US1135654A - Intercommunicating trunk-line telephone system. - Google Patents

Description

R. M. BEARD. INTERCOMMUMCATING TRUNK LINE TELEPHONE SYSTEM. APPLICATION FILED MAR. I, 1907. RENEWED AUG. 25. 19m.

1 1 6% Patented Apr. 13, 1915.

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ATTORNEY-5 R. M. BEARD.

INTERCOMMUNICATING TRUNK LIN'E TELEPHONE SYSTEM. APPLICATIQN FILED MAR-1,1907, RENEWED AUG. 25. 1914.

Patented Apr. 13, 1915.

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7% Mfl 7% 6/ T //v VE/V I05 12 Audi 71 4; dd 1 By ATTORNEYS srarne rarnnr ornrpn.

nronann M. BEARD, on NEW roan, n. r.

INTERCOMMUNIOATING TRUNK-LINE TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Apr. 13, 1915.

Application filed March 1, 1907, Serial No. 360,006. Renewed August 25, 1914:. Serial No. 858,520.

. T aZZ whom it may concern:

sarily large number of wires required con- I Be it known that I, RICHARD M. BEARD, a citizen of the United States, residing at New York city, in the county of New York and State of New York, have invented certain new and useful Improvements in Intercommunicating Trunk-Line Telephone Systems, of which the following is a full, clear, and exact description.

My present invention relates generally to telephone systems, and specifically to an intercommunication trunk system for con necting two or more groups of intercommunication telephones, each of which said groups is wired according to a modification of a method fully set forth-inmy former patent application Serial-No. 292,916, filed December'22, 1905.

The system of my former application is, like all other intercommunicationsystems in one respect, subject to a certain limitation, inasmuch as it is not readily adaptable to a very great number of stations. The necesstitutes a practical limitation of the number of stations, and besides the station to station method does not readily lend itself to the needs of a large factory, or other institution, having a great number of telephones. Such institutions are usually systematically divided into a number of departments, each of which is under aresponsible head, and

each department is as a rule so extensive as to require several telephones. It is found objectionable from the standpoint of proper system and discipline, for the party at any telephone to be able to call and talk directly with any other station in the system. Although'it is important to have telephones located at many places toreach the lesser employees, it is also a prerequisite of good management for the responsible heads to exercise a certain amount of supervision.

The small isolated central exchange .has

the objection that another separate telephone, or system of telephones, has to be used for talking with the outside public; and the private branch exchange for handling both local and outside traffic has the disadvantage that any station in the local system can get connection through the switchboard with the outside world. Manufacturers of the latter type of switch boards haye frequently been called upon to build a switchboard inwhich it is impossible for certain local stations to be connected with the public system. This has the serious ob ection of inflexibility. Without some inflexible construction of the switchboard, the local operator must be relied upon to use indivldual judgment in making proper connections. In this matter, it is as difficult for a central operator to exercise autaoritative control over the traflic, as it for any central oflicial to direct the details of so large an establishment. many responsible heads is the accomplished fact in .the management of great institutions, such as large manufacturing plants,

Departmental division under one system, and to develop a plan of supervision by monitor stations to more correctly meet the departmental conditions in the large institutions requiring so many telephones.

Another object of equalimportance is to secure absolute secrecyof communication.

' A further object, no less in importance than any, is thelcomplete abandonment of all bell-hanger methods and the substitution of strictly telephonic methods throughout, so the system may be connected to the public telephone system without detrimental effect. T accomplish these objects by dividing the telephones into separate local groups, each 'of which constitutes a complete intercommunication system, and connecting the separate groups for inter-departmental communication by means of suitable trunks.

The telephones of one group may be con v eniently located at various points in a'sin gle department, and a certain telephone may be designated amonitor station where all audible trunk-signals are'located and where all incoming trunk calls are received.

The monitor station would appropriately be partment would come under competent su-' pervision, and at the same time all communications would be absolutely secret."

\Vithout regard to the exact scope and novelty, which'will be pointed out in the claims, my invention generally consists, first, of a sealed Secret service or private line systemof telephonic intercommunication from one station to another of three or more stations,'with0ut the necessityof a central oflice, and without the serious ob]ect1on of a third party being able, through any manipulation of his own telephone or switching devices 'or even by tapping any wires, except by opening up sealed parts, to listen in while two other parties are 1n communication; and secondly,

of a secret trunk line connecting a group of stations insaid system to another group -in the same system, and also sealed at every point where the said trunk could otherwise be tapped for listening in, .said trunk line being arranged so that, in each of said groups, only one station at a time 'can be connected therewith, unless the party at the said one station desires by means of his own switching apparatus to connect other stations, and provided at each station with means to indicate when in use at some other station.

Generally'the organization comprising my invention consists of the combination of telephone, signaling and switching apparatus located at each of three or more stations, in-

dependentwires respectively connecting the apparatus at each one of the stations forming a group with the apparatus at each one of the remaining stations in said group, a trunk line connecting all the stations of one group to all the stations of another group, a common battery located at some convenient point for supplying signaling and talking currents, and common wires connecting the common battery with the apparatus at all of the stations. ,L,

By reference to the drawings, which form a part of this specification, a more detailed description will be given, and afterward the'operation will be explained.

In, the drawings: Figure 1 is a diagrammatic view showing the nature and principles of the system of the various local and trunk lines used in an embodiment of my invention;

dinary local station.

Fig. 2 is a diagram of circuits for a pair of stations connected by a trunk line; Figs. 3 and '4; are face views respectively of the telephone sets of a monitor station, and an or- Fig. 5 is a diagrammatic view showing the actual circuit conditions during trunk line telephonic CulllDHL- 'nication; the circuit conditions during local communication may be traced in this figure by the dotted lines.

I will first generally consider the broad features and general aspects of the invention, and afterward describe in detail all the particular connections and circuits of a practical embodiment thereof.

Referring to Fig. 1, there is shown diagrammatically a complete system of twentyfive stations, each represented by a circle. The lines connecting the different stations represent ordinary telephone connections or wires, each line representing a pair of metallic wires of the usual form used in telephone work. In practice these wires are, of course, collected into compact cables and sometimes inclosed in metallic tubing cx-. tending from one station to another, but in the diagram they are drawn in a conventional way so as to more clearly illustrate the theory of the arrangement. It will be observed that the twenty-five stations are divided into five groups, and each group may be considered some local department of a factory. For instance, the different groups may correspond to five different buildings of a manufacturing establishment, and each building has five telephones at the different departments or rooms thereof. The

different telephones or stations of the groups are designated by the numerals I, :2, 3,4 and 5, and the different groups are designated by the characters A, B, C, D and E. Some of the calls of this system will be local between the different stations of the same department, While part of the traffic will be interdepartmental, z'. 6., from stations of one group to stations of other groups. In the first instance the system is purely an intercommunicating one, and operates in the same way as set forth in my prior application, No. 292,916. In the second case, the system is intercommunicating in the sense that it operates without any central exchange, but is a trunk system in the sense that it makes use of certain trunk wires or connections, which are common to a number of stations for connecting separate systems or groups of stations. The arrangement by which the intercommunicating groups of stations may be connected over trunk lines without the use of any central exchange, I consider 'an important feature of the invention. I also consider an important feature of the invention the arrangement by which busy signals are given when trunk messages are being sent. I also consider a very important feature of above and the particular arrangement ofv the circuits by which the busy signals are given in case of trunk messages will later appear from a consideration of the other figures of thedrawings.

It will be observed that there are extending from the stations 1 of each of the groups A, B, C, D and E, four lines or pairs of wires, and these wires lead to each of the other four groups of the system'inevery case. For clearness, the connections are shown in direct single lines, but it isto be understood that in ,practice pairs of wires will be collected into cable in metallic pipes or conduits. These lines or pairs of wires are the trunk lines or connections. They are extended through all of the stations 1, 2, 3, 4: and 5, of each of the groups, as shown. The last station at which they terminate in each group is what I call the monitor station, because at this station is located the monitor or person who looks after incoming trunk calls from distant stations. In addition to the four trunklines passing through stations 1, 2', 3, 1 and 5, there are other lines or pairs of wires which interconnect between the diflerent stations of each separate group. There are four of these lines or pairs of wires extending from each station to the other four stations of the group, and these would also be collected into cables and inclosed in metallic pipes in lines as distinguished from the trunk lines.

,There are, therefore, eight difierent tele-' phone lines or pairs of wires terminating in each station of the entire system, and by means of these eight telephone lines or pairs of wires, it is possible to reach any one of the other twenty-four stations of the system and establish an absolutely secret communication therewith. From this it is clear that a great saving of wiring is effected. The particular means by which this is accomplished will be later more fully described,

but in order to enable the broad principles to be understood, I will consider the action in making different kinds of calls, both local and trunk. It is to be understood that certain signals at are located at each monitor station 5, in which the trunk lines or wires respectively terminate.

Supposing that station 5 of group E desires to communicate with station 2 of the same group: It is merely necessary for station 5 to so manipulate keys or switches or plugs as to apply a telephone set at the terminal 2 thereof. It station 2 now applies its telephone set to its terminal 5, it is evilocal intercommunication for any group are taken care of.

I will now assume that a station of group E, for example, station 5 desired to communicate with a station of group A, for example, station 1. The procedure is as follows: Station 5 of group E by certainkeys and appliances hereinafter described applies a telephone set and also a battery current at the terminal A thereof. The efiect of applying battery current to this trunk line or pair of wires is to produce both a visual and an audible signal at the monitor station No. 5 of group A. The monitor thereupon connects a telephone set to this particular trunk line and inquires what is wanted. The person at station 5 of group E, who has his telephone set connected, answers that he wishes totalk to station 1 of group A, and the monitor at station 5 of group A then calls up station 1 over the local system. As soon as station 1 of group A has its telephone set connected to the trunk line, the desired communication isestablished. Not only is this communication established, but, it is absolutely secret, because, on account of certain appliances hereinafter described, the con-. nection ofthe telephone set of any station cuts off the line to stations beyond during given time. As has been already mentioned, I

the battery current is applied to the trunk lines during the time that they are busy, and these battery currents exhibit busy signals at all the stations to prevent interruption by mistake. Thus the three important features of the invention are secured, namely, the

various groups of stations connected by in- I tercommunicating trunks; secondly, the absolute secrecy of the conversation, not only between stations of the same group, but in trunk messages as well; and, finally, the production of busy signals when the trunk lines are being used. There is also secured the monitor supervision mentioned in the first part of this specification, since only the monitor stations of the various groups are amas er "provided with signals d for the incoming even from the monitor.

trunk messages. Accordingly the monitor of eachlocal group or'departnient passes on the propriety of the incoming message before the communication is established, and in case it is'not ofi icial or proper, the monitor is able to take-the appropriate action. If the communication is .a proper one, he merely notifies the appropriatestation of his group which then goes in on the line and the com- .munication thereafter is absolutely secret ever, the monitorcould give-all necessary in formation Without referring to other stations, since the monitor station is located in the ofiice of the departmental head.

I will now describe more in detail the practical embodiment of my invention heretherefore, each end of every trunk normally terminates in a signal device, so either monitor station in each of which one of the signal devices is located, is available to-be signaled at all times when the trunk is idle. These signal devices are adapted to be operated by the steady battery currents which are supplied from a central source to each stationthroughout the system. by a common pairv of feed'wires.- This same battery is used for all signaling and talking, the'advantage being, of course, the saving in cost of equipping for more than one current source- Each signal device when operated displays a visual signal which indicates the I trunk over which the call comes. The op era-tion of the visual signal also actuates the closing of a. circuit to give an audible signal which is adapted to operate withany individual visual signal. This is inelfect an 'annunciator, and the audible signal is the-ordinary battery bell or buzzer which is located at each station for calling the party to the telephone. To call the distant mon-, itor station battery is simply applied to the line at any one of the local stations. In applying this battery current, however, it is essential that the connections are'p'rop erly polarized for reasons which will later appear. The battery" is applied to the line: simply by bridging the primary of the telephone set across the trunk, and lifting the telephone receiver from the-hook to supply the transmitter and primary coilwith current in the usual manner. Whether the monitor station or oneof the other local telephones is connected as above to the trunk, "the extension of the trunk to the Ordinarily, how

'are omitted from the drawin so only the distant monitor is called. From the moment the battery is applied to the line by a telephone of a local group to signal the monitor station of a distant group, all intermediate stations in both groups are notified by. visual signals, one of which is located in each telephone, that the trunk is busy. To keep these busy signals actuated the battery current remains on the line during the conversation.

Further details will now be explained by referenceto Fig. 2. In this figure is shown diagrammatically and typically a full de-.

tail arrangement of the circuits and parts of two different stations, for example, station 1 of group A and station 5 of group E, with the trunk line or pair of wires EA AE' connecting between the two sections.- Station 1, group A, is the first station which the trunk line AEA'E enters in this group. Passing into. station 1, over the binding posts marked E on terminal strip tZ, the trunk wiresAE and AE, in nor- -mally closed circuit through the trunk key E pass out over binding posts marked "2 on terminal strip tZ, and then to station itor statiomand this station has a different assemblage of trunk apparatus and the trunk Wiring is different from that of the other stations in the same group. But-all the monitor stations are alike, and station 5, group A, would be like station 5, group E, which is shown complete in Fig. 2. The trunk wires AE and AE" enter station 5, group E, over the binding posts marked A, and terminate in the springs '02 and re respectively of the trunk key A". It is understood that the trunk is looped in and out of each of thestations 1,2, 3 and 4, which as indicated by the dotted lines in the trunk wires AE and AE. At the monitor station each trunk line terminates in a trunk key which in normal position connects the trunk with a drop signal. The trunk AE, AE normally ends in the drop A B C arid D are the signals for the trunks connecting with groups B, C and D respectively. Each oneof these drop signals has its night bell contacts connected to ring the signal bell E whenthe drop shutter falls.

The visual signal E" at station 1, group A, is bridged across the trunk wires AE and AE, to indicate when the trunk is busy at some other station in the same group. The visuals B", C and D are for the trunks connecting with groups B, G and D respec- These keys are used to switch the local lines tively. From station 5 in group E there are, I

of course, also the, independent directlines to the other four stations in this group. The lines to stations 1, 2, 3 and 4 would terminate at pairs of binding posts marked 1, 2, 3 and 4 respectively on terminal strip 25 The pair of binding posts marked 0 are used for the battery feed Wires. Springs w and w of keys ,70 70 and 7c areconnected to binding posts marked 1, 2, 3 and 4 respectively, and therefore constitute the permanent terminals of the local line wires.

from the signaling circuit to the talking circuit of the station. The grouping key 9 used to determine the calling station'when the signal comes from one of the stations in the same group.

The telephone set at each station consists of the transmitter T, receiver R, induction coil 1, retardation coils 1' and r. The hook switch h also plays a part-in switching battery on and oii the telephone set according to whether the receiver is off oron the hook.

The condensers c and a put the secondary circuit of the telephone in closed inductive relation with'the primary without subjecting the receiver to the passage of direct battery current through it, and at the same time keep the battery currents from passing to local lines and interfering with the local line signaling. The transmitter T and primary g) 01 the induction coil I are in series and connected permanently through the retardation coil 7" to the negative battery feed, and through the retardation coil'r to the hook switch it by means of the wire a, and hook switch it, which is open when the receiver R is on the hook, is in turn connected to the positive battery feed. The receiver R and secondary s of the induction coil I are in series and connected to the wires u and u. The wires u and a" are connected to wires to and u respectively through the condensers c and 0, the wires u, and ubeing connected to the negative and positive battery feeders through. the retardation coils r and. a respectively. The telephone set therefore has its primary and secondary circuits connected in multiple through the condensersc and a. An important feature in this construction and one to which particular attention is called is the fact that the adjacent terminals of the primary and secondary windings are joined together through the condensers, and, of course, the transmitter and receiver, i. e. the terminal of the secondary winding adjacent to the negative battery teri'ninal of the primary winding, is connected by wire it, condenser c and wire a" to the terminal or" the primary coil having negative battery, and the terminal of the secondary adjacent to the positive terminal of the primary is connected through the receiver. R, by, wire a, condenser c,

wire u, and through. the transmitter T,

to the terminal of the primary coil having- I positive battery. The reason for this will the same group, and also the operation of go them has already been fully explained in my application, Serial Number 292,916, filed December 22, 1905, and, therefore, only the details of the trunks need be explained herein.

At station 1, group A, the trunk wires AE and AE connect through binding posts E on terminal strip H, to the movable springs 02 and w of trunk key E, and the spring blades of the other trunk keys are correspondingly connected to the other trunk line wires. This key operates to disconnect the rest of the stations of group A from the trunk Wires AE and AE, and to connect these trunk wires tothe telephone set at station 1. The inside springs 71 and i, normally in contact with spring blades m and m respectively, are connected to binding posts marked 2 on terminalstrip tZ, at station 1, from which the trunk connection is continued to station 2 of group A. -The coil terminals of the visual signal E", at station 1, group A, are connected to the springs 11 and i of key E. This visual is, therefore, bridged across the extension of the trunk line leading to station 2 of group A. At stations 2, 3 and 4c of group A and stations 1, 2, 8, and 4: of group E, the trunk line would be wired as above shown for station 1 of group A, the visualsignal being'always connected to the extension of the trunk leading to the next station. At station 5, of group A, the trunk line would be terminated in a drop signal and wired as shown at station 5, group E.

I have said that in applying battery to the line to call a distant monitor, it is essential that the connections are properlypolarized. This will be clear from an inspection of the drawing. The bell E has one terminal per- 'with the night bell contacts w, must, there,-

fore, receive .a positive. current. Tethis end the shutters of the drops d, which ngage contacts w, are connected in each instance to receive a positive current. For example,

the shutter f of the drop A at station 5, group E, is connected to the contact 2', normally in contact with the spring blade at of the trunk A The spring blade a in any trunk key is adapted to be brought'into contact with contact point 0 of the same key, and the latter contact point is in every .case connected to the positive battery tap of the retardation coil 7* at the same station. It is, therefore, essential that the line spring as in every trunk key connects with the corresponding spring 00 in every other-key-of the trunk at other stations. Thus it will be seen that if a positivebattery current is sent over thetrunk wire AE, by bringing the blade 00 of the trunk key E at station 1, group A, into contact with the contact point 0 of the same'key, when the receiver R is ofi the hook h, the positive current will enter station 5, group E, over the blade :21 of the trunk key A. Therefore when the night bell contacts are closed in the drop A- the positive battery current will be conveyed to the bell E over the wire 6'.

The method already explained for connecting'all of the stations of group A With all of the stations of group E is the one em-.

ployed to connect all the stations of any group with all the stations of any other group in the system. The means by which the stations along the extension of a trunk line, which extension has been interrupted at a preceding station on the line, may determine whether the trunk line is in use, will later appear from the description of the operation.

"An occasional condenser 0" may be bridged across the battery feed atany point in the system to absorb stray telephonic currents.

In my present arrangement ofthe local apparatus for the stations, I have adopted a slightly modified construction of thepush button' 5 for signaling on the local lines. This push button is adapted to-open the wire it to the secondary of the induction coil when .the battery is applied to this side of the circuit for signaling. The reason for doing this is that when the secondary circuit of the telephone is connected to a very long line, a considerable condenser effect may be built up through the secondary .9, wire it, and the open side of the line, if the connection of the wire '.u to the secondary s is not interrupted. The static charge thus given would be com municated to parallel lines by induction andmight be suflicient to interfere with the proper working of a very extensive system. The opening of the circuit to the other side of the line at the push-button b, when the signal battery is applied to one side of the line,-thus destroying the open branch, eliminates all chances of static kicks. With this 1 slight modification of the circuit at the push button I; and the changes shown in the primary and secondary circuits of the telephone set, the apparatus and circuits for the operation of the local lines is identically the same as disclosed in my former application, No. 292,916. The operation is exactly the same.

Fig. 3 showsa sealed cabinet or containing casefor inclosing all parts of the apparatus and circuits located at the monitor station of any of the five groups. Mounted on the outside of the cabinet are only the transmitter, the bell, the buttons for the push butotherwise stripped of details. The telephone set here shown has already been explained withreference to Fig, 2. he telephone sets of both stations are shown connected through retardation coils to common wires from the battery B, which is, of course, the

common battery of the system. For conversation between two stations in the same group the line circuit is represented by the dotted lines, while the circuit for trunk line communication is represented by full lines. This diagram will be found convenient in considering the action of the telephonic currents which will later be explained.

The construction having been sufiiciently described, the operation will now be ex plained.

Let it be assumed that a party at station 1 of group A-desires to call and talk with the monitor at station 5 of group E. The party at station 1, group A, will determine from the visual signal E whether the trunk to group E is busy. If the trunk is not in use at some other station, the party at station 1 will operate the trunk key and lift his receiver from the hook and place it to his ear. In removing the receiver R the hook switch it closes battery through the primary circuit of the telephone, and by operating the key E" the primary circuit of the telephone is connected with trunk line wires AE and AE. Thus a. part of the battery which is being supplied to the primarycircuit of the telephone is shunted out over the line wires All and AE" which have signals bridged across them at other sta tions. In operating the key E the line spring blades 0; and 6' are moved out of contact with the contacts i and i. thus openiug the extension of the trunk to the visual E and to the other stations in the same Ill) group A, and the springs m and m are moved into contact with contacts -0- and '0 respectively, thus connecting the trunk wires AE and AE with the primary of the telephone and also with positive and negative battery-through wires u and u and retardationcoils r and r respectively. Thus the telephone is connected and battery is applied to the trunk wiresAE- and AE' at station 1 of group A. At stations 1, 2, 3 and 4: of group E, the visual busy signals there bridged across the line will be operated and held from the moment the battery is applied at station 1, group A At the monitor station 5 of group E the drop signal A, in which the trunk wires AE and AE normally terminate in this station, will be operated by the battery applied at station 1 of group A. The shutter f in falling will close the positive side of the trunk to the battery bell E in the manner already made clear from the detailed description of the construction. The bell E will be rung, and will continue to ring as long as battery is being supplied from r the distant calling station, oruntil the monitor answers. The shutter 7' will remain down until restored by the monitor. Thus, if no one is on hand to answer the call, the bell E will cease to ring when the calling party clears out and removes battery at the other end, but the drop shutter remaining down will always indicate the department which has called. Assuming the monitor is on hand to answer the call, he does this by connecting his telephone in exactly similar manner. and operating the trunk key in same way as did the party at station 1 of group A. In operating the trunk key A the spring blades and m break contact with inside contacts a and z" and make contact with outside contacts 0 and 0' respectively. Thus the drop A is cut off from the trunk and the flow of battery being interrupted, the bell E ceases to ring. The monitor may now restore the shutter f. Battery current is now being supplied to the trunk at the monitor station in the same manner as at the distant station, thus augmenting the current for holding the visual busy signals at the intermediate stations. It is to be understood that the impedance of the coils in the busy signals is so high as not to interfere with the flow of the telephonic currents, and the parties at the two stations now proceed to talk. Should the calling party desire to talk with some one at another station, say station 2 of group E, he would make the fact known to the monitor, whereupon, it being a proper call and the connection permissible, the monitor would call station 2 over the local system and tell the party there to go in on the trunk to group A. In so doing the party at station 2 would cut oil stations 3', t,'and

also the monitor station 5 of group E in exactly the same manner as station 1 of the stations along the extension which is cut off cannot cut in at all. The manner in which the monitor ca ls the local station 2 in group E need not be explained, as the operation is the same as in my former application of record. It is sulficient to assume in this instance that the monitor is. able to transact the business with the calling party withoutrel'erring to any other station. When they have finished talking, each party hangs up his receiver. At each station the receiver hook-switch it automatically removes battery from the trunk as well as from the telephone set by opening the positive side of the battery. A trip mechanism attached to the receiver hook (not shown because well known) also automatically restores the trunk key to the nor-- mal position. Thus at station 1 of group A the trunk circuit is made continuous on to the monitor station of thesame group, and at the monitor station 5 of group E the drop A is again bridged across the trunk and either monitor station is again available to be called from any station of the distant group.

From the foregoing it has been made clear how the'intermediate stations between two connected stations are notified by visual sig nals that the trunk is busy. It may not have been apparent, however, that the stations along an extension of the trunk which is cut oil also have means of determining when, the trunk is in use at some other station. The stations of the interrupted c tension have no visual means of knowing, bill they may determine whether the line is bi v by connecting to the trunk 'and. listening thereon. The primary and secondary of the telephone set being closed in parallel with themselves, and besides the busy signals at other cut oil stations, would give closed circuitconditions to the line and the usual side tone would be heard in the receiver speaking into the transmitter, so this would give no indication. But if the trunk is cut off at some other station the line will be quiet, whereas, if the line is continuous to the distant monitor the action of the vibrating bell, in first closing and then interrupting the connection of the positive side of the line through the bell, will set up electrical oscillations in the line which will manifest themselves in the receiver of the be by increasing the resistance of the drop I over that of the vibrating bell, which is, of

' course, ordinarily very low. Thus it will be seen that every station has a practical means of determining when a trunk line is busy at some other station even when the trunk is interrupted at a preceding station.

The ordinary operation having been explained, other conveniences of the system will readily occur to the minds of those versed in'the art. Without describing further details in the manipulations of the ap ran gement.

paratus and switching of the circuits, I will now considerv the action of-the telephonic currents in both local and trunk connections. Attention has already been called to the novel construction of the circuits of the telephone instrument. It now remains to point. out the advantages of this new ar- It has been noted that the primary and secondary circuits of the telephone are connected in parallel to the line.-' This is true whetherthe line in question is a trunk or a local line, but the connection between the primary and secondary is merely inductive, and the connection of trunk lines is made to the primary while the connection of local lines is made to the secondary. This iselearly. illustrated in the diagram, Fig. 5. It will be seen that the condensers c and 0 separate the primary and secondary circults of the instrument, and that the conthe. condensers.

v on each class of lines and to nection of the trunk 'line is" made on one side of-the condensers, while the connection of the local line is made on the other side of The condensers therefore, to keep steady battery currents out of the reoeiver,'thus making it unnec essary to polarize the receiver, and also pre ventbattery current from flowing to the local lines and interfering with the local line signaling. At the same time the condensers permit the telephonic connection of the receiver or secondary circuit to trunk lines,

which may have steady battery current from the city exchange passing through them while in use for the operation ofsignals as already described. Thus it will b'e-seen that the arrangement of the telephone circuits and their connection to the lines is 'such' as to permit of the properelectrical conditions telephonic eonditions also.. I, In addition to permitting proper electrical and giving propertelephonic conditions to the lines, the construction of the circuits.

serve,

givethe proper cation and clearly illustrated in the diagram, Fig. 5. This'diagram will be referred to in considering the combined action of the primary and secondary.

' Assume the transmitter T is at rest. It has a certain normal resistance. Steady current will flow from the positive battery terminal through the trans'mitetr T and primary p to the negative battery terminal. The direction of this flow willbe as indicated by the arrow adjacent to the primary p. The condensersc and 0, being in series -with each other .'(through the receiver and secondary) and" bridged across the battery 'feed, will be charged to the same potential that exists on the battery feed. The po-- larity of the charge in the condensers is indicated by positive and negative signs. If

.the transmitter T now be spokeninto, the

instantaneous effect of the voice pressure upon the diaphragm will be to lower the resistanceof the transmitter and increase the flow of current through the transmitter and primary. in the direction of the arrow. The increased flow of current in the primary will cause a current tobe induced in the secj acent to the latter, and the lowei'ing 0f the ondary s in the direction of the arrow adpotential across the. terminals of the primary will cause the condensers c and c to be discharged. The discharge from the condenser c will pass from the positive plate through the transmitter T and primary p, in the direction of the adjacent arrow, and by wire u to the negative plate of the condenser c. This discharge being in the same 3 direction as the primary battery current Wlll augment it. The discharge from the condenser a will pass from-the positive plate through the secondary s, in the direction of the adjacent arrow, and the receiver Rto the negative plate of the condenser 0. This discharge being in the same direction as the induced current-in the secondary will augment it. Upon the return of the transmitter diaphragm tothe normal position, the resistance will be raised to normal, the current flow in the transmitter and primary will ebb and the potential between the terminals of the primary will be raised again.- The ebbing of the current flow in the primary will cause a current to be induced in the secondary s in the direction opposed to the arrow adjacent to the latter, and the rise in potential between the terminalsqf the primary will cause the condensersc and c to be charged again to the same potential. The flow of current to the positive plate of the condenser 0, whether drawn from theline or from the positive battery terminal, will tend to still further diminish the flow of current through the transmitter and primary. v The current flowing to the positive plate of the condenser 0 will pass through the receiver R and secondary s in the direction opposed to battery current to the line.

niaaeaa I cuits connected as shown. It will, of course,

be'understood that the, retardation coils 1' and r at each stati n are to keep the quick variations in the resistance of the telephone circuit from .efiecting the steady flow of keep the full range of the current changes on the line, thus producing the maximum eiiect on the receiver of the receiving sta-. tion. Thus the action of the primary and secondary circuits, when connected as shown, betters the transmission, and the combined action is mutually augmentative. But if the connections between the primary and secondary are reversed, the converse will be true. I. have verified this in my experiments by reversing the connection of the secondary to the condensers, connecting the wire a to the condenser c and the wire at to the condenser c, and a falling ofi' in both volume and clearness approximating 50per cent. resulted.

The action and efficiency of the telephone set is about the same on both local and trunk lines. In the tests made on a given line, no difl erence could be detected in the transmission, whether the line wasconnected to the primaryor secondary circuits of the two telephone sets, nor did it make any difierence in the transmission when the primary of one set and the secondary of the other set a were connected to the line. Furthermore, the action of the telephonic currents was the same with one side of the line connected to the primary and the other side connected to the secondary. The experiments thus proved that the telephonicaction is the sameon the line when connected to any point .in the bridge between'the primary and secondary and on either side of the condensers. Reversal of the line wires of course, made no difference, but reversing the connection be-. tween the primary and secondary cut down the transmission in each line test above described.

Referring now briefly tothe flexibility of and general utility of my system, it may be seen from the foregoing specification that the economy of line wiring, or cabling, is so great as to render practical the connection of 100 or'more intercommunication stations in one'system. The reduction of the number of lines also reduces the number of line switching devices at each station, thus making practical the use of a small telephone cabinet or containing case for inclosing all of the switching apparatus and parts which are necessary for connection with 100 or- This tends to more stations. For example, in a system of 100 stations divided into 10 groups of 10 stations each, only nine local and nine trunk keys would be required at each telephone, these 18 keys together with the local signalingand local grouping keys at each station making in all only 20 buttons for each telephone ina system of 100 stations. For any number of stations found in practice the monitor supervision will be found effective,

' for long-distance talking. In fact cachintercommunication telephone is also .a good long-distance telephone.

What I claim, is 2- a 1.111 a telephone system, a plurality of groups of stations every group of which is connected to every other group by separate line wires constitutingtrunk connections, and a plurality of stations'in each group every station of which is connected to every other station by separate local line wires, said trunk line wires being extended through all of the stations of their respective groups, and means whereby both battery and voice currents are impressed upon the trunk lines during telephonic communication. I

2. In a telephone system, a plurality of groups of stations every group of which is connected to every other group by separate line, Wires constituting trunk connections, and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, said trunk line wiresbeing extended through all of the stations of their respective groups and terminating in a station having signals different from the other stations and con stitutinga monitors station for each group, and means for impressing a battery current on said trunk line wires when they are transmitting messages, to operate the said signals.

3. In a telephone system, a plurality of v.busy signals connected to said trunk line wires, and means for impressing a battery current on'said trunkline wires when they are transmitting messages, to operate the said signals.

4. In a telephone system, a plurallty of groups of'stations .each groups of which is connected to every other group by separate are trunk line wires constituting trunk connections and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, said trunk line wires being extended through all the stations of the respective groups, and means for interrupting said trunk line wires beyond any station of a group when such station is in telephonic communication over said trunk line wires.

5, In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk connections and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, said trunk line wires being extended through all the stations of the respective groups, means whereby induced currents alorr are impressed on the local line wires during telephonic communication, and means whereby both battery current and voice currents are impressed on the trunk lines phonic communication.

6. In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate vline wires constituting trunk connections and a plurality of stations in each-group every station of which is connected to every other station by separate local line wires, said trunk line wires being extended through all the stations of the respective groups, busy signals bridged across said trunk line wires at each station, and means whereby a busy indication is given at said signals when said lines are connected for telephonic communication.

7. In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk connections and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, said trunk line wires being extended through all the stations of the respective groups, busy signals, and means whereby a busy indication is given at said signals when said trunk lines are connected for telephonic communication.

8. In a telephone system, a plurality of groupsof stations each group of which is groups of stations each group of which is connected to' every other group by separate trunk line wires, and a plurality of stations during telewhereby battery current in said. trunk line is interrupted in case of local connnunieation.

10. In a-telephone system, a plurality of groups of stations each group of which is connected to every other group by Separate line wires constituting trunk connections and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, a source of potential dill'ercnce, a transmitter connected across the terminals thereof, and having the usual induction coil, and means whereby the fluctuating potential across said transmitter and the primary oi. said induction coil is impressed directly on said trunk lines during telephonic communication, and means whereby the induced voice currents in. the secondary of said induction coil are inductively impressed on said trunk lines during telephonic communication.

11. In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk connections and a plurality of stations in each group every station of which is-conneeted to every other station by separate local line wires, a telephone set including a transmitter, receiver and an induction coil, means whereby the potential across said transmitter and the primary of said coil is directly impressed on said trunk lines during telephonic communication, and means whereby the fluctuating potential of the secondary of said coil is inductively impressed on said trunk lines during telephonic communication.

12. In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk connections and a plurality of stations in each group every station of which is connected to every other station by separate local line wires, a telephone set including a transmitter, a receiver, and an induction coil, means whereby the battery current through said transmitter and the primary of said coil is directly impressed on the trunk lines during telephonic communication thereover, and means whereby said current is cut oil from the local lines.

13. In a telephone system, a plurality of local lines, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk connections, means whereby, a

battery current is permanently impressed on the trunk lines during telephonic communiineacea cation, and means whereby battery current may be temporarily impressed on the local lines during telephonic-connection for sig nal purposes. r

14.. In a telephone system, a line having a plurality of stations, each of said stations having a telephone setand means for connecting said setto the lineandcutting off succeeding stations of the line, means for applying battery cum'ent and telephone sets to the line -at the succeeding stations, and a call bell at a distant station of the line, whereby the circuit connections of said bell produce a buzz at a subscribers station when no intermediate station is in the circuit, but no buzz when an intermediate station is in the circuit.

15. In a telephone system, a line having a plurality of stations thereon each of said stations having a telephone set and means for connecting said set to the line and cutting off succeeding stations of the line, means for applying battery current and telephone sets to the line at the succeeding stations,

and means for producing a buzz at the tele phone set of such succeeding stations when any'intermediate station is not in connec-.

. tion with theline.

16. In a telephone "system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk lines, a pmrality of stations in each group every station of which is connected to every other station by separate line wires, a common trunk line includingall the stations of anygroup said trunk terminating in a monitor station, and means for establishing signals at the momtorls station to the exclusion of all other stations whereby all trunk communication is supervised at the monitors station.

17. In a telephone system, a plurality or rality of stations in each group every station of which is connected to every other station by separate line wires, a trunk line common to every station of any group and terminating in a monitors :station, .and means at such monitor station by which the trunk communication is supervised thereat.

18. In a telephone system, a plurality of groups of stations each group of which is connected to every other group by separate line wires constituting trunk lines, a plurality of stations in each group every station of which is connected to every other station by separate line wires, a trunk line common to every station of any group and terminating in a monitors station, and means at the monitors station for supervising the trunk communication but not the local communication between stations of the same group. v

In witness whereof, I- subscribe my signature, in the presence of two witnesses.

RICHARD 1H. BEARD. Witnesses 2' WALDO M.- CHAPIN, MAY Bren.

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