US2110278A

US2110278A - Translating circuit

Info

Publication number: US2110278A
Application number: US605243A
Authority: US
Inventors: Robert C Shaw
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1932-04-14
Filing date: 1932-04-14
Publication date: 1938-03-08
Anticipated expiration: 1955-03-08

Description

March 8, 1938. R. c. SHAW TRANSLATING CIRCUIT Filed April 14, 1932 |E I c lu uuucsa N CIRCUIT V 1 5 l, T

l 6 9 v d lNl/L'NTOR R. c. SHAW.

A TTORNEV Patented Mar. 8, 1938 STATES PATENT orrlcs Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application April 14, 1932, Serial No. 605,243

20 Claims.

in short wave radio transmission. The slightest unbalance in the output circuit of a push-pull amplifier, for example, may be suflicient to create a singing condition that will render the amplifier useless. Where, also, an antenna of balanced type is to be connected to a remote transmitter or receiver through a transmission line, one side of which is grounded, it is desirable, though for a different reason, that the balanced 2O condition remain undisturbed. One of the chief sources of unbalance in such systems is in the device used to couple the balanced circuit to a circuit that is not electrically balanced with respect to ground.

An object of the present invention is to couple an unbalanced or grounded circuit to a balanced I circuit without disturbing the balance of. the

latter.

In accordance with the invention, the trans- 30 formation from a balanced circuit to .an unbalanced. circuit is eiiected by taking advantage of the changes in phase that a wave transmitted along a conductor undergoes. The nature of the present invention will more fully appear in the following description of several specific embodiments which are illustrated in the three figures of the accompanying drawing.

In the accompanying drawing, Figure 1 shows a device for coupling an unbalanced circuit to a balanced circuit.

Figure 2 shows a different embodiment of the invention.

Figure 3 shows still another embodiment of the invention.

Referring to Fig. 1, there is shown a device providing for the bilateral translation of electrical waves between an unbalanced circuit L1 and a balanced circuit L2. The unbalanced circuit is represented as a coaxial conductor pair comprising a central conductor l and a grounded, tubular return conductor 2 surrounding the central conductor and effectively shielding it. The balanced circuit shown comprises a pair of ordinary conductors connected to winding 8 of transformer T, winding 8 being grounded at its center point. The balanced circuitLz may be coupled to another balanced circuit associated with winding 9 of transformer T,. such as the input of a push-pull amplifier; or circuit L2 may, for example, comprise an open wire transmission line connected to the members of a horizontal double-V, or diamond-shaped, antenna or of a similar balanced radiating structure. The unbalanced circuit L1, likewise, may comprise a transmission line of open wire, or other type, or merely a connection to adjacent apparatus.

Between the terminals 0, d, of the balanced circuit is connected a linear conductor 3, the terminals of which are represented as a and b. Shielding the conductor 3 is a tubular conductor 4, which is grounded preferably at a plurality of points. The connections between the terminals of conductor 3 and the terminals of circuit L2 are made of the, same length l and preferably are balanced physically with respect to ground, so that the electrical balance at terminalsc, d is not affected.

The length of conductor 3 is critically related to the frequency of the waves which are to be transmitted, or more accurately, to the length of the waves as they are transmitted through the conductor. As an approximation, the length of conductor 3 may be one-half wave length or any odd multiple thereof, or symbolically,

where n is an integral number and A is the wave length.

Where conductor 3 is thus proportioned it is apparent that the phase of a wave transmitted from terminal 0 of. the balanced circuit and through conductor 3 to terminal b of the latter, will be altered exactly one-half cycle with respect to a similar wave transmitted directly from terminal d of the balanced circuit to terminal b. Since, then, the phases of the voltage waves appearing at the respective terminals 0, d, of the balanced circuit are exactly opposite, it follows that the waves transmitted through the two sides of the circuit to point b will be in phase with respect to any external load connected between point b and ground. Because of the phase reversal in conductor 3, point b is effectively at the same potential withreference to both terminals of the balanced circuit. Any circuit connected to point b, therefore, will have the same effect on the two sides of. the balanced circuit and the balance of the latter will notbe affected. Circuit L1, being connected between point b and ground accordingly has no unbalancing ef fect'on necessary for the translationiof waves through V the transformer.

Fig-'2 illustrates an embodiment of the inventionas utilized ior coupling the output circuit of ;a balanced or push-pull. amplifier; :to Ian balanced circuit such a's 'a coaxial ciomiuctorv he must be,

. each other,

changing load conditions;

transmission line L1. In thisgcase 'the separate conductor 3 of critical length shown in Fig.- -1

is omitted and the terminals. c and d of. the bal v anced circuit areconnected directly-to the point b and the unbalanced circuit connectedfthereto.

' Therequired phase changeis obtainedby'making,

"the-conductor bc electrically longer than 'con- 'ductor 1 bd by an amQunt'equivaIent to one-half a wave length or an oddmultiple thereof. Thus, v v i vides animpedance match for theantenna, while the coaxial conductor line provides an efllciently if the length bd be represented by l, the length 7 i The embodiment:- of "the inventionshown "in to compactness, flexibility and accurate matching of the impedances of the connected circuits. J It is similar; to the system shown in Fig. 1'- with the. substitution" of e l a UQ-shaped conductor l3 for" the linear conductor 3 of the-latter figure and r with the insertion of tuned'circuits in the om nections, acand 'bd'. Arrangingconductor l3 in the-form of a U or long, 'narrowiloop does f not materially alter its effectiveness as a phase shifting device and it hasthe advantage'that the terminals need not. be widely separated. from Moreo'verthe over-all dimensions are reduced, With fa straight conductor as in Fig. 1, a length of, the order OfthlItYfGBt would be required in a system operating at fifteen megacycles per second, whereas therlength" ofthe' I space required may be reduced to approximately half the amount by using the U construction.

In any, of these cases an unshielded conductor may alternatively beemployed. V

Operation at different frequencies is made possible by providing short-circuitingconnections across. the loop at difierent"points',i'these connections being selectivelycompleted by 'means of remotely controlled switches l5, l6. Thegxact;

location of the'short-circuiting connections may be adjusted from" time to time to accommodate Terminals ,a and b of conductor l3 are connected to intermediate points of inductance coils 2| a-ndlll, respectively, the adjacent terminals of' whichare grounded. Condensers C1 and C2 are connected between ground andtaps 22 and 23; respectively, of the respective coils 20 and 2|. The terminals c, d of the balanced line In. are symmetrically connected to taps on the twocoils; .The tuned circuits comprising condensers C1 and C2 and coils Y20 and 2Iperm'it an adjustm ent of, the impedance ratio or the transforming system. "Without such" adjustment an impedance-ratio or 1:4 is obtained; looking from the unbalanced circuitto the balanced circuit.

7 waves transmitted therethrough. r

sents the voltage across' the unbalanced circuit and I, the current therein. Going into the balanced. circuit the current I divides and produces in that circuit a circulating current. of 1/2.

The voltages E producedacross both halves of the balanced circuit are added in phase, resulting in a total of 2E. The impedance of the balanced circuit therefore appears as .orfour times the impedance (E/I) ofthe an balanced-circuit. The tuned: circuits are also useful, in correcting small phase .difierences that may exist at'the terminals of the balanced circui't. 'By slight yariations'in the length of the conductor l3, likewise, impedance and phase .dissymfmetries of the system maybe compensated for.

The combinationof coaxial conductor line and balanced openfwire lineillustratedin Fig. 3 may beus'edg-forexample, where a'balanced or sym-' metricaliantenna array is to be. connected to a remote radio' station; The open wire line proshielded transmission path to the station.

' Although the invention has been described with.

reference to "specific embodiments and applications of it, it is to be understood that the invention is limited only by the scope andspirit of the appended claims. 1 "What is claimed is:

1. In a high frequency transmission system, a circuit balancedto ground, a circuit one side of which is grounded," and leads from the terminals of said balanced circuit'tothe ungrounded side of said second mentioned circuit, the electrical lengths of said leads difieringfrom each other by an odd number of-half-wave lengths of the 2. In a high'frequency transmission system, a circuit balanced to ground,a circuit one side of which is grounded, and connections from the terminals of said balanced circuit to the un-.

grounded side ofsaid second mentioned circuit,

and means in said connections for reversing the relative phases of wavestransmitted there through. V

In a 'high frequency transmissionsystem, a

ber of half-wave lengths of the waves transmitted, symmetrical connections from the terminals of said balanced circuit to .the terminals of balanced circuit, an unbalanced. circuit, means 'for coupling said circuitsin energy transfer relation comprising connections from the terminals 7 of. said balanced circuit to one side of said unbalanced circuit, the relative electrical lengths of said connections being such that the balance of said'first mentioned circuit is maintained. 7

- '5. In a high frequency transmission system, a

circuit balanced to ground, a conductor having 1 an electrical lengthequivalent to anodd numbalanced circuit, an unbalanced circuit, and/ meansfor coupling said circuits in energy transferrelatlon comprising connections from the terminals of said balanced circuit to onefside of said unbalanced circuit, oneof saidconnections including a phase reversing device comprising a conductor greater in length than the shortest distance between its terminals.

6. A combination in accordance with claim 4, comprising means for adjusting the relative effective geometrical lengths of said connections to adapt said coupling means for operation at difierent frequencies.

7. In a high frequency transmission system, a balanced circuit, an unbalanced circuit, and means for coupling said circuits comprising connections from said balanced circuit to said unbalanced circuit, the electrical lengths of said connections being substantial and different by an amount such that the balance of said first mentioned circuit is preserved.

8. A combination in accordance with claim 7, in which said connections consist of conductors.

9. In a high frequency transmission system, a circuit substantially balanced with respect to ground, a circuit unbalanced with respect to ground, and means coupling said circuits in energy transfer relation, said coupling means comprising a first connection from a point on one side of said balanced circuit to a point in said unbalanced circuit, a second connection from a point on the other side of said balanced circuit to a point in said unbalanced circuit, said connections differing in electrical lengths by an amount corresponding to the difierence in phase between said respective points on said balanced circuit and ground.

10. In a high frequency transmission system, a balanced circuit and an unbalanced circuit and means for coupling said circuitsv together comprising connections from said balanced circuit to a common point on said unbalanced circuit,

the electrical lengths of said connections differing by an amount suflicient to introduce the phase change required to maintain the electrical balance of said balanced circuit.

11. A combination in accordance with claim 10 in which said coupling includes means effective to match the impedances of said balanced and unbalanced circuits.

12. A combination in accordance with claim 10 comprising means for suppressing radiation from said coupling connections.

13. A combination in accordance with claim 10 in which each of said connections comprises the inner conductor of a coaxial pair, the outer conductor of each pair being grounded at a plurality of points.

14. In combination, a circuit balanced with respect to ground, a circuit unbalanced with respect to ground and means for coupling said circuits in energy transfer relation comprising a conductor connected across said balanced circuit, said conductor being electrically and physically symmetrical with respect to ground and said balanced circuit, and a connection from said unbalanced circuit to a point on said conductor that is an odd number of half wave-lengths farther from one end of said conductor than from the other end.

15. In a high frequency coupling arrangement comprising a circuit which is normally unsymmetrical with respect to ground potential, a second circuit which is normally symmetrical with respect to ground potential, means for providing a circuit coupling arrangement between said unsymmetrical and symmetrical circuits, said means comprising conductor leads from the terminals of said symmetrical circuit to the ungrounded side of said unsymmetrical circuit, the electrical lengths of said conductor leads differing from each other by an odd number of half wave lengths of the waves transmitted therethrough.

16. In a high frequency coupling arrangement comprising a circuit which is normally unsymmetrical with respect to ground potential, a second circuit which is normally symmetrical with respect to ground potential, means for providing a symmetrical circuit coupling arrangement between said unsymmetrical and symmetrical circuits, said means comprising concentric conductors, at least one of said conductors being grounded and branched, the difference in the geometric length of said branch lines being differently chosen so as to compensate for the unsymmetrical circuit. arrangement.

17. In a high frequency coupling arrangement comprising a circuit which is normally unsymmetrical with respect to ground potential, a second circuit which is normally symmetrical with respect to ground potential, means for providing a symmetrical circuit coupling arrangement between said unsymmetrical and symmetrical circuits, said means comprising concentric conductors, at least one of said conductors being grounded and branched, the difference in length of said branches being such as to compensate for the unsymmetrical circuit arrangement.

18. In a high frequency coupling arrangement comprising a circuit which is normally unsymmetrical with respect to ground potential, a second circuit which is normally symmetrical with respect to ground potential, means for providing a symmetrical circuit coupling arrangement between said unsymmetrical and symmetrical circuits, said means comprising concentric conductors, at least one of said conductors being grounded and branched, the difierence in length of said branches being an uneven number of half waves so as to compensate for the unsymmetrical circuit arrangement.

19. In a high frequency transmission system, a circuit substantially balanced with respect to ground, a circuit unbalanced with respect to ground, and means coupling said circuits in energy transfer relation comprising a connection from a point in said balanced circuit to a point in said unbalanced circuit and a connection from a point of different phase in said balanced circuit to a point in said unbalanced circuit, the electrical lengths of said connections differing by an amount sufficient to introduce the phase change required to maintain the electrical balance of said balanced circuit at the frequency of transmission.

20. A combination, in accordance with claim 19, in which at least the electrically longer of said connections comprises the inner conductor of a coaxial pair.

ROBERT C. SHAW.