of the Related Art A two-way CATV system is widely used in which a center station can send a television signal to each subscriber's house while transmitting a signal from each subscriber's house to a center station. In such a system, the downlink signal frequency from the center station is generally 70 MHz or higher, while the uplink signal frequency transmitted from the subscriber's house to the center station is lower than 10 MHz to 5 MHz.
5 MHz is commonly used.

However, since the frequency of noise radio waves generated from terminal equipment such as a television receiver installed in each subscriber's house and other electronic equipment also includes a lot of this upstream frequency band, it is generated from these equipment. There is a problem of ingress noise in which noise radio waves flow into an upstream signal and travel along the CATV line to adversely affect the center station.

As a countermeasure against this, the applicant of the present invention has disclosed in Japanese Unexamined Patent Publication
A protector (a noise mixing prevention device) disclosed in Japanese Patent Laid-Open No. 103447 is proposed. This protector is configured as shown in the circuit diagram of FIG. 7, and the core wires of the input terminal 13 and the output terminal 14 are connected to each other in the front-stage coupling transformer 15 and the rear-stage coupling transformer 1.
6 are connected via a two-stage coupling transformer. Coupling capacitors C1 and C2 are provided between the input terminal 13 and the pre-stage coupling transformer 15, and a capacitor C3 is provided in parallel on the primary side of the pre-stage coupling transformer 15. Also,
One end of the rear coupling transformer 16 and the output terminal 14 are connected via a coupling capacitor C4, and the rear coupling transformer 16 is connected.
And the outer conductor of the output terminal 14 are grounded via a capacitor C5.

Both the front-stage coupling transformer 15 and the rear-stage coupling transformer 16 are formed by winding a primary winding and a secondary winding around a ferrite ring body, for example, three times each, and are symmetrically arranged and connected in an inverted manner. The center of the secondary winding of the front stage coupling transformer 15 and the center of the primary winding of the rear stage coupling transformer are grounded. Reference numeral 17 is an arrester, and 18 is a choke coil. By interposing a protector having such a noise removing function in the signal transmission path, noise from terminals is prevented from entering the trunk line, and it is effective in reducing ingress noise at the CATV center station. It was

[0006]

However, even if the above-mentioned protector is provided, noise will intrude upstream from the unidirectional transmission equipment installed at the indoor wiring transmission path or the receiving end downstream of the protector and beyond the protector. In some cases, it was not possible to exert a sufficiently satisfactory effect on the reliability of two-way communication. Therefore, in view of the above problems, it is an object of the present invention to provide a bidirectional CATV system capable of reliably preventing noise from entering a trunk line from a terminal.

[0007]

In order to solve the above-mentioned problems, the invention of claim 1 introduces a coaxial cable for transmitting a signal into a subscriber's house, and thereafter, at least one of the open magnetic core and the closed magnetic core is provided with the signal. A two-way CATV system in which a noise eliminating device having a coil formed by winding a coaxial cable for transmitting a signal is interposed and at least one signal distributor is provided on the downstream side thereof, the noise eliminating device being grounded. The thickness of the side conductor is not less than twice the skin depth due to the skin effect of the upstream transmission frequency, and the signal distributor has at least one unidirectional terminal incorporating a high-pass filter and at least one bidirectional terminal. Characterize.

According to a second aspect of the present invention, in the first aspect of the present invention, a protector is interposed when the protector is inserted into the subscriber's house, and the protector includes two stages of a coupling transformer having a primary winding and a secondary winding. It is characterized by comprising a noise mixing prevention circuit.

The invention of claim 3 is characterized in that, in the invention of claim 2, a signal amplifying device is provided between the protector and the noise removing device.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a main part of a bidirectional CATV system according to the present invention, showing from the middle of a trunk line to a terminal device. In the figure, 4 and 4 are signal amplifying devices provided on the trunk line, 5 is a branching device, and 1 is a protector. The output line of the protector 1 is drawn into each subscriber's house to further amplify bidirectional signals. Is connected to the signal distributor 3 via the signal amplifier 10 and the noise eliminator 2, and the personal computer 8 or the like is connected to the signal distributor 3 with one side as the bidirectional terminal 2a and the other side is the unidirectional terminal 2b.
A television receiver 9 and the like are connected as. Incidentally, 6 is a modem, 7 is a home terminal, and a coaxial cable is used for the signal transmission path.

The protector 1 is composed of the circuit shown in FIG. 7 and has a noise removing function to reduce noise that tends to flow into the trunk line from the terminal side. However, it is not necessary to limit to the configuration of FIG. 7, and as shown in FIG. 3A, one coupling transformer may be used, or as shown in FIG. Even if the secondary winding is formed by connecting the secondary winding in series between the terminals, the noise removing function can be provided. Further, if a noise removing device as described later is provided, noise can be effectively reduced even if the protector does not necessarily have a noise removing function.

The noise eliminator has the structure shown in the sectional view of FIG. In the figure, reference numeral 22 is a plug type coaxial connector, and 23 is a jack type coaxial connector, which are provided at both ends of a housing made of a resin cylinder 21 and are insulated from each other. A noise removing circuit 24 is formed inside the cylinder 21.

At the inner ends of the housings of both coaxial connectors 22 and 23, the base ends of the core wire connecting pins 22b and 23b project, and are connected to the core wires of the coaxial cable 25 of the noise elimination circuit 24 via chip capacitors 26, respectively. ing. Further, the connecting screw portions 22a and 23a electrically connected to the outer conductor of the coaxial cable to be connected have male screw portions 22c and 23c projecting in the cylindrical body, and the ring type feedthrough capacitor 2
After externally fitting 8, the base of the cylindrical shield fitting 29 is externally fitted and fixed by nuts 30 made of an insulating material.
Connection screw portions 22a and 23a via the feedthrough capacitor 28
And the shield fittings 29, 29 are electrically connected.

The shield fitting 29 further has a funnel-shaped metal shield plug 31 connected to the tip thereof, and the noise elimination circuit 24
Is connected to the outer conductor of the coaxial cable 25 forming a gap without a gap. The noise elimination circuit 24 is a closed magnetic ferrite core 32.
It is composed of a coil formed by winding a small-diameter coaxial cable 25 around the core. The core wires of both coaxial connectors 22 and 23 and the outer conductors respectively block passage of a transmission signal and pass low frequency or direct current. First choke coil 33a
And the second choke coil 33b, the first choke coil 33a and the first coil 34, which is the core wire of the coaxial cable 25, and the two chip capacitors 26.
Are connected in parallel with each other, and the second choke coil 33b and the second coils 35 and 2 formed of the outer conductor of the coaxial cable 25 are connected.
The individual ring type feedthrough capacitors 28 are connected in parallel. To connect the first choke coil 33a, the shield metal fitting 31 is provided with the through terminal 36, and the lead wire connected to the internal core wire connecting pins 22b and 23b is connected to the through terminal 3.
It is carried out by pulling out from 6.

In this way, the core wires of the connector and the outer conductors are connected to each other by the coil or the choke coil via the capacitors. However, the chip capacitor 26
Is a cut capacitor for blocking passage of the operating current superimposed on the transmission signal, and choke coils 33a and 33b.
Is for cutting the transmission signal frequency and allowing the operating current to pass therethrough, and is formed by winding a large-diameter conductor wire around ferrite. The thickness of the grounding conductors such as the connecting portions of the two connectors 22 and 23 to the tubular body 21, the shield fitting, the shield plug, and the outer conductor of the coaxial cable is 0.1 mm or more.

Here, the thickness of the ground conductor will be described. The thickness of the ground conductor (0.1 mm or more) is 4 times or more the skin depth with respect to the transmission signal frequency. For example, the skin depth h due to the skin effect of copper is calculated by the following equation.
h = 0.066 / √f where: f (MHz) By this calculation, assuming that the transmission signal frequency is 10 MH, h =
It becomes 0.02087 mm. Therefore, by setting the thickness of each of the ground conductors to be 0.1 mm or more, the thickness can be four times or more the skin depth.

As described above, by making the thickness of the ground conductor 4 times or more the skin depth, noise near the transmission signal frequency induced in the ground conductor flows only in the ground conductor skin and does not appear inside. . Therefore, the ground conductor side component of the transmission signal flows inside the ground conductor, so that noise is not superimposed on the transmission signal itself. Therefore, by providing the noise removing device, new intrusion of noise does not occur. However, as a result of the experiment, the effect of making the thickness of the grounding conductor 4 times or more the skin depth can obtain a great effect when the signal transmission line length becomes long. 2 is relatively short, the external noise is not superposed on the transmission signal itself even if the thickness is about twice the skin depth, and a sufficient effect is achieved. The coil of the noise removing circuit may use an open magnetic core instead of the closed magnetic core, or may be formed in two stages using both the closed magnetic core and the open magnetic core.

5 and 6 show another example of the noise elimination device. Both of them show a mode in which they are used for a line in which a low frequency or direct current operating current transmitted with a signal is relatively small or not, and the choke coil is not provided. More specifically, in FIGS. 5 and 6, 122 is a plug-type connector, 123 is a jack-type connector, and the jack-type connector 123 is connected via a coaxial cable 126 to a main body made of a resin cylinder 121. There is. The noise elimination circuit 24 formed in the cylindrical body 121 is formed by winding the coaxial cable 125 around the oval ferrite core 132, and includes the first coil 134 formed of a core wire and the second coil formed of the outer conductor. The coil 135 is formed so that a relatively small operating current can be transmitted.

The coaxial cable 125 is directly connected to the core wires and the outer conductor portions of both connectors 122 and 123, and the outer conductor portions of both connectors 122 and 123 and the noise elimination circuit connecting portions 122a and 123a of the connectors and noise. The thickness of the ground conductor such as the outer conductor of the coaxial connector 126 to which the coaxial cable 125 and the jack-type connector 123 that form the removing circuit 24 are connected is 0.1 mm or more.

As described above, when the operating current is relatively small or absent, the choke coil can be dispensed with,
The circuit configuration can be simplified. Further, by interposing a coaxial cable on at least one terminal, it is possible to give a degree of freedom to the connection with the CATV signal line. 5 and 6, the form of the connecting portion between the coaxial cable 126 and the tubular body 121 is different, and in FIG. 6, the coaxial cable 126 is covered with a resin cover member 127 to improve the airtightness and the strength of the connecting portion. ing. Further, the coaxial connector including the configuration of FIG. 2 has been described as the FT type, but it may be the F type or the J type.

In the signal distributor 3, one of the distribution terminals is a unidirectional terminal having a high-pass filter 38, the television receiver 9 is connected thereto, and the other of the distribution terminals is a bidirectional terminal. Etc. are connected. The high-pass filter 38 has a characteristic of passing the downlink frequency and blocking the passage of noise in the uplink signal frequency band, and prevents the noise that has entered from the terminal from entering the trunk line.

FIG. 4 shows another example of the signal distributor, (a)
Is provided with a switching means so that the high-pass filter 38 can be selectively mounted, and bidirectional and unidirectional switching is possible. Further, (b) is provided with a switching means and the distribution circuit section 4a.
And the high-pass filter section 4b can be separated.
Thus, switching means may be provided to allow all distribution terminals to be bidirectional.

With this configuration, noise generated on the terminal side by both the noise eliminator and the high-pass filter is C
It is possible to prevent entry into the ATV trunk line,
Ingress noise can be reduced. In addition, the protector also has a function of removing the upstream noise, so that the CATV can be more reliably performed.
Noise can be prevented from entering the trunk line and ingress noise can be reduced. Furthermore, by providing a signal amplifier between the protector and the noise eliminator, the signal loss in the transmission band of the signal distributor and the noise eliminator can be improved. In the above-described embodiment, the system is provided with one signal distributor for dividing into 2 at the subscriber's house after passing through the security device, but the distributor is divided into 3 or more parts. A plurality of them may be provided, or at least one distribution terminal may be a unidirectional terminal to which a high-pass filter can be attached.
It is also possible to use a branching device instead of the distributor.

[0024]

As described above in detail, according to the invention of claim 1, noise generated at the terminal side is prevented from entering the CATV main line by both the noise eliminator and the high-pass filter. Noise can be reduced.

According to the invention of claim 2, in addition to the effect of claim 1, since the upstream noise is removed also in the protector, it is possible to surely prevent noise from entering the CATV trunk line.
Ingress noise can be reduced. According to the invention of claim 3, in addition to the effect of claim 2, it is possible to improve the signal loss in the transmission band of the signal distributor and the noise eliminator.

[Brief description of drawings]

FIG. 1 is a bidirectional CAT showing an example of an embodiment of the present invention.
It is a principal part block diagram of a V system.

FIG. 2 is a cross-sectional explanatory diagram showing an example of the noise removal device of FIG.

FIG. 3 is a circuit diagram showing another example of the protector shown in FIG.

FIG. 4 is a block diagram showing another example of the signal distributor of FIG.

FIG. 5 is a cross-sectional explanatory view showing another example of the noise elimination device.

FIG. 6 is a cross-sectional explanatory view showing still another example of the noise elimination device.

FIG. 7 is a circuit diagram of a protector forming a part of a conventional two-way CATV system.

[Explanation of symbols]

1 ... Protector, 2 ... Noise elimination device, 2a ... Bidirectional terminal, 2b ... Unidirectional terminal, 3 ... Signal distributor, 10 ...
Signal amplifying device, 15 ... Front stage coupling transformer, 16 ... Rear stage coupling transformer, 25 ... Coaxial cable, 32 ... Ferrite core, 38 ... High pass filter, 125, 12
6 ... Coaxial cable, 132 ... Ferrite core.

Claims (3)

[Claims] 1. A noise eliminator comprising a coil formed by winding a coaxial cable for transmitting a signal into a subscriber's house and winding the coaxial cable for transmitting the signal around at least one of an open magnetic core and a closed magnetic core. A bidirectional CATV system in which at least one signal distributor is provided on the downstream side of the intervening interposition, and the thickness of the ground side conductor of the noise elimination device is set to the depth of the skin due to the skin effect of the upstream transmission frequency. A two-way CATV system, which is more than doubled and the signal distributor has at least one unidirectional terminal incorporating a high-pass filter and at least one bidirectional terminal. 2. A noise interposition preventing circuit comprising a two-stage coupling transformer having a primary winding and a secondary winding with a protector interposed when the protector is inserted into the subscriber's house. 1. The interactive CATV system described in 1. 3. The CATV system according to claim 2, further comprising a signal amplifying device provided between the protector and the noise removing device.