US1855303A - Multiple coaxial conductor system - Google Patents

Description

April 26, 1932. R. G. MCCURDY MULTIPLE COAXIAL CONDUCTOR SYSTEM Filed May 9, 1950 INVENTOR E. 61%6121 "(9 MNQQ ATTORNEY Patented Apr. 26, 1932 RALPH G. MCCURDY, OF ENGLEWOOD, NEN JERSEY, ASSIGNOR TO AMERIGAN TELE- PHONE AND TELEGRAEH COMPANY, A CORPORATION OF NEW YORK MULTIPLE COAXIAL CONDUCTOR SYSTEM Application filed May 9,

This invention relates to coaxial conductor circuits, and more particularly to terminal arrangements for such circuits.

It has been proposed to use a multiple coaxial conductor system of more than two tubular conductors for the purpose of obtaining additional circuits. For example, if a triple conductor system were employed, the middle and inner conductor might be used as one circuit and the middle and outer conductors as another. At high frequencies these two derived circuits would be eii'ectirely separate since the currents of one circuit would flow on the inside ofthe middle conductor and those of the other circuit on the outside of the middle conductor. The chief diiiiculty with such an arrangement is that of applying the currents to the two circuits at the trans mitting end and taking them off at the receiving end in such a manner asto avoid'objeo tionable mutual interference.

The arrangement comprising the present invention offers av solution of this diliiculty.

This arrangement consists in terminating each circuit in a shielded compartment in which the line currents are passed'through a double shieldedtransformer and then are led through a shielded circuit to the terminating apparatus which may be, for example, a repeater amplifier. Owing to the concentric arrangement of the line conductors the shielded'containers are arranged one inside the other. The double shielded transformer serves as a connecting link between the apparatus circuits (such as the amplifiers) which are shielded with respect to one another in the usual way and the line circuit where the shield and the conductor are the same physical structure. The invention will now be more fully understood from the following description, when read in connection with the accompanying drawing, Figure 1 of which is a schematic circuit arrangement embodying the principles of the invention, andFigs. 2, 3, r and 5 of which are cross-sectional views of the various conductors and shielded compartments used in connection with the system.

Fig. 1 illustrates an arrangement in which a multiple concentric conductor system com- 1930. Serial No. 451,136.

prising four conductors is employed in such a manner as to obtain three distinct derived circuits. In order to illustrate the principles of the invention an arrangement is shown for lnterposing three independent one-way repeaters between two sections of the concentric conductor, each repeater corresponding to one of the three derived circuits. ,The concentric conductor arrangement comprises four tubular conductors, A, B, C andD, so connected that conductors A and B constitute one transmission circuit, conductors B and C a second transmission circuit, and conductors C and D a third transmission circuit. Each. conductor of a pair comprising an independent transmission circuit acts as a return for the other conductor of the pair. The section of concentric conductors A, B, C and D is to be connected through three repeaters, one for each circuit, to a similar section of multiple concentric conductors comprising conductors A, B, C, and D, these latter conductors being also arranged to constitute three independent conducting systems.

Each of the conductors B, C, and'D is terminated in a shielding compartment, these compartments beingshown at B C and D respectively, and being arranged one within the other. Likewise each of the conductors B, C, and D is terminated in a shielding compartment, these compartments being shown at B C and D In order to connect the repeater CDR between the two sections of circuit comprising conductors C-D and C-D, respectively, the terminals of the input transformer of the amplifier are connected, respectively, to two concentric conductors C and D which are in turn connected to the shielding compartments C and 1);. Likewise the terminals of the output transformer of the repeater are connected to two concentric conductors C; and D which are in turn connected to the shielding compartment (3, and D By this arrangement the circuit comprising conductors J and is connected to the input of the repeater CDR through the shielding compartments C and D and concentric conductors C and D the circuit comprising conductors C D being likewise connected to the output of the repeater through the shielding elements C and D and through the concentric conductors C and D The repeater CDR itself is shielded by means of a shielding compartment D connected to the conductors D and D If desired, the stages of the amplifier may be shielded from each other by the provision of shielding partitions in the compartment D as shown.

Since the repeater CDR must have its filament grounded to the surrounding shield D the outer conductors D and D and the corresponding compartments D and D will be grounded. This of course does not produce any eifect on the currents flowing over the several concentric conductors A, B, G and D as the electric field between conductors U and D, for example, and substantially the entire magnetic field, due to the current flow over said conductors, is confined within the outer conductor D.

The repeater BUR, for interconnecting the circuit comprising conductors BG to the circuit comprising the conductors B C, and the repeater ABR, for similarly connecting the circuitcomprising conductors AB to the circuit comprising conductors A-B, are likewise included in shielded compartments C and B which will likewise be grounded in order to provide a ground connection for the filaments of the amplifier contained within the shielding compartments of the repeaters. The two concentric conductor sections comprising conductors B and C and conductors B and C for connecting the repater BCR to the circuit including conductor sections BC and B'-C, respectively, must pass into the proper shielding compartments of thefour-conductor system through the outer compartments D and D Likewise the concentric conductor sections AL -B and A -B for connecting repeater ABE to the circuit sections comprising conductors A.-B and 131 B, respectively, must also pass through the outer shielding compartments D and D These outer compartments D and D are grounded, and since the conductors A, B, and C and likewise the conductors A, B, and C are not at ground potential, it is necessary to establish the connections to the repeaters ABR and BUR by means of transformers.

Accordingly the conductor system B-G is associated with the conductor system B; i through a transformer BCT. having its terminals connected DELWQGD the shielding elements B and C and having its secondary connected to the conductors B and G The transformer is thus included within a shielding compartment to shield it from external influence. The primary and secondary windings of the transformer are likewise provided with separate shields for reducing the efiect of capacity between the windings. In

a similar manner the. conductors B and are associated with the conductors B and C through a transformer BUT! having the terminals of its primary winding connected to the shielding compartments B and C and having its secondary winding connected to the conductors B and C The outer conductors C and while conduetively related to the shielding compartments D and D are insulated from the, shielding compartments C and C A further complication in establishing the connections to the repeater ABR arises from the fact that the concentric conductors B and B must in effect pass through all three of the shielding compartments associated with the main concentric conductor sections. The outer compartment such as D is grounded, the next compartment C is at a diiferent potential from ground, and the inner compartment B is at still a different potential. Therefore the circuit comprising conductors A and B is connected through a transformer ABT whose primary winding has its terminals connected to conductors A and B and whose secondary winding has its terminals connected to a short concentric conductor section comprising conductors A and B extending through the inner compartment B and to the intermediate compartment C The outer conductor B is directly connected to the shielding compartment C but is insulated from the inner shielding compartment B The outer conductor of the concentric conductor section A B is connected directly to the outer shielding compartment D and the two concentric conductor sections AL -B and A -B are then interconnected through a transformer ABT having its primary winding connected to the conductors A; and B and its secondary winding connected to the conductors A and B This transformer by being included between the compartments C and D is shielded from external influences and each of its windings is separately shielded one from another to reduce the effect of the capacity between windings.

Similarly the concentric conductor section A -B is connected through a transformer ABT to a short concentric conductor system A 'B passing from the coi'npartment C to the inner compartment- B and insulated from the latter. The concentric conductor section A P is in turn connected through a transformer ABT to the circuit comprising concentric conductors A and 13. The capacity between the windings of the transformers ABT and ABT is reduced by the provision of shielding arrangements between the windings.

Notwithstanding the fact that the individ ual repeaters of each of the three transmission systems above dcscritmd have their shielding compartments grounded and connected toether, the above described arrangemei'it en- (1 ables the connections from the repeaters to be over the conductors B and G Leeaaoe made to the transmission circuits which have their potentials above ground with-out objectionable mutual interference. Let us assume that dueto signaling currents passing over the circuit section comprising conductors C and D a potential difference exists between those two conductors. This produces a corresponding potential difference between the shielding compartments C and D so that current flows through the primary winding of the input transformer of the repeater (IDE- and the signal is passed through the repeater. Conductors D, D D and D are at ground potential and hence current flows to ground through the primary winding of the input transformer of the repeater CDR. If it were not for the shielding arrangements above described, current due to the potential of the conductor C would find an alternative path to ground from the inner shielding compartment C through the capacity between the windings of the transformer BCTB and thence over the outer conductor C; to ground. Since this current would pass through the primary windings of the transformer BUR, a disturbing current would be induced in the secondary winding of thetransformer which would be transmitted to the repeater BOB This is prevented, however, due to the double shielding arrangement between the windings of the transformer BOT. which provides a path to ground from the inner shielding conductor C directly across the capacity between the two shields-of the windings of the transformer BCT and thence to the conductor C ity between the windings of the transformer ABT to the outer conductor A and thence through the capacity betweenthe windings of the transformer ABT to the grounded conductor B The current flowing through the primary of the transformer ABT would induce a current in thesecondary winding of 'said transformer which would be transmitr ted through the transformer ABT to the said transformers which causes'the disturbing-current to pass to ground through the capacities between the shielding elements of the transformers without passing through the capacity between the windings of the transformers. This would still leave a current flowing through the primary of the transformer lBCT which would cause a disturbance in the repeater BCR but this is prevented by reason of the fact that both conductors C and B are at the same potential with respect to a potential difference between C and D due to the connection from the conductors C through the outer conductor B of the concentric section A B and thence through the capacity between the two shields of the windings of the transformer ABT to the left-hand terminal of the transformer BOT This connection prevents any potential difierence existing across the terminals of the primary of the transformer BCT due to a potential difference between the conductors C and D Let us now consider the case of a signaling potential difference between the conductors B and C. Such a difference in potential would cause a current to flow froni the conductor C through the primary winding of the transformer BCT, to the conductor B thereby inducing a current in the secondary winding of the transformer BUT. which is transmitted over the concentric conductor section B (L, to the repeater BUR. The corresponding signal will therefore be transmitted through the repeater. Due to the potential difference between conductors B and G a path to ground exists from the conductor C through the capacity of the double shielding arrangement of the transformer BCT ing current which might be expected to reach ground from the conductor C over the inner conductor C and through the primary of the input transformer of the repeater CDR and thence over the outer conductor D to ground, does not exist due to the fact that both terminals of the input transformer of the repeater CDR are at ground potential with respect to a potential difference between conductors B and C by reason of the direct connection from the lower terminal of the input winding of the repeater over conductor D over conductor D conductor C capacity between the shields of the transformers BUT. and thence over conductor (1-, to the upper terminal of the input transformer of the repeater CDR.

The potential difference between the conductors B and C might also be expected to produce a disturbance in the repeater AER due to the path to ground from the conductor B through the capacity between the windings of the transformer ABT over the conductor B: and through the capacity between the windings of the transformer ABT and thence over outer conductor B to ground. Y The current flowing over this path would produce disturbingimpulses in the secondary windings of the transformers ABT and 'ABT were it not for the double shielding arrangements provided between the windings of each transformer which in effect shortcir'cuit the capacities between the windings of the two transformers so that current passes to ground from the conductor B through the capacity between the shields of the transformer ABT vcr the conductor 13:, and through the capacity between the shields of the transformer ABT and thence to ground over the conductor B without producing a disturbing etfectin the secondary windings of the two transformers.

Finally, let us suppose that a signaling potential difference exists between the conductors A and 13 causing current to flow through the primary winding of the transformer ART so that the signal will be transmitted through the transformer ABT over theconductors A and B and through the transformer ABl and thence over the conductors A and B to the repeater ABE. A

ground now exists from the conductor B through the capacity between the double shielding arrangement of the transformer ABT over the conductor B:, through the capacity of the double shielding arrangement of the transformer ABT and over the outer conductor B to ground. An alternative path to ground might be expected to exist from the conductor B, through the primary of the transformer BUT through the inner conductor C and through the primary winding of the input transformer of the re-.

peater CDR, and thence over the conductor D to ground. Current flowing in this path would produce a disturbing impulse in both repeaters BQR and CDR. Such disturbing current does not flow, however, due to the fact that both terminals of the primary of the transformer BCT, are at the same potcn tial with respect toa potential ditl'erence between conductors A and B due to the connection from the right-hand terminal of the pri mary winding of the transt'mm-er BCT over the conductor G over the outer conductor B and through the capacity between the double shielded arrangement of the transformer ABT to the left-hand terminal of the transform-er BC'L. Likewise both terminals of the input transformer of the repeater CDR are at the same potential due to the connection from the lower terminal over the conductor D thence over conductor D outer conductor (1,, and the capacity between the shielding arrangement of the transformer BCT and thence over the conductor C to the upper terminal of the input winding of the transformer ot the repeater CDR, Consequently, no disturbing influence results in either of the repeaters BCE and CDR due to a potential difference across the conductors A and B.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a. multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from thetranslating device of another circuit passing through the outer compartment to an inner compartn'ient, and a transformer within said last mentioned compartment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said inner compartment and the concentric conductor within said lastmentioned conductor.

2. In amultiple concentric conductor system of'which the conductors are connected to form a plurality of independent transmission circuits, a separate translatin device for each circuit, and means to associate each translating device with a corresponding transmission circuit said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from the translating device of another circuit passing through the outer compartment to an inner compartment and a transformer within said last mentioned com partment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said inner compartment and the concentric conductor within said last mentioned conductor, said transformer having double shielding between its windings.

3. In a multiple concentric conductor system of which the conductors are connected to forma plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductorexeept the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of onecircuit, shielded connections from the translating device of another circuit passing through the outer compartment to an inner compartment, a transformer Within said last mentioned compartment for associating said lastmentioned shielded connections with the circuit formed by the concentric conductor connected to said inner compartment and the concentric conductor within said last mentioned conductor, said transformer having double shielding between its windings, and means to shield each of said translating devices.

4. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from the translating device of another circuit passing through the outer compartment to an inner compartment, a transformer within said last mentioned compartment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said inner compartment and the concentric conductor within said last mentioned conductor, said transformer having double shielding between its windings, and means to shield each of said translating devices, said shielding means being grounded. I

5. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits. 'a separate translating device for each circuit. and means to associate each translatin device with a corresponding transmission circuit. said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connectedto each concentric conductor except the inner conductor. shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit. shielded connections from a second translating device extending through the outer compartment and the next compartment in order to the interior of said next compartment. and a transformer .within said next compartment for associating said shielded connections with the circuit comprising the conductor connected to said next compartment and the succeeding inner conductor.

Eng

tem of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the nextcompartment in order to the translating device of one circuit, shielded connections from a second translating de vice extending through the outer compartment and the next compartment in order to the interior of said next compartment, and a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductor connected to said next compartment and the succeeding inner conductor, said transformer having double shielding between its windlngs.

7. In a multiple concentric conductor sys tem of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associated each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from a second translating deviceextending through the outer compartment and the next compartment in order to the interior of said next: compartment, a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductor connccted to said next compartment and the succeeding inner conductor, said transformer having double shielding between its windings, and means to shield each of said translating devices.

8. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connectcd to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from a second translating device extending through the outer compartment and the next compartment in order to the interior of said next compartment, a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductor connected to said next compartment and the succeeding inner conductor, said transformer having double shielding bet-ween its windings, and means to shield each of said translating devices, said shielding means being grounded. v

9. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from a second translating device extending through the outer compartment and the next compartment in order to the interior of said second compartment, a transformer Within said next compartment for associating said shielded connections with the circuit comprising the conductors connected to said next compartment and the succeeding inner conductor, shielded connections from a third translating device extending through the compartments in order to the innermost compartment, and a transformer within the innermost compartment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said innermost compartment and the extreme innermost conductor.

10. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shield ed compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from a second translating device extending through the outer compartment and the next compartment in order to the interior of said second compartment, a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductors connected to said next compartment and the succeeding inner conductor, shielded connections from a third translating device extended through the compartments in order to the innermost compartment, and a transformer within the innermost compartl'nent for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said innermost compartment and the extreme innermost conductor, said transformers having double shielding between their windings.

11. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartment in order to the translating device of one circuit, shielded connections from a second translating device extending through the outer compartment and the next coi'np'artment in order to the interior of said second compartment, a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductors connected to said next compartment and the succeeding inner conductor, shielded connections from a third translating device extending through the compartments in order to the innermost compartment, a transformer within the innermost compartment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said innermost com partment and the extreme innermost conductor, said transformers having double shielding between their windings, and means to shield each of said translating devices.

12. In a multiple concentric conductor sys tem of which the conductors are connected to form aplurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other, there being one shielded compartment connected to each concentric conductor except the inner conductor, shielded connections from the outer compartment and the next compartn'ient in order to the translating device of one circuit, shielded connections from a second translating device extending through the outer compartment and the next compartment in order to the interior of said second compartment, a transformer within said next compartment for associating said shielded connections with the circuit comprising the conductors connected messes to said nextcompartment and the succeeding inner conductor, shielded connections from a third translating device extending through the compartments in order to the innermost compartment, a transformer within the innermost compartment for associating said last mentioned shielded connections with the circuit formed by the concentric conductor connected to said innermost compartment and the extreme innermost conductor, said transformers having double shielding between their windings, and means to shield each of said translating devices, said shielding means being rounded.

13. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmis sion circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other and individuall connected to certain of said concentric conductors, shielded connections leading from the compartments to said translating devices, and transformers within said compartments for associating said shielded connections :with the concentric conductors comprising each transmission circuit.

14. In a multiple concentric conductor system of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality ,of shielded compartments one within the other and individually connected to certain of said concentric conductors, shielded connections leading from the compartments to said translating devices, and transformers within said compartments for associating said shielded connections with the concentric conductors comprising each transmission circuit, said transformers having double shielding between their windings.

15. In a multiple concentric conductor s vstem of which the conductors are connected to form a plurality of independent transmission circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transn'iission circuit, said means comprising aplurality of shielded compartments one within the other and individually. connected to certain of said concentric conductors, shielded connections leading from the compartments to said translating devices, transformers within'said compartments for associating said shielded connections with the concentric conductors comprising each transmission circuit, said transformers. having double shielding between their windings, and

means to shield each of said translating devices.

16. In a multiple concentric conductor sys tem of which the conductors are connected to form a )luralitv of independent transmis u L sion circuits, a separate translating device for each circuit, and means to associate each translating device with a corresponding transmission circuit, said means comprising a plurality of shielded compartments one within the other and individually connected to certain of said concentric conductors, shielded connections leading from the compartments to said translating devices, transformers within said compartments for asso ciating said shielded connections with the concentric conductors con'iprising each transmission circuit, said transtormers having double shielding between their windings, and means to shield each of said translating devices, said shieldlng means being grounded.

1'7. A system comprising two coaxial conductor circuits whose conductors are at different potentials with respect to ground, and means to connect said circuits in tandem, said means including a double shielded transformer.

18. A system of transmission circuits derived from a plurality of conductors arranged concentrically, certain of said conductors being used jointly in two diii'erent transmission circuits, a second system of tr: nsmission circuits wherein each transmission circuit is derived from two separate concentric conductors, connections for joining together corresponding circuits of the two systems, and means for avoiding inter-circuit interference interposed in said connections.

19. A system o1 transmission circuits de rived from a plurality of conductors arranged concentrically, certain of said conductors being used jointly in two different transmission circuits, a second system oftransmission circuits in which each transmission circuit consists of two conductors arranged concentrically, each conductor being used in only one transmission circuit, and connections for joining together corresponding circuits of the two systems, said connections being such as to preserve the shielding which is provided by the concentric conductor transmission systems. j

20. A system of transmission circuits derived from a plurality of conductors arranged concentrically, certain of said conductors being used jointly in two different transmission circuits, a second system of transmission circuits in which each transmission circuit consists of two conductors arranged concentrically, each conductor being used in only one transmission circuit, and connections for joining together corresponding circuit" of the two systems, said connections including shielding compartments whose walls have thickness comparable with the thickness of the walls of the concentric conductors to which the shielding compartments are connected.

21. A system of transmission circuits derived from a plurality of conductors arranged concentrically, certain of said con-' used in only one transmission circuit, and

connections for joining together corresponding circuits of the two systems, said connections including means to shield the circuits from interference due to external causes.

22. A system of transmission circuits derived from aplurality of conductors arranged concentrically, certain of said conductors being used jointly in two different transmission circuits, at second system of transmission circuits in which each transmission circuit consists of two conductors arranged concentrically, each conductor being used in only one transmission circuit, and connections for joining together corresponding circuits of the two systems, said connections being such as to preserve the shielding which is proyided by the concentric conductor transmission systems, and means for amplifyingthe signal energy in said second system of transmission circuits.

23. A system of transmission circuits derived from a plurality of conductors arranged concentrically, certain of said conductors being used jointly in two difl'erent transmission circuits, a second system of transmission circuits in which each transmission circuit consists of two conductors arranged concentrically, each conductor being used in only'one transmission circuit, and connections for joining together correspondingcircuits of the two systems, said connections including shielding compartments whose walls have thickness comparable with the thickness of the walls of the concentric conductors to which the shielding compartments are connected, and means for amplifying the signal energy in said second system of transmission circuits.

2a. A system of transmission circuits de rived vfrom a plurality of conductors arranged concentrically, certain of said conductors being used jointly in two different transmission circuits, a second system of transmission circuits in which each transmission circuit consists of two conductors arranged concentrically, each conductor being used in only one transmission circuit, and

RALPH G. MGCURDY.

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