JPS59183578A - Overall information transmission system for home use - Google Patents

Abstract

PURPOSE:To form an overall information transmission system for home use possible for two-way transmission by using a branching device having no coupling loss in opposite direction. CONSTITUTION:Since the circuit is formed symmetrically when viewed from an input terminal 19 and an output terminal 20, the coupling loss in opposite direction and the branching loss are equal, a matching transformer 23 and the value of a resistor 22 are adjusted to minimize the branching loss. A VTR35, a television camera 13 and a personal computer 36 are connected to the post stage of television receiver 9 having a video intermediate frequency of 58,75 MHz or plural television receivers via a branching device 18, allowing to attain two-way transmission. When the intermediate frequency is 58.75 MHz, the local oscillating frequency at receiving of low channel falls down to a mid-band without broadcast and falls down to out-band of 12ch at high channel receiving, then no disturbance due to the leakage of local oscillation is produced and there exists a probability to exert disturbance on a band over 9ch as to the UHF band, but such channel is not used in the same service area.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a home comprehensive information transmission system using a home public listening system.

<Background/River> With changes in lifestyles, it has become necessary to use two or three televisions in each home and create a communal listening system that allows television to be viewed in each room. These days, just like power outlets,
Many homes have common listening lines installed at the time of construction and TV antenna terminals are installed in all rooms, and this trend is expected to grow stronger in the future.

On the other hand, the development and lower cost of new video sources such as television cameras, VTRs, and personal computers have had a major impact on our home lives, and televisions and public listening systems have become more important than just receiving on-air broadcasts. , there has been a demand for transmitting and receiving various video signals. Of course, it should be noted that this transmission medium must be bidirectional.

<Prior art> Fig. 1 shows an example of a conventional TV common listening branch, in which one end of the primary winding of a high frequency transformer l is connected to the input terminal 2, and the other end is connected to the input terminal 2. Connect to output terminal 3,
Similarly, one end of the secondary winding lb is grounded, and the other end is connected to the branch terminal 4.
In addition, the input terminal 2 and the branch terminal 4 are connected via a resistor 5.

FIG. 2 shows an example of a public listening system using such a splitter 6. That is, the antenna 7 is connected to the input terminal 2 of the branch 6, and the output terminal 3 is connected to the next branch 6.
The output terminal 3 of the branching device 6 at the end is terminated with a terminating resistor 8. Then, a television receiver 9 may be connected to the branch terminal 4 of each branch 6.

Next, the operation of the conventional turnout 6 as an example will be explained with reference to FIG. As shown in Figure (a), the current 10 that flows in from the input terminal 2 is divided into a current 1 that flows out to the output terminal 3 and a current that flows out to the branch terminal 4. A current I3 is induced in the secondary winding lb according to the turns ratio of the wire lb and flows out to the branch terminal 4. Further, as shown in FIG. 2(b), the current I4 flowing from the dividing terminal 4 is the current I7 flowing to the secondary winding 1b, and the current I flowing to the input terminal 2.
5 and the current I6 flowing to the output terminal 3,
The current I7 flowing through the secondary winding lb causes the negative winding 1a to
A current I8 is generated in a direction that cancels out 16.

In this way, the power of the signal source connected to the input terminal 2 passes to the output terminal 3 with low loss, and passes to the branch terminal 4 with a loss of about I OdB to 20 dB. A part of the signal source power connected to branch terminal 4 passes to input terminal 2 with the same loss as the branch loss (passage loss from input terminal 2 to branch terminal 4), but almost no signal is transmitted to output terminal 3. . That is, a reverse coupling loss of 30 dB or more is provided.

This is to avoid mutual interference due to unnecessary radiation from TV receivers, and the intermediate frequency of older model receivers is 26.75MHz.
This is because there is a type z type and a lower hetero gain method is adopted, so in the high band, there is a possibility that local leakage voltage may cause interference to the upper channel of the four channels.

Therefore, in a conventional public listening system using such a splitter 6, it is not possible to transmit video signals or the like in both directions, so a system configuration as shown in FIG. 4 is often adopted. This figure shows a system in which a television camera 13 is installed at the entrance for example to monitor visitors or for crime prevention, and the image can be received by a television receiver 9 in each room. Branch terminal 4 from
Since the transmission loss leading to is large, from the television camera 13,
Another cable 10 is drawn and by the mixer II located between the antenna 7 and the nearest branch 6,
It is mixed with the on-air broadcast signal. 12 is a converter for converting the frequency of the camera signal to an available TV channel.

However, in such a system, separate cables (cable 10 shown in the figure) are used for downlink signals (signals in the direction from the antenna 7 to the television receiver 9) and upstream signals (signals in the direction from the television camera 13 etc. to the antenna 7). ), which has the major drawback of increasing wiring costs.

As another method, there is a method of bidirectionally transmitting upper and lower lines by frequency division using a single cable, but an example of the configuration of a branching device in this case will be explained with reference to FIG. That is, within each branching device 17, the upstream signal and the downstream signal are mixed and demultiplexed by the mixing/demultiplexing filter 14,
Conventional branching devices 6, 6 are provided separately for uplink and downlink, and the mixing and demultiplexing filter 14 performs mixing and demultiplexing again, which complicates the configuration of the branching device I7 itself, and also makes the system configuration difficult. , branch terminal 15 or I6 must be selected depending on whether to receive uplink signals or downlink signals, and when connecting a video source such as a camera, a converter compatible with uplink and downlink must be selected. A frequency must also be selected. Furthermore, at this time,
A suitable converter is also required on the receiver side.

<Background...2> By the way, as mentioned above, some older TV receivers had a video intermediate frequency of 26.75MHz, but now most TV receivers have a video intermediate frequency of 58.75MHz. For the HF band, I channel video carrier frequency -9], 25MHz local oscillation frequency -91, '25MH7 + 58.75MH2 = 150M
H2 3Ch scissor image carrier number = I O3, 25MHz local oscillation frequency = 10325MH2 + 5875MH2 = 162M
As in H2, the local oscillation frequency when receiving low channels falls to the mid-band (108MHz to 170MHz) where there is no broadcasting, and the 4ch video carrier frequency = 171.25MHz local oscillation frequency 2 171.25MH2 + 58.75MHz = 23
When receiving 0MHz high channel, 12ch (216M, H2
~222 MH2), so no interference due to local leakage voltage occurs. Regarding the UHF band, Q
Although there is a possibility that interference may occur in the band on a channel, channels that may cause interference are usually not used within the same service area. Furthermore, due to advances in technology, the performance of television receivers has improved, and unnecessary local emissions have been kept below the performance standards reported by the Radio Technology Council.
It is believed that performance will further improve in the future. In other words, reverse coupling loss is not necessarily required in the splitter.

<Purpose of the Invention> In view of the above points, the present invention uses a branching switch capable of two-way transmission with an extremely simple circuit configuration in the home, and is capable of transmitting not only on-air television broadcasts but also television cameras and
It is an object of the present invention to provide a comprehensive information transmission system for home use that can easily transmit video information such as TR in both directions.

<Embodiments> Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 6 to 10.

FIG. 6 shows an example of a circuit configuration of a branching switch used in the present invention. The input terminal 19 and the output terminal 20 are directly connected, and the input terminal 19 or the output terminal 20 is connected to one end of a matching high frequency transformer 23 via a resistor 22, and the other end of the transformer 23 is grounded. The tap is assumed to be a branch terminal 21. For convenience, the input terminal 19 and the output terminal 20 are described separately, but as is clear from the figure,
It is obvious that the two are equivalent due to the symmetry of the circuit, and that the reverse coupling loss and the branching loss are equal. Value R1 of resistor 22
The larger the matching transformer 23, the larger the branching loss.The matching transformer 23 is not necessarily necessary, and one end of the resistor 22 may be used as the branching terminal 21, but compared to a device with a matching transformer 23, the branching loss will be lower if the search loss is the same. If the branch loss is the same, the search loss will be large.

If the ratio of the total number of turns of the matching transformer 23 to the number of turns at the tap-ground side end is n-1, an optimal relationship exists between n and R1, and this relationship can be expressed as shown in FIG. 7(a). b). A signal source 25 with a signal source impedance 24 of ZS and voltage E is connected to the input terminal 19, and a load 26 of impedance ZL is connected to the output terminal 20 and branch terminal 21, respectively.
．． 27 and find the relationship between R1 and n such that the power consumed by the load 27 connected to the branch terminal 21 is maximized, that is, the branch loss is minimized. Matching transformer 2
3 is regarded as an ideal transformer, the impedance seen from the secondary side to the primary side load is n2ZL, and the same figure (b
) can be expressed by an equivalent circuit as shown in Since the composite impedance seen from the input terminal 19 to the load side is (n2+I)ZL+R1, the voltage yB generated across the load 27 is Z5+
(n2ZL+R1)Zt, /((n2+I)ZL+R
1) n2ZL＋R1n (Z3+ZL)ZLn2+(ZL+Z5)R1+ZL
Since the power consumed by the ZS load 27 is maximum when vB is maximum, when R1 is given, n to maximize VB
All you have to do is find the value of δn ((Zs+ZL)ZL
n2+ (Zt, +Zs) Rx+ZLZs) 2 ((Zs ten Zt,) ZLn 2+ (ZL+ZS) R1+ZLZS)
From the condition of 2=0, R1+ZLZS / (ZL+ZS) -n2ZL=
0 Normally, Z 5 = Z L = 75 (Ω), so the above formula is R1 + 37.5 75n2 = 0...
. . . f+), and when R1 and n have the relationship expressed by the formula f+), the branching loss is minimized for a given constant.

FIG. 8 shows an example of calculating search loss and branch loss for R1. However, n was selected so as to satisfy equation (1).

Next, another example of the turnout will be described in detail using FIG. 9. In this case, the input terminal 19 and the output terminal 20 are directly connected, the input terminal 9 or the output terminal 20 is connected to one end of the matching high frequency transformer 24, and the other end is grounded.
From the tap of the matching transformer 23, connect the resistor 22 (resistance value R2
) is connected to the branch terminal 21. When viewed from the branch terminal 21, the input terminal I9 and the output terminal 20 are symmetrical, and the coupling loss between the input terminal 19 and the branch terminal 21 and the coupling loss between the output terminal 20 and the branch terminal 21 have equal directionality. It is clear that there is no such thing.

By the way, the circuit shown in FIG. 9 is equivalent to the circuit shown in FIG. 6 when the resistor 22 is converted into the primary side of the matching transformer 23 and replaced.
When considered as an ideal transformer, R2=R1/n2...
・・・・・・・・・・・・・・・・・・－・・・ (2)
If so, Figures 6 and 9 are theoretically exactly the same. Therefore, from equations (+) and (2), the optimal relationship between R2 and n is R2+37.5/n 275 = O------・
・f3).

FIG. 10 shows an example of the configuration of a household comprehensive information transmission system using a branch 18 as shown in FIG. 6 or 9. Although this is a system in which lines are simply connected vertically using two coaxial cables 10, there is no problem if lines including vertical connections are connected in parallel from arbitrary points.

As shown in the figure, a branch i18 at an arbitrary point of the coaxial cable IO,
18. ...-, there are television receivers 9, 9 . ... ,
A VTR 35, a television camera 13, a personal computer 36, etc. are connected, and as already mentioned, a branch +8.18. ... has no direction, so VTR3
5. Images from the personal computer 36 or the television camera 13 are transmitted to any of the television receivers 9, 9. Needless to say, it is also possible to receive on-air broadcast programs. Television receiver 9,9. The video intermediate frequency is 58.75M
Hz.

Incidentally, in large-scale systems such as school broadcasting, a complicated branching device (for example, Fig. 5) is used to bidirectionally transmit upstream and downstream lines by frequency division, and television signals other than those on air are temporarily transferred to the head end (one receiving point and the broadcasting equipment). It is necessary to send the signal to the vTR3, etc.), amplify it with a head amplifier, etc., and send it back to the TV receiver in each classroom. However, at home, there is not much need for amplification, and the
5. From the television camera 13 or the personal computer 36, etc., to each television receiver 9, 9. It is fully possible to send video information directly to...

Note that in this embodiment, not only video information but also audio (
It is also possible to bidirectionally transmit information (intercom, audio, etc.) and digital signals as various control information, and it goes without saying that it can be easily expanded to form a comprehensive information transmission system.

<Effects of the Invention> As described above, the present invention uses a single coaxial cable for not only on-air broadcasting, but also for TV cameras and VT connected to the rear stage of a TV receiver or between multiple TV receivers.
This system allows video information such as R to be transmitted in both directions, and if you live in Sumiyo where there is an existing public listening line, no new construction is required, and the turnout, which is one of the components of the system, is extremely simple. To provide a useful comprehensive information transmission system for home use that can be realized with a simple circuit.

[Brief explanation of the drawing]

Figure 1 is a circuit configuration diagram of a conventional branch switch, Figure 2 is a configuration diagram of a public listening system according to the prior art, and Figures 3 (a) and (b).
85 is a diagram for explaining the operation of a conventional switch, and FIG. 4 is a configuration diagram of a public listening monitor system according to the prior art.
The figure is a circuit configuration diagram of a bidirectional branching device according to the prior art.
The figure is a circuit configuration diagram showing one embodiment of the turnout in the present invention, FIG. 7 is a diagram for explaining the optimum values of the constants in the turnout of FIG. 6, and FIG. FIG. 9 is a diagram showing an example of calculation of input loss and branch loss, and FIG.
FIG. 0 is a configuration diagram showing an example of the configuration of a home comprehensive information transmission system according to the present invention. 7... TV receiver, 8... terminating resistor, 9... television receiver, 10... coaxial cable, 12... converter, l i'iq6 rev camera, 18... branch,
19...Input terminal, 20...Output terminal, 21...
Branch terminal, 22...Resistor, 23...High frequency matching transformer, 35...VTR, 36 Personal computer. Agent Patent attorney Aihiko Fuku (2 others) Figure 5 P Figure 6 Figure 7 Figure 8 Figure 1 θ

Claims (1)

[Claims] 1. A plurality of branchers that do not have a reverse coupling loss in which the coupling loss between the input terminal and the branch terminal is equal to the coupling loss between the output terminal and the branch terminal, and connected 5 8
．． and a television receiver with a video intermediate frequency of 75 MHz, at least through the branch after the branch to which the television receiver is connected, or between the branch to which the television receiver is connected, TV camera. A comprehensive information transmission system for home use, characterized in that it is connected to one or more television signal generating devices other than a television receiver, such as a VTR and a personal computer.