JPS60248030A - Two-way branching device - Google Patents

Abstract

PURPOSE:To select the branched direction depending on a frequency band of a signal by connecting mutually output sides of plural branch circuits and inserting a filter passing a specific frequency only between at least a couple of output terminals among them. CONSTITUTION:Outer conductors 3A-3C of coaxial cables 1A-1C are connected together via a shield box 8 and core wires 2A-2C are connected respectively to an input terminal 6 of branch circuits 5A-5C. Each input terminal and output terminals 71, 72 of the circuits 5A-5C transmit a signal in two ways with a low loss and the output terminals 71 and 72 are brought into high loss state. Since the characteristic impedance among the cables 1A-1C is matched by the impedance circuits 5A-5C, no signal reflection and phase change is caused. When a video signal transmitted via the cable 1B is set in a pass band of a filter circuit 9, the signal is transmitted to the cable 1C while keeping the impedance matching. Similarly, when the signal transmitted to the cable 1C is within the pass band of the circuit 9, the signal is transmitted to the cable 1B with low loss.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a bidirectional transmission system used in a bidirectional transmission system that enables multiplex transmission of video signals, audio signals, data signals, etc. in both directions using a coaxial cable. This relates to a branching device.

[Background technology]

Figure 3 shows an example of a bidirectional branching device used in conventional TV intercoms, etc., in which each core wire (2A) of a three-tree coaxial cape Jl/(IA)(IB)(to)
(2B) (2G) are connected to each other, and the external conductor (
3A), (3B), and (30) are also connected bK to each other. In the conventional example, it is possible to branch the video side transmitted from one coaxial cable (i, 1A) to other coaxial cables (IB) and (1o) and transmit it. In addition to this, you can use a coaxial cable (IB) or (1
o) to another coaxial cable (
It is now possible to branch to IA) (io) or Ike (IB) and (1C) and transmit. However, in such a conventional example, each coaxial cable (1A) (1B)
Since an impedance mismatch occurs at the connection point f41 of (10), for example, the video signal transmitted from the coaxial cable (IA) is reflected at the connection point (4), and a portion of it is transferred to the original coaxial cable (IA). ).

For this reason, there is a problem that a part of the energy of the video signal from the coaxial cable (IA) is not transmitted to the coaxial cable (IB) (1c) side, resulting in a decrease in transmission efficiency. . Furthermore, there is a problem in that the impedance mismatch at the connection point (4) causes a large change in the phase of the video signal, causing color shift etc. in the case of a color video signal.

On the other hand, as a device that can branch signals while maintaining the characteristic impedance matching condition, there is a branch circuit (5) such as a branch or divider for common television viewing as shown in Figure 4, for example.
is commercially available, but such a branch circuit (5) can transmit signals bidirectionally with low loss between the input terminal (6) and the output terminals (7t) (7g); Terminal (
7,) and (78), there was a problem in that it was impossible to transmit video signals, etc., and that it could not be used as a bidirectional branching device.

Therefore, the present inventors have proposed combining such unidirectional branch circuits (5) to form a bidirectional branching device, which allows video signals and audio signals to be connected between arbitrary terminals. It has become possible to bidirectionally branch and transmit data signals, etc., but for example, VHF and UH
For broadcast signals such as TV broadcast signals such as F and FM broadcast signals, it is better to have the same characteristics as the previous branch circuit (5) to prevent interference waves generated on the receiver side from being transmitted to other receivers. Therefore, it is strongly desired to add a function that allows the branching direction to be selected depending on the type of signal.

[Purpose of the invention]

The present invention has been made in view of the above points,
The purpose of this is to prevent impedance mismatching from occurring at signal branching points, and to prevent the occurrence of impedance mismatches at signal branching points. It is in Kokichi that allows you to choose the direction.

[Disclosure of the invention]

The configuration of the present invention will be described below with reference to illustrated embodiments. 1st
The figure shows one embodiment of the invention. In the same figure, (1A) (1B) (Ic) I/i coaxial cable,
The external conductors (3A), (3B), and (3o) are connected to each other via a shield box (8). Also, each coaxial cable (1A) (IB) (l.) core wire (2A) (2
B) (20) are branch circuits (5A) (5B) (5
0) input terminal (6). Branch circuit (5
One output terminal (7,) of A) is connected to the output terminal (7,) of the branch circuit (5B), and the output terminal (7,) of the branch circuit (5A
) is connected to the output terminal (7,)K of the branch circuit (5o). Also, branch circuit (5B)
The output terminal (7,) of the filter circuit (9) is connected to the field, and the other terminal (11) of the filter circuit (9) is the output terminal (7,) of the branch circuit (5o). As the filter circuit (9), for example, a π-type or T-type band-pass filter or band-elimination filter is used.

In addition, each branch circuit (5A) (5B) (5G) is the fourth
It has the same configuration as the branch circuit (5) shown in the figure, and has an input terminal (
6) and the output terminal (7, 1 (71)) with low loss (the loss value does not necessarily have to be the same).
The output terminal (7t) (7g
), the loss is high. Therefore, for example, a video signal transmitted from the coaxial cable (IA) is transmitted from the output terminal (7t) of the branch circuit (5A) to the coaxial cable (IB) via the output terminal (7,) of the branch circuit (5E). and the other output terminal (?) of the branch circuit (5A).
, ) to the coaxial cable (1o) via the output terminal (7,) of the branch circuit (5o). At this time, the characteristic impedance between each coaxial cable (+A) (1B) (l.) is the branch circuit (5A) (5B)
(5G), so there is no signal reflection,
It is impossible to cause a change in phase.

The video signal transmitted via the star coaxial cable (IB) is transmitted to the coaxial cable (1°) via the filter circuit (9) with impedance matching maintained. Now, if the video signal is set to the passband of the filter circuit (9), the video signal is transmitted from the coaxial cable (IB) to (io) and (IA), and the video signal is set to the passband of the filter circuit (9). If the attenuation band is set to , the video signal will only be transmitted from the coaxial cable (IB) to (IA).

Similarly, the video signal transmitted via the coaxial cable (1o) is also transmitted to the coaxial cable (1A) with a loss of 100 Hz, and the coaxial cable (IB) is connected to the filter circuit (9
) is transmitted with low loss if the video signal is included in the passband,
If the video @ is not included in the passband, it will not be transmitted.

Taking as an example the case in which the filter circuit (9) in the embodiment of FIG. It has the same characteristics as 5) and operates with a completely non-directional branching device 17 in other frequency bands.

In the embodiment shown in FIG. 1, the filter circuit (9) is inserted between the branch circuits (5B) and (50), but the present invention does not limit the insertion location.

Next, FIG. 2 shows another embodiment of the present invention, 1
One input terminal (6) and three output terminals (71) (7,)
(7,) and four branch circuits (5A) (5B) (
50) (5D), coaxial cable (IA) (IB
) (Ia) (1D) are connected to each other, and the filter circuit +91H branch circuit (5B), (5o), (5
o) and (5D), and between (5D) and (5B), respectively. In this embodiment, for example, if the filter circuit (9) uses the television broadcast signal band as an attenuation band, the branching device shown in FIG. Coaxial cable (IA
) to the coaxial cable (IB) (Io) (ID), but the signal is distributed from the coaxial cable (IB) (l o) c l
D) shows the characteristic that no signal is transmitted, and operates as a completely non-directional branching device in frequency bands other than television broadcast signals.

[Effects of the Invention] The present invention is configured as described above, and enables bidirectional signal transmission between an input terminal and a plurality of output terminals with low loss, and a high loss state between each output terminal. In a bidirectional branching device that combines a plurality of branch circuits, at least one output terminal among the plurality of output terminals of any branch circuit, and an output terminal of another branch circuit connected to the output terminal. During this period, only certain frequency bands are allowed to pass through,
For other frequency bands, a filter circuit is inserted to block the passage of signals, so the branching direction can be selected depending on the frequency band of the signal. Frequency multiplexing allows transmission signals that need to be branched in both directions, such as transmission signals for remote control and monitoring systems, and transmission signals that do not need to be branched in both directions, such as ladder broadcast signals and FM broadcast signals. If used in a transmission system such as the one described above, it will be possible to obtain the same characteristics as the previous branching device for broadcast signals, and it will be convenient because it will prevent interference between receivers. be.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is a circuit diagram of another embodiment of the present invention, and FIGS. 3 and 4 are circuit diagrams of a conventional example. (IA) to (ID) are coaxial cables, (2A) to (2D
) tri core wire, (3A) to (3D) are external conductors, (5A
) to (5D) are branch circuits, (6) is input terminal, (7,)
-(7,) are output terminals, and (9) is a filter circuit. Agent Patent Attorney Ishi 1) Chief 7 Figure 1 Figure 2

Claims (1)

[Claims] (1) Has one input terminal and multiple output terminals, enables bidirectional signal transmission with low loss between the input terminal and each output terminal, and creates a high loss state between each output terminal. A plurality of branch circuits are provided, and the core wires of coaxial cables having the same characteristic impedance as the input terminals are connected to the input terminals of each branch circuit, and the external conductors of each coaxial cable are connected to each other. The plurality of output terminals are respectively connected to the output terminals of all other branch circuits, and at least one output terminal among the plurality of output terminals of any branch circuit is connected to the output terminal. A bidirectional circuit characterized by inserting a filter circuit between the output terminals of other branch circuits that passes signals in a specific frequency band and blocks signals in other frequency bands. Branching device.