JPH0773237B2 - Two-way information transmission system - Google Patents

Description

The present invention relates to a bidirectional information transmission system in which a plurality of terminal devices are connected by a single coaxial cable and communication is performed between the terminal devices, and information for connecting the coaxial cables and the respective terminal devices. The present invention relates to an outlet and a bidirectional information transmission system using the information outlet.

Conventionally, large-scale transmission systems of this type have been used in broadband local area networks (LA
N), and the one mainly composed of video signals,
There is a two-way CATV system for in-house broadcasting. In a broadband LAN and a CATV system for private broadcasting, in order to realize bidirectional transmission using one coaxial cable, an uplink signal output from each terminal device on the coaxial cable and a downlink signal input to each terminal device are used. Divide the signal into a dedicated frequency band, that is, the transmission band and the reception band, set each channel so as not to interfere with each other,
Carriers transmit encoded data, video signals, and the like. That is, in order to realize communication between terminal devices,
First, a translator (a kind of frequency converter) for converting a transmission band signal into a reception band signal is installed at the end of the coaxial cable. Here, the signal transmitted by a certain terminal device is converted into a transmission band by the modulator and sent to the coaxial cable. This transmission band signal is received by the above-mentioned translator at the end of the coaxial cable, and its frequency band is converted into the reception band and transmitted again to the coaxial cable. This reception band signal is received by being demodulated by the demodulator on the reception terminal device side.

As described above, in the conventional system, the head end including the translator function is required in order to realize the communication between the terminal devices, and at the same time, each terminal device requires the modulator / demodulator. This is an expensive transmission system when implementing a small-scale bidirectional network system for home use, for example. In particular, RF modems for data transmission are expensive and complex.

It is an object of the present invention to provide an inexpensive bidirectional information transmission system that solves the above-mentioned drawbacks.

According to the present invention, in a system in which an RF signal typified by a television signal or an FM audio signal and a data signal are bidirectionally transmitted between respective terminal devices on a common coaxial cable, the data signal is A first terminal device for bidirectional transmission in a base band on the coaxial cable; a second terminal device for receiving or transmitting the RF signal in the RF band on the coaxial cable; or a second terminal device for transmitting and receiving the RF signal; RF signal branching circuit for branching signal, RF mixing circuit for sending out the RF signal on the coaxial cable, for inputting and outputting the data signal to the baseband on the coaxial cable so as not to affect the RF signal And an information outlet composed of a combination of two-way low-pass filters, the coaxial cable and each terminal device via the information outlet. And the bidirectional transmission of the RF signal is performed in the RF band on the coaxial cable.

That is, according to the present invention, it is possible to realize an inexpensive and highly reliable bidirectional information transmission system that does not require a headend and does not require an RF modem for data transmission.
Embodiments of the present invention will be described below with reference to the drawings. First
FIG. 1 is a configuration diagram of an embodiment of a bidirectional information transmission system using four information outlets forming part of the first and second terminal devices according to the present invention. The RF signal including the VHF band and the UHF band from the broadcasting FM / TV signal receiving antenna 1 is mixed with other RF signals 2 and 3 by the mixer 4 and output to the main line 5. The trunk line 5 here corresponds to one common coaxial gable referred to in the present invention. For example, RF signals 2 and 3 are CATV reception signals and RF output signals of video disk devices.
It is assumed that the used frequency bands of 2 and 3 do not overlap at the same time.

The terminal device A includes a data processing terminal 10 _a having a baseband data transmitting / receiving function, a television receiving terminal 11 _a having _a broadcasting television receiving function, and a television camera 12 having an RF modulator having a carrier frequency of _a preset channel. _a
Composed of and. Data processing terminal 10 _a is connected via a signal line 7a to the baseband input and output terminals of the information outlet 6 _a. TV receiving terminal 11 _a is connected via a signal line 8 _a to the RF output terminal of the information outlet 6 _a.

Television camera 12 _a is information outlet 6 _a via the signal line 9 _a
Connected to the RF input terminal of. In the same manner other terminal devices B, C, D, are respectively connected to the information outlet _{6 b, 6 c, 6 d} . Here, each information outlet _6a , _6b , _6c , _6d
The terminal devices A, B, and CD will be described as being the same. The main line 5 is matched and terminated by a matching unit 13 at an end point. FIG. 2 shows a more detailed structure of the information outlet.
The connection between the trunk line 5 and the information outlet 6a is made at the input terminal IN and the output terminal OUT. The RF signal flowing through the trunk line 5 is branched from above the trunk line 5 by the RF signal branching circuit 14 and output to the RF signal output terminal RFout. The RF output signals from the respective terminal devices A, B, C, and D, in which the frequency bands used do not overlap,
It is applied to the RF signal input terminal RFin of the information outlet 6 _a, RF
It is configured to be sent out on the main line 5 by the mixing circuit 16 and propagated bidirectionally on the main line 5. Further, the data signals from the respective terminal devices A, B, C, D are applied to the baseband signal input / output terminal BBio, and the lower limit frequency of the RF signal band is set so as not to affect the RF signal band on the trunk line 5. It is configured to be filtered by a bidirectional low-pass filter 15 having a cutoff frequency sufficiently smaller than that, and propagate bidirectionally on the trunk line 5. Similarly, the baseband signals on the trunk line 5 via a bidirectional low-pass filter 15, the baseband input and output terminals BBio from each terminal apparatus A, B, C, D of the data processing terminal _{10 a, 10 b, 10 c} , It is output to the 10 _d. With the above configuration, in the transmission system shown in FIG. 1, for example, the frequency band on the coaxial cable of the trunk line 5 is changed from DC to
If you set up to 10MHZ as the base band and preset the RF band from 30MHZ to the upper limit 770MHZ of UHF band TV broadcast signal,
Circuit constant of each circuit 14, 15 and 16 information outlets in 6 _a is determined. It is possible to separate the RF signal of the baseband signal and the RF band to each other by the filter function of the information outlet 6 _a is determined. Further, in each terminal device A, B, C, D, the used RF modulation frequency of each television camera 12 _a , 12 _b , 12 _c , 12 _d is not used in the broadcasting FM, TV signal or CATV signal band, respectively. If assigned to the channel of each terminal device A,
The TV camera signals between B, C, and D can be bidirectionally transmitted on the trunk line 5 without interfering with each other. This means that the television receiving terminals _11a , _11b , _11c and _11d of the respective terminal devices A, B, C and D receive the TV signals bidirectionally flowing on the trunk line 5 at the respective terminal devices. It will be possible. On the other hand, each data processing terminal _10a , _10b , _10c , _10d
For the transmission of the baseband data signal between them, the control function of the bus type LAN represented by the already known CSMA / CD method is directly applied by the filter function of the information outlet 6 in the bus type LAN using the coaxial cable, for example. This is possible.
In this case, naturally, the data transfer bit race is limited by the band of the base band, that is, the cutoff frequency of the bidirectional low-pass filter 15, so that it is necessary to set it appropriately.

The above is a description of the basic operation of the bidirectional information transmission system of the present invention. Here, 10a and 15 shown in FIG. 1 and FIG.
Corresponds to the first terminal device referred to in the present invention, and 11a, 12a, 1
Reference numerals 4 and 16 correspond to the second terminal device referred to in the present invention.

An example of a specific information outlet used in the present invention that operates based on the above basic operation is shown in FIG. In the figure,
The input / output terminals IN, OUT, BBio, and RFin correspond to the terminals shown in FIG. 2, respectively. Transformer T ₁ , T ₂ and resistor R ₁ ,
The RF signal branch circuit 14 of FIG. 2 is realized by the circuit composed of the capacitors C ₂ C ₃ and C ₄ . Also, the RF mixing circuit shown in FIG.
In FIG. 3, reference numeral 16 designates resistors R ₂ , R ₃ and a capacitor C ₅ ,
It can be realized by a resistance type mixed circuit composed of C ₆ . On the other hand, the bidirectional low-pass filter 15 of FIG. 2 is replaced by the coil of FIG.
It is realized by a low-pass filter circuit consisting of L ₁ , L ₂ and capacitor C ₁ .

Thus, the information outlet shown in FIG. 3 can realize the bidirectional information transmission system shown in FIG.

In the information outlet described above, the terminal devices A, B, C, and D of the system in FIG. 1 have a data processing terminal and a television signal transmitting / receiving terminal, respectively. The terminal device A in the figure is
The data processing terminal _10a and the television receiving terminal _11a are only included, or the terminal device C is the television receiving terminal 11a.
In _c and TV camera 12 _a may have the structure of the terminal device such as constructed. In such a case, if all the information outlets are realized by the information outlets shown in FIG. 3, the system becomes expensive.

Examples of information outlets suitable for this case are shown in FIG. 4 and FIG.
Shown in the figure. The example shown in FIG. 4 is effective in connecting a terminal device consisting of a data processing terminal and a television receiving terminal to a main coaxial cable, and has a smaller circuit and a smaller circuit than the information outlet shown in FIG. It can be realized at low cost.

Similarly, the information outlet according to the example shown in FIG. 5 is effective when connecting a terminal device having a television transmitting / receiving function.

Here, since the configuration of the bidirectional information transmission system using the information outlet shown in FIGS. 4 and 5 can be easily inferred from the system configuration of FIG. 1, the description and the configuration diagram are omitted here. To do.

As described in detail above, according to the present invention, an inexpensive and highly reliable bidirectional information transmission system can be realized.

The bidirectional information transmission system has been described with reference to the embodiments, but these descriptions do not limit the scope of the present invention.

In the above description, a television signal is mainly used as an example of the RF signal, but the present invention can be easily applied to the case of using an audio signal including voice. In this case, a bidirectional audio signal transmission system can be constructed.

These subtle modifications can be easily analogized by combining the present invention and the prior art, and are included in the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a bidirectional information transmission system using an information outlet according to the present invention, FIG. 2 is a diagram explaining a basic operation of the information outlet used in the present invention, and FIG.
FIG. 4 is a circuit diagram showing a first example of an information outlet used in the present invention, FIG. 4 is a circuit diagram showing a second example of the information outlet, and FIG. 5 is a circuit diagram showing a third example of the information outlet. 1. FM · TV broadcast receiving antenna in figure 4 is RF signal mixer, 5 coaxial _{cable, 6 a, 6 b 6 c} , 6 d is the information outlet, A, B, C, D is a terminal device .

Claims (1)

[Claims] 1. A system for bidirectionally transmitting an RF signal represented by a television signal or an FM audio signal and a data signal between respective terminal devices on a common coaxial cable, wherein the data signal is the coaxial signal. A first terminal device for bidirectional transmission in a baseband on the cable; a second terminal device for receiving or transmitting the RF signal in the RF band on the coaxial cable; or a second terminal device for transmitting and receiving the RF signal, and the RF signal from the coaxial cable An RF signal branch circuit for branching the RF signal, an RF mixing circuit for sending the RF signal onto the coaxial cable, and an input / output unit for inputting / outputting the data signal to / from the baseband on the coaxial cable so as not to affect the RF signal. An information outlet composed of a combination of bidirectional low-pass filters is provided, and the coaxial cable and each terminal device are connected via the information outlet. Then, the bidirectional information transmission system is characterized in that the bidirectional transmission of the RF signal is performed in an RF band on the coaxial cable.