GB1575346A - Communications transmission links including intermediate amplifiers - Google Patents

Abstract

In remotely fed repeaters, blocking capacitors are provided between the reference potential and the outer conductor connection. In repeaters of this type, a maximum open loop loss is intended to be achieved with low signal power attenuation. For this purpose, the invention provides for a division of the amplifier into at least two sub-amplifiers (11, 12), each with its own capacitor (33, 34) disposed between the reference potential and the outer conductor connection, the feed voltage inputs (o, +) of the sub-amplifiers being RF-decoupled from one another via inductors (53, 54). In addition, a filter circuit can be provided between two consecutive sub-amplifiers as a multi-gate circuit (5). A repeater according to the invention is particularly suitable for coaxial data transmission paths. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO COMMUNICATIONS TRANSMISSION LINKS INCLUDING INTERMEDlATE AMPLIFIERS (71) We. SIEMENS AKTIENGESELLSCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to communications transmission links including remote-fed intermediate amplifiers of the type that are arranged between an input-end line and an output-end line and connected to one another via an outer conductor connection, wherein the outer conductor connection and a feed voltage terminal which simultaneously possesses an a.c. voltage reference potential are capacitively connected.One intermediate amplifier of this type is described in the German Patent Specification No. 1,940.517.

In amplifier stations or wide-band transmission systems. for example carrier frequency line amplifiers. w hitch are in series and remotely supplied with d.c. via the inner conductors of the coaxial cables employed therein. the amplifier reference potentials carry the d.c.

potential of the cable inner conductors and therefore cannot be directly connected to the cable outer conductors. Therefore generally speaking a housing is provided to which the earthed outer conductors of the coaxial cables are connected. Between the amplifier reference potential and the housing it is necessary to provide an a.c. connection that is of low impedance in the frequency range of the transmission band. which connection is established by a blocking capacitor.

Fiilrre 1 illustrates a known principle for a simple branching circuit with a remotepowered intermediate amplifier. using d.c. remote supply. The supply d.c. which flows via the inner conductors of a coaxial cable formed bv sections 21 and 22 is caused to circulate around the remote-fed amplifier 1 via chokes 51. 52 and is used to produce the supply voltage U. The base X of the chokes is therefore connected to zero potential for a.c.. and therefore with this type of remote supply it is connected via a capacitor 3 to the outer conductor Y of the coaxial cable.This capacitor 3 must exhibit a dielectric strength of several kV. for example. as a considerable voltage difference can occur between an inner conductor and an outer conductor of a cable. and this capacitor must be able to withstand excess voltages due to thonderstorms.

The construction of such hih-voltage capacitors involves various problems. On account of the high voltage rating. it must possess specific minimum dimensions. which in turn lead to a self-inductance which is not inconsiderable at high frequencies. and to parallel resonances at specific frequencies. An a.c. current i,, flowing in the output circuit must flow across the capacitor 3. where it gives rise to a voltage drop U(. if the impedance of the capacitor 3 is no longer negligible. This voltage in turn produces a current iE in the input circuit. thus giving rise to a reaction from the output to the input. This can lead to instability. or at least to alterations in the frequency response of the amplifier 1.

Therefore. for example by means of a special design of the capacitor 3. measures must be taken in order to achieve a sufficiently high circulating attenuation. i.e. a sufficiently low feedback from output to input. A capacitor which is specifically designed for this purpose has been described in the German Patent Specification No. l,94().517.

When. in order to compensate the amplifier field attenuation. the amplifier 3 must exhibit a particularly high degree of amplification in a specific frequency range close to the upper band limit. it can occur that the requisite circulating attenuation can no longer be achieved. even when a special capacitor is used. Neither is it readily possible to connect a plurality of identical or of different capacitors in parallel, as parallel resonances can again occur since at a specific frequency, certain elements will behave inductively whereas others still behave capacitively, so that the desired effect is in fact reversed.

It is also possible to provide, in the d.c. supply path, a voltage transformer whose output is electrically isolated from the input, so that the reference potential of the intermediate amplifier can be directly connected to the cable outer conductor, and obviates the need for a capacitor in this connection (compare the German Patent Specification No. 2,355,014). In this case a special current supply device is required for every intermediate amplifier.

However, apart from the questions of component outlay and reliability, a current supply device of this type has the disadvantage that its efficiency is limited, which means that supply energy is lost and the equipment is subjected to additional heating.

One object of the present invention is to achieve the desired high circulating attenuation in remotely supplied intermediate amplifiers having blocking capacitors provided between a reference potential connection and an outer conductor connection.

The invention consists in a cornmunication transmission link including a remote-powered intermediate amplifier which is arranged between two sections of a coaxial cable having a common outer conductor connection, wherein said amplifier is divided into at least two sub-amplifiers, wherein the power supplies for said sub-amplifiers are derived from the inner conductor of the coaxial cable and are mutally decoupled for high-frequencies, and wherein an individual capacitor is connected between one power supply terminal of each of said sub-amplifiers and the common outer conductor connection. Advantageously, the capacitors consist of low-inductance capacitors having a high resonance frequency. The intermediate amplifier is preferably a HF-amplifier or a LF-amplifier of wide band-width, or a regenerative amplifier or regenerator of a PCM-system.

These measures advantageously serve to achieve a high circulating attenuation with a low signal power attenuation.

Preferably, the intermediate amplifier has at least one line choke provided to connect two consecutive sub-amplifiers, and that one of the two sub-amplifiers is supplied with reference potential via the line chokes arranged in the high frequency signal transmission path, and is supplied with the other potential of the supply voltage via an inductance. The line choke, which connects the output of one sub-amplifier to the input of a following sub-amplifier, advantageously acts as an HF-choke for currents of like direction.

A filter circuit can be provided which is designed as two-gate circuit, and which consists of a line choke or a coaxial choke. Since the length of coaxial cable is limited due to losses at high frequencies. the filter action which can be achieved in this case is limited.

Advantageously the circulating attenuation of the intermediate amplifier can be further increased by providing that at least in the case of a connection between two consecutive sub-amplifiers, a filter circuit is provided which is designed as multi-gate circuit, and which in addition to the two gates arranged in the communications transmission path, possesses at least one further gate, one side of which leads to the outer conductor connection of the intermediate amplifier.

These measures advantageously provide an intermediate amplifier having a particularly high circulating attenuation, wherein the blocking capacitors of the sub-amplifier can be designed without regard to the desired circulating attenuation, apart from the requirements relating to the useful signal transmission.

The invention will now be described with reference to Figures 2 to 12 of the drawings, in which: Figure 1, as stated in the introduction, illustrates a known simple branching circuit for a remote-supplied intermediate amplifier; Figure 2 illustrates an intermediate amplifier assembled from two sub-amplifiers; Figure 3 illustrates details of a line choke; Figure 4 is an equivalent circuit diagram of the line choke shown in Figure 3; Figure 5 illustrates an intermediate amplifier assembled from two sub-amplifiers, with short-circuited lines in the current supply branch circuits; Figure 6 illustrates constructional details of an intermediate amplifier in which the sub-assemblies are accommodated in chambers; Figure 7illustrates an intermediate amplifier in which two sub-amplifiers are connected in series in respect of their current supply; ; Figure 8 illustrates a remote-fed intermediate amplifier with a filter circuit between two sub-amplifiers; Figure 9 is a fundamental theoretical circuit diagram of the intermediate amplifier shown in Figure 8.

Figure 10 illustrates details of a multi-gate circuit with a transformer, whose windings are each connected in parallel with one gate arranged in a communications transmission path; Figure 11 illustrates a multi-gate circuit with a transformer, whose windings are each arranged in a series arm of the communications transmission path; Figure 12 is another fundamental circuit diagram of the intermediate amplifier; and Figures 13 and 14 show two further filter designs.

Figure 2 shows an intermediate amplifier or wide-band amplifier for coaxial communications transmission links, which contains two sub-amplifiers 11 and 12. The intermediate amplifier is remote-supplied via the incoming coaxial cable 21 and outgoing coaxial cable 22, to form part of a d.c. series supply path. Whilst the outer conductors of the cables 21 and 22 are directly connected to one another, the inner conductors are each connected to a current supply branching component which separates the communications transmission band, which does not extend to zero frequency, from the supply d.c. The inner conductor of the cable 21 here leads across a shunt arm choke 51 to the terminal C of the supply voltage input of the sub-amplifier 11. The other amplifier supply terminal "+" is connected via a choke 52 to the inner conductor of the outgoing coaxial cable 22.

In the sub-amplifiers 11 and 12, on the one hand the supply voltage terminals C and D, which are connected with amplifier earth or the reference potential 0, are connected to one another via a series choke 53, and on the other hand the respective supply voltage terminals "+" are connected to one another via the inductance or choke 54, so that the supply voltage inputs are connected in parallel with respect to d.c.

The choke 54 can be replaced by a choke of a type not illustrated in the Figure, which is arranged between Zener diode 4 and choke 52, so that the feed voltage terminal "+" of the sub-amplifier 12 is then connected to the connection point between this choke and the choke 52. Furthermore, in a modification of the exemplary embodiment schematically illustrated in Figure 2, the sub-amplifier 12 can be directly supplied and the sub-amplifier 11 can be fed via chokes.

The supply d.c. which flows across the cable inner conductors produces a voltage drop, namely the supply d.c. voltage across the parallel arrangement of the load resistors, which have not been illustrated in the Figure, but which act upon the feed inputs, and which are formed by the sub-amplifiers. The Zener diode 4, which is arranged in parallel with the supply inputs of the sub-amplifier 11, is not vital, and expediently exhibits a Zener voltage which is somewhat higher than the supply d.c. voltage, so that normally it does not conduct current, but merely has a voltage-limiting effect. However, it can also serve as a voltage source by producing a constant d.c voltage from the supply current.

The supply terminal C of the sub-amplifier 11 is connected via a capacitor 33 to a connection y linking the cable outer conductors, in order to close the input circuit with respect to a.c. signals. The supply input D of the sub-amplifier 12 is connected via a capacitor 34 to the cable outer conductor connection y, in order to close the output circuit with respect to u. c. signals.

The inner conductor of the incoming coaxial cable 21 leads across the capacitor 31 to the input of the sub-amplifier 11. The output of the sub-amplifier 12 is connected via a capacitor 32 to the inner conductor of the outgoing coaxial 22. Furthermore, the output A of the sub-amplifier 11 is directly connected to the input B of the sub-amplifier 12. The input impedance and output impedances of the sub-amplifiers 11 and 12 possess a value Z, and thus are connected to one pole to the reference potential 0 at least with respect to a.c.

signals.

A current iA in the output circuit flows through the capacitor 34, and produces a voltage UC 2 across this capacitor. This voltage itself gives rise to a current ix which flows across the capacitor 33 and produces a current iE in the input circuit. However, the voltage Uc2 is not connected in full to the capacitor 33. but is connected via a voltage divider which is formed by the capacitor 33, the input impedance of the sub-amplifier 12, and the output impedance of the sub-amplifier 11. As a result the circulating attenuation is considerably increased.

The circulating attenuation can be further increased by designing the high-pass path or signal path between the sub-amplifiers 11 and 12 as a line choke. details of which are shown in Figure 3. The line choke consists in particular of a coaxial cable onto which ferrite rings have been placed. Apart from parasitic effects, the line chokes produce no attenuation of the transmission path. The equivalent circuit diagram of such a choke is shown in Figure 4.

The line chokes possess like-directed windings. so the signal current which is to be transmitted produces oppositely directed magnetic fields, which mutually cancel out in the two windings. For like-directed currents B-A or D-C, the arrangement acts as an HF-choke.

Via the outer conductor. the line choke establishes the connection between the terminals C and D, so that in this case the choke 53 can be dispensed with.

The other requisite inductances are preferably achieved with ferrite rings or ferrite beads.

In the case of a very wide-band transmission. it can be favourable to emply coaxial lines or stub lines which are short-circuited at the output end. in place of lumped inductances and chokes. An embodiment of this type is illustrated in Figure 5. Stub lines of appropriate length have been used, which posses a p/4-resonance, which in particular is located at or above the upper cut-off frequency of the system in which the intermediate amplifier is being used. Stub lines of this type likewise basically represent inductances at low frequencies.

Stub lines 510 and 520 replace the chokes 51 and 52 of Figure 2. A parallel stub line 540 replaces the choke 54, and can itself be replaced by a series stub line 540', as shown by a broken-line connection. The line choke 55, which is located in the HF-signal transmission path between the sub-amplifiers 11 and 12, connects the supply terminals C and D.

In a structural design particular attention should be paid to avoiding direct couplings between the input and output. An earth connection between the sub-amplifiers 11 and 12 can only be allowed to take place via the connection Y of the cable outer conductors.

In the exemplary embodiment schematically illustrated in Figure 6, this is achieved in a particularly advantageous manner by arranging the sub-amplifiers 11 and 12 in separate chambers, which are themselves decoupled from one another by virtue of an insulated arrangement supporting them in respective further chambers. In this case adequate high voltage strength between the cable outer conductor connection Y and the inner chamber walls Xl and X2 should be ensured.

In the intermediate amplifier illustrated in Figure 6, in which the sub-amplifiers are arranged in a chamber system, to provide a decoupling of the high voltage capacitors, an outer chamber is provided which, as overall screen of the line amplifier, is connected to the outer conductors of the incoming and outgoing coaxial cable 21 and 22, and establishes the cable outer conductor connection. This outer chamber is divided into two outer sub-chambers by a partition. Each of these outer sub-chambers contains an inner chamber which is insulated from the outer chamber to give high dielectric strength. The one inner sub-chamber contains the sub-amplifier 11, and the other contains the sub-amplifier 12.

The arrangement has the further advantage that the capacitances or capacitors 33 and 34 can be formed at least in part by the capacitances between the chamber walls and bases of the internested chambers.

The inductance 53 of Figure 2 or the line 540' of Figure 5 and 6 can be arranged in the one and/or of the other inner chambers and/or also between the chambers. Ducts a and c for the line, which is choked by the stub line 540', and must pass through the inner chamber walls, must in this case be sufficiently low in capacitance at least in respect of the inner chamber wall in which this stub line or choke is arranged. whereas each duct through the outer chamber partition wall is to exhibit a high capacitance for decoupling, and preferably takes the form of a lead-through capacitor of high dielectric strength.

In the case of the construction, illustrated in Figure 5 and 6, where the chokes of Figure 2 are replaced by short-circuited lines, if coaxial lines are employed it should be ensured that the inner conductor and outer conductor of each stub line are connected on the correct side.

For example in the case of the line 540', the outer conductor cannot be allowed to be connected to the line which leads through the inner chamber wall a, as the outer conductor exhibits a relatively high stray capacitance relative to the inner chamber X2 which would shunt the stub line 540'.

If no line choke 55 is provided in the illustrated example, the earth connection C-D is likewise choked and the connection A-B is designed with low capacitance.

In the exemplary embodiments illustrated in Figure 2, 5 and 6, a parallel supply is provided, whereas in the exemplary embodiment illustrated in Figure 7 a series supply of the sub-amplifiers is provided.

In the exemplary embodiment illustrated in Figure 7. the sub-amplifiers Ii and 12 are accommodated in a chamber system as described with reference to Figure 6. As a deviation from Figure 6, the sub-amplifiers supply voltage inputs are not connected in parallel, but in series. a separate Zener diode 41 and 42 respectively being arranged in parallel to each of the two supply voltage inputs. The series connection of the two supply voltage inputs is established via the outer conductor of the line choke 55. This outer conductor is connected to the inner chamber in which the sub-amplifier 12 is accommodated. but its other end is insulated from the inner chamber of the sub-amplifier 11. The line choke also passes through the partition wall between the two outer chambers in insulated fashion. Between each of the two inner chambers and the outer chamber partition wall. ferrite cores 55 are placed onto each coaxial line which connects the output of the sub-amplifier 11 to the input of the sub-amplifier 12.

Although the series supply illustrated in Figure 7 possesses a higher overall voltage drop, it has the advantage that no additional duct is required for a d.c. path. which. as illustrated in Figure 7. can in this case flow across the line choke.

However, the d.c. connection can be supplied across a separate, choked line instead of a line choke.

In the description of Figures 1. 2 5 6 and 7 it has in each case been assumed that the operating voltage terminals of the sub-amplifiers (referenced 0 and +) are capacitively connected to one another. The corresponding blocking capacitor 35 closes the output circuit of the sub-amplifier in respect of a.c. signals.

Figure 8 illustrates an intermediate amplifier which is largely identical to that shown in Figure 2. The operating voltage terminals 0 and "+" of the sub-amplifiers are capacitively connected to one another, which has not been shown in detail in the Figure.

As a modification of the embodiment shown in Figure 2, a filter element 5 is arranged between the sub-amplifiers 11 and 12, designed as a four-gate circuit, and is connected by the gate 6 to the output of the sub-amplifier 11, and by the gate 7 to the input of the sub-amplifier 12.

The other gates 8 and 9 are connected to one another by one pole and this connection point 98 leads to the correction of the cable outer conductors. The other terminal is connected by the gate 9 to the supply voltage terminal C of the sub-amplifier 11, and by the gate 8 of the supply voltage terminal D of the sub-amplifier 12.

Figure 9 fundamentally illustrates the theoretical circuit diagram of the intermediate amplifier or underground line repeater amplifier schematically shown in Figure 8. Only those connections which are necessary for the HF-signal have been shown, and the path for the remote supply d.c. is not represented in Figure 9. The capacitors 33 and 34 constitute the branching elements which separate the two outer conductors from the respective sub-amplifiers. The capacitors 33 and 34 are arranged in the signal path, and therefore represent an undesired coupling resistance between the output circuit and input circuit. The branching circulating attenuation represents a gauge of the coupling.

if the throughgoing connection existed between the capacitors 33 and 34, and from terminal 62 to terminal 72, then as the two outer conductors are conductively connected to one another via the connection)', the effective output source, EMK, E2 of the amplifier 12 would produce a current both across the capacitor 34 and across the capacitor 33. The current through the capacitor 33 is directly related to the circulating attenuation.

The filter circuit 50 which is designed as multi-gate circuit comprising the gates 6 to 9 is arranged between the two sub-amplifiers 11 and 12. The attenuation from gate 8 to gate 9 should be as high as possible, whereas on the other hand the signal transmission from gate 6 to gate 7 should not be impaired as far as possible. The higher the impedance between the terminals 62 and 72 of this multi-gate circuit. the greater the circulating attenuation.

The conditions governing the attenuation of the filter circuit 50 are illustrated in Figure 2 'nd 5. The circulating attenuation a, amounts to: e"" = 112/U, With a voltage attenuation a of the filter element then in an operating completion:: U',/U', = e" If the impedance of the parallel circuit consisting of the capacitor 34 and the resistor R'2 is reference P. we have U'2 = U2.P/(Z + P) (1) U', = U, (R1 + Z)/R1 (2) U'21U'1 = e' = (U2/U1)P.R1/(Z + P) (R, + Z) (3) K = P.R,/(Z + P) (Rt + Z) e = e""K and = = a-In K (4) The relationship between the circulating attenuation al, and the four-pole attenuation of the filter circuit 5() between the operationally terminated gates 8 and 9 can be gathered from equation (4). The factor K contains the capacitive resistance of the branching capacitor 34, whereas the attenuation a is dependent upon the value of the capacitance 33. For example.

if the capacitance C2 of the capacitor 34 approaches x then -ln K approaches + and therefore the circulating attenuation also approaches x The same is achieved when the capacitance C2 approaches x In this case the voltage attenuation a approaches -ç- and thus the circulating attenuation a,,.

However. it can also be gathered from equation (4) that even with a relatively high value K. i.e. low capacitances Cs and C of the branching capacitors 33 and 31 the circulating attenuation a, can be raised to the desired value by appropriate values of the voltage attenuation a. In this way it is possible to design the branching capacitors 33 and 34 exclusively in accordance with the requirements of the useful signal transmission. The effect of the filter circuit 50 is increased the greater the impedance of the branching capacitors 33 and 34, and the lower the capacitance values.

The circulating attenuation a, is determined by the attenuation of the four-gate circuit.

The advantage which can thus be achieved consisting in particular, in that higher transmission band widths can be achieved than without an interposed four-gate circuit. If, in order to achieve very wide band widths, the branching capacitors 33 and 34 are contrived td be merely of sufficient magnitude to ensure that the self-resonance exceeds the useful band limit, insufficient circulating attenuation values can occur in the transmission band.

The filter circuit 50 produces an increase in the circulating attenuation without any reduction in the upper cut-off frequency. Furthermore, a more favourable signal to noise ratio is achieved.

When the intermediate amplifier or underground line repeater device is divided into n sub-amplifiers, expediently n-l multi-gate circuits are connected. The underground units are expediently carefully screened from one another, in order to avoid, in particular capacitive couplings.

For the intermediate amplifier embodiment illustrated in Figure 8, Figure 10 illustrates a filter element 50 which contains a transformer 56 in the communications transmission path.

Here the transformer 56 is connected by its primary winding to the terminals 61 and 62 of the gate 6. The secondary winding is connected to the terminals 71 and 72 of the gate 7.

The terminals 62 and 98 of the gate 9 are connected to one another via the impedance 58.

The impedance 59 lies between the terminals 72 and 98 of the gate 8.

A screen arranged between the windings of the transformer 56 is directly connected to the terminal 98. On the other hand, it can be expedient to provide a capacitor between screen and terminal 98. This capacitor can, in particular, consist of one of the impedances 58 and 59.

In the case of the filter elements illustrated in Figures 11, 13 and 14, a transformer 57, 571 and 572 is in each case connected by its windings into the communications transmission path in such manner than the one winding lies between the terminals 61 and 71, and the other winding lies between the terminals 62 and 72. Therefore the gates 6 and 7 are electrically connected to one another via the two windings of the transformer 57, 571 or 572 so that in this case the choke 52 shown in Figure 2 can be dispensed with.

In accordance with the filter element construction shown in Figure 11, as in the case of the filter element shown in Figure 10, the terminals 62 and 98 of the gate 9 are connected to one another via the impedance 58. The impedance 59 lies between the terminals 72 and 98 of the gate 8.

lii the filter element shown in Figure 13, the winding of the transformer 572 arranged between terminals 62 and 72. is provided with three tappings, each of which lead via one of the impedances 580, 581 and 590 to the cable outer conductor connection y. A different number of tappings, e.g. one tapping can possibly be provided. In addition, one or both of the winding ends. or of the terminals 62 and 72 can each lead across an impedance to the terminal 98.

The impedances 58, 59, 5SO. 581, 590 provided in the filter elements illustrated in Figures 10. l1 and 13 are preferably low-inductance capacitors. The capacitance of these capacitors is expediently contrived to be such, taking into account the self-resonance, that a maximum circulating attenuation is achieved in the frequency range of interest.

In the filter element shown in Figure 14, the transformer 571 is provided with a screen which is capacitively coupled to the one winding arrangement between the terminals 62 and 72. This screen leads directly to the cable outer conductor connection y. Preferably the transformer can consist of a triaxial cable or a coaxial cable with an additional screen.

The division and decoupling which has been described with reference to the exemplary embodiments can be applied correspondinglv to more than two stages. When the input stage and/or end stage are suitably designed. the capacitors 31 and/or 32 can be omitted.

WHAT WE CLAIM IS: 1. A communications transmission link including a remote-powered intermediate amplifier which is arranged between two sections of a coaxial cable having a common conductor connection. wherein said amplifier is divided into at least two sub-amplifiers, wherein the power supplies for said sub-amplifiers are derived from the inner conductor of the coaxial cable and are mutually decoupled for high-frequencies. and wherein an individual capacitor is connected between one power supply terminal of each of said sub-amplifiers and the common outer conductor connection.

2. A transmission link as claimed in Claim 1. in which a parallel supply of the sub-amplifiers is such that one of the sub-amplifiers is directly connected to a supply source,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (22)

**WARNING** start of CLMS field may overlap end of DESC **. attenuation a, can be raised to the desired value by appropriate values of the voltage attenuation a. In this way it is possible to design the branching capacitors 33 and 34 exclusively in accordance with the requirements of the useful signal transmission. The effect of the filter circuit 50 is increased the greater the impedance of the branching capacitors 33 and 34, and the lower the capacitance values. The circulating attenuation a, is determined by the attenuation of the four-gate circuit. The advantage which can thus be achieved consisting in particular, in that higher transmission band widths can be achieved than without an interposed four-gate circuit. If, in order to achieve very wide band widths, the branching capacitors 33 and 34 are contrived td be merely of sufficient magnitude to ensure that the self-resonance exceeds the useful band limit, insufficient circulating attenuation values can occur in the transmission band. The filter circuit 50 produces an increase in the circulating attenuation without any reduction in the upper cut-off frequency. Furthermore, a more favourable signal to noise ratio is achieved. When the intermediate amplifier or underground line repeater device is divided into n sub-amplifiers, expediently n-l multi-gate circuits are connected. The underground units are expediently carefully screened from one another, in order to avoid, in particular capacitive couplings. For the intermediate amplifier embodiment illustrated in Figure 8, Figure 10 illustrates a filter element 50 which contains a transformer 56 in the communications transmission path. Here the transformer 56 is connected by its primary winding to the terminals 61 and 62 of the gate 6. The secondary winding is connected to the terminals 71 and 72 of the gate 7. The terminals 62 and 98 of the gate 9 are connected to one another via the impedance 58. The impedance 59 lies between the terminals 72 and 98 of the gate 8. A screen arranged between the windings of the transformer 56 is directly connected to the terminal 98. On the other hand, it can be expedient to provide a capacitor between screen and terminal 98. This capacitor can, in particular, consist of one of the impedances 58 and 59. In the case of the filter elements illustrated in Figures 11, 13 and 14, a transformer 57, 571 and 572 is in each case connected by its windings into the communications transmission path in such manner than the one winding lies between the terminals 61 and 71, and the other winding lies between the terminals 62 and 72. Therefore the gates 6 and 7 are electrically connected to one another via the two windings of the transformer 57, 571 or 572 so that in this case the choke 52 shown in Figure 2 can be dispensed with. In accordance with the filter element construction shown in Figure 11, as in the case of the filter element shown in Figure 10, the terminals 62 and 98 of the gate 9 are connected to one another via the impedance 58. The impedance 59 lies between the terminals 72 and 98 of the gate 8. lii the filter element shown in Figure 13, the winding of the transformer 572 arranged between terminals 62 and 72. is provided with three tappings, each of which lead via one of the impedances 580, 581 and 590 to the cable outer conductor connection y. A different number of tappings, e.g. one tapping can possibly be provided. In addition, one or both of the winding ends. or of the terminals 62 and 72 can each lead across an impedance to the terminal 98. The impedances 58, 59, 5SO. 581, 590 provided in the filter elements illustrated in Figures 10. l1 and 13 are preferably low-inductance capacitors. The capacitance of these capacitors is expediently contrived to be such, taking into account the self-resonance, that a maximum circulating attenuation is achieved in the frequency range of interest. In the filter element shown in Figure 14, the transformer 571 is provided with a screen which is capacitively coupled to the one winding arrangement between the terminals 62 and 72. This screen leads directly to the cable outer conductor connection y. Preferably the transformer can consist of a triaxial cable or a coaxial cable with an additional screen. The division and decoupling which has been described with reference to the exemplary embodiments can be applied correspondinglv to more than two stages. When the input stage and/or end stage are suitably designed. the capacitors 31 and/or 32 can be omitted. WHAT WE CLAIM IS:

1. A communications transmission link including a remote-powered intermediate amplifier which is arranged between two sections of a coaxial cable having a common conductor connection. wherein said amplifier is divided into at least two sub-amplifiers, wherein the power supplies for said sub-amplifiers are derived from the inner conductor of the coaxial cable and are mutually decoupled for high-frequencies. and wherein an individual capacitor is connected between one power supply terminal of each of said sub-amplifiers and the common outer conductor connection.

2. A transmission link as claimed in Claim 1. in which a parallel supply of the sub-amplifiers is such that one of the sub-amplifiers is directly connected to a supply source,

and at least one further sub-amplifier is connected via an inductance arranged in the current supply lines to the supply source.

3. A transmission line as claimed in Claim 1, in which at least one line choke is provided to connect two consecutive sub-amplifiers and that one of the two sub-amplifiers is supplied with reference potential via the line choke arranged in the high frequency signal transmission path. and is supplied with the other potential of the supply voltage via an inductance.

4. A transmission link as claimed in any one of Claims 1 to 3, in which the cable inner conductors each lead across an inductance to the terminals of the supply voltage source. the terminal which leads towards the reference potential of the supply source leads from one sub-amplifier via an inductance to the supply input of a further sub-amplifier. and that an inductance arranged between the supply source and the further sub-amplifier is arranged in the cable inner conductor connector or in the supply line between cable inner conductor connection and supply terminal of the further sub-amplifier.

5. A transmission link as claimed in any preceding Claim, in which the sub-amplifiers are arranged in separate chambers, and that the chambers are themselves accommodated in further chambers in insulated fashion.

6. A transmission link as claimed in Claim 5, in which the further chambers possess a common partition wall.

7. A transmission link as claimed in Claim 6, in which a low-capacitive duct for the choke line passes through the inner chamber wall.

8. A transmission link as claimed in Claim 6 or Claim 7, in which the duct through the outer chamber partition wall possesses a high capacitance.

9. A transmission link as claimed in Claim 8, in which said duct is a lead-through capacitor which has a high dielectric strength.

It). A transmission linli as claimed in Claim 7. Claim 8 or Claim 9. in which the inductances are designed at least in part as coaxial lines which are short-circuited at the output end. and that the coaxial line is in each case connected in such manner that the straY capacitance between outer conductor and inner chamber does not shunt the coaxial line.

11. A transmission link as claimed in any preceding Claim. in which a series suppl!- of the sub-amplifiers is provided.

1 A transmission link as claimed in any preceding Claim. in which at least one connection between two consecutive sub-amplifiers has a filter circuit which is designed as a multgate circuit and which. in addition to the two gates arranged in the communications transmission path. possesses at least one further gate which on one side leads to the outer conductor connection of the intermediate amplifier.

13 A transmission link as claimed in Claim 12. in which the filter circuit is designed as a fourgate circuit. and that the four-gate circuit which is connected bv a first gate to the output of the one sub-amplifier and by a second gate to the input of the other sub-amplifier.

a thitd and fourth gate being each connected bv a common terminal to the cable outer conductor connection. that the four-gate circuit contains a transformer which is arranged between the first and the second gate and that the terminals which are each connected to reference potential via one said individual capacitors simultaneouslv form the terminals of the third and fourth gates.

14. A transmission link as claimed in Claim 13. in which the transformer is connected by a primary winding to the first gate and by a secondarv winding to the second gate and that the terminals which are each connected to reference potential via one of the capacitances of the first and second gates are each connected via an impedance to that terminal of the gate which leads to the cable outer conductor connection.

A A transmission link as claimed in Claim 13. in which the transmission contains two windings via which the first and second gates are electrically connected to one another. and that. of the two wtndings. one is arranged between the terminals which are capacitixely connected to reference potential. and the other lies between the other terminals of the first and second gates.

16. A transmission link as claimed in Claim 15. in which one winding of the transformer leads bv at least one end andior by at least one tapping across an impedance to the cable outer conductor connection.

17. A transmission link as claimed in Claim 15. in which the transformer is provided with a screen which is capacitively coupled to the one winding. and that the screen is connected to the cable outer conductor connection.

18. A transmission link as claimed in Claim 14. in which the transformer is provided with a screen which is arranged between the windings. and that the screen leads via a capacitor to the cable outer conductor connection.

19. A transmission link as claimed in Claim 16 or Claim 17. in which at least one of the impedances consists of a low-inductance capacitor.

20. A transmission link as claimed in Claim 1, in which said one power supply terminal of one of the sub-amplifiers is connected to the inner conductor of one of said two cable sections through a first inductor, in which the other power supply terminal of said one of said sub-amplifiers is connected through a second inductor to the inner conductor of the other of said cable sections, and in which the supply terminals of the other sub-amplifier, or sub-amplifiers, are connected to the supply terminals of said one sub-amplifier through respective further inductors.

21. A transmission link as claimed in Claim 1, in which at least one line choke is provided to connect two consecutive sub-amplifiers, in which said one power supply terminal of one of the two sub-amplifiers is supplied via the line choke, and in which the other power supply terminal of said one of the sub-amplifiers is supplied via an inductor.

22. A communications transmission link including a remote powered intermediate amplifier substantially as described with reference to Figure 2, Figure 5, Figure 6 or Figure 7.