Interactive video distribution systems – Video distribution system components – Transmission network
Reexamination Certificate
2000-03-22
2003-05-06
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system components
Transmission network
C725S128000, C725S129000, C333S101000, C361S816000, C174S034000, C174S060000
Reexamination Certificate
active
06560778
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a tap device of a cable broadcasting system in which a part of transmission signal running through a transmission line leading to a terminal side from a center equipment is branched and transmitted to a plurality of subscriber terminal devices, particularly to a tap device of a cable broadcasting system in which it can be switched on the side of the center equipment whether the transmission signals are to be transmitted or not to the terminal devices.
(ii) Description of the Related Art
In a conventional cable broadcasting system such as CATV system in which broadcasting signals such as television signals are transmitted to a subscriber's terminal device via one transmission line formed of a coaxial cable, and the like, the transmission line is provided with a tap device, a so-called tap-off, for taking in signals in order to branch the broadcasting signals from the transmission line and leading the signals into the subscriber's terminal device.
Moreover, in a known tap device, it can easily be switched according to a subscriber's request or the like whether or not the broadcasting signals are distributed to the subscriber's terminal device.
Specifically, the tap device is provided with a relay, a so-called high-frequency relay, disposed in a signal path between a directional coupler for branching a part of the broadcasting signals from the transmission line and a tap output terminal for outputting the branched broadcasting signals toward the subscriber's terminal device, in which high-frequency broadcasting signals can be passed with a reduced loss. By operating the relay in response to a command signal transmitted from the center equipment via the transmission line, the connected/disconnected state of the signal path, in other words, whether or not the broadcasting signals are outputted to the terminal device, can easily be switched on the side of the center equipment.
Additionally, since this type of tap device is usually disposed outdoors, a directional coupler, a relay operating control circuit, and the like are all incorporated in a conductive sealed housing.
Therefore, a noise generated by the switching of the relay, or a noise from the relay operating control circuit easily enters the broadcasting signal path for leading the broadcasting signals branched from the transmission line by the directional coupler to the tap output terminal, and the broadcasting signals outputted from the tap output terminal is deteriorated in some cases.
On the other hand, to solve such problems, various shield materials may be used to shield the signal path of the broadcasting signals.
However, there is a tap device in which not only the broadcasting signals flowing through the transmission line are branched but also the branched broadcasting signals are further split and outputted from a plurality of tap output terminals, respectively. In this tap device, the broadcasting signal paths of the same number as that of the tap output terminals are formed, and relays are disposed on the respective paths. Therefore, it is difficult to shield each signal path using a shield material in order to prevent the leakage of the high-frequency broadcasting signals in a limited space.
Specifically, since the tap devices are arranged in series on the transmission line of the CATV system or the like, the size reduction is required, and the enlargement of the volume of the sealed housing is limited. On the other hand, in the tap device provided with a plurality of tap output terminals, the number of components such as relays to be incorporated in the sealed housing is increased. As a result, in the tap device provided with a plurality of tap output terminals, the housing has therein little space left for housing the shield material, and it is difficult to shield each signal path using the shield material.
Moreover, when a plurality of relays are arranged in the housing, in a circuit substrate with these relays mounted thereon, the leakage of high-frequency broadcasting signals is caused by the capacity coupling between wiring patterns forming the broadcasting signal paths, or between the wiring patterns and the relays. In this case, even when some of the relays are turned off, the broadcasting signals are disadvantageously outputted from the corresponding tap output terminals.
SUMMARY OF THE INVENTION
Wherefore, an object of the present invention is to provide a tap device of a cable broadcasting system for branching a part of transmission signals running through a transmission line and selectively transmitting the signals to subscriber terminal devices via a plurality of tap output terminals, in which a signal path for leading the transmission signals to each tap output terminal can easily and securely be shielded.
To achieve this and other objects, according to one aspect of the present invention, there is provided a tap device which includes a first housing member provided with a pair of input and output terminals for connecting the tap device to a transmission line leading to the terminal side from the center equipment of a cable broadcasting system, and a second housing member provided with a plurality of tap output terminals for branching and transmitting transmission signals running through the transmission line of the cable broadcasting system to subscriber terminal devices. These housing members have openings which can be connected with each other. By combining the housing members via the openings, a sealed housing is formed.
Moreover, the following three types of circuit substrates are disposed in the sealed housing formed of the first and second housing members:
(1) a directional coupler substrate provided with a directional coupler for connecting the input and output terminals and passing the transmission signals between these terminals while branching a part of the transmission signals;
(2) a splitter substrate provided with a splitter for splitting the transmission signals branched by the directional coupler and transmitting the signals to the tap output terminals, and a plurality of relays for connecting/disconnecting signal paths leading to the tap output terminals from the splitter; and
(3) a control circuit substrate provided with a receiving circuit for taking in the transmission signals branched by the directional coupler and receiving a command signal superimposed onto the transmission signals and directed to the tap device from the center equipment, and a control circuit for operating the relays in response to the command signal received by the receiving circuit to control the connected/disconnected state of each signal path in accordance with a command from the center equipment.
The splitter substrate, the control circuit substrate, and the directional coupler substrate are arranged and housed in this order from the second housing member.
The relays are mounted on the surface of the splitter substrate facing the second housing member. Furthermore, grounding patterns are formed to surround the relays and the connecting portions of the relays and the tap output terminals on the side of the second housing member. Disposed on the surface of the second housing member facing the splitter substrate are partition walls which surround the tap output terminals, abut the grounding patterns of the splitter substrate, and separate the relays and the connection portions of the relays and the tap output terminals.
Therefore, when these substrates are housed in the sealed housing, the signal path leading to the tap output terminal from each relay of the splitter substrate is shielded by the grounding pattern formed on the surface of the splitter substrate on the side of the second housing member and the partition wall disposed on the second housing member. Therefore, the noise generated on the side of the control circuit substrate is prevented from entering the signal path leading to the tap output terminal from each relay of the splitter substrate, and the transmission signals outputted fr
Chung Jason
Davis & Bujold P.L.L.C.
Faile Andrew
Masprodenkoh Kabushikikaisha
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