FR2767006A1 - Telecommunications network for CATV distribution networks - Google Patents

Abstract

The network includes a directional coupler (1) which has four terminals. If the coupler is used on its own, a signal input (6) applied to terminal a is divided between the other terminals b, c & d in the ratio 90% : 10% : 0%.When the two switches (S1,S2) are in the normal position, 90% of the signal is fed to the user (b) and 10% is fed back (V). The switches are operated to accomplishes three other connection situations. Both outputs are disconnected, the user output is blocked but the return signal is connected or the user signal is connected and the return signal is disconnected. (Dwg.5/7)

Description

The present invention relates to a telecommunications network which

  comprises a number of interconnected signal distributors / collectors, each of these distributors / collectors comprising a directional coupler comprising at least four two-pole terminals, in which the first terminal of one of the signal distributors / collectors is connected to a common signal input line, the second terminal of each signal distributor / collector is connected to the first terminal of an adjacent signal distributor / collector, the third terminal of each signal distributor / collector can be connected to a station user, and the fourth terminal of each signal distributor / collector is connected to a signal output line, which signal distributors / collectors are each arranged to distribute the signals received from the signal input line to user stations in a predetermined manner, and so as to essentially collect the user signals reader, coming from user stations, sent to the signal output line, the network being characterized according to the invention in that each of the signal distributors / collectors comprises means for allowing the distribution of the signals received towards the user stations and collecting user signals on the signal output line independently of each other. In a first embodiment, said means are arranged so as to interrupt the connection between the signal input line and the user station, and also to connect the user station

at the signal output line.

  For the distribution of signals as they are used in practice in local area networks of a telecommunications network, such as a replay device or a cable television network, the signals coming from a place, such as community center, are distributed to a large number of users using signal distribution elements, which term is understood to mean both regular and non-regular distribution elements. This distribution gives the network

local a star structure.

  On the other hand, additional signal distribution is usually carried out in the path of the signal from the community center towards users in the local networks of existing cable television networks, using one or more distributors, to which a small number or a few dozen users are directly connected

by means of cables.

  Radio and television receivers which are connected to the local network at the end of the users usually have the disadvantage that they produce unwanted signals which are perceptible on the "antenna socket" of said receivers. It is precisely via said antenna sockets that said receivers are connected to the network, so that it becomes possible that said signals, as well as all kinds of other undesirable signals which have been generated at the end of the users, are returned to the cable television network. These signals

  in return undesirable which are so produced do not constitute in themselves-

  same a problem as long as these signals are prevented from being transferred to other users. Consequently, the distributors which are used for the distribution of a signal to the users must be designed in such a way that they cannot transfer any return signals which may occur originating from the connection of a user or said return signals. arrive at any other user station. This desired characteristic of signal distributors is indicated by the term decoupling or isolation between user stations. As far as said insulation is concerned, the technical requirements generally imply that the voltage which is transferred must not exceed a specified value, which, depending on the applicable rules, can amount to approximately 1% of the voltage (approximately 40dB) of the return signal which

  initially arrived at the distributor level.

  To this end, the distributors are designed to include one or more couplers called "directional couplers". In principle, such a directional coupler comprises four terminals with two poles. In principle each of said terminals can function as a signal input, in which the input signal is distributed over two of the three terminals

  remaining, the fourth terminal in theory not receiving a signal at all.

  For a clear understanding of this matter, it is possible to represent the terminals of such a directional coupler as constituting the four points of angles of a square, and that a signal which is delivered to any one of the four terminals is distributed to the two terminals adjacent to said terminal (above and below), and not at all to the terminal positioned

  in the diagonal opposite to said terminal.

  A directional coupler can be frequency dependent or frequency independent. A frequency dependent directional coupler may for example include a number of conductors which are interconnected both inductively and capacitively. The expected signal attenuations can be adjusted by varying the distance between the conductors. A directional coupler independent of the frequency consists for example of transformers in which the

  transformation ratios determine the signal attenuations.

  The aforementioned directional couplers make it possible to build multi-distributors which meet the requirements of

  distribution and insulation that are made.

  In recent years there has been a need in cable television networks to provide the possibility of deliberately processing generated signals, also known as desired return signals or user signals, in addition to distribution signals which are intended for users. In this regard, the signals corresponding to the originally planned distribution (for example an interactive television and radio and the like), but also signals which are entirely independent of said distribution, for example safety signals and the like, can be considered. The known signal distributors mentioned above are passive distributors. A feature of passive distributors is the fact that they are able not only to distribute signals from a signal input line, but also to collect signals from a few user stations towards an output line signal. When collecting a signal, a loss appears, which loss of signal is equal to the loss of signal which takes place in the above distribution; in other words, signal distributors can function as collectors of

signal to an equal degree.

  It should be noted that, in theory, the same frequencies can be used for the desired return signals and for the distribution signals. However, for technical reasons, this is not possible and the repetition of the frequencies used should be avoided when choosing frequencies for distribution signals and desired return signals, so as to prevent harmful interference. . An appropriate selection is, for example, from 5 to 50 MHz for user signals or return signals, and 50 to 1000 MHz for reception signals or

distribution signals.

  The invention will be explained in more detail below with reference to the drawings in which: Figure 1 schematically shows a known directional coupler; Figure 2 schematically shows a number of interconnected signal distributors, each distributor comprising a directional coupler according to Figure 1; Figure 3 shows schematically a variant of Figure 2 which further comprises a signal output line; Figure 4 shows schematically one of the signal distributors of Figure 2, which is provided with a switching means .; Figure 5 schematically shows one of the signal distributors / collectors from a variant according to Figure 3, which is according to the invention provided with switching means; and Figures 6 and 7 schematically show two alternative embodiments of a signal distributor / collector according to the invention. Figure 1 shows a signal distributor in the form of a

  directional coupler. By way of example, this description will be based

  on a signal distribution (power) ratio of 10% / 90%, at what

  end we suppose that we use non dissipative directional couplers.

  When a signal is delivered to terminal a, 10% of this signal will become available at terminal c, 90% will be available at terminal b and 0% at terminal d. In practice, we will prefer to carry out a signal distribution

  varying from 5% to 10% / 95% to 90%.

  Figure 2 shows a set of some directional couplers 1 - 5 for a multidistributor. The letter u indicates the terminal of the supply system of the assembly, and the letters v, w, x, yet z are the terminals to which the user stations are connected. The signal to be distributed is delivered on the signal input line 6 (as in the example above, a power distribution ratio of 10% / 90% is used for this example as well. ). Terminal la receives 100%,% then becomes available on terminal lc, 90% on terminal lb and 0% on terminal ld. The 10% of LC is transported to the exit of user v. The% of lb are delivered to terminal 2a. 9% become available at terminal 2c (10% of 90%), 81% ((90%) 2) become available at terminal 2b and 0% at terminal 2d. The 9% of 2c is delivered to user station w. Said 81% is issued at terminal 3a, etc. The special operation becomes apparent only with return signals, for example in the case of the delivery of signals (desired and unwanted) from a user, for example for user station x. 100% of said signal is delivered to 3c, 10% then becomes available on 3a, 90% becomes available on 3d and 0% on 3b. As a result, no signal becomes available on 3b, nor on 4a. Posts

  users y and z are thus protected against signals from x.

  The 90% of 3d ends in the resistor (R3 in Figure 2) which is connected to it. The 10% from 3a is issued to 2b. 1%. ((10%) 2) become available at terminal 2d, 0% at terminal 2c. No signal becomes available on 2c, any more than on w and, similarly, no more on v. The 9% of 2a is delivered to lb, they eventually become

  available on the, and thus on u, with a rate of 8.1% ((90%) 2 x 10%).

  In summary, the known signal distributor / collector performs the expected operation: 1. The received signal which has been delivered to the signal input line is distributed to user stations with attenuations up to 10%, 9%, 8.1%, 7.3%, etc .; 2. The user signals which have been delivered by the user stations are collected at the signal input line with attenuations ranging from 10%, 9%, 8.1%, 7.3%, etc .; 3. User signals from one of the stations

  users cannot reach other user workstations.

  A variant is shown in the arrangement according to FIG. 3. This embodiment makes use of the situation that 90% of the return signals become available on the terminals of directional couplers 1, 2, etc., where they are then connected. to earth via resistors R1, R2, etc. (according to figure 2). Preferably, the resistors R1 to R5 each have a resistance value of substantially 75Q. An alternative path for the return signals is created when said resistors (in accordance with FIG. 3) are not connected to the earth, but to a signal output line 7, and, via said signal output line, to the terminal 1. Since it was already necessary, for various reasons, to select different frequencies for the distribution signals and the desired return signals, it is now possible to use this situation and to combine the terminals q and u outside the multidistributor using selective means, such as those called duplex filter, which will contribute to flexible use of the distributor. The resistance values of resistors R6 to R10 are

  preferably adapted so that the terminals ld to 5d "see" 75Q.

  The signal processing described above is complicated by the fact that the signals used in a cable television network have relatively high frequencies (approximately between 5 and 1000 MHz) and by the fact that the directional couplers and other components have to be used are actually not ideal. First, with signals having the frequencies above, measures must be taken to ensure that the impedance of the signal paths is everywhere the same, so as to prevent the production of points where the signals in question could to be reflected. These measurements are called impedance match (or in the opposite case, impedance deviation). In the case of television by

  cable, the desired impedance is usually 75Q.

  Furthermore, it appeared that it was useful in the technical and commercial operation of a cable television network, to configure the last distributor described above so that the signals distributed can be interrupted or admitted at will by each individual user connected (see Figure 4). This useful aspect of technical and commercial exploitation is even increased when the said possibility of interrupting / admitting the signals for each individual user connected, is also used for the return signals to be

collected (see Figure 5).

  It appears in the sense that it is essential that the cutoff required for such interruptions is itself sufficiently effective, in the sense that it is avoided that the undesirable capacitive and inductive coupling which easily occurs at very high frequencies, and which can thus cause the transfer of cut-off signals to be avoided; this desired cutoff characteristic is indicated by the term insulation. As far as this isolation is concerned, it is generally technically required that the voltage to be transferred does not exceed a specific value, which in practice corresponds to approximately 0.1 to 1% of the voltage of the original signal (- 60 to - 40 dB). This insulation can be achieved with some difficulty

  when using the high frequencies in question.

  The proper impedance matching sought for signal paths also becomes extremely complicated during cutoff, since the interrupted signal path usually should not be left open or discharged. Depending on the circumstances, one or both ends of the signal path which have been opened as a result of said cut-off must be connected to earth by a resistor of 75f2, which, among other things, requires the use of switches which are

  configured as swap switches.

  Possible signal interruption will be explained below in

  referring to Figures 4 and 5.

  Note that swap switches are used in the examples below. Contact e is referred to as "break contact" here, and contact f is referred to as "establishment contact". The contact that switches from 1 to 2 (and vice versa) is called "break-in-and-out contact". For easy reference, switch S1 is called "distributor switch"

  and the contact S2 is called "collector switch" in the examples below

  below. Figure 4 shows part of the assembly of Figure 2. The connection from terminal lc to user V passes through the distributor switch S1. This switch has two positions. In position e (as shown) the user station v is connected to the

  terminal lc via the set-and-break contact and the break contact.

  The switch is configured so that in position f (not shown), all feedback signals from the user are connected to ground via the set-and-break contact and the set contact via resistance R11. The value of the two resistors

R11 and R12 is 75M.

  FIG. 5 shows part of the assembly of FIG. 3.

  Also in this example, the connection from terminal lc to user station v goes through the break-in and break-out contact and the break contact of the distributor switch S1, as well as via terminal ld and the resistor R11. The connection to the signal output line 6 passes through the collector switch S2. This switch has two positions in the same way. In position e (as shown) the signal from the resistor R13 is connected to the signal output line 7 via the break contact and the set-and-break contact. In position f (not shown), the signal output line is connected to earth by means of the establishment-and-break contact and the establishment contact, via resistor R13. The resistance values are preferably chosen as follows: RU = 75 1, R13 = 270Q, R14 = 100Q,

R15 = 220.

  In this embodiment, the distributed signals can be interrupted at the same time as the collected signals, by means of the distributor switch S1. In addition, the collected signals can be interrupted separately by means of the collector switch S2. It is however not possible to interrupt the distribution signals and

  simultaneously admitting the collection signals.

  In connection with the return signals which may be desired in a cable television network, which return signals are totally unrelated to distribution, it may be important to be able to accommodate the return signals also when the return signals

distribution are interrupted.

  It is for example conceivable that, if the cable television network offers the service "supply of radio and television signals" as well as the service "electronic security", these services must be offered independently of each other ( marketing should not be conditional), while it should be possible to interrupt and admit signals independently of each other. The network of

  telecommunications according to the invention makes this possible.

  The invention will be explained in more detail below by making

reference to Figures 5 and 6.

  Since the break contact of the switch Si1 in the arrangement according to Figure 5 inevitably cuts the user signals at the same time as the received signals, it will be necessary, in this situation, to open a new signal path for the signals users in order to carry out the invention. In position f of the distributor switch, the user station v is connected to earth by means of the establishment contact and the establishment and break contact. In position f of the commutator switch S2, the connection 1 is connected to earth, through the signal output line, by means of the establishment and break contact and the establishment contact via the

resistance R13.

  According to the invention, in FIG. 6, the establishment contact of the distributor switch S1 and the establishment contact of the collector switch S2 are no longer (only) connected to earth

  via resistors, but also via resistor R17, with each other.

  In this way, the signal path to the signal output line is made available for user signals from the user station v in the position f of the distributor switch S1, as well as when the collector switch S2 is placed in the position f .

  R16 = 100 and R17 = 220Q are preferably chosen.

  It should be noted that the different diagrams (Figures 6, 7 and 8) only show the principles which can be further developed in practice. For example, one can substitute for resistors Rll-R17 a more complicated network of resistors or filtering circuits in order to obtain the optimum insulation, the agreement of the impedance and the consistency of the

signal level.

  The table below gives an overview of the various switching possibilities. Position of the circuit breakers Signal path conditions S1 S2 distributed signal return signal 1 1 admitted admitted 2 1 interrupted interrupted 2 2 interrupted admitted 1 2 admitted interrupted By configuring the distributor switch S1 and / or the collector switch S2 as a switch double pole permutation, insulation properties and impedance matching

  can be improved. This is shown in Figure 7.

  In the technical and commercial operation of a cable television network, it is useful to be able to control the interruption of the signal and thus, the connection and disconnection remotely from a central position. For this purpose, the switches must be configured as relays. In order to obtain a minimum electricity consumption, it is

  on the other hand useful to configure the relays as a pulse relay.

  A data communication system in which the availability of telecommunication networks can be used is greatly

  useful for controlling the above relays.

  It will appear that a large number of variants of the illustrated embodiment are conceivable without departing from the scope of the present invention.

Claims (11)

  1. Telecommunication network comprising a certain number of signal distributors / collectors (1, 2, 3, 4, ...) which are interconnected, which distributors / collectors each comprise a directional coupler comprising at least four terminals (a, b , c, d) two-pole, in which the first terminal (a) of one of the signal distributors / collectors is connected to a common signal input line (6), the second terminal (b) of each signal distributor / collector is connected to the first terminal (a) of an adjacent signal distributor / collector, the third terminal (c) of each signal distributor / collector can be connected to a user station (v, w, x , y, ...), and the fourth terminal (d) of each signal distributor / collector is connected to a signal output line (7), which signal distributors / collectors are each arranged to distribute signals reception from the signal input line (6) to the user stations in a predetermined manner and for essentially collecting the user signals from the user stations on the signal output line (7), said network being characterized in that each signal distributor / collector comprises means (S1, S2, R17) for allowing the distribution of the signals received to the user stations and the collection of the signals from the users on the signal output line independently of each other. 2. Telecommunication network according to claim 1, in which said means are arranged so as to interrupt the connection between the signal input line and the user station, and also so   to connect the user station to the signal output line.   3. Telecommunication network according to claim 1, in   which said means are switching means (S1, S2).   4. Telecommunication network according to claim 3, in which said switching means comprise a first switch (SI) which can be switched between a first position, in which said first switch connects the user station to the signal input line, and a second position in which said first   switch (S) connects the user station to the signal output line.   5. Telecommunication network according to claim 4, in which said switching means comprise a second switch (S2) which can be switched between a first position, in which said second switch (S2) connects the directional coupler to the output line of the signal, and a second position in which said second switch connects   the signal output line at the user station.   6. Telecommunication network according to claim 5, in which said means further comprise a resistor network, which is incorporated in the link between the user station and the signal output line, and which connects said first and said second switch (If,   S2) in the second position of said switches.   7. Telecommunication network according to claim 3, in   which said switching means comprise relays.   8. Telecommunication network according to claim 7, in   which said relays are pulse relays.   9. Telecommunication network according to claim 3, in which said switching means comprise switches double pole permutation.   10. Telecommunication network according to any one of   previous claims, wherein one or more of said   signal distributors / collectors are arranged so that substantially 95% of a signal on the first terminal is available on the second terminal, and substantially 10 to 5% of said signal is available on the third terminal, while substantially 0% of said signal   is available on the fourth terminal.   11. Signal distributor / collector as described in one   any of the preceding claims for use in a network of   telecommunication as described in any one of the claims previous.