JPH02101885A - Bidirectional catv system - Google Patents

Abstract

PURPOSE:To improve the quality of an incoming signal while reducing the effect of concurrent noise by coupling a modulator or a terminator to an indoor CATV mixer. CONSTITUTION:An outgoing signal from a head end 1 reaches an indoor device 8 at a terminal equipment side and is inputted to a CATV mixer 9. An incoming signal from a signal transmitter 13 is sent to the head end 1 via a modulator 14 and an LPF in the mixer 9. On the other hand, a disturbing wave from a defective location in a connector of a device or a coaxial cable is absorbed by a terminator 16 via the LPF of the mixer 9.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention transmits downlink signals such as downlink TV signals from the node end to the terminal side, and transmits uplink signals such as uplink TV signals from the terminal side to the head end. Bidirectional CAT transmitting
Regarding the V system.

(Prior art) Traditionally, two-way CATV systems have been equipped with multi-signal input terminals at several locations within the system, and television cameras that photograph local objects and events are connected to these terminals to broadcast relay broadcasts. TV signals are sent to the head end. At the head end, the received signal is frequency-converted and sent to the terminal side together with the downlink TV signal such as normal broadcasting, and the terminal side converts the received signal into a downlink TV signal and sends it out to the terminal side via the respective CATV converter to the TV receiver. Receiving signal.

(Problem to be solved by the invention) However, in the above conventional two-way CATV system,
For example, if the connector that connects the equipment in the system (amplifier, branch, etc.) and the coaxial cable is loose, or if the coaxial cable has a cut part in the outer conductor due to force such as twisting, shortwave broadcasts can be made from those parts. etc. may be mixed in. These interference signals have almost the same frequency band as the upstream television signal, and are also outside the passband of the CATV converter at the subsequent stage, so they are reflected by the CATV converter and flow toward the head end.

Therefore, if there are several places in the system where interference waves are mixed as described above, the interference signals overlap and are transmitted to the head end. This is a type of noise called crossover noise, and is a cause of significant deterioration of the CN ratio of upstream television signals.

The object of the present invention is to provide a two-way CATV system in which each terminal is provided with a terminal capable of inputting upstream television signals, thereby making it possible to transmit upstream television signals, while reducing the influence of crossing noise. An object of the present invention is to provide a two-way CATV system with improved quality of upstream signals.

(Means for Solving the Problems) In order to solve the above problems, the measures described in the claims above have been taken, and their effects are as follows.

(Operation) Downlink signals such as downlink television signals are transmitted from the head end toward the terminal side. The downstream signal reaches the indoor device on the terminal side and is applied to the first terminal of the CATV mixer of the indoor device. In the CATV mixer, only the downlink signal is sent out from the third terminal by a high-pass filter, and is received by the television receiver at the subsequent stage.

Next, uplink signals will be explained.Among the indoor devices, some are equipped with an upstream signal transmitting device. The upstream original signal from the upstream original signal sending device is converted into an upstream signal by a modulator. This signal is applied to the second terminal of the CATV mixer and passed through a low pass filter and sent out from the first terminal to the end end.

On the other hand, we will explain the case where interference waves enter the system from a loose part of a device connector or a damaged part of a coaxial cable. The mixed interference waves flow to the terminal side,
It is applied to the first terminal of the CATV mixer of the indoor equipment. The signal then passes through the low-pass filter, flows from the second terminal to the terminator, and is dissipated by the resistance of the terminator. For this reason, interference waves flow into the headend side and the CN of the above upstream signal
This can prevent the ratio from worsening.

(Example) The drawings showing the embodiments of the present application will be described below.

Figure 1 shows a system diagram of a two-way CATV system. ol indicates the head end, and although not shown, it includes a receiving amplifier, a frequency converter that converts the frequency of upstream TV signals and transmits them as downstream TV signals, etc. It is equipped with 2 is a main line, and several to several dozen bidirectional main line branch amplifiers 3 are interposed in the middle. 4 is a distribution line, 5 is a tap-off, 6 is a lead-in line, 7 is a protector, and 08 is an indoor device.

The indoor device 8 includes a CATV mixing device 9 described later, a distributor 10 and a CATV converter 11 provided as necessary.
, a television receiver 12, etc. Reference numeral 13 indicates an upstream signal transmitting device such as a video camera. Note that a VTR, a computer, or the like may be used as the upstream signal sending device 13, and video signals, audio signals, data signals, etc. from these devices are referred to as upstream signals in this specification. Reference numeral 14 denotes a modulator, which converts the signal from the upstream original signal transmitting device 13 into an upstream signal of a frequency that can be transmitted in a bidirectional CATV system and transmits it. 15 indicates a terminator, which is used in a CATV mixer to which the modulator 14 is not connected.

Next, details of the CATV mixer will be explained.

FIG. 2 is a block circuit diagram of the CATV mixer 9, and FIG. 3 is a perspective view of the CATV mixer 9. Reference numeral 9a designates a first terminal to which a downstream signal is input and an upstream signal is output. For example, a coaxial connector is used, and the terminal is connected to the protector 7 via a coaxial cable 16. Reference numeral 9b is a second terminal to which an upstream signal is input, and a coaxial connector is used, for example. 9c is the third terminal to which the lower signal is output; for example, a coaxial connector is used, and the coaxial cable 17 is used to connect the distributor 10 or the CATV converter 1.
1. ! :It is connected. 18 is a high pass filter,
It allows downlink signals (FM broadcast signals, downlink television signals, etc.) of 70 MHz to 450 MHz to pass through, and blocks other signals. 19 is a low pass filter, 10 to 5
It allows upstream signals of 0 MHz (upstream television signals, etc.) to pass through and blocks other signals. 20 is a variable attenuation circuit, which is used to adjust the level of the downstream signal. 21
is an amplifier that amplifies the downstream signal. 22 is a power supply separation p-wave device, 23 is an AC plug, and 24 is an AC 100V AC 2
A power transformer that transforms voltage from 0 to 30V is shown. 25 is a changeover switch, which connects the power supply separation filter 2 from the third terminal 9c side.
When a voltage of 20 to 30 VAC is sent through the AC plug 23, the contact X side is used, and when power is supplied from the AC plug 23 side, the contact Y side is used.

26 is a rectifier circuit, and 27 is a constant voltage circuit.

In Fig. 3, 28 is the case of the CATV mixer 9;
29 is the operation part of the changeover switch 25, 30 is the top screw, 3
1 indicates a chain for preventing loss of the terminator 15.

Next, the operation of the bidirectional CATV system having the above configuration will be explained. An upstream signal is sent to the head end 1 from the indoor device 8 in which the upstream signal transmitting device 13 and the modulator 14 are connected to the CATV mixer 9 . To explain this process in detail, first, a video-audio signal is output from the television camera 13 as an upstream signal transmitting device. This signal is converted by the modulator 14 into an upstream television signal having a frequency band of, for example, 18 to 24 MHz. This upstream television signal is applied to the second terminal 9b of the CATV modulator 9, passes through the protector 7 and the drop-in line 6, and reaches the tap-off 5. This upstream television signal further passes through a distribution line 4, a bidirectional main line branch amplifier 3, and a main line 2, and reaches the head end 1.

On the other hand, the downstream signal is transmitted from the headend 1 to the indoor device 8 on the terminal side.
sent to. This process will be explained in detail.

At head end 1, received FM radio waves, VHF/UH
The above-mentioned upstream signal together with the F-band television broadcast wave is subjected to signal processing such as frequency conversion, and is turned into a 70-450 MHz band downlink signal and sent to the subsequent stage. Those down signals are
The main line 2 and the bidirectional main line branch amplifier 3 are divided into a large number of distribution lines 4. In each distribution line 4, tap-off 5
, the lead-in line 6 and the protector 7, and reach the CATV mixer 9 of each indoor device 8. Downlink signal is CATV mixer 9
is output from the third terminal 9c of the CA
The signal reaches the TV converter 11, where only the signal of the desired channel is selected and converted into a signal of a predetermined channel, for example, channel 2. The signal is then received by a television receiver.

Next, the crossing noise will be explained. For example, assume that a break occurs in the outer conductor of the coaxial cable at one terminal portion 2 of the tap-offs 5. If, for example, a shortwave broadcast radio wave enters from this Z portion, this noise passes through the lead-in line 6 and the protector 7 and is added to the first terminal 9a of the CATV mixer 9. This noise passes through the low-pass filter 19, appears at the second terminal 9b, and is dissipated by the resistance of the terminator 15. In other words, in the CATV mixer 9 where no upstream signal is sent out, the second terminal 9b is connected to the terminator 15 as shown in FIG.
It is closed off by. Therefore, the terminal part Z mentioned above
This prevents noise mixed in from the tap-off 5, the distribution line 4, and the bidirectional trunk branch amplifier 3 from going back up to the head end. That is, in this two-way CATV system, it is possible to prevent the quality of upstream signals from being degraded by crossover noise.

Although the upstream signal is transmitted from only one of the indoor devices 8 in the above example, it may be transmitted from two or more indoor devices. In this case, the channels of uplink signals obtained by each modulator 14 are assigned differently.

(Effect of the invention) As described above, in the present application, upstream signals can be sent from any indoor device on the terminal side to the head end side via the CATV mixer. Even in a highly efficient two-way CATV system, the indoor equipment that sends out upstream signals and connects terminals has a terminator connected to the CATV mixer, so interference waves can mix in near the terminal side of the system. However, it can also be dissipated. Therefore, it is possible to prevent interference waves from flowing into the head end side as crossover noise and deteriorating the CN ratio of the upstream signal.

[Brief explanation of the drawing]

The drawings relate to an embodiment of the present application, and FIG. 1 shows a bidirectional C
A system diagram of the ATV system, FIG. 2 is a block circuit diagram of the CATV mixer, and FIG. 3 is a perspective view of the CATV mixer. 1... Reference head end, 8...-Indoor equipment, 9-Φ・C
ATV mixer, 9a...first terminal, 9b...second terminal
terminal, 9c... third terminal, 11-ψ/CATV converter, 12-... television receiver, 13... upstream original signal sending device, 14... modulator, 15... terminator . Patent applicant Maspro Electric Works Co., Ltd. Representative Takashi Hatade Figure 2 Figure 3

Claims (1)

[Claims] The downlink signal from the head end is transmitted to a plurality of indoor devices on the terminal side, and at least one of the indoor devices
In a two-way CATV system, in which an upstream signal is sent to the head end, each of the indoor devices includes a first terminal, a second terminal, and a third terminal.
A mixer is provided, and each CATV mixer applies the downlink signal from the head end to the first terminal, passes it through its own high-pass filter, and then sends it from the third terminal to the television receiver. Furthermore, each CATV mixer is provided with a low-pass filter that passes the band of the upstream signal between the first terminal and the second terminal; Mixer 2nd
A bidirectional C, characterized in that a modulator or a terminator connected to an upstream signal transmitting device is connected to the terminal of
ATV system.