Pulse or digital communications – Cable systems and components
Reexamination Certificate
1999-12-29
2003-05-27
Phu, Phuong (Department: 2731)
Pulse or digital communications
Cable systems and components
C375S220000, C725S149000, C725S127000
Reexamination Certificate
active
06570928
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a cable broadcasting system in which operation modes of a tap device, an amplifier and the like provided on a transmission line for transmitting broadcasting signals are set by command signals transmitted from the center equipment to a transmission
DESCRIPTION OF RELATED ART
Heretofore, in a cable broadcasting system such as a CATV system where broadcasting signals such as television signals and the like are transmitted to a subscriber's terminal via a transmission line, various electronic devices for transmitting broadcasting signals such as an amplifier for amplifying broadcasting signals, a tap device for branching the broadcasting signals (the so-called tap-off) from the transmission line and transmitting the signals to the subscriber's terminal are equipped on the transmission line.
Some of such electronic devices for the cable broadcasting system are known to be provided with receiving circuits and control circuits for setting operation modes so that the operation modes can be automatically set by command signals transmitted to the transmission line from the center equipment.
For example, a relay that can transmit broadcasting signals of high frequency with a small loss is provided in the signal pass between a directional coupler by which broadcasting signals are partially branched from a transmission line and a tap output terminal outputting the branched broadcasting signals to the subscriber's terminal. The relay is the so-called high frequency relay. Usually, a latching relay capable of keeping the condition of on or off is used. In the above-mentioned electronic device, or the tap device, it is designed that by supplying the relay with electricity in response to a command signal transmitted from the center equipment via the transmission line, the condition of on or off of the signal pass is easily changed (that is, the broadcasting signal is transmitted to the subscriber's terminal or not) from the center equipment.
In a cable broadcasting system equipped with such electronic devices, a characteristic identifying data (simply referred to as an address, hereinafter) is given to an electronic device capable of setting operation modes. When the center equipment sets the mode of a specific electronic device, the center equipment produces a command signal by adding a command data (also called only “command”, hereinafter) indicating a content of the command to the address of the corresponding electronic device and transmits the command signal to the transmission line after converting it to a command signal for transmission.
As a result, in the electronic device like the tap device provided on the transmission line, command signals transmitted from the center equipment are received by the receiving circuit, a command signal having the same address as its own address is selected among the received command signals by a control circuit and the operation mode is set according to the command contained in the command signal.
Therefore, in such a kind of cable broadcasting system, the operation mode of the electronic device can be easily set by the center equipment such that, for example, a command signal to a specific tap equipment is transmitted from the center equipment to stop broadcasting signals to the subscriber's terminal from the tap output terminal of the tap device. In the case, there is no need for the operator to visit the place where the electronic devices are equipped for setting the operation mode of the electronic devices.
However, in such a conventional cable broadcasting system, normal command signals can not occasionally be transmitted because of noises occurring at the periphery of the transmission line, despite that command signals are transmitted to the electronic devices on the transmission line from the center equipment
Specifically, by noises superimposed at the periphery of the transmission line, several bits of the data constituting the command signal are possibly dropped off or some bit data are reversed from “1” to “0” or vice versa. In such a case, normal command signals can not be transmitted and therefore the operation mode can not be set as desired.
On the other hand, in the field of communication for transmitting data, it is known that the same data are transmitted repeatedly and continuously to overcome the noises. Therefore, also in the cable broadcasting system, such a method is thought to be applied for transmitting command signals from the center equipment to the electronic devices on the transmission line and is being put to practical use. Specifically, in order to transmit surely the command from the center equipment to the targeted electronic devices, the same signals are transmitted repeatedly and continuously from the center equipment and the operation mode is set according to one of the received normal command signals among the continuous command signals in the electronic device.
However, according to such a method, though it is effective when noises are sporadically superimposed at the periphery of the transmission line, it could be a problem that the electronic devices confronted with an instantaneous power failure as well as electronic devices positioned at the terminal side than the electronic devices can not receive any of the command signals, when, for example, by a thunderbolt, the instantaneous power failure that instantaneously shuts power supply to the electronic devices on the transmission line occurs.
Specifically, since the duration time of the instantaneous power failure is 0.2 second at the longest, it does not heavily influences the transmission of broadcasting signals but the duration time of the instantaneous power failure is extremely long compared with the time of the sporadic noises superimposed at the periphery of the transmission line. Therefore, according to the above-mentioned conventional method against noises, the period of time when the same data are transmitted repeatedly and continuously and that of the instantaneous power failure could overlap each other and, as a consequence, occasionally the data can not be transmitted to the electronic devices on the transmission line.
SUMMARY OF THE INVENTION
An object of the invention is to provide a cable broadcasting system in which operation modes of various electronic devices such as tap devices, amp lifiers and the like provided on a transmission line are set by command signals transmitted from a center equipment to the transmission line, wherein the command signals can be surely transmitted to the electronic devices even when an instantaneous power failure occurs in the system due to a thunderbolt and the like.
In a cable broadcasting system of the invention, the center equipment is provided with a broadcasting equipment and a transmission equipment. In addition to broadcasting signals outputted from the broadcasting equipment, command signals outputted from the transmission equipment are transmitted to a transmission line. The command signal is a signal for setting operation mode of an electronic device (for example, above-mentioned tap device, amplifier and the like) provided on the transmission line. The electronic device capable of setting operation mode of itself automatically by receiving the command signal as well as a power supply device for supplying the electronic device with electricity are provided on the transmission line.
In the electronic device on the transmission line, a receiving circuit receives the command signal transmitted from the center equipment via the transmission line, a control circuit sets its own operation mode in response to the command signal when the command signal is a command signal to itself, a power source circuit takes in a power signal supplied to the transmission line by the power supply device and converts the power signal to a voltage for operation to supply the built-in circuits like the receiving circuit and control circuit with electricity
In such a cable broadcasting system, it is difficult to transmit a command signal to an electronic device
Davis & Bujold P.L.L.C.
Masprodenkoh Kabushikikaisha
Phu Phuong
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