CH626481A5 - Radio-frequency transmission system with a radiating cable - Google Patents

Description

626481

PATENT CLAIM High-frequency transmission system with a radiating cable (8) consisting of one or more sections for the bidirectional wireless transmission of information between at least one fixed station (3) and moving stations (2) moving along this cable, in which system a transmitter (30 ) feeds the cable at the beginning and a receiver (40) connected at the end receives the signals impinging on the cable, in which, if there is more than one section, between the end of a section and the beginning of the next one in the direction of The first amplifier (21) acting as a receiver and having a fundamentally fixed degree of amplification is arranged, characterized by in each case a hybrid circuit (22) assigned to the beginning and the end of each of the sections mentioned, with a line connection (25), a simulation corresponding to the input impedance of the relevant cable section (N) and a first (23) and a second (24) amplifier connection, the beginning or end of the cable cut (8) being connected to each of the line connection (25) and the first amplifier connection (23) in the hybrid circuit (22.12) at the beginning of the cable section (8.2) with the Output of the associated first amplifier (21.1) or the transmitter and in the hybrid circuit (22.21) at the end of the cable section (8.2) is connected to the input of the associated first amplifier (21.2) or the receiver and is characterized by one to each of the Sections of the radiating cable running in parallel, but spatially separated, having similar electrical properties, a section of a non-radiating cable (9), in the beginning of which a second (27) and in the end a third (26) in the direction from the beginning at the end effective amplifier with automatically adjustable degree of amplification is inserted, which section together with control amplifiers between the second amplifier connections (24) of the At the beginning and at the end of the section concerned, hybrid circuits (22) are connected, the second amplifier (27) having such a degree of amplification that the level of a pilot signal emitted by the transmitter is kept at a constant value, and the third Amplifier (26.2) has such a degree of amplification that in the hybrid circuit (22.21), to the second amplifier connection (24.21) of which its output leads, the level of the pilot signal at the first amplifier connection (23.21) is regulated to a constant value, all in such a way that the energy flow between the first amplifiers (21) in the trouble-free, well-balanced forks (22) operation predominantly via the sections (8) of the radiating cable and on the occasion of an interruption or short circuit (28) occurring in one of these sections as a result of the poorly balanced forks about the corresponding section (9) of the nich t-radiating cable runs.

The present invention relates to a radio-frequency transmission system with a radiating cable consisting of one or more sections for the two-way wireless transmission of information between at least one fixed station and moving stations moving along this cable. This system has a transmitter that feeds the cable at the beginning, and a receiver connected at the end receives the signals arriving on the cable. The devices referred to as “transmitters” and “receivers” can each be a plurality of transmitters and receivers that transmit and receive independently of one another on different frequencies. The transmission and reception frequencies are preferably selected at mutual intervals, which allow simultaneous transmission and reception. However, it is also possible to send and receive alternately on the same frequency.

In this system, if there is more than one section of the cable, between the end of one section and the beginning of the next a first amplifier acting in the direction from the transmitter to the receiver with a fundamentally fixed gain is arranged.

Systems of the type described are known, for example, from British Patent 1,371,291 for the radio coverage of tunnels and mines. Since with every radio connection the signals to be sent out from the transmitter to the mobile station and the signals to be received from this station run from the station to the receiver via the radiating cable, a malfunction, i.e. an interruption or a Short circuit of the cable on the route between the transmitter and the fault only from the transmitter to the moving station and on the route between the fault and the receiver only from the moving station to the receiver.

It is known to remedy this deficiency by arranging the radiating line together with the transmitter, receiver and amplifiers in such a way that the signals run on the cables in the opposite sense. Under these conditions, in a case in which both cables are disturbed at the same point, which can occur in particular in the event of a fire, the radio coverage of the movable stations is guaranteed at all points in the tunnel in both directions of traffic, but the effort for a double system is considerable because of the high cost of the radiating cables.

It has also already been proposed to lay a non-radiating coaxial cable in such a safe manner parallel to the radiating cable, but spatially separated from it, that an interruption or short circuit is unlikely there. According to this proposal, the non-radiating cable is divided into the same sections as the radiating cable, at the output of each amplifier or the transmitter the signal is fed to both cables in equal parts and at the end of each section there is a switching device, which in the case of a Fault switches the amplifier input from the radiating cable to the non-radiating cable. With such an arrangement, radio communication is guaranteed in the area of all sections preceding and following the disturbed section, but this is not the case within the disturbed section. This is particularly disadvantageous because it must be assumed that the disruption was caused by an accident and that, therefore, perfect radio connections would be most important at that point.

The present invention is now a further development of the latter proposal. With their help, even with the use of only a single radiating cable in the event of interference on this cable, it is possible to achieve perfect radio communication in both directions in the area of the interference. The invention is based on the fact that, on a hybrid circuit with a line connection, a simulation, a first and a second amplifier connection and a cable that is short-circuited or open at the end, the transition loss between the two amplifier connections increases with increasing length of the cable and vice versa . The invention makes it possible to dispense with changeover switches between radiating and non-radiating cables. It is characterized by the auf2 in the characterizing part of the patent claim

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led characteristics.

The invention will now be explained using an exemplary embodiment. Figure 1 shows the basic structure of a transmission system for radio communication between two fixed intercoms and vehicles in a tunnel.

FIG. 2 shows a detail of FIG. 1 with as much detail as is necessary to understand the invention.

Figures 3 and 4 show details of the equipment installed at the beginning and end of the tunnel.

FIG. 1 shows a main tunnel 1, in which vehicles 2 provided with radio systems run. The conversation with the vehicles is handled from the two microphone units 3. In a service tunnel 4 running parallel to the main tunnel, device groups 5, 6 and 7 are arranged, between which sections 8 of a radiating cable and sections 9 of a non-radiating coaxial cable are arranged. Sections 8 run in the main tunnel, sections 9 in the auxiliary tunnel, where they are assumed to be safe from all interruptions and short circuits caused by accidents. Two low-frequency lines 10 and 11, which also run in the auxiliary tunnel 4, connect the two microphone units 3 to the device groups 5 and 7 located at the ends. When traffic is in the direction from a fixed microphone unit to a mobile station 2, the modulation signal is transmitted from one of the microphone units 3 supplied directly or via the connection 10 to the device group 5, and the transmitter contained therein emits a transmission signal to the first section 8.1 of the radiating cable. This section ends at a device group 6.1, where the incoming signal is amplified by an amount corresponding to the attenuation of section 8.1 and is fed to the beginning of the next section 8.2. In this way, the radiating cable is provided with a sufficient level of the signal to be emitted over the entire length of the tunnel.

In the opposite direction, a signal emitted by a movable station 2 and incident on a section 8 of the radiating cable reaches the next device group 6, where it is amplified and fed to the next section 8. The signal, which is always amplified in this way, reaches the device group 7 at the end of the tunnel via section 8.4, where it is demodulated in the receiver contained therein and fed to the microphone units 3 directly or via line 11.

In addition to one or more signals used for voice transmission, the device group 5 preferably generates a pilot signal which can be used to regulate the degree of amplification in all amplifiers described later. A continuously transmitted signal, which also serves to transmit the call, can also be used as the pilot signal.

FIG. 2 now shows two device groups 6 (6.1 and 6.2) each containing a first amplifier 21 (21.1 and 21.2), between which a section 8.2 of the radiating and a section 9.2 of the non-radiating cable runs. Each of the groups contains two hybrid circuits 22 (22.11 and 22.12 or 22.21 and 22.22). Each of these hybrid circuits known from the two-wire amplifier technology used in telephony has a line connection 25, a first amplifier connection 23, a second amplifier connection 24 and a replica N, which simulates the input impedance of the cable section 8 connected to the line connection 25. By means of an attenuator (not shown) arranged between the two amplifier connections or by means of a simulation whose impedance deviates slightly from the impedance of the cable section 8, the transition attenuation is reduced compared to the ideal value to such an extent that the conditions explained later are fulfilled. With a fork, the transition loss also decreases as the length of a connected open or short-circuited cable piece decreases. The attenuation that occurs between the cable section 8 and the two amplifier connections is referred to below as continuous loss.

Section 9.2 of the non-radiating cable runs between the second amplifier connections 24.12 and 24.21. The beginning of the illustrated cable section 9.2 is connected via the second amplifier 27.1 to the second amplifier connection 24.12 of the hybrid circuit 22.12, while the end of this cable section is connected via the third amplifier 26.2 to the second amplifier connection 24.21 of the hybrid circuit 22.21. The second amplifier 27.1 is a control amplifier, the degree of amplification of which is regulated in such a way that the level of the pilot signal is at its output the same size as that which occurs at the line output 25.12 in the normal case described later. The third amplifier 26.2 is also a control amplifier. Its degree of amplification is regulated in such a way that the level of the pilot signal at the first amplifier connection 23.21 of the relevant hybrid circuit 22.21 is somewhat below the level occurring at this point in the normal case described later.

FIG. 3 shows the device group 5, which forms the beginning of the cable and therefore has, in addition to only a single hybrid circuit 22.0, the second amplifier 27.0 and, instead of the first amplifier, the transmitter 30. As previously mentioned briefly, this transmitter comprises the pilot transmitter and possibly several individual transmitters. In contrast, FIG. 4 shows the device group 7, which forms the end of the cable and therefore, in addition to only a single hybrid circuit 22.4, has the third amplifier 26.4 and, instead of the first amplifier, the receiver 40, which optionally comprises several individual receivers.

In the normal state, i.e. as long as section 8.2 of the radiating cable is in the correct state, the transition loss is greatest between the two amplifier connections of the hybrid circuits. A signal which strikes the device group 6.1 via the section 8.1 is then fed via the hybrid circuit 22.11, the first amplifier 21.1 and the hybrid circuit 22.12 to the cable section 8.2 and from there reaches the cable section 8.3 in the same way via the device group 6.2. Part of the signal also reaches the input of the first amplifier 21.2 via the second amplifier connection 24.12, the two amplifiers 27.1 and 26.2 and the hybrid circuit 22.21. Since the transition damping of the forks is large and the level at point 24.12 is low, the amplifier 27.1 is regulated to the highest possible amplification; the amplifier 26.2, on the other hand, is regulated to the smallest possible amplification because at point 23.21 there is a level exceeding the setpoint value intended for the regulation. It follows from this that the signal from point 23.12 to point 23.21 can be neglected in relation to the signal coming via the section of the radiating cable via the last-mentioned route.

The signal received by the mobile stations on section 8.2 reaches point 23.21 via line connection 25.21 and hybrid circuit 22.21 as well as via line connection 25.12, hybrid circuit 22.12, cable section 9.2 and hybrid circuit 22.21. However, in the worst case, the level caused by the first route is higher than the level caused by the second route, so that the second route is not disruptive.

If, for example in the middle of section 8.2, a short circuit or an interruption in the radiating cable occurs at point 28, the adjustment of the two deteriorates

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Fork circuits 22.12 and 22.21. The level of the pilot signal at point 24.12 increases accordingly, and the degree of amplification of the second amplifier 27.1 decreases. Since no more pilot signal is transmitted via section 8.2 after the first amplifier connection 23.21 of the hybrid circuit 22.21, the degree of amplification of the third amplifier 26.2 is increased to such an extent that at the first amplifier connection 23.21 there are approximately the same level relationships as if the pilot signal had arrived via section 8.2. The transmission of all types of signals from section 8.1 to section 8.3 is guaranteed despite a fault in section 8.2.

The section of section 8.2 running between the line connection 25.12 and the fault point 28 is still supplied with the transmission signal originating from the transmitter in the normal way, and the part transmitted by a mobile station and impinging on the section 8.2 between the fault point 28 and the line connection 25.21 Signals still reach the amplifier 21.2 in the normal way. Thanks to the effectiveness of the two amplifiers 27.1 and 26.2, the signals emanating from a mobile station that strike section 8.2 between the hybrid circuit 22.12 and the fault point 28 are now routed via the hybrid circuit 22.12 to the second amplifier 27.1, where they are amplified. fed to the third amplifier 26.2 via section 9.2 and amplified there again. Via the hybrid circuit 22.21 they reach the first amplifier 21.2, from where they are transmitted in the usual way. Another effect is that the level of the signals emitted by the transmitter, which is the same at the output of the second amplifier 27.1 as in normal operation, the signals at the line connection 25.12, is higher than due to the effect of the third amplifier 26.2 at the output of this amplifier the one occurring in normal operation at point 25.21. The level which is supplied to the part of section 8.2 running between the hybrid circuit 22.21 and the fault point 28 via the hybrid circuit 22.21 is so high that sufficient radiation is achieved over the entire length of this part.

It has been shown that the conditions described can be selected not only qualitatively, but also quantitatively, as described above, in such a way that there is sufficient radio coverage of the tunnel in all cases. The impedance measured at the input of a line that is short-circuited or open at its end is proportional to the hyperbolic tangent or cotangent of the damping of the power unit in question, and the transition loss of a hybrid circuit depends on the quotient of the sum and the difference in the impedances of the connected line and the simulation. There is therefore no linear relationship between transition damping and damping of a cable section running between the hybrid circuit and the fault location, but when the right boundary conditions are created for extreme cases, the deviations from the ideal course are within limits that are acceptable for practical operation. Under «extreme cases»

the two cases are understood in which the fault in a cable section occurs immediately at the beginning or at the end. The transition loss of a hybrid circuit in the case of an open or short-circuited line connection is 6 dB; the transmission loss between an amplifier connection and the line connection has the same value.

So that the conditions described can be met in extreme cases, every second and third amplifier must have a gain between zero and the sum of the attenuation of a cable section and the through loss of a fork. Under these conditions, in one extreme case, the attenuation of the radiating cable section and its feed via the hybrid circuit for transmission is compensated for by the highest possible amplification of the third amplifier, and in the other extreme case, the attenuation of the radiating cable and the signal curve via the fork by the highest possible amplification of the second amplifier balanced for reception. In practice, a length of the cable sections has proven to be suitable, the attenuation of which is 20 dB, so that under these conditions the amplifiers must have an amplification level between zero and 26 dB. It also follows that in extreme cases the transition attenuation of the hybrid circuits must change by the same amount as the change in gain, thus between 6 and 32 dB. While the lower value inevitably results, the upper value can be set arbitrarily to a certain extent by measures described earlier. In the event of faults in a cable section which occur between the two extreme positions, intermediate values result for transition attenuation and degrees of reinforcement, which as an overall result do not create ideal conditions, but they are easily usable in practice.

The first amplifiers 21, which have not been mentioned up to now, basically have a fixed gain, which corresponds to the sum of the attenuation of a cable section and the double pass attenuation of a hybrid circuit. However, these amplifiers are preferably also designed to be controllable to a small extent, the regulation being dimensioned such that the pilot signal at the output of the amplifiers is kept at a constant value. This not only compensates for differences in the cable attenuation caused by temperature differences, but also minor discrepancies which can result from the signal diversion that occurs as a result of a disturbance and previously described.

Since not only the first, but also the second and third amplifiers are in continuous operation and transmit the pilot signal, all amplifiers can be continuously monitored by suitable measures.

Provided that the signal arriving at the undisturbed radiating cable via the non-radiating cable, which is superimposed on each section of the radiating cable on the signal that has reached the relevant section in the normal way, disturbs circuit means, not shown, can be provided, which in the normal state the way fails over the non-radiating cable.

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1 sheet of drawings