US2131870A - Telegraph system - Google Patents

Description

Oct. 4, 1938. w. w. cRAMl-:R

l TELEGRAPH SYSTEM Filed Oct. l0, 1936 4 Sheets-Sheet l o 8 om mv /A/VE/VTOR W WCRAMER A TToRA/EV Oct. 4, 1938. w. w. CRAMER TELEGRAPH SYSTEM Filed Oct. 10, 1936 4 sheets-sheet 2 R V RE E mM M NLA m VR T Wm A Ww.,u W

Oct. 4, 1938. w. w. CRAMER TELEGRAPH SYSTEM 4 sheets-sheet s Filed 0G11. l0, 1936 www .www Mu HHHMWM m M+ l 0 L L NQ@ Hwnwnw HN IN1 m Hlll Mw w WW Oct. 4, 1938. w. w, CRAMER TELEGRAPH SYSTEM Filed Oct. l0, 1936 4 Sheets-Sheet 4 /N VEN Tof? W W CRA MER A from/Ey vPatented ct. 4, 1938 UNITED STATES j A j V2,131,8711 TELEGRAPHSYSTEM i Walter W. Cramer, Rutherford, N.

J., assignor to Bell TelephoneLaboratories, Incorporated,l New York, N. Y., incorporation ofNew York .Application october 1o193s,scra1`Nc. 164,959

This invention relates to telegraph systems and more particularly t'o improved arrangements `for transmittingtelegraph signal impulses over'long open-wire telegraph lines and over the telegraph channels of long open-wire toll lines.

Long open-Wire lines of thesev types are subjected to varying weather conditions. This causes a varying leakage resistance Vwhich varies over wide limits from a very high value under dry conditions to a relatively low value under wet weather conditions. Both` the duplex and upset duplex telegraph transmitting and receiving arrangements usually employed at the ends -of long lines of this type'must be adjusted to Compensate for this variation in the leakage current of the line in order to insure the correct reception ofthe telegraph signals. Variation of the leakage of the line `tends to cause aV variation'in the bias of the received signals which must be compensated for by `a variation of the biasing current of the receiving relays at each end of the line. This adjustment must be made in accordance with the variations in the 'leakage of the line so that it is necessary, at times, to adjust this bias current at the ends'of the line at rather frequent intervals, thus causing a high cost of circuit maintenance. This is particularly true in the case of an outlying subscriber Where it is very difficult lto provide suitable maintenance of the telegraph circuit because the subscriber is soi far removed from the telegraph station vor repeater point, as is the usual case when transmitting telei graph signals over long circuits of this type.

It is an object off this invention to greatly re- Y duce the amount of maintenance and adjustment required, rst, at the outlying or subscribers end of the lineV and, second, at both ends of the line without introducing any biasing or other distortion of the telegraph signals from any other source. Y

In accordance with one embodiment of this invention the outlying subscriber or telegraph station is arranged to be self-compensating or to require no balancing with changes in the leakage or leakage resistance of theline connectingv that station to the central station. This arrangement, however, requires additional maintenance and adjustment of the biasing current and balance at the central station because the signals received at the central station vary more with leakage than do signals received from the usual duplex arrangements which require balancing at bot ends of the line. In accordance with another embodiment of this invention; however,I after the central oiiice 29 claims. (ci. 17u59) end has been adjusted to correctly receive the signal impulses, Vthe adjustments atboth ends of the line need not be altered with changes in leakageolf the. line because thesignal impulses arriving thereat will cooperate with the receiving apparatus to produce signal impulses substantially unaffected by variations in the leakage of` the line. In 'other' words, the circuit is arrangedto fully and automatically compensate for changes in the Aleakage resistance of the line. A Itis `also within the scope of this invention to combine line sections of' the two` above arrangements and to combine either one with existing typesof line Sections in suitable comprehensive telegraph communication networks. Within the Scope'of this invention to modify and adapt these arrangements to operate satisfac- It is also l,

to-rilyV with various types of telegraph equipment and vario-us `types of telegraph circuits.

While the vnovel features of this invention are specifically set forth in the claims Vappended thereto, the foregoing and other objects and features fof `the invention may be more readily and more-'fully understood from the following descriptionwhe'n readA with reference to the'attached drawings in which:

Fig. 1 illustrates an embodiment of this invention requiring adjustment at only one end of the line'tocompensate for changes or variations in thel'eakagc of the line; Fig 2 shows an embodiment of the invention Viivhi'ch'requires no change in adjustment at either endof the line to compensate for variations in the leakage of the line;

Figs. B-A YtoY 3-C, inclusive, illustrate the various signaling conditions normally encounter'- ed in the system shown in Fig. 2;

. Figs; ihA to Ll-F, inclusive, illustrate in diagrammatic form the manner in which the various currents received from the telegraph line vary with leakage under various conditions;

Fig. 5 shows the manner in which Figs. 6, 7 and 8 are arranged to form a typical comprehensive system to which this invention is applicable; and Y Figs. 6, 7 `and 8 when arranged as shown in Fig. 5 show a comprehensive telegraph system embodying features -ofathe systems shown in Figs. 1 and v2-1nodiiied and adapted for use with different telegraph circuits. Referring now to Fig. 4l, A represents the iirst telegraph station and B the-second telegraph station `.which areconnected by telegraph line I0. Telegraph line I0 may be of any suitable direct current telegraph Vline or channel and may include or comprise a telegraph leg of a composited long distance toll line in which case it will include terminal composite sets as well as intermediate composite sets. In addition, various sec'- tions of the line may include entrance cable and open-wire lines. Various sections of the line may also be simplex lines and other sections may be straight direct current telegraphl lines. The open-wire sections of said line I0 are subject t0 varying leakage due to changes inthe weather conditions. sistance of the line is very high and usually may be neglected. However, during wet weather the leakage resistance of the line falls to a relatively low value which seriously interferes with the transmission of telegraph signal impulses over the line unless compensating changes are made.'

However, in accordance with Fig..1.the terminal equipment is so arranged that no compensation for changes in the leakage of the line need to be made at station B. At. statiorrB the line I0 is normally connected to ground through vthe sending contacts II of a suitable transmitting device such as for example the transmitting contacts of a teletypewriter` shown in Fig. 1. At station A telegraph signal impulses are transmitted from the contacts of the sending relay I2. The marking and spacing contactsof relay I2 are connected to two substantially equal sources of potential or batteries I3 and I4 of negative and positive polarity, respectively. These signals are transmitted over line III and actuate the receiving relay I5 at station B. Any leakage of the line to ground will affect both the positive and negative signal impulses or currents equally. Consequently, on arriving at station B these currents will operate the receiving relay I5 equally fast in both directions and will not therefore affect the bias of relay I5. In other words, the algebraic sum of these currents is constant. Since relay I5 is a polar relay and receives equal positive and negative current, it may be given a zero bias. In other words, it will operate as wellv and as, fast in one direction on positive current as it will operate in the opposite direction on negative current. Consequently, when this relay is so adjusted and receives positive and negative signal impulses from the contacts of relay I2, the response of relay I5 will be substantially independent of the leakage in line I0. This condition is further illustrated in Fig. 4-A which shows in diagrammatic form the current received by relay I5 as the leakage of the line decreases from innity to zero. Itis to be noted that the marking current received by relay I5 as shown by curve M,of Fig. 4-A increases just as much as the spacing current receiv-ed by relay I5 at station B decreases as the leakage resistance of the line decreases. It is to be understood that the curves in Fig. 4 are to illustrate this feature and that the scale of the leakage resistance has not been shown. Such a scale of leakage resistance is assumed as will make the curves M and S be straight lines. In actual practice if the scale of the leakage is linear, curves S and M will not be straight lines but curved lines which will approach the zero current condition asymptotically as the leakage resistance approaches zero. However, as-shown in Fig. 4-A at any given value of leakage the marking current received by relay I5 has the same magnitude as the spacing current received by relay I5. Consequently, relay I5 will respond to both marking and spacing current Without any addition of bias to the signal.

The term bias as applied to signals indicates During dry weather the leakage rea lengthening of one signal impulse and a shortening of the other signal impulse. For example, marking bias means that the marking signal impulses are lengthened and the spacing impulses shortened, whereas spacing bias means that the spacing signals are lengthened and the marking signals are shortened. Thus the greater the bias of the signals the less satisfactory they are for operating telegraph apparatus or the poorer in quality they are, while the less the bias the better `the quality of the signals.

A common cause for this lengthening and shortening of the various signals is that the marking and spacing currents are unequal, for example, for marking biasthe marking current is greater than the spacing current whereas for spacing bias the spacing current is greater than the marking current. However, as pointed out above with the arrangement shown in Fig. l, the receiving device I5 at station B receives equal marking and spacing current and consequently does not introduce any bias in the received signal and requires no biasing winding tocompensate for any such bias. The terms marking and spacing as used in this applicationv'diierentiate the two line or signaling conditions transmitted between telegraph stations. The term marking is used to designate the line or'signaling condition employed during the time no signal impulses are being transmitted but the system Vis energized and ready totransmit signal impulses. The term spacing designates other signal or line condition.

Referring again to Fig. 1, ytransmission from station B is effected by the opening and closing of the contacting device II in accordance with the signal impulses to be transmitted. During the open periods of these contacts battery I6 is connected through resistance Il to the line II). The potential of battery I5 is of the same polarity as the source of potential I3 normally connected to the telegraph line at station A. However, the source of potential I6 is of a greater magnitude than the source of potential I3 or the potential of point 23 so that it overpowers the potential source I3 and causes current to ilow in the reverse direction over line I0. If, as in the preferred embodiment, source I6 is twice the magnitude of source I3, or rather the potential of point 23, then the two line .currents will be of equal magnitude `lout opposite polarity. Under these conditions the receiving relay I8 would require no additional biasing or balancing winding. However, since a balancingwinding I9 is provided, a biasing winding 2l] must also be provided to compensate for the direct current flowing in winding I9 to insure proper operation of the receiving relay I8. The balancing winding I9 and balancing network 2I are required to prevent the operation or relay I8 during the transmission of signal impulses from the sending relay I2 over line I to station B. If there were no leakage ori-the line,'current through the biasing winding 20 could be adjusted once by means of resistance 22 and thereafter remain constant.

However, in case a variable lead due to varying weather conditions is encountered in line I0, it will be necessary to alter the adjustment of the biasing current by varying resistance 22 to compensate for variation in the leakageV current. Fig. 4-B shows the manner in which the marking and spacing currents received at station A from station B vary with variations of the leakageresistance of line III.r In order to compensate for variations` of the leakage resistance it is necessary to adjust the bias of the receiving relay |8 along line 89 of Fig. l-B. It is also possible to control the'potential of point -23 by varying the-resistance 24 and thereby also eiiect the compensation `forthe variation of the leakage ofV the line. It should be noted that the values of both the positive and negative potentials applied to line ||l are varied by resistance 24,` thus insuring that the bias of the signals received by the receiving relay |-5 at station B will be unaffected by the Avalue of the leakage resistance of the line. i

Coils25, 26 and elements 21, 28 and 29 are provided tok reduce thenoise in aI telephone circuit due to the operation of the transmitting devices at the respective telegraph stations and also `to properly adjustland control the magnitude of the line current flowing in line I0. Itis to be understood that anysuitable filter arrangement may beused in place of the coils 25 and 2B to reduce noise in the telephone circuit. In addition this noise reducing arrangement maybe omitted in case the line is not composited and transmits only direct current telegraph signal impulses. l* w At station B printer magnet Y3|.' is connected to the contacts of the receiving relay l5. A compensating resistance 3| is also-connected to these contacts. The compensating resistance '3| is provided to maintaina load on sourcelE-, `which is the same as the source 32, so that substantially constant potential is applied to the printer magnet and line I during the operation of receiving relay l5. When the relay moves to its'opposite or spacing conta-ct it interrupts the circuit of magnet 3|), thus decreasing the load on source I5. The potential of source I6 will then tend to increase. To prevent this resistance'Sl is connected to the source 32 which is the same as I6 and providesa compensating load to maintain the voltage thereof substantiallyconstant. In addition, when contacts Il open during transmission of signal impulses, relay l moves to its opposite contact. This reduces the impedance between the line and the source of potential shown as |6 and 32. Resistance 3| serves, under this condition, to reduce this impedance and maintain it ata low value and thus tends to improve the transmission from station B. This resistance `is more essential in case the load carrying capacity of this source of potential, which may be a rectifier or small motor generator, is just about adequate to supply the load.

Elements 33 provide contact protection for the contacts of receiving relay |5. Y

Sending relay |2 and receiving relay |8 may receive signals from and transmit signals to other relays of other types of suitable telegraph repeaters, as, for example, duplex telegraph repeaters, Vvoice frequency carrier current telegraph repeaters, carrier current telegraph repeaters, etc., as Well as from subscribers lines. In addition sending contacts may be replaced by sending relay contacts actuated by another subscribers line. In this case the contacts of relay |5` would transmit toV the subscribers line. In the embodiment of this invention shown in Fig. 2, the terminal circuits of line |0'are arranged to transmit and receive telegraph signal impulses so that the received signal impulses at both ends of the line will be substantially independent of variations in a leakage of the line'.

For the purpose of illustration, it will be first assumed that the leakage resistance of the line is concentrated at a single point and is represented' byA leakage resistanceRa inY Fig. 2 connected to line.. lll. The resistance of line I0 is represented by resistance R1 and R2, which also include the resistance of theterminal apparatus connected to the respective ends of -line I0. As in Fig. 1, it is to be understood that line il may comprise any suitable direct current telegraph channel, including the telegraph channel of a composite-toll line, inwhich case the line may include both terminal and `intermediate composite sets. In addition, line |l may include portions of cable circuits including entrance cables commonly employed in open-wire lines, where these lines pass through cities and towns. As in Fig. 1, the line at station B is normally connected to ground through the contacts oa sending relay 38. Signals are transmitted from station A to station B by means of sending relay 2 which may be actuated by signal impulses received from anysuitable source, including various types of telegraph repeaters. Relay |2htransmits the corresponding signal impulses or currents by connecting the positive and negative sourcesof potentials i4 and i3, respectively, to the telegraph line Ill. These sources ofV potential are of `substantially equal magnitude so that substantially equal currents of opposite polarity will be transmitted over line IE! in accordance with the `operation of relay |2. These currents will be equally attenuated by the line and the leakage resistance and will have substantially the same value when received by relay l5 at station B. Receiving relay l5 at station B is provided with substantially no or `Zero bias so that receiving relay I5 will respond equally well to both of the signaling currents received thereby and will, consequently, introduce 4no bias distortion as described in connection with Fig.V l and shown inlig. l-A. f

In order to more readily understand the opera- `tionfof the transmission of the signals in the reverse direction from station B to station A, referencewill be made to Figs. B-Ato 3-C`, inclusive, which-illustrate the various signaling conditions.

. Fig. 3-A illustrates the connections to line |0 when .both stations are normal or transmitting marking signal impulses. ,.li'ig. S-B shows the conditions when station A is transmittinga spacing impulse to station B. As may be readilyseen from these gures, the positive current transmitted to station B under these conditions will be attenuated substantially the same amount as the negative current from station A under marking conditions. Consequently, the algebraic sum of. these two currents, as received at station B, will be independent of the leakage resistance Rs of line lll because the sum will always be zero.

Fig. S-C shows the circuit connections during the time a spacingimpulse is being transmitted from station B to station A and if the receiving device at station A is torespond to this spacing impulse as readily as it does to the marking impulse, when the line lil is connected to ground as shown inr Fig. S-A, it will be necessary for the algebraic sum ofV the currents received at station A to be independent'oi the leakage resistance Raof the line. It will be also necessary to adjust themagntude of the bias of the receiving relay i8' at station A to the'average of these two currents to insure proper operation which is inderent i1 received at station A during the transmission of marking impulses from station B, as illustrated in Fig. 3-A, is as follows:

Rz'Ra R1+R2+R3 and the current i2 received at station A during the time the spacing impulse is being transmitted from station B is as follows:

E2R3 i2 E- 1+ RH- R3 Rz-Rs R1+R2+Ra The sum S of these currents i1 and i2 is E2-R3 2E1+R2+R3 Rz'Rs R1+122+R3 As pointed out above, if the signals received from station B are to be substantially independent of the line leakage resistance R3, it is essential that the sum of these two currents shall be independent of the value of the leakage resistance R3 or dS fr Diiferentiating the sum S with respect to R3, equating it to Zero, and simplifying, the condition required for the sum S to be independent of the value of R3 is as follows:

Thus we see that by controlling the relative magnitude of the potentials at each end of the line with respect to the location of the leakage resistance along the line, it is possible to maintain the algebraic sum of the marking and spacing currents as received at station A substantially independent of the value of the line leakage resistance.

In the above example, it was assumed that the line leakage resistance R3 Was concentrated at a denite point along line I0. In practice, however, this leakage resistance is usually distributed along the line or along some portion of the line. If the exposed portion of the line which experiences the variation of line leakage is somewhere near the center of the line,rthe line leakage may be replaced by a concentrated effective line leakage resistance which is at the center of the exposed line and the potentials at the ends of the line adjusted in accordance with the position of this concentrated effective leakage resistance R3. In case the line is substantially all open-wire line and all, therefore, subjected to varying distributed leakage throughout its length, the concentrated eiective resistance may not be at the center of the line. It has been discovered that if the terminal impedance of the receiving and transmitting devices connected'to the line is very low, the distributed leakage of the line I0 may be replaced by a concentrated effective leakage resistance which is located approximately 0.4 of the resistance of the line from station A. If the terminal resistance of the line is relatively high, then thc distributed leakage of the line should be replaced by an effective resistance which is substantially at the center of the line between stations A and B. In practice, the position of the equivalent concentrated Vresistance is usually between about 0.45 and 0.5 of the resistance of the line from station A.

The action of the circuit during the transmission of signal impulses from station B to station A may be also explained by reference to Fig. L.l-C. In this gure the line marked M represents the variation in the marking current received at station A during the time a marking impulse is transmitted from station B by sending relay 38 connecting ground to line I0 over an obvious circuit. Similarly, curve S illustrates the manner in which the current received at station A varies with the leakage resistance of the line during the times spacing impulses are transmitted from station B by relay 38 connecting the source of positive potential 93 to line I0. It is to be noted that as the marking current increases the spacing current decreases a corresponding amount so that the sum of the currents is substantially constant. By providing a biasing current for the receiving relay at station A which is equal in magnitude but opposite in direction to the average of these two currents represented by line I3 of Fig. 4-C, the resultant magnetic eiect oi these two currents upon the received relay I8 will be substantially equal under all conditions of line leakage. Thus, the response to the receiving relay at station A is also independent oi the line leakage resistance R3.

It should be noted that during spacing signal impulses transmitted from station B to station A of Fig. 2, the line current is increased because the source of potential 93 at station B aids the source of potential I3 connected to the line at station A. This is just the opposite from the arrangement shown in Fig. l in which the source of potential I6 connected to the line at station B opposes the potential I3 normally connected to the line at station A. In the usual telegraphic circuit, resistances R1 and R2 are approximately equal so that the magnitude of the source of potential I6 should be approximately twice the magnitude of the source of potential I 3. Under these conditions the line current is increased to about three times its normal Value when a spacing signal is transmitted from station B to station A. When resistances R1 and R2 are approximately equal, substantially equal powers or currents are received by the receiving relays at both ends o1" the line. This means that the relays at each end of the line should be of the same sensitivity and that the length of the line is not limited by the apparatus or relays at one end more than by the equipment at the other end of the line.

In order to readily adjust the effective values of these potentials, a variable resistance 24 is connected between the armature of the sending relay I2 and line I0, as shown in Fig. 2. rIihis variable resistance permits the potential of point 23, which is the effective potential applied to line IIJ, to be varied because resistance 24, in combination with resistance 29, the resistance of the balancing windings of relays I8, 34, 35, and the resistance of balancing network 2i, form a potentiometer. Thus, by varying the resistance 24, it is possible to vary the potential of point 23 and thus adjust the effective value of the potential applied to line Ill at station A. It should be noted that with this arrangement, the values of both the positive and negative potentials applied to line I0 are simultaneously varied, so that they are both of substantially the same magnitude and thus transmit currents of substantially the same magnitude to station B independently of the value of resistance 24, thus insuring that the bias of allo receivinglrelay I at station B will .be unaffected by Variations 91" the;.1a.kagez l." esistane 0f @913155 As shown in Eig. 2, the particular system i'sv adaptedfor `use in a telegraphic system in which an averageu of `the twoline conditions `received from stationB. It isto be understood thatthese relays may be provided. additionfal. ,vs'liruiings-, .l Y 1 bythe usual vibrator ywindings connected inthe usualvibratorfcircuit and con-` Y as, for example,

`milled by the vibrating relay V35.11;@@sito `be understood that `a similar arrangement may also-l be provided, at station Av of 1.` ,Howeven under certain conditions, i as, for exarnple,` with relatively short lines, the vibrating relay maynot,`

be required. .t y. Y* t f t l l Since no bias orv zero biasis required for. the; receiving relay l5 at station B, the balancing network 36, connectedto the balancing; Winding `3'I of relaylj, `isprovided to balance onlyY the `alter- `hating-current componentspi the telegraph sig-V .nals transmitted over line `I t). With this arrange-f.

ment the auxiliary bias Vwindings shown-on the relays at station `A :are eliminated. It `is-.to be understood that a similar arrangement'of the receiving relay may be employed at station `B` in the arrangementvshown in Fig-V. l. The arrangement shown :inFigtvZl has `a further advantage in that the received telegraph" signal impulses and` particularly the higher frequency alternating-c11r` rent components.ofA these received signal impulses do notl need to pass through the `high inductance of element 2t of the transmitting noise vlter.

' The printing magnetv or :relay 3Q of Fig.-2 .is arranged toreceive, polar signalV impulses from ref ceivingrelay. I5. One terminalY of thegwinding of relayrisconnectedto the armature of relay I5, while the other `terminal `of the windingof relay 3E) is `connected toaboutthe mid-point of potentiometer comprising resistances 46 so .that this mid-point issubstantially'at half the'poten-v tial of source 93.. Ihe'marking and spacing. con-V tacts of relay I 5 are connected to ground through marking contacts of thefsrending relay 38 `and-tc battery 39 through the rupper winding `of-.the

break relay 4I, respectively. `Thus when receiveY ing relay I5 is; on one contact, current :flows from the mid-pointv of potentiometer `comprising` resistances throughthewinding of relay ormagnet 30 to ground and when relayQ-I 5 is onits other contact, current flows` in the ,opposite direction through `the windingof relay Gr :magnet- I5 from battery through the contacts of relay I5.l to the mid-.point of potentiometer` llt.A f

Break relay 4I isprovided to insuratheY inten# ruption or, the home copy of the `teletypewriter machine at,stationBduring,the reception V-ofza break: signal over line it?. Thishrelaylisonly re-V quired for teletypewriters which are not provided with a break lock.l `In addition, relay 43` is provided to normally connecttherline I0, toground through resistance Il'l'during thei'time the appa ratus at station'Bis lshut down and the power supply 'disconnected It is to be understood that additional `telerypa writer apparatus may be connected in `series withv the teletypewriterapparatusfshown atV station B. For example, additional transmitting contacts IImay be connected in seriesrwith Vthe transmi-L additional `receiving relays or magnets 3i? may be connected-in series With'th'e magnet M30 shown in Fig. 2, providing additional local telegraph transmittingtandreceivingstations; anyone of which may .transmit messages to' all of theothers and over vline I,as` well asreceive messages from line I Il.;V Furthermoregthe` .transmitting and receivinglapparatusfcohnected to both ends cf the line maybe" part of repeaters'connected to any type of,v Llegr'iph linesandapparatus su'chas to subscribfr'slinescomposited toll lines, carrier curfait` 1ines,.etc.i ,t v l ',.A compensating Altiadl is` connected to the contacts of the Vceivingvrelayf I5 and the source oipotential' 4l) to lprovidefa more constant load andthus a more constant Vsource of potential,

thus insuring moreuniform ,operation of the circuitfarrangement during lthe transmission of sig-` n'al irnpul'sesjbyfrelay 38j.,` Thisv compensating resistarjice'-3l isparticularly desirable when the sources of potential 16,33 and '4t are provided by a rectifier or motor` generator of small power Capacity. t l

. 4IrlV adjusting "the circuitV arrangement shown in Fig. YZgit, is` usually`, desirab1e to provide asource ofpdtential'BS abouttwice as Ygreat as the sources of potential v,I3 .and I4, and vto make minor adi iustinehts'ifthe'effective potential transmitted to line tIfllfroni station A byfvarying the value of advantage thatpallfthe adjustments may be made aton en'dlofjthe line; preferably at the central, inter nnecting or branch point or station shown as statior1 ,A,i`rl Fig. 2.j 1

M`fI,ria's'muchas.thepowenreceived by the receiv- V ingrelays `aticach of the stations is less during wet"weathe`r ,ortimes oflow leakage resistance;

is usually Vdesirable to adjust resistance 24 and alsothe resistance 22 of the biasing circuits of the receiving relays at station A at this time so as tojinsure'proper operation` of these relays. Thenfwhen the Lleakagefresistance R5 increases duringthe dry Weather," the power available to operate the relays increases and the'adjustments are not so critical." However, the magnitudes of `both the marking and spacing currents increase biaspf receiving relays is to adjust the biasing currentowing through the biasing windings, as

` forexample, by adjusting the values of resistance 2 2. atfstation-Ajof Figi. 2. This has the effect vof raisingor lowering thevbias line shown in Figs. 1 Aj to` Lf-F.Y ;InFig. ,4f-D, this condition is il lustrated where the bias line 45 is shown raised. Under. these conditions', it should be noted that the-spacing current crosses the biasline in some position valongthe line, depending upon the amount `thebiasis varied. IThis means that as the leakage current varies, the biasing current through the relaysmust also be varied to provide the same amount ofbias tot the signals received thereby vand transmitted from its contacts. However, by also varying the resistance 24 at station vA it is possible to raise orlower the apparent intersection ofthe-marking and spacing curves, as

`shown in Figefi-,IEi so that they will intersect on resistance. L This arrangement has the further the new bias line 44 as shown in Fig. 1 -E. When this is done, the amount of bias addedjto the signals by the biasing current flowing through the biasing windings is more nearly independent of the value of the leakage resistance R3 and consequently will require much less adjustment as the leakage resistance of the line varies.

As pointed out above, the curves shown in Figs. fl-A to 4-F are shown as intersecting straight lines merely to illustrate the relative manner in which these two currents vary, it being understood that the leakage scale is not linear but is so proportioned that the marking and spacing curves M and S are straight lines. If the leakage scale were linear, then the lines M and S would be curved and .approach the bias lines as asyxnpf totes.

It is to be noted that the transmitting impedance of transmitting apparatus at both ends of line Il) in both Figs. 1 and 2 is substantiallythe same during the transmission of both signaling conditions. Thus the cable capacity will be charged and discharged equally under both signaling conditions when either of the two stations is transmitting. Consequently, no distortion will be introduced from this source in the arrangements shown in Figs. l and 2. In Fig. 2 the marking contact of relay 38 is connected directly to ground while the spacing contact is connected to a source of positive potential 93 through a protective resistance 92. Resistance 92 is usually so small, however, that the impedance as seen from the line is substantially the same when relay I5 is on either contact. Likewise contacts I I. of Fig. 1 are connected directly to ground, while line I0 is connected to sources I6 and 32 through additional resistances when these contacts are open. These additional impedances or `resistances should be as small as possible without placing too great a load on the power supply. In practice the impedance to ground is substantially constant under both signaling conditions so thatV it is only necessary to make very slight bias adjustments at the other end of line Ill (station A) to compenfl sate for these different impedances.`

While only single line sections have been shown in Figs. l and 2, it is to be understood that these embodiments of the invention may be modied and adapted to i-lt into comprehensive telegraph systems connecting a number of stations over both single section and multisection lines. A typical system of this type is illustrated in Figs. 6, 7 and 8 when arranged in accordance with Fig. 5. The system shown in these figures is designed to provide communication between the outlying subscribers or telegraph stations 49, 50, 5I, 52 and 53 by means of line sections in'accordance with this invention. Fig. 7 shows a more or less central connecting or branch station or point. 'Ihe apparatus shown in Fig. 7 will usually be located in one central oflice or interconnecting'station. However, it is to be understood that this need not necessarily be so because each one of the repeaters shown in this gure may be located at a Vdifferent point and still be connected together by telegraph lines to provide satisfactory communication between the various outlying telegraph stations.

The subscribers or outlying telegraph stations 49, 5G and 5I are connected to the central point by means of circuit arrangements in accordance with Fig. 1. However, inthe case of stations v50 and 5I an additional outlying station close to the other station is shown connected to the same line to the central station. In this case, instead of connecting ground to the common terminal of the transmitting device I I located at station 5I, a line is extended from this common connection of the contact device II at station 5I over a short local telegraph line 54 to a second station 50. The circuit arrangement at station 50 is somewhat modied from that shown at station 5I of Fig. 6 and at B in Fig. 1 in that the printing magnet of a printing telegraph machine or other receiving device 30 is shown connected directly to the contacts of the receiving relay I5 and is not connected in the circuit of source of potential I6 and resistance I1. Either arrangement works equally well. However, the arrangement shown at 50 requires slightly more power than the arrangement shownlat station 5I of Fig. 6 and station B of Fig. 1. It should also be noted that the source of power at station 5I is shown to be a rectifier and it is to be understood that the power supplied at any of these stations which are illustrated by either batteries or rectiers in the various gures of the drawings, may be rectiers, batteries, motor generator sets, or other suitable sources o direct current power. In addition, it is essential in the case of the rectifier 55 shown at station 5I that the direct current side be ungrounded and insulated conductively from the alternating-current power supply 56 connected to the rectier.

As in Fig. 1 the line from the receiving relay I5 passes through elements 26 and 21 to reduce the noise of the telegraph signals in telephone circuits in case the line passes over a composited telephone and telegraph line. In addition, the line I0 extends to the repeater 51 at a distant point. The lineV side of the repeater 51 is similar to the arrangement shown at station A of Fig. l` The receiving relay is provided with a line winding, balancing winding and a biasing winding. In addition, the sending relay 58 connects negative and positive battery to the line through the noise lters or filtering element 25 and resistance 24. 'I'he telegraph line at the subscribers station yis normally connected to ground so that the positive and negative signal impulses transmitted from repeater 51 to both telegraph stations 5I and 52 are equally attenuated. Consequently, receiving relays I5 at these stations when adjusted to have Zero bias respond equally well to both types of signal impulses independent of the leakage resistance of the line I0. The spacing signal impulses transmitted from stations 50 and 5I to the repeater51, however, connect the source of potential 55 or battery I6 to line I0. The sources of potential 55 and battery I6 are about twice the magnitude of the sources of potential I3 and I4 of repeater 51 shown in Fig. 7. This causes the line current to reverse during spacing impulses transmitted from stations 50 and 5I to repeater 51. However, as pointed out above in case of line leakage, variations in the bias of the receiving relay I8 of repeater 51 shown in Fig. 7 must be adjusted to compensate for the different line leakage resistances as shown in Fig. Ll-B. The local side of the repeater 51 is provided with a sending relay 58 and a break relay 59 which are in turn connected through a single line repeater 60 to other repeaters as shown on Fig. 7. Repeater 6l) may be located at the same point as repeater 51 or may be connected thereto by means of `a short telegraph line or conductor 6I. It is to be understood, however, that the length of this line 6 I, also the length of line 54, is short in comparison with the length of line I0.

Single line repeaters 60 may be of any suitable 75 ratus lshown at station 52. However, the source of power associated with terminal apparatus 88 is usually insufficient to permit loops of several miles between the terminal apparatus and the teletypewriter 52.

The terminal apparatus of. repeaters and 84 connected to line 85 is also arranged in accordance with the embodiment of this invention shown in Fig. 2, which is self-compensating and requires no adjustment in the apparatus at either of these repeaters and repeater stations to compensate for variations in the leakage resistance of line 85. It is to be understood that the repeaters or repeater stations 82, 84, 86 and 88 are all located along the telegraph line or channel between the interconnecting station shown in Fig. 7 and the outlying station 52 shown in Fig. 8. However, it is to be noted that the equipment connected tothe ends of line 85 has been reversed. In other words, the end of line 85 towards the interconnecting station shown in Fig. 7 is connected to ground and positive battery by repeater 86 instead of to positive and negative battery, while the 'end of line 85 more remote from the interconnecting station of Fig. 7 is connected to positive and negative sources of potential by the equipment in repeater 84. It is thus obvious that the equipment at the ends of the long telegraph lines or composited, telegraph channels may be inter- Vchangedto that shown and described'in and with reference to Fig. 2. This also applies with respect to the embodiment of this invention shown in Figi, it' being obvious that the transmitting and receiving apparatus shown at station A might be equally well located at station B if the apparatus at station B were located at station A. It is also possible to arrange either or both the systems shown in Figs. 1 and 2 in long lines with either end of any of the sections toward the central oiiice and the other end away from the central oiiice. Thus, it is possible to have a repeater comprising two terminal equipments similar to that shown at station B connected together or two similar to the equipment shown at station A in Figs. 1 and 2 connected together, or it is possible to have equipment shown at station B connected to equipment similar to that shown at station A of either Fig. 1 or 2 and either of these embodiments connected to the line extending towards the central oiiice and the other equipment connected to a long toll line extending away from the central oice or interconnecting point.

As shown in Fig. 2 variable resistance 24 isprovided to control the potential of point 23 and thus make all the controls for insuring that both ends of the line will be self-compensating at the central office end rather than at the outlying end. In case, however, the apparatus at two ends of -the line are interchanged, in other words, the apparatus at station B is located at the central or interconnecting point, apotentiometer may be provided between the contacts ofthe sending relay 38 and line I 8. This will permit the adjustment of the potential applied to this end of the line so that all the adjustments still can be made at the central point and none at the outlying subscribers telegraph stations.

The repeaters connected to line 81 are similar to those connected to line 85 excepting as pointed out before. The equipment located at the interconnecting station shown in Fig. 7 connects sources of positive and negative potential to line 81 whereas the repeater equipment of repeater 88 connected to line 81 connects positive potential and ground to the line. vIn other words, the

equipment at the two ends of the line is reversed from that of line 85.

It is to be noted that the system shown in Figs. l and 2 will not operate as a full duplex telegraph system. That is, signal impulses cannot be transmitted over the line connecting the stations A and B in both directions at the same time and independently of each other. It is only possible to transmit these signals over the system in one direction at a time. This is due to the fact that when the source of potential is connected to the line at station B by the transmitting devices at this station, the receiving relays at both stations A and B are positioned independently of the transmitting device I2 at station A. In Fig. l the receiving relays I5 and I8 at stations B and A, respectively, are positioned to their spacing contacts or positions when the transmitting contacts I I are open, so that sources of potential I6 and 32 are connected to line I0. The armatures of these relays remain on their spacing contacts so long as the contacts Il, or any break contacts in series with them, remain open independently of the position of transmitting relay I2 at station A. In Fig. 2 the armature of relay I5 at station B is positioned to the marking contact while the receiving relay I8, break relay 34 and vibrating relay 35 at station A assume their spacing positions when sending relay 38 connects the source of potential 93 to the line. These relays assume these positions and maintain them during the time the sending relay 38 is connecting battery to the line independently of the position of the sendingrelay I2 at station A. It is thus evident that during the time potential is connected to the line at station B it is impossible to transmit signals from station A to station B. Consequently, it is impossible to operate these systems on a full duplex basis.

The arrangements shown in Figs. 1 and 2, however, have the advantage, when operated in the so-called half duplex manner of operation in which signaling impulses are transmitted in only one direction at a time, that the usual number of break relays are not required. This can be mor-e fully understood by reference to the more comprehensive system shown in Figs. 6, 7 and 8.

As described above, stations 50 and 5I are connected to a central interconnecting point or station by means of the telegraph system shown in Fig. 1.

When it is desired to senda break signal from stations 50 and 5I during the time they are receiving signalimpulses from the interconnecting stations shown in Fig. 7, the transmitting device Il at either of these stations, or a break contact connected directly in series with them, is open. This connects either source of potential i6 or 55, as the case may be, to line I8. As pointed out above, under this condition, the receiving relays i5 at stations 50 and 5I as well as the receiving relay I8 of repeater 51 at the central interconnecting station shown in Fig. 7 assume their spacing positions and maintain these spacing positions independently of the position of the sending relay 58 of repeater 51. This insures the breaking of the signals received at stations 58 and 5| and also the transmission of a break signal through repeater 51 by the receiving relay I8 over line SI to the other repeaters and stations oi .the system shown in Figs. 6, 7 and 8.

When it is desired to transmit a break signal from some other station of the system to either stations 58 or 5I during the time they are transmitting telegraph signal impulses to the other stations, a break signal will be transmitted from the station desiring to send the break signal. Assume that the break signal is transmitted through the singlelinerepeater 60 of Fig. 7 over the line 6I to repeater 51 and thence over line I to stations 5| and 50. Under this condition, the line 6I is opened bythe single line repeater 60 sothat the lower windings of the sending relay 58 and the break relay 59 control these relays. Since these windings are connected to thereceiving relay I8, these relays will follow the receiving relay I8. Now, the receiving relay I8 of the repeater 51 will follow the signals transmitted from the transmittingdevice Ilat stations 58 or 5I independently of the position of the sending relay 58 of repeater 51 so that relay I8 may continue to followthe signal impulses transmitted from stations 50 and 5I. However, under these conditions the break relay 59 connects the same potential to both contacts of the receiving relay' I8 so it will not cause relays 58 and 59 to follow the operation of relay I8, thus insuring that the sending relay 58 remains on its spacing contact and transmits aspacing signalto stations 58 and I. This spacing signal will interrupt the recording of the home copy fat these stations `and i thus indicate to the attendant ,that another staover this system.` y

tion wishes to break in and transmita message It is thus evident that a break relay` is required at onlyone end of theline I0,V namely, the end at which signals are transmitted by connecting potentials of opposite polarity to the line.

As pointed out above, signal impulses are transmitted from station 49 over line 62to repeater 63 by meansof the system shown in Fig. 1. Since the other line 64 connected to repeater 63 is provided with anintermediate station 65 which may open the line 64 toztransmit break signals tostation -ll9, it is necessary that repeater v63l be also provided with a break rel-ay 12 which operates in a manner similar to that described with reference to the break relay 59 of repeater 51. In case line 54 does not include an intermediate telegraph station, then the break relay 12 will not be required because the line 64. would neverbecome open-circuited. Consequently, both the windings of relays 1I and 12 would be atall times effective so that the positionof` the armatures ofthese relays would be independent of the position of the armature of the receiving relay I8. `Under these conditions no break relay would be required because the sending relay 1I would move to its spacing contact on break signals received from line 64 and remain there so' long, as the break signalis received by this relay.l It'will, therefore, transmit this break signal to station 49' during the time station 49 is transmitting the signal impulses and indicate to the operatorithere that another station of the system may wish tol break in and transmit a message.

Signal impulses are transmitted over the line 61 between repeaters 56 and 68 in accordance with the telegraphV system shown in Fig. `2. Whenjit is desired to-transmit a break signal from station 49 orstation 6:5 whichA is connected to repeater 66 by means of line 64 during' the time theV signal impulses are being received at these stations' from another station connected` to the telegraph system shown in Figs. 6, 7 and 8,

line 56 may be open at station 65. This causes the sending relay 10 of repeater 61 to move toits spacing contacts during thev next marking. signal impulse received by receiving relay94 from line 61.` This will. maintain relay 94 in its marking the transmitting station indicating to the trans-YV mitting operator or attendant that station 65` wishes to interrupt the transmission of signals andtransmit to the other stations of the system.

vIn case it is desired to'transmita break signal from some other station of the system to station 55 during the time station 65 istransmittingsignal impulses, the break signal will be transmitted from these stations' through repeater 58. Assume that the break signal isltransmitted through single line repeater 60 which will open line 69to transmit a break signal to repeater 68. This interrupts the circuit of the upper or line windings of the Ysending relay 96 and the break relay 91 of repeater 68. This means that these relayswill beoperated by theirlower windings from the received. relay 95 which will follow thesignal impulses-'transmitted from stationV 65. To prevent sending relay 96 from following these signals and interfering with the break signal it (relay 96) Vline 61 `after the break signal is received over line 69. This insures'that both thersend andbreak relays 96 and 91 thereafter remain on their spacing contacts and transmit a spacing or break signal to station {i5-through repeater 66. It is thus evident that in the'arrangement shownV in Fig. 2"as in-the system'shown in Fig. l, a break relay is required only at the end of the line that positive and negative sources of potential are used to transmit the signal impulses over the line.

The same break arrangement is also shown in the repeaters 13 and 14 connectedto the ends of line 15'. Repeater 13` connects sources of both positive and negative potential to line 15 to transmit signal impulses to repeater 14. Consequen'tlya break relay 98 is required at this repeater.Y Repeater 14, however, transmits impulses .of one polarity and ground over line 15. Consequently, no break relay is required andnone is provided.

As pointed out above with reference to line 84, no break relays are provided for repeater 84 of Fig..8" because repeater 84 of Fig. 8 is a through repeater andthe line.85 connected thereto does not come to an intermediate station, so that this line is neveropen.` Thus, both the line and balancing.V windings of relay 99 to repeater 8d are always effective to control this relay. Consequently, the position of the armature of this relay isindependent of the position of the receiving 'relay' |90 of this repeater, sothat break signals willbe transmitted through repeater 84 in both directions without the use of break relays.

TheY telegraph station 52 is connected to repeater'82- by means of two loops, one loop being used to transmit signal impulses and the other loop" being used to receive signal impulses at station 52. In this case due to the divided loop between station 52 and repeater 82, it is necessary to makesome provisionsin repeater 82 to insure theprope'r transmission of break signals to and from station 52. The transmission of break signals from'station 52 duringthe reception of signal impulses thereby is similar to the transmission of break signalsV from station 53 in that the receiving ,relay 38 of repeater 82 is operated to its spacing position. This connects a source of potential IIlI to the line 83 which causes receiving relay I5 to be maintained in its marking position, thus insuring the transmission of the break signal independently of the reception of signals from line 83.

However, in case it is desired to transmit a break signal to station 52 during the time signal impulses are being transmitted from station 52, some means must be provided to prevent the sending relay 38 of repeater 82 from operating the receiving relay to its marking position during the time the receiving relay I5 is in its spacing position. If such additional means are not provided, the operation of relays 38 and I5 as described will interfere with the transmission of the spacing or break signal from relay I5 to station 52. As shownin repeater 82 the spacing contact of relay I5 is connected to the upper or line winding of the receiving relay 38. This causes relay 38 to lock in its marking position when relay I5 has been operated to its spacing position by the reception of the break signal as soon as relay 38 is operated by a marking signal transmitted irom station 52. This insures the proper transmission of the break signal received over line 83 to station 52 because relay 38 is locked operated so relay I5 will be maintained in its spacing position so long as the break signal is received over line 83 and will transmit the signal to this station 52 independently of the operation of the transmitting device II at station 52.

In case the received signal impulses` are transmitted over the receiving loop of the split or divided loop by means of polar signals, that is,

the signal impulses of positive and negative polarity, both contacts of the receiving relay I5 are required to transmit these signal impulses. Consequently, the spacing contact is not available to lock the transmitting relay 38 in its operated position during the time the break signal is received and thus insure the proper transmission of the break signal to the telegraph station or apparatus. In this case, as shown in Fig. 2, an additional break relay 4I is required. This relay is connected in series with the spacing contact of the receiving relay and connects ground in parallel with the transmitting contacts or device II at station B, thus insuring the proper transmission of a break signal from receiving relay I5 to the receiving apparatus at thestation during the time signal impulses are being transmitted by the transmitting device II because the operation of transmitting device II at thisY time cannot cause relay 38 to repeat the signal impulses transmitted thereby.

It should be noted that the receiving relay I5 at station B- of Fig. l correctly responds to both the signal impulses received from station A and to the signal impulses transmitted from station B so that the receiving magnet of the printing or recording device 30, when connected directly to the contacts of this receiving relay I5, will record both signal impulses received from station A and the impulses from station B, which is usually called the home copy.

However, the receiving relay I5 of station B of the system shown in Fig. 2 responds only to the signal impulses transmitted to station B from station A but does not respond to the signal impulses transmitted from station B. Consequently other provisions must be made for the recording of the home copy at station B. As shown in Fig. 2, the circuit of the printing magnet 30 of the receiving or recording'device at'this stationis connected in series with the transmit- -ting contacts of relay 38, so that it will also receive the signal impulses transmitted by the transmitting relay 38 from station B.

.This is also true of the circuit of magnet 3U at station 52 which is connected to the transmitting contacts of the sending relay 38 so that it will receivezthe same impulses as are transmitted from station 52 and thus provide a home copy of the ymessages transmitted from station 52. In the case of station 53 the receiving magnet is connected directly in series with the transmitting contacts II so that it will follow all the signal impulses transmitted by these contacts. In this arrangement no special provision is, therefore, necessary.

The term source of potential as used in this specication and, in particular, in the appended claims includes sources of zero potential, i. e., ground potential, as well as sources of both positive and negative potentials.

What is claimed is:

l. A telegraph communication system comprising a first station, a second station, a direct current telegraph line connecting said stations, terminal composite circuitsr included in said line, intermediate composite sets included in said line, an open-Wire portionsubject to varying leakage conditions included in said line, receiving means at each of said stations, transmitting means at each of said stations connected to the ends of said line for transmitting two signaling conditions to the other of said stations the values of which are soi related to each other and to said line that the algebraic sum of the currents of said signaling conditions at the other of said stations is substantially independent of variations of the leakage resistance of said telegraph line, said transmitting means being arranged to have substantially the same impedance when transmitting both of said conditions to the opposite station, and variable biasing means at one of said telegraph stations for adjusting the receiving means thereat to respond equally to said two conditions transmitted thereto from the other of said stations.

2. Atelegraph system comprising a rst station, a second station, a direct current telegraph signaling channel connected between said stations, transmitting means at said first station for connecting sources of potential of substantially equal magnitude but opposite polarities to said telegraph channel, transmitting means at said second station for normally connecting ground to said telegraph channel and for connecting a source of potential to said channel in accordance With signal impulses to be transmitted thereby which is so related to said other sources of potential and to said channel that the algebraic sum of the currents received at said iirst station is independent of variations of the leakage resistance of said telegraph channel, receiving apparatus at said second station for responding to the sources of potential of opposite polarities connected to said channel at said rst station whereby the algebraic sum of the signaling conditions received at said second station is independent of variations of leakage of said telegraph channel, receiving apparatus connected at said first station,`variable biasing means connected to said receiving apparatus at said first station for biasing said receiving apparatus to respond equally to both signaling conditions connected to said channel at said second station.

3. A telegraph system comprising a first station, a second station, a direct current telegraph communication channel connecting said stations, receiving apparatus connected to said channel at each of said stations, transmittingapparatus at said rst station for normally connecting a source of potential to said channel and transmitting apparatus at said second station for normally connecting ground to said channel, additional means connected to said transmitter at said rst station for connecting to said transmission channel in accordance with the signals to beitransmitted a source of substantially equal magnitude, but of opposite polarity to the source of potential normally connected to said transmission channel at said lrst station, and additional means at said second station for connecting a source of potential to said transmission channel in accordance with the signals to be transmitted of such a value that the current normally flowing over said line is increased, said sources 4of potential being so related to each other and said transmission line that the algebraic sum of the `signaling currents received at each of said sta-` tions from the other of said stations isgsubstantially independent of the leakage of said line.

4. A telegraph system comprising arfirst station, a second station, a direct current telegraph channel connecting said stations, said channel including terminal and intermediate composite sets and a portion of open-wire line subject to varying leakage, means for transmitting and receiving two diierent signal conditions to and from each of said stations, resistance means connected in said line cooperating with the transmitting means at each .of said stations for rendering the algebraic sum of the signaling currents received at each of said stati-ons substantially independent of said varying leakage, and biasing means associated with said receiving means at each of said stations for producing a biasing eiiect upon saidrreceiving means which is substantially one-half Vthe effect of the algebraic average of said received signaling currents but opposite in direction thereto.

5. A telegraph system in which the receiving apparatus responds equally well to all signaling impulses for any given value of leakage resistance comprisinga telegraph line subject to varying weather conditions, means for normally transmitting current over said line, means/for transmittingv signal impulses of opposite polarities over said line connected to one end of said line, means for transmitting signal impulses of current substantially three times the magnitude of said normal current from the other end of said line, and receiving apparatus connected to each end of said line which is responsive to the signal impulses transmitted from Vthe other end of said over and means for adjusting the magnitude ofV said sources of potential so that the ratio of substantially twice said rst potential to said second potential, is equal to the ratio of the `resistance of said line measured from said first end to the point where an equivalent concentrated leakage resistance would be connected to the line to the remainder of the resistance of said line.

'7. A telegraph system comprising a telegraph line, transmitting and receiving apparatus connected to each end of said line, sources of positive and negative potential connected to the transmitting apparatus at. one-end of said line,

ground'and a source of one potential connected to the transmitting apparatus at the other'end of said line and potentiometer means connected between the transmitting apparatus at the iirst end of said line and said line for so adjustingthe relative potentials connected to the ends of said line that the sum of the currents received at each end of theline is substantially constant and independent of the leakage resistance of the line.

8. A two-way self-compensating telegraph system comprising a rst station, a second station, a telegraph line connected between said stations, means for normally connecting a source of potential to one end of said line and for connecting ground to the other end of said line, means for transmitting signal impulses of opposite polarity connected to the iirst end of said line, and means for transmitting signal impulses of increased magnitude from the other end of said line, receiving means connected tof each end of said line for receiving impulses transmitted from the opposite end of said line, and variable bias means connected to the receiving apparatus at said first end of said line, and means connected to said line for controlling the relative magnitudes of said impulses so that the algebraic sum of impulses of different character is substantially constant and independent of the leakage resistance of the line.V

9. A telegraph system in accordance with claim 8 characterized in this that a potentiometer is connected between the transmitting means at said rst end of said line and said line for adjusting the relative magnitudes of said impulses of different character, whereby all of the adjustments ofthe relative magnitudes of said impulses by which the .algebraic sum of the received impulses is made independent of the leakage of said line, may be made at said rirst end of said line. 10. A self-compensating telegraph system comprising a rst'telegraph station, a second telegraph station, means for normally transmitting a current over said line, meansrfor transmitting signal impulses of opposite polarity in o-ne direction over saidf line and signal impulses of increased magnitude in opposite direction over said line, the receiving means connected to each end of said line for receiving the impulses transmitted from the opposite end of said line, and means for adjusting said receiving apparatus and the magnitude of said impulses so that the bias of the received impulsesis substantially independent of the leakage of said line.

11. A two-way telegraph system comprising a first station, a second station, adirect current telegraph channel connected between said stations, means for transmitting two signal conditions of opposite polarity from said rst station to saidl second station, means for transmitting two signaling conditions of different magnitude from4 said second station to said first station, receiving apparatus at each of said stations connected to said line for receiving the signal conditions transmitted from the other of said stations, and means for adjusting said receiving apparatus and the relative 'magnitudes of all said signaling conditions so that one of said signaling conditions at each of said stations increases as much as the other of said signaling conditions decreases with a change of the leakage of said line.

12. In a two-way telegraph system, a rst station, a second station, means for transmitting signal impulses from each of said stations to the other of said stations, means at each of said stations for receiving impulses transmitted to it from .the other of said stations, means for so adjusting the bias of said receiving apparatus and means for so adjusting the magnitude of the signaling impulses that the eiective bias of said receiving apparatus is automatically varied with changes of the leakage of said line to maintain the quality of the received signals substantially constant.

13. A telegraph system comprising a line, a portion of which is subjected to variable leakage resistance, receiving apparatus connected to each end of said line, apparatus for transmitting two diierent signaling currents from each end of said line the sum of which as received at the opposite end of the line is substantially constant and independent of said line leakage resistance and biasing means connected to said receiving apparatus which produces an eiect opposite to and substantially equal to one-half the magnetic effect of the sum of the signaling currents received by said receiving apparatus.

14. A method of operating a telegraph system in which two signaling currents are transmitted in each direction thereover which comprises adjusting the magnitude of the two currents received at each end of the line so that their sum is substantially constant and independent of the leakage resistance of said system and adjusting the bias of the receiving apparatus at each end of the system so that its magnetic effect is opposite to and equal in magnitude to substantially one-half the magnetic eiect of the sum of the two signaling currents received thereby.

15. A signaling system comprising a line, a portion of which is subjected to a variable leakage resistance, transmitting apparatus connected to each end of said line for transmitting two signaling conditions thereover the sum of the currents of which, as received at the opposite end, is substantially constant and independent of the value of said variable leakage resistance, receiving apparatus also connected to each end of said line, and biasing means connected to said receiving apparatus which produces a magnetic effect thereupon opposite to substantially onehalf the magnetic effect of the sum of said currents received thereby.

16. The method of operating a telegraph system in which two signaling conditions are transmitted over a telegraph line in each direction which comprises adjusting transmitting potentials at both ends of the line so that the sum of the currents received at each end of the line for both signaling conditions remains substantially independent of the value of the leakage resistance of the line and adjusting the receiving apparatus at each end of the line to respond equally to both signaling conditions received thereby.

17. The method of operating a telegraph system a portion of which is subjected to a variable leakage resistance and in which two signaling conditions are transmitted in each) direction' thereover which comprises adjusting the transmitting potentials at each end of the system so that substantially the same magnitude of current leaks o through the leakage resistance for each of the signaling conditions transmitted over the system in each direction and adjusting the rcceiving apparatus connected to the system to respond equally to the two signaling conditions received thereby.

18. The method of operating a telegraph system a portion of which is subjected to a variable leakage resistance in which two signaling conditions are transmitted in each direction thereover which comprises adjusting the transmitting potentials at each end of the line so that potentials of substantially the same magnitude appear across the effective leakage resistance for 'both the signaling conditions transmitted in each direction over the system and adjusting the receiving apparatus to respond equally to the signaling conditions transmitted from the opposite end of the system.

19. The method of operating a telegraph line a portion of which is subjected to a variable leakage resistance which comprises applying three signaling conditions thereto, adjusting the potentials for causing said signaling conditions so that the potential across the eiective leakage resistance of said line is of substantially the same magnitude for all of said signaling conditions.

20. An impulse transmitting system comprising a line, impulse receiving apparatus connected to each end of said line, impulse transmitting apparatus connected to each end of said line having two positions, means effective when said transmitting apparatus connected to one end of said line is in either of said positions for connecting to said line sources of potential which are so related to each other and to the electrical characteristics of said line that the bias or the impulses transmitted in one direction over said line is substantially constant and independent of the leakage resistance of said line, means eiective when said transmitting apparatus connected to the other end of said line is in either of said positions for connecting to said line sources of potential which are so related to each other and to the electrical characteristics of said line that the bias of the impulses transmitted in the other direction over said line is substantially constant and independent of the leakage resistance of said line.

21. An impulse transmitting system comprising a line, impulse receiving apparatus connected to each end of said line, impulse transmitting apparatus connected to each end of said line having two positions, means for connecting sources of potential to said line when said transmitting apparatus are in their respective positions for causing impulse currents to flow thereover, which potentials are so related to each other and to the electrical characteristics of said line that the algebraic sum of the impulse currents received at either station from the other station is substantially constant and independent of the leakage resistance of said line.

22. An impulse transmitting system comprising aline, impulse receiving apparatus connected to each end of said line, impulse transmitting apparatus connected to each end of said line having two positions, means for connecting sources of potential to said line when said transmitting apparatus are in their various positions, which sources of potential are so related to each other and'to the electrical characteristics of said signaling conditions transmitted from either end of said line is the same.

23. An impulse transmitting system comprising a line, impulse receiving apparatus connected to each end of said line, impulse transmitting apparatus connected to one end of said line for transmitting two different impulse currents over` said line, means for so establishing the polarities and magnitudes of said currents with respect to each other and the electricalcharacteristics of said line that their sum as received at the opposite end of said line is substantially constant and independent of the leakage resistance of said line, impulse transmitting apparatus connected tothe other end of said line for transmitting two different impulse currents over said line, means for so establishing the polarities and magnitudes' of said currents with respect to each other and the electrical characteristics of said line that their sum as received at the opposite end of said line is substantially constant and independent of the leakage resistance ofsaid line.

24. An impulse transmitting system comprising a line, impulse receiving apparatus connected to each endof said line', impulse transmitting apparatus connected to each end of said line for transmitting two different impulse currents over said line, means forso establishing the polarities and magnitudes of said currents with respect to each other and to the electrical characteristics of said line that the bias of said impulses as received at the opposite end of the line is substantially constant and independent of the leakage resistance of said line.

25. An impulse transmitting system comprising a line, impulse receiving apparatus connected to each end of said line, impulse transmitting apparatus connected to each end -of said line for transmitting two different impulse currents over said line, means forso establishing the polarities and magnitudes of said currents with respect to each other and to the electrical characteristics of said line that said impulses as received at either end of said line differ by the same amount from an average value for any given value of leakage resistance` of said line.

26. An impulse transmitting system comprising a rst station, a Isecond station, `an impulse transmitting channel connected between said stations, impulse transmitting apparatus connected to said channel at one of said stations for transmitting impulsesof .two different magnitudes over said channel, the magnitudes of which are so related to each other and to the electrical characteristics conditions transmitted of said channel that their sum remains substantially constant and independent of the leakage resistance of said channel and receiving apparatus connected to said channel `at said second station for responding to said impulses.

27. An impulse transmitting system comprising a first station, a second station, an impulse transmitting channel connected between said stations, impulse transmitting apparatus having two p0- sitions connected to said channel at one of said stations for transmitting impulses of two diilferent magnitudes over said channel, impulse receiving means connected to said channel, means for connecting a source of potential to said channel at said second station and means for connecting sources of potential to said` channel when said transmitting apparatus is in either of said positions, which potentials are so related to each other and to the electrical characteristics of said channel that the sum of the currents received at said second station is substantially constant and independent of the leakage resistance of said channel.

28. A telegraph system comprising a telegraph line, means at each end of said line for impressing upon the line two signaling conditions, a biased receiving instrumentality at each end of the line to respond to said two signaling conditions trans- Vmitted from the other end, means effective with any leakage current between zero and a large value whereby one of said vsignaling conditions transmitted at either distant end of said line adds an eiTect of a certain magnitude to the biased condition of said receiving apparatus, and means effective with the same line leakage current whereby the other condition subtracts an effect of equal magnitude therefrom.

29. A telegraph system comprising a telegraph channel of a composite toll line subjected to variable leakage resistance conditions, receiving apparatus connected toI each end of said line, means for applying two signaling conditions to each end of said line, potential means connected to said transmitting apparatus so related to each lother and to the distribution of the line resistance and leakage resistance that the magnitude of potential across the equivalent concentrated leakage resistance of any given value is substantially the same for all the signaling conditions b-ut of opposite polarity for the two signaling from either end of the line. l

WALTER W.` CRAMER.

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