US1396760A - Signaling-circuit - Google Patents

Description

K. S. JOHNSON. SGNALING CIRCUITS. APPLICATION msn 1AN.4. 191B.

Patented Nov. 15, 1921.

/fvl V e /7 fo /fe/me f// 5. 7a/msm? 1y g Yonx.

UNITED STATES PATENT OFFICE.

KENNETH S. JOHNSON, 0F JERSEY CITY, NEW JERSEY, ASSIGNOR T0 WESTERN ELEC- TRIO COMPANY, INCORPORATED,

0F NEW YORK, N. Y., A. CORPORATION OF NEW SIGNALING-CIRCUIT.

Specification of Letters Patent.

Application ined January 4, 191s. seriai No. 210,265.

T o allwhom t may concern:

Be it known that I, KENNETH S. JOHNSON,

a citizen of the United States, residing at Jersey City, in the county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Signaling-Circuits, of which the following is a full, clear,

bination of a substation and a telephone line.

Its Object is to provide a signaling circuit arrangement which, in cooperative combination with asimilar and equal communicating arrangement or station, shall deliver the maximum amount of energy to the receiving apparatus of said communicating station or arrangement. A further obj ect is to provide an arrangement such that the receiving apparatus is protected from interference by the transmission energy originating at the saine station.

The particular substations herein illustrated are modifications of a general type described in a U. S. patent of George A Campbell, No. 1,254,472, dated January 22, 1918, and are closely related to the forni shown in Fig. 1 (a) of the said patent.

' The object of the invention is attained, in its specific aspect, by providing a substation consisting of transmitter, receiver, a balancing network consisting in the simplest form of an auxiliary resistance, and a transformer having a plurality of windings which, in combination with a telephone line, shall satisfy the following fundamental requirement'.

Given two identical substations designed for invariable two-way communication, and

connected by a line of given impedance, the

amount of energy absorbed by the receiver at the receiving station shall be the maximum part of the total telephonie energy developed by the transmitter at the transmitting station consisent with. invariable two-way. communication, and* as .hereinafter explained, consistent with a desirable amountof discrimination against disturbing line noise.

` This fundamental requirement may be stated inv terms of the following subordinetereline', assuming quirements which are necessary for its satisfaction: (l) the transmitter and receiver shall be conjugate, that is, there shall be negligible side tone in the receiver in consequence of the actuation of the transmitter by sound waves; (2) the line and auxiliary resistance shall be conjugate in order that a negligible amount of' the energy absorbed by the substation from the line shall be wasted in said auxiliary resistance; (3) for a given line having a deinit-e impedance, the teleplionic energy delivered by the transmitter shall be a maximum; (4) the amount of energy delivered by the line to the substation shall be a maximum, in other words, the impedance of the substation as seen from the line shall be numerically equal to the impedance of the line; (5) at a small sacrifice of eliciency it shall be possible to discriminate effectively against disturbing line noise asv distinguished from the telephonie signals from the communicating station.

A substation satisfying the above-mentioned requirements is ideal in that its overall eliicienc from transmitter of one substation to receiver of the communicating substation is a theoretical maximum which cannot Patented Nov. 15,1921.

be exceeded by any two similar invariable siibstations whether satisfying the requirement of transmitter and receiver conjugacy or not. It is further ideal in the sense that a minimum number of elements is employed, since at least one auxiliary element is necessary to secure freedom from side tone.

It might be inferred that the addition of an auxiliary resistance element, necessary as it is to secure freedom from side tone, would at the same time necessarily reduce the eilicienc of the substation since energy is unavoi ably wastedin said auxiliary resistance. That this is not the case and that the eiliciency of the substation of my invention is a theoretical maximum which cannot be exceeded by any two-way substation whether with or without side tone, the following considerations will show.

The simplest form of substation for invariable two-way communication is that in 'which the receiver and transmitter areconances of the receiver-and transmitter are each equal to one-half the resistance of the that the total reactances in are diagrams showing erable distributed ythe winding ratios i' and'r the circuit are negligible. lVhen this condition is satisfied, obviousl on receiving, fifty percentum of the eneigy delivered by the line to the substation enters the receiver, and on transmitting an amount of energy equivalent to fifty perceiitiini of the maximum energy which can be delivered by the transmitter, enters the line. However, such an arrangement labors under the disadvantage of full side tone. In the substation of this invention, fifty percentum of the energy delivered by the line to the substation enters the receiver when no discrimination against line noise is made, and none enters the auxiliary resistance, since the said auxiliary resistance and said line are conjugate; hence ,the receiving efficiency is as gicat as that of the simple series substation. When transmitting, fifty percentiim of the energy delivered by the transmitter, now delivering its maximum power, enteis the line. The remainder of' the energy is wasted in the auxiliary resistance since none is lost in the receiver. The ti'ansinitting efficiency is therefore also a theoretical maximum and neither transmitting nor receiving efficiency is reduced by the addition of the auxiliary resistance which is necessary to secure freedom from side tone. The foregoing consideration will sei-veto explain the desirability of having the line and auxiliary resistance conjugate as well as the transmitter and receiver.

In my present invention, I station comprising transmitter, receiver, auxiliary resistance and transformer, and so proportion said component elements and so relate them to a telephone line and to each other that, in combination with vsaid telephone line, said substation satisfies all of the foregoing requirements.

This invention is illustrated in the accompanying drawings, in which Figure 1 is a schematic diagram of the invention in its provide a` subfnndamental form; Fig. 2 shows the circuit.

of Fig. 1 in `greater detail; Figs. 3 and 4 'the relative direction of current flow dm'ingjransm-ission and reception, respectively; Figs. 5 and 6 are forms of the invention which are assumed by it upon mechanical rearrangement of the elements for practical reasons; Fig.`7 is an arrangement of a substation fundamentally like that of Fig. 6 but modified for practical reasons; and Fig. 8 is a diagram of the elements of the balancing' network used in the substation of Fig. 7 when that substation is used on an unloaded line having considcapacity.

.It will be clear from an inspection of the design formulae hereinafter set forth that may, in general, be `either positive or negative, depending upon the values of theline and transmitter resistances. If, therefore, onel or both of the winding ratios results in a negative value, 1t is to be interpreted as meaning that the relative direction of winding of the coils whose winding ratio is negative must be the reverse of that shown in the diagram. lositive values should in general be used in practice.

In order to illustrate the scope of niy inventioii and elucidate the principles on which all specific embodiments rest. a` gcnei'al theoretical discussion will now. be given which applies to all substations satisfying the requirements heretofore stated in this specification. ln this discussion and the equations and forinulay inchided in this specification. the subscripts 1,2. 3 and 4: will refer to transmitter. receiver. auxiliary rcsistance and line. respectively. 'lhus 1 1 L. l, will denote the currents flowing iii transmitter, receiver, auxiliary resistance and line respectively. while li, will denote the resistance of the transmitter, lig. the rcsistaiice of the receiver, etc.

Consider a substation consisting of transmitter, receiver, auxiliary resistanceand appropriate transformer windings. connected to a line of given impedance. The line usually connects two similar and equal substations between which coniniunication is established. lt is a well-known principle that if a terminal impedance is connected to a` source of electroinotive force through a line of impedance 'LIRA-IRQ. where lt, is the resistance and RQ, the reactancc coniponent of the impedance, the terminal iinpedance mu'st be ILJR, for maximum absorption of energy. In particular. if the line impedance has no reactance con'iponent. thel iinpedanceof the tei'ininal arrangement as seen from the line should be equal to the resistance of the line. The condition. then. that the substation4 shall have maximum energy absorption from the lineI is that its impedance, as seen from the line. shall be numerically equal to the effective line inipedance. The significance of the foregoing ltice small, may: be eliminated by neutralizing reactance', and may be ignored in this theoretical discussion. The condition, then. that the substation have maximum energy ab sorption fromthe line is that its impedance as seen from the' line be a pure resistance of value equal to the effective resistance of the i impedance across must be R41 as seen .int

line. This condition is evidently equivalent 'to the following requirement; let an electromotive force be impressed on the substation terminals through a resistance equal to the impedance of the line; then the energy consumed in the substation shall be equal to the energy consumed in said resistance.

Further, line and auxiliary resistance are conjugate by requirement (2) as hereinbefore stated, or in other words, the auxiliary resistance is connected to points of equal potential with respect to an electromotive force applied to the line terminals. Moreover, the impedance of the substation as seen from the line should be equal to the impedance ofthe line to the signaling impulses. Let, then, an electromotive force E4 be impressed through a resistance R4 on a substation whose transmitter and receiver re*- sistances are R1 and R2 respectively, and let the resultant currents in line, transmitter and receiver be L, I1 and I2 respectively; the

from the line and the total resistance in series with E4 is 2R4, and since the current in the line is I4, it follows that -The total energy consumed may then be expressed by the formula Since the energy consumed by the substation is equal to that consumed by the resistance R, and is therefore onehalf of the total energy consumed, it follows that requirement (4) may r.be formulated by the following:

RLY (LYR: 'i' (102B:

This equation states that the energy consumption in the resistance R, is equal to that e substationrand` that the substation is equivalent, as seen from the line, to a resistance of value R4.

Similarly, if transmitter and receiver are conjugate the condition that the transmitter lshall have its maximum output to line and auxiliary 'resistance may be formulated as follows: Let an electromotive force E1 in the transmitter produce currents I1, 1 and I3 intransmitter, line and auxiliary resistance. Then, for maximum output, it fo llows that y I z I 2R I 2R (Ez (l and may be interprete as follows by re erence to Fig. 2. Let the transmitter be disconnected from the terminals b and c the substation terminals Equation (2) is the analogue of equation and let the impedance be measured across said terminals. Then if equation (2) is satisfied, the impedance so'measured is equal f I to the impedance of the transmitter itself. In other words, the impedance of the coinbination as seen from the transmitter is 'equal to that of the transmitter itself.

As hereinafter shown for the particular embodiments of my invention equation (2) follows as a consequence of the conditions of double conjugacy and equation (l). Therefore, the foregoing four requirements impose but three restrictions on the substation.

To complete the general discussion it remains to consider the energy division between receiver and transmitter when receiving, and between line and auxiliary resista-nce when transmitting. Let W0 be the total amount of telephonie energy developed by the transmitter at the transmitting substation; then, by equation (2) LLWO is the amount of energy delivered to line and auxiliary resistance. Let the amount of energy taken by the auxiliary resistance be a' times that taken by the line, then the amount of energy taken by the line is The over-all efficiency from transmitter 'of one station to receiver of communicating station is clearly proportional to the product ofthe transmitting efficiency and receiving efficiency; therefore, the over-all efliciency is by formulae (3) and (4) (fle) (re) If :v and y were independent, clearly the over-all efliciency would be a maximum for wzyzzo. For all substations embodying the -principles of my invention it may be readily shown, however, that a' and 3/ are connected by the relation .ry-:1. Eliminating a: from the above formula by means of this relation, the expression for the over-all efficiency becomes In order to demonstrate the above lstatement, namely that .mg/:1, designate the elements or branches T, R, X and L by 1, 2, 3 and 4, respeetively,land let 1 and 2 be conjugate and also 3 and 4 be conjugate. Further it Will be' assumed for an electromotive force in branch 4, equation (l) is satisfied, while for an electromotive force in branch 1, equation (2) is satisfied. Let S1, denote the current produced in branch or element 1 y a unit electromotive force S12 the current produced in branch 2 by a unit electromotive force in branch 1, etc. Then, by the eonjugacy of branches 1 and 2 and branches 3 and 4, it follows that Also by equation (l) 4R, 1 and by equation (2) (Soma:(Sams. (o

Now in accordance with the notation adopted in this specification, the energy consumed in branch 3 is m timesI that consumed in branch 4 when an electromotive force acts in branch 1; therefore (S14)2R1:.7/(S24)2R2 (e) Multiplying (b) and (c) (Sia)ZRlR'sT-l/(S24l2R2R4 (d) 'From (a) and (fl) it follows at once that energy developed Obviously the expression given'by iormula (5) is a maximum when jz/rl. This means that for a given amount of telephonie in the transmitter at the transmittingsubstation a maximum amount is usefully delivered to the receiver at the receiving substation connected by the line, when v/:L Sincethe maximum amount of energy in the receiver is the prime desidera- A tum oty telephonyait.would appeaizthat the substation should be designed to make yr-1.

Another consideration, however, modifies in branch 1,

(sec equation 4) while the amount. o'lE energy delivered from the transmitter of the communicating statlon 1s proportional to i/* (1w)2 (see equation 5). The ratio of the latter to the former is L, 1 'l-y and this increases as 1/ increases beyond unity. It will be clear, then, that ilE y is made greater than unity, the substation discriminates against line noise as compared with the signals it is desired to receive. The amount ot' discrimination desired depends of course on the amount ot line noise present. For conditions occurring in practice, it has been found by experiment that a desirable value for I1/ is 1.4. )Vith this value of y, the over-all efficiency is reduced 2.8% below the maximum for j/zl, while the receiving efficiency alone is reduced 16.6%. seen that a good degree ot' discrimination against line noise is obtained with a small loss in over-all eilieiency.

The above considerations as to over-all efiicieney and discrimination against line noise may be formulated as for an electromotive force inserted in the line. ln this equation 1/ is to have a value lying between 1 and 1.5 preferably.

Proceeding now to a description of the specific circuits, one form of my invention is illustrated in Fig. 2, in which L represents a telephone line terminating in a substation comprising a transmitter T, a receiver R, and an induction coil comprising windings N1, N2, and Nw findings N, and N2 are ot' negligible resistance,-but winding N., is of high resistance in order to balance the line L. The windings N N2 and N,i are conneetcd in series with the line L, while the transmitter T .is connected to terminals b and o .so as to shunt the winding il, and receiver R is connected to terminals c and e so as to shunt the high resistance winding N lf desired, the high resistance winding N3 may be replaced by a winding N., of negligible resistance and a se )arate resistance element X Condensers 11 and 12 may be inserted as indicated in order to determine the path 0f the direct current. through the substation. Condenser 11 will cause direct current to lt is thus as shown in liigs. 3 and 4.

flow through the transmitter T, and the condenser 12, if used, will also cause all the direct current to flow through the receiver. Direct current from the line will flow through the `winding N1 to terminal b, through the transmitter T, receiver R, terminal e and back over the line.

The operation during transmission is indicated in Fig. 3, in which the arrows represent the direction of current flow at any given instant. When the transmitter T is operated, variations in the current flow are produced, the effect being equivalent to applying a variable electromotive force to the transmitter. At a given instant, a current- I1 Hows from the terminal c through the transmitter to terminal b. At terminal b, the current divides and a current I4 equal to I3 flows throu h the winding N1 over the line L, through t e resistance X and wind-l ing N3 to terminal c, while a current I,--I,i flows in arallel therewith through the winding 2. Potentials are induced in the windings of the transformer of such value and direction that terminals c and e are brought to the same potential, so that no currentl flows through the receiver during transmission and consequently the substation isanti-side tone.

The action during reception is indicated in 'F ig. 4 and is as follows: Upon the application of a receiving potential to the line terminals, since no current flows through the auxiliary resistance, the' line and receiver are in a series circuit and aV current I2 equal to I4 flows from terminal f, through the receiver to terminal e, over the line L and through the winding N1 to terminal b. From terminal b a current I1 flows through the transmitter to terminal f. The transmitter current is greater than the line current and consequently a current I,-Ii flows from terminal c, through the winding N2 to terminal b. Potentials are inducedin theY transformer windings of such value and direction that terminals d and e are brought to the same potential, so that no energy is wasted in the auxiliary resistance during reception. v

The proportionin of the arrangement of Fig. 2, to satisfy t e fundamental requirem'ents of the substation of the invention will now be given. In deriving the design formules, the resistances of the transformer windings .will be ignored. It will be assumed further that there is no magnetic leaka e between the transformer 'windings and t at the self-impedances are vvery large compared with the impedances of any of the component elements of the substation or the impedance of the line. Experience has shown that these simplifying assumptions are justified and that the assumed conditions maybe closely realized in practice by careful design.

To formulate the condition ofconjugacy of transmitter T and receiver R, assume an electromotive force in the transmitter circuitl l and assume that the required condition of conjugacy is satisfied. In other words, assume that the terminals of the receiver are at points of equal potential with respect to an electromotive force applied to the transmitter. Let I1, I2, I3 and I4 denote the currents flowing in the transmitter, the receiver, auxiliarv resistance and line, respectively, and R1, R2, R3 and R4 denote the resistances of the corresponding elements. The condition of conjugacy of the receiver with respect to the transmitter requires that no current flow through the receiver during transmission and hence I2=0. It is also clear from Fig., 3 that 13:14. Since the auxiliary resistance, line and the three transformer windings are'in a series circuit, the algebraic sum of the drops through the transformer windings and the IR drop of the line and auxiliary resistance is equal to zero. Remembering that I3:I4, this condition ma be expressed as follows: l

Whence 1a3-=n3i3=n`312 Solving these equations we have R3-R4 n1 +fn2+frt3 R3 n3 which may be expressed En ein HB3- 1 ,n

whence wr RSI-,nl gnz-'R' Also the alegbraic sum of the ampere turns of the transformer" windings must equal zero, so that which reduces to I1= w-WMZML 8) lll;

the transmitter and the drop through the Also from equations (a) and (c) it follows winding N2 is equal to zero, so that that :[{qtzzRlIl R 7 1 ,3 )R (71), +7L2l7t3 2R *R s 3- n +11 n 1 urthermore, slnee ternunals el and e are at 1 2 2 70 the saluepotential, the algebraic sum of the whence drop through the winding N and the lll +72 n +7? M 2 lrop through the receiver equals zero. Re- @L f 2 3R4= `1 "2 "-1 R1 membering that 14:12 during reception, the n1 HL2 "Lz 1 l0 above condition may be expressed. 01' 75 IQLFRJFRJ, 2 R

422% .El (15) Also the algebraic sum of the ampere turns ((n" +n2) (nlhnzl-ns) 4 of the transformer windings equals zero, so

5 that Designating the ratios and as 1' and i" 80 @1142712 (I1-I4) respectively, equations (w14) and (15) may be From the above equations we get the. fol- Written lowing: r -l- 1" y z=a r R, (15) 85 R1 I1 'nz (T4-7") (T-I-T/-I-U-E @211:(711 'H1/Q14 Solving equations (1G) we have Rz nfs 14'772 u 72 Rl g *M moo R1 'n2 n2 :ye/+1) R.

rl/30731 nz) 01' -71'22 R1 1 i *UH/)y (17) u hence d R4 95 RZJHQZ n2)R1 9) a R I' I n, I 10 Mya/Kiowa 18) '2: 55ml `Substituting r and r" in equation we get Substituting the values given by equation the following: (8) in equation (2), we have l -R 1 )+r/)2 2 3` l 1 R1=R3+11 (12) y T 4o u2 l y2 R 105 Alsosubstituting the values given by equay n 1 Vtion (10) in equation (6), We have R4 HI/)y "YI/2 2 L i ,5 Rl-y 1%)112 13) 1M/R4 19) o Collecting formulae We get Also substituting 1' and 7" in equation (a) n3 *1 -l Ral ,)Rl e) RB-,Ri-Ri 20) 00 R =n3(n,+n2)R` (b) 'llhe design formulae .for the substation of 115 2 n2? 1 141g. 2 then become z 1 (LZMB R1=R3+R4 0) Rfm/R 55 2 2 1 12o nig 1 R1 il/(n1 +nz) R2 (d) Rs y-R4 (A) From formulae (b) and (d) it follows that R,

T=y Br/(Hy) o R ZQWLQR sl n1+m 2R 4 125 z'- nzz 1"?! ,n2 1 l l 1 whence 7" i Ely( +9) 1 Y i i l v; 1 1 n3=g n1+n2 (14) It will be seen fiom th I .tbme folmula,

that the impedanees of the receiver and auxiliary resistance are given in terms of the impedance of the line and ratio y. Also the transformer ratios r and r are given in terms of the ratio y and the impedances of the line and transmitter. Consequently', the impedance of the line being known and having selected a suitable value for the impedance of the transmitter and the ratio y, the remaining elements of the substation may be readily computed.

nspection of Figs. 1 to 4 inclusive, shows that there is a series arrangement of four components consisting of (l) line L, (2) windin N1, (3) the mesh consisting of transmitter T and winding N2 and (4) the mesh consisting of receiver R in parallel with winding N3 and resistance `X. Any rearrangement of parts which keeps those four components in series will be electrically equivalent. Fig. 5 isone example of rear rangement in which winding N,L is placed between the two meshes, and Fig. 6 is another example in which the line L and winding N1 are merely interchanged. Figs. 2 and 5 are particularly adapted for common battery substations and Fig. 6 is a suitable arrangement for a local battery substation, but may also be used as a common batbery substation. The design formulae above given are equally applicable to all of these several arrangements.

In Fig. 5, the condenser 13 will cause direct current from a common battery to pass through transmitter T. The condenser 14 may be used, if desired, to cause direct cui'- rent to be sliunted around the receiver R in case a permanent magnet receiver is used. If condenser 14 is notused, a part only of the direct current will pass through the receiver R. This will serve to magnetizethev receiver in case a neutral'receiver` is used. A neutral receiver is one whose core consists of a soft iron core which is only magnetized while current is being supplied to the receiver. If the arrangement of Fig. 6 is used with a common battery system, the condenser 15 may be used.

The assumptions upon which the theory for the forms of substation above discussed is based, are that the impedances of the line and substation elements consist of pure resistance. In cases where greater exactness 1 is required correction must be made for such departures from the assumed conditions as would reduce the operating efficiency below that required. Assuming a line of considerable distributed capacity or inductive reactance, then it becomes advisable to substitute for the pure resistance X, a balancing network, other than a non-inductive resistance, of such nature that its ratio of resistance and -reactance components closely app-roximates,

over the required range of voice current or signaling frequencies, the resistance and reactance components of the line in question.

lNecessarily, however, a substation which at one time is connected to a line of one length and at another to a line of another length, should be Idesigned for the averagesort of line with which it is to beused.

The substation in Fig. 7 is designed for use with a local battery. This circuit is iden tical in respect to the five fundamental properties mentioned in the beginning of this specification with that of Fig. 6. Forsecuring greater efficiency, the inductive reactance of the receiver R is balanced by a condenser 8 in series therewith. X represents a balancing impedance means or network. Network X may be a resistance or have different forms depending upon the nature ofthe line, the maximum cost allowable, and the degree of exactness required. For a line having considerable distributed capacity such as submarine cable, a suitable form is shown in Fig. 8 and consists of a capacity 9 in parallel with a resistance 10. The elements are of such values that the characteristic impedance of the line is approximately simulated. In other words, if a voltage of signaling frequency be impressed upon the line and a similar voltage upon the network X', the current will lead the voltage by an equal angle in the two cases while the ratio of the numerical values of the impedance of the line and the network depends upon the valueof the energy ratio y, as ex pressed by the second of equations (A).

Certain auxiliary elements are are battery B, a retardation coil, a three point switchhook contact S, ai ringer and a hand generator. `The battery B supplies current to the transmitter T and receiver B. The retardation coil 'has a very large iinpedance to alternating current-of voice frequency but allows the direct current to pass through to the receiver R. The effect of the retardation coil in shunting voice current is negligible. The usual three-point contact switchhook S is arranged to open the circuit of the battery B and also to cut off the substation from the line. The usual high impedance ringer and normally open circuit hand generator are bridged across the line as shown. Consideration will lshow that this circuit is fundamentally identical with that of Fig. 6. By eliminating the generator, ringer, switchhook'contacts, retardation coil, battery B and condensers 8^ and 9, the circuit reduces to the form of Fig. 6. Fig. 7 shows one .only of many possible adaptations and modifications of the circuits of Figs. 1, 5 and 6 for practical application.

The type of substation disclosed above and illustrated in the accompanying drawings is but one of a number employing only one used, which l land all of them are vemployed in its generic sense transformer and one auxiliary resistance, ideal in the sense that they satisfy the fundamental re uire'ments for an ideal substation, as statedclieretofore in this specification. The substations herein are of a type related to that of Figs. 1, 2, 3, 4 and l' (c) of U. S. patent to George A. Campbell, No. 1,254,472, dated January 22, 1918, and to those substations disclosed in U. S. patent to George A. Campbell, No. 1,254,117, dated January 22, 1918.

The circuits disclosed in both of the said applications are hereby disclaimed asa part of this invention, which is an improvement on and extension of the work of Campbell. However, as there are a large numberof possible substations of this general type which are not disclosed in the said applications, it will be understood that this invention is not limited to the specific embodiments herein illustrated, but is intended to include such equivalent arrangements as come Within the scope of the appended claims. Furthermore, it is not desired to limit'the design of the substations herein disclosed and illustrated to the accompanying design formulae. These 'formulae are derived on the assumption that ideal transformers are employed and that the component elements of the substation have no reactance, assumptions Which are only approximately justified in practice. The formulae may be modified when greater precision is desired by taking into account the fact that thetransformer is not physically perfect and that the line and the various substation elements may in general have some characteristic reactance. The accompanying formulae, how-ever, give quite satisfactory results, and Vthe methods by. which they are derived will enable one skilled in the art to compute more precisely the substation constants when desired.

It will be understood that in the appended claims, Where certain elements are said to be conjugate, or certain impedance relations aresaid to exist, since in practice these conditions can in general only be approximated, these expressions will be satisfied by structures substantially conforming thereto, especially Where some compromise With respect to the rigid requirements is necessaryv order to discriminate against line noise. It

Will also be understood that While my invention has beenspecifically illustrated and described as lembodied in a telephone substation, it is ca able of many and varied embodiments wh1ch render 1t applicable iin other kinds of signaling systems and conseuently the-invention is not to .be limited to t e particular form and use herein lidisclosed. It will be further understood that in this specification the Word substation is and that consequently its significance isnot limited to a subscribers telephone station but embraces broadly any telephone station including a repeater station for relaying telephonie sig- 'mitting apparatus` a path of high resistance,

and a receiver, said first and last mentioned paths and a winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said second mentioned path being included in a circuit shunted about said transformer Winding, said last mentioned circuit, said receiver path and said high resistance path' having a common terminal with respect to alternating signaling current.

2. A signaling circuit comprising a transformer, a path for the transmission and reception of signals, a path including a transmitting apparatus, a path of high resistance, and a receiver, said first and last mentioned paths and a Winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said second mentioned path being included in a circuit shunted about said transformer winding; said last mentioned circuit, said receiver path and said high resistance path having a common terminal with respect to alternating signaling current, said elements being so proportioned and related that the impedance of the combination comprisin said transformer, said first and third mentioned paths and said receiver, as seen from said second mentioned path, is equal to the impedance of said second mentioned path.

3. A signaling circuit comprising a translfolmer, a path for the transmission and reception of signals, a path including a transmitting apparatus, a path of high resistance, and a receiver, said first and last mentioned paths and a winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said second mentioned path being included in a circuit shunted about said transformer Winding, said last mentioned circuit, said receiver path and said high resistance path having a common terminal with respect to alternating signaling current, said elements being so proportioned and related that the impedance of the combination comprising said transformer, said second and third mentioned paths and said receiver, as seen from said first mentioned path, is equal to the impedance of said first mentioned path.

'4. A signaling circuit comprising a transformer, a path for the transmission and reception of signals, a path including a transmitting apparatus, a path of high resistance, and a receiver, said first and last mentioned paths and a Winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said sec ond mentioned path being included in a circuit shunted about said transformer winding, said last mentioned circuit, said receiver path and said high resistance path having a common terminal with respect to alternating signaling current, said elements being so proportioned and related that said receiver and said second mentioned path are conjugate.

5. A signaling circuit comprising a transformer, a path for the transmission and reception of signals, a path including a transmitting apparatus, a path of high resistance, and .a receiver, said first and last mentioned paths and a Winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said second mentioned path being included in a circuit shunted about said transformer winding, Said last mentioned circuit, said receiver path and Said high resistance path having a common terminal With respect to alternating signaling current, said elements being so proportioned and related that said third and irstmentioned paths are conjugate.,

6. A signaling circuit comprising a transformer, a path for the transmission and re ception of signals, a path including a transmitting apparatus, alpath of high resistance, and a receiver, said first and last mentioned paths and a Winding of said transformer being included in a series circuit, said receiver being included in a path shunted about said high resistance path, said second mentioned path being included in a circuit shunted about said transformer Winding; said last mentioned circuit, said receiver path and said high resistance path having a common terminal With respect to alternating signaling current, saidelements being so proportioned and related that the impedance of lthe combination comprising said transformer, said first and third mentioned paths and said receiver, as seen from said second mentioned path, is equal to the impedance of said second mentioned path, the impedance of the combination comprising said transformer, said second and third mentioned paths and said receiver, as seen from said first mentioned path, is equal to the .impedance of said first mentioned path, said receiver and said second mentioned path'are conjugate and said thirdand first mentioned.

paths are conjugate.

7. A signaling circuit' including in series four components, the first of said components including a line, the secondl of said components including a transformer winding, the third of said components -including a transformer Winding and a source of transmitting voltage in parallel, and the fourth of said components including a receiving instrument in parallel with a balancing impedance meansl and a transformer Winding in series, said windings having a common magnetic field.

8. A signaling circuit including in series four components, the first of said components including a line, the second of Isaid components including a Winding of a transformer, the third of said components including a second Winding of said transformer and a transmitter in parallel, and the fourth of said components including. a receiver in parallel vvvith a series arrangement of balancing impedance means Whose reactance approximately simulates the reactance of the line over the range of voice current frequencies, and a third Winding of said transformer. j

9. A telephone system adapted for use with a common battery system including in series four components, the first of said components including a line; the second of said components including a Winding of a transformer ;the third of said components includ1 ing a transmitter in parallel With a path containing a second Winding of said transformer; the fourth of said components 1 ncluding a receiver in parallell Withv a series arrangement of a balancing resistance means and a third Winding of said transformer.

10. A signaling circuit including in series four components, the first of said components including a line; the second of said ycomponents includinga Winding of a transformer; the third of said components including a second Winding of said transformer and a transmitter in parallel; and the fourth of said components including, a receiver in parallel with a series arrangement of balancing impedance means and a third Winding o-f said transformer, said elements being so proportioned that the impedance of said combination comprising said trans-y former, said` line, said receiver and said impedance mea-ns, as seen from said transmitter, is equal to the impedance of said transmitter. f

11. A signa-ling circuit including in series four components, the first of said compo# nents including a line; the second of said components including a Winding of a transformer; the third of said components including la second Winding of said transformer and a transmitter in parallel; and the fourth of said components including a receiver in parallel with a vseries arrangement of balancing impedance means and a third Winding of said transformer, said elements being so proportioned that the impedance of the combina-tion comprising said receiver, said transmitter, said transformer and said impedance means when seen from the terminals of said line is equal to the'effective impedance of said line. Y

12. A signaling circuit including in series 'four components, the first of said components including a line; the second of said,

components/including a winding of a transformer; the third of said components including a second winding of said transformer and a transmitter in parallel; and the fourth of said components including a receiver in parallel with a series arrangement of balancing impedance means and a third winding of said transformer, said elements being so 'proportioned that said receiver and said transmitter are in conjugate branches of said circuit. n

13. A signaling circuit including in series four components, the first of said components including a line, the second of said components including a winding of a transformer; the third of said components including a second winding of said transformer and a transmitter in parallel; and the fourth of said components including a receiver in parallel with a series arrangement of bal- -ancing impedance means and a third windformer; the third of said components including a second Winding of said transformer and. a transmitter in parallel; and the fourth of said components including a receiver in parallel with a series arrangement o f balancing impedance means and a third winding of said transformer, said elements being so proportioned that the impedance of said combination comprising said transformer, said line, said receiver and said impedance means, as seen from said transmitter, is equal to the impedance of said transmitter; andthe 1mpedance of the combination comprising said receiver, said transmitter, said transformer and said impedance means when measured from the terminals of said line is equal to the effective' impedance of said line; said receiver and said transmitterbeing in conjugate branches of said circuit; and said line and impedance means being in conjugate branches of said circuit.

' 15. A telephone circuit including in series four components, the first of said components includinga line; the second of said components including a winding of Aa transformer; the third of said components including a second winding of said transformer and a transmitter in parallel; and a fourth of said components-including a receiver in parallel with a series arrangement of balanc- Yto received telephonie currents.

17. A telephone substation including a neutral receiver and a transmitter which are in substantially conjugate branches, said substation having two points to which a local source of direct electromotive force may he connected, a complete conducting path from one of said points through said transmitter to the other of said points and another such path through said receiver, and a coil of large self inductance located in at least one of said paths. f

18. A telephone substation including ziy neutral receiver and a transmitter, conduct ing paths in said substation through which a local source of direct elcctromotivc force may propel current through each of said re ceiver and transmitter, one of said paths comprising means4 for retarding the flow of alternating current therethrough.

19. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmission circuit, another of said windings being included in said balancing circuit, and the third winding being included between said transmission and balancing circuits; a terminal of said transmission circuit, said icceiving circuit and said balancing circuit being joined together, the' other terminal o`f said receiving circuit being connected between said third winding and the circuit including one of the other two windings; said transmitting circuit being connected in shunt with said third winding, and a source of direct current so connected as to supply current to both said transmitting and said receiving circuits.

20. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmission circuit,.another of said windings being included in said balancing circuit, and the third winding being,included between said transmission and balancing circuits; a terminal of said transmission circuit, said recei'ving circuit and said balancing circuit being joined together, the other terminal of said receiving circuit being connected between said third winding and the circuit 1n- `cluding one of the other two windings; said 'transmission and balancing circuits; a terminal of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal ot said receiving circuit being connected between said third winding and the circuit including one of the other two windings; said transmitting circuit being connected in shunt with said third winding; and a source of direct current so connected as to supply current to both said transmitting and said recelving circuits, one terminal of said source beingconnected to said receiving circuit through a path of high impedance and low resistance.

22. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmission circuit, another of said windings being included in said balancing circuit, and the third winding being included between said transmission and balancing circuits; a ter-- minal of said transmission circuit, said receiving circuit and said, balancing circuit being joined together, the other terminal of said receiving circuit being connected between said third winding and the circuit including one of the other two windings; said transmitting circuit being connected in shunt with said third windin and a source of direct current included in series with said third winding, one terminal of said source being connected to said receiving circuit through a path of high impedance and low resistance.

23. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmis- 'sion circuit, `another ofsaid windings being included in said balancing circuit, and the third winding being included between said transmission and balancing circuit; a terminal -of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal of said receiving circuit being connected between said third winding and the circuit including one of the other two windings; said transmitting circuit being connected in shunt with said thirdwinding; and a source of direct current so connected as to supply current to both said transmitting and said receiving circuits, one terminal of said source being connected to said receiving circuit at a point adjacent its junction with said transmission and balancing circuits through a path of high impedance and low resistance.

24. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmission circuit, another of said windings being included in said balancing circuit, and the third winding being included between saidV transmission and balancing circuits; a terminal of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal ot said receiving circuit being connected between said third winding and the circuit including one offthe other of two windings;

said transmitting circuit being connected in shunt with said third winding; and a source ci direct current included' in series with said third winding, one terminal of said source being connected to said receiving circuit at a point adjacent its junction with said transmission and balancing circuits through a path of high impedance and low resistance.

25. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmission circuit, another of saidwindings being includedin said balancing circuit, and the third winding being included between said transmission and balancing circuits; a terminalof said transmissionl circuit,\said receiving circuit and said balancing circuit being joined together, the other terminal of said receiving circuit being connected to the junction point between said third winding kand said balancing circuit; said transmitting circuit being connected in shunt with said third winding, and a source of direct current so connected as to supply current to both said transmitting and receiving circuits;

26. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of saidv windings being included in said transmission circuit, another of said windings being included in said balancing circuit, and the third winding being included between said transmission and balancing circuits; a terminal of said transmission circuit, said receivwinding, l -cluded inseries with said third winding.

-ing circuit and said balancing circuit being joined together, the other terminal of said receiving circuit being connected to the junction point between said balancing circuit; said transmitting circuit being connected in shunt with said third and a source of direct current in- 27. In a signaling system, a transmission circuit, a transmitting circuit, a receivingcircuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmisd sion circuit, another of said windings being included in said balancing circuit, and the' third winding being included between said transmission and balancing circuits; a terminal of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal lof said receiving circuit being connected to the junction point between said third winding and said balancing circuit; said transmitting circuit being connected in shunt with said third winding; and a source of direct current so connected as to supply current to both said transmitting and receiving circuits, one terminal of said source being connected. to said receiving circuit through a path having high impedance and low resistance. f

28. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit, and a transformer having three windings, one of said windings being included in said transmis,

sion circuit, another of said windings being included in 'said balancing circuit, and the third winding being included between said transmission' and balancing circuits; a terminal of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal of said third winding and,

said receiving circuit being connected to the junction point between said third winding and said balancing circuit; said transmitting circuit being connected in shunt with said third winding; and a source of direct current included in series with said third winding, one terminal of said source being connected to said receiving circuit through said third winding and an inductance circuit.

29. In a signaling system, a transmission circuit, a transmitting circuit, a receiving circuit, a balancing circuit and a transformer having three windings, one of said windings being included in said transmission circuit, another of said windings being included in said balancing circuit, and the third winding being included between said transmission and balancing circuits; a terminal of said transmission circuit, said receiving circuit and said balancing circuit being joined together, the other terminal of said receiving circuit being connected to the junction point between said third winding and said balancing circuit; said transmitting circuit being connected in shunt with said third winding; a source of direct current so connected as to supply current to both said transmitting and receiving circuits; an inductance element through which said direct current may be supplied'to the receiving circuit, said inductance element being connected in shunt with a circuit including said balancing circuit, and its inductance being sufficiently high to substantially prevent the transmission of alternating talking currents through the inductance element while its resistance is so proportioned as to supply the optimum value of direct current to the receiver. i

In witness whereof, I hereunto subscribe my7name this 29th day of December, A. D. 191

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