US1905359A - Channel selection - Google Patents

Description

April 25. 1933. H. A. AFFEL CHANNEL SELECTION Filed NOV. 14, 1931 3 Sheets-'Sheet l MQSE QST SS INVENTOR vATTORNEY April 25, 1933. H A AFFEL 1,905,359

CHANNEL SELECTION Filed Nov.'14, 1951 s sheets-sheet 2 AIZ: Rec. Distributor ATTORNEY April 25, 1933.

H. A. AFFEL CHANNEL SELECTION Filed NOV. 14V, 1931 3 Sheets-Sheet 3 INVENTOR ATTORNEY rammed, Api. 25, A1933 uNiTlzo STATES PATENT ori-ica ERIAN A. AEREI, 0F RIDGEWOOD, NEW JERSEY, ASSIGNR T0 AIlBICAN TELE- PHONE AND TELMBAPH COMPANY, A CORPORATION F NEW YORK,

om america limitation mea rovente; 14, isai. sei-iai no. 575,124.

distance telephone circuits, carrier telephone circuits, two-way radio communication circuits, etc. In fourf: ao

wire'cable operation, for example, a pair of wires together with the necessary terminal ap ar'atus and intermediate repeaters are de nitely assigned for transmission in each direction. Similarly, in the case of carrier communication a frequency band with the required terminal apparatus and intermediate amplification is set aside for each direction of transmission. Qonsiderin the idle periods due'to time lost in switc ing and making connections, incidental pauses in conversation, etc., a long distance circuit is at best actually carrying speech only a part of the time. In the case of a two-way communication circuit of the four-wire type where a'separate transmission path is set up in each direction, this ineliiciency in the use of the communication channel is aggravated by the fact that when one channel is. being used for transmission in a given direction, the channelv in theopposite direction is usuallv idle. In'other words, even after the communica- -tion'is set up and the subscribers have control of the circuit, each one-way path of a four-wire circuit is used at an average efficiency of only percent because on the avera e, transmission `takes place in each direction only about one-half of the time.

. This lack of efficient use of the circuit facilities may 'not be of such serious consequence in connection with theaverage telephone circuit. However, in connection with super-distance circuits such as transoceanic radio, or the proposed transatlantic telephone cable, the talking paths provided are necessarily very expensive and anyimprovement in the eiliciency of use will be proin other forms of v the groups of circuits existing between the that theyv may be set up not as individual circuitsv with definite cilities assigned for the period o a conversation but rather that the choice ofa particu-l lar idle circuit may be made automatically each time the subscriber s ks. This arrangement lends itself particularly to operation in the case of four-wire circuits where the one-way trunks can be grou ed to ther in each direction. In the case of a s ciently large number of circuits between two points the proposed method of operation offers the possibility of providing for at least twice the number of simultaneous conversations-obtained with existing arrangements in which the two separate directional paths are definitely set up to form a particular twoway circuit.

The arrangement for selecting channels automatically each time the subscriber speaks may obviously assume many forms, and for purposes of illustration only, a commutator type of selecting arrangement is herein illustrated. Upon this commutator Aarrangement all of the one-way trunks terminate, and rotating switch arms are connected to the subscribers terminals, these switch arms being capable of speedily covering in a single-revolution all of the switch points representing the terminations of the grou spea s his voice operates relay arrangements to cause the rotating arm at his terminal to pause in its rotation at an idletrunk. The

physical faof trunks. When the subscriber rotating switch arms at the two subscribers terminals are arranged to rotate synchronously so that the corresponding switch arm at the receiving end will also be causedto pause at the desired points by virtue of the voice potentials appearing at the receiving terminal. v While the foregoing arrange; ment serves to illustrate the principles involved, it will be understood that the invention is not confined to any particular type of selecting arrangement.

The mvention will now be more fully understood when read in connection with the accompanying drawings, in which Figure 1 is a schematic layout showing in a general way the manner in which the trunks are associated with the terminal stations which they serve to connect; Fig. 2 is a circuit arrangement showing the manner in which the trunks are associated with the transmitting selecting apparatus at one terminal; Fig. 3 similarly shows how the trunks are associated with the receiving selecting apparatus at the other terminal; and Fig. 4 is a detail showing the coupling between the distributor arm and the driving shaft for the various distributors.

As previously stated, no regular circuit assignments of the one-way channels between two points will be made, but in connection with the subscribers talk, each time a person speaks he will automatically pick out an idle trunk-not a .particular circuit, but merely one which at that time is not in use. The general la out of such a scheme is shown in Fig. 1. ere two sets of terminals are shown connected by a number of one-way trunks. In the exam le illustrated the trunks are eight in num er in each direction and are desi ated A, B, C, etc., from west toeast and A, BB, CC, etc., from east to west. These trunks may be one-way cable circuits for trans'ooeanic telephony, radio channels, or telephone transmission circuits of any type. If the practice of the prior art were followed, one set of trunks would be used for transmission in each direction, that is, two channels, one for each direction, would provide one talking circuit and the total number illustrated would, therefore, provide eight four-wire tratlic circuits. The proposed arrangement, however, permits approximately double this number of talking circuits.

Each talking circuit is provided with a speech controlled distributor arrangement comprising two distributors at each end of the circuit, as shown schematically on the drawings. Four sets of distributors are shown out of a possible number approaching sixteen, the sending distributors at the West terminal being designated TD1, TD2, etc., the receiving distributors at said terminal being designated RD1, RD2, etc., while the corresponding distributors at the east terminal have similar reference characters primed. One transmitting distributor and one receiving distributor are associated with each line terminal. When a person talks, for example, at the No. 1 terminal west, the

- transmitted speech will reach the associated sending distributor TD1. The function of this distributor is to pick out approximately instantaneously one of the idle sending trunks designated A to H, inclusive. For the duration of the articular word or phrase spoken by the ta er the connection will be established over this particular trunk. At the receiving terminal the trunk will be correspondingly switched means of the reb ceiving distributor RDl'y to the No. 1 terminal for the same period of time. As soon as the talker finishes the word or phrase the trunk will be released and will then be available for any other subscriber talking in that direction. The arrangement of course, functions simultaneously in t e reverse direction. Thenature of and the connections to the sending and receiving distributors are shown in Fi 2 and 3, respectively. In Fig. 2 only t e sending distributors associated with the terminals are shown, and in Fig. 3 only the receiving distributors associated with the corresponding terminals at the other end are shown so that the actual circuit arrangements illustrated only take care of transmission in one direction, the similar arrangements for transmission in the op osite direction being schematically indicated).

Each distributor consists of a commutator having several sets of segments passed over by brushes attached to a rapidly rotating switch arm. Each set of segments corresponds to one of the one-way trunks to which the distributor has access. In the case illustrated the number of trunks is four and, consequently, the number of sets of segments is limited to four, but with an increase in the numberof trunks the number of sets of segments will obviously be correspondingly increased. Also it will be noted that while only three sendingdistributors are illustrated at the one terminal and three receiving distributors at the other terminal, the number of distributors sending or receiving as the case may be at each terminal will correspond to the number of terminal stations which may approach twice the number of trunks transmitting in a given direction. For example, if there are four west to east trunks, there might be upwards of eight terminal stations at each terminal, and hence, upwards of eight transmitting distributors and a similar number of receiving distributors at each terminal. If the number of west to east trunks is increased to, say, twenty, the number of terminal stations at each terminal will then approach forty witha corresponding increase in the number of distributors.

Each distributor is provided with a rotating brush arm such as BA1 to which are attached brushes which pass over the various segments. The rotation of this brush arm is governed by a shaft common to all of the distributors at a particular terminal and the connection between the rotating arm and shaft is of the frictional type permitting the arm to be held by a stop clutch mechanism arranged to stop the arm at any set of commutator segments while the shaft continues to revolve. 1

5 For reasons which willaappear more fully hereinafter it is desirable that when a particular' arm is stopped and then again released, it should start in rotation again in the same phase relation with respect to other rotating distributor arms on the same' shaft that existed before the arm was stopped. To permit of this possibility the friction clutch arrangement etween the brush arm and the shaft ma be of the type illustrated in Fig. 4 where t e brush arm BA is freely mounted upon-the rotating shaft 20. The rotating shaft 20 is provided with a shallow socket into which may enter a ball 21 carried in a suitable recess in the brush arm and spring pressed a ainst the shaft by a spring 22. Whenever t e brush arm BA is held by the'stop clutch arrangement, the ball 21 will ride out of the socket in the shaft 20 and the shaft will continue rotating while the brush arm is held stationary. When the brush arm is again released the friction between the ball 21 and the shaft 20 is not suiicient to set the brush arm again into motion until the shaft rotates to the point where the ball 21 can again ride into the socket provided for it, whereupon the brush army will again rotate in the same phase relation which had previously existed with respect to other rotating brush arms on the same shaft.- Presumably the brush arms for the diiferent distributors should each occupy a different normal angular position with res ect to the shaft, and consequently, the soc ets for the balls such as 21 on the vari- 4) angular positions as shown in dotted lines in Fig. 4. For example, in the case illustrated in Fig. 2, -where there are four trunks and may be as many aseight sending distributors and, consequently, eight sending brush arms associated with said trunks, there should be eight different angular positions for the brush arms and hence, the several sockets corresponding to the brush arms- TD1 and the receiving branch leads to the'- corresponding receiving distributor, not shown. The connection to the receiving disous brush arms will be arranged in diiferent should be 45 degrees apart. The angularv tributor will be as indicated from the correi sponding hybrid coil HC1 at the opposite terminal (see Fig. 3). The transmitting c0nnection from the hybrid coil is in turn divided into two branches one of which includes an amplifier-detector such as shown at AD1, the

function of this amplifier-detector bein to produce an operating current for control ing the switching operations to be later described. The other branch includes a delay circuit for holding u the transmission of the speech currents until the switching operation has taken place. 1

Each set of commutator se ents comprises four segments of which t e outer air is connected to a trunk such as the trun D and of which the inner pair is connected to a relay such as the relay R11 of Fig. 2. The brush arm carries a correspondin number of wi ers. Each distributor, as, or example, t e distributor TD1, is provided with four sets of stop magnets, one for each set of commutator segments, the stop magnets being designated SM1., SM1, etc. One of these stop magnets corresponds to each of the trunks A, B, etc., and Awhen the trunk is idle the stop magnet -will be deenergized so that a detent upon its armature will be in the path of a corresponding detent upon the armature of a voice-operated relay VR1 carried by the brush arm. Consequently, if the voice-op-l erated relay VR1 is energized, its armature will engage with the detent of the first stop magnet which it encounters and brings the brush arm to rest upon the corresponding set of commutator segments. The relays, such as R11, R11, etc., associated with the several sets of commutator segments of a given distributor, serve the purpose of energizing corresponding stop ma ets of other distributors, thereby with rawing their armatures and rendering the corresponding segments of such other commutators busy so that the brush arms of such other commutatore will not stop at a corres nding position. The voice-operated relay' 1 is connected to the output of the amplifier-detector AD1 and loo therefore only swings the detent of its armature into the path of the detent of a nonenergized stop magnet when voice waves arrive from the terminal 1. Each brush arm also carries a wei hted switch arm such as S1. The inertia o the switch arm serves to hold open a contact in the talking circuit from the delay network DN1 while the brush arm is in rotation. When the brush arm comes to a stop, however, the momentum of the switch arm causes it to close said contact. This prevents talking currents being picked up from talking segments over which the brush arm thereby causing vthe possibility of false operation, as will be explained later.

The above general description applies to all of the sending distributor arrangements ias asses during its rotation and iso shown in Fig. 2. The apparatus associated with the several receiving distributors shown 5 corresponding reference characters prime The essential diiferencebetween the sending and receiving distributors is that the amplifier-detector arrangement such as AD1 of Fig. 3 is connected to the outer brushes'of the brush arm, and therefore serves to rectify currents incoming from one of the trunks such as D to the corresponding talking segments of the distributor. The output of the amplifier detector is then connected through one branch to the voice-operated relays such as VR1 which serves to stop the brush arm, and through `another branch to the brushes which pass over the control segments such as CS 1d to which the relayssuch as R 1d are connected: The talking brushes of the brush arm are connected over a branch ahead of the amplifier-detector to the receiving side of the hybrid coil such as HC1. This talking connection is normally held open during rotation by a weighted switch arm such as S 1 similar to the switch arm described in connection with the sending distributor.

Further details of the apparatus will be clear from a description of the operation,

`which is as follows:

Let us assume that a subscribers line is connected to the jack` 1 and that the subscriber is carrying on a conversation with-another subscriber whose line is connected to the jack 1. If the subscriber connected to the jack 1 should speak, voice currents would pass into the transmitting connection from the hybrid coil and enter the delay network DN1 which serves to delaly7 the transmission of the voice currents until t e voice-operated relay VR1 has operated. Some of the voice energy will be diverted into the amplifier-detector AD1 and appear upon the output side thereof in rectified form. A part of the rectified current then enters the .Winding of the voice-operated relay VR1 to energize said relay and thereby cause the detent on the armature of the relay to be moved into such a position that it will engage the corresponding detent of any deenergized stop magnet. All stop magnets correspond to any of the trunks A, B, C, D, which are at the moment engaged will be energized and have the detents of thelr armatures drawn out of the detent of the armature of the voice relay VR1.

If we assume that the trunk D is at the moment not engaged, the stop magnet SM111 will be deenergized at the moment the wipers of the brush arm BA1, pass over thel group of segments opposite the stop magnet SMM. Consequently, the detent on the armature of the voice relay VR1 engages the detent on the stop magnet SM'111 and therefore brings the brush arm to rest with brushes upon the corresponding group of segments.

When the brush arm thus comes to rest, some of the rectified current on the output side of the amplifier-detector AD1 asses over the inner air of brushes of the rush arm and over t e segments CS111'tothe winding of the relay R11. Relay R11 is thereby energized and connects ground to the wire d. All of the stop magnets of the various distributors whose subscripts are d are connected to the now grounded wire d and hence, all of the stop magnets such as SMM and SMM of other distributors will be energized and their armatures will be pulled out of the paths of txthe detents of the voice rela s carried by other rotating brush arms. onsequently, any other brush arms that are rotated will not be stopped on the segments corres ondin to the trunk D. The stop magnet @M11 ofg the distributor associated with terminal 1, however, is not energized by the connection of ground to the Wire d as the engagement of its detent with the detent of the voice relay VR1 connects a short circuit about its wind- 1ng.

4 During the time that the brush arm was rotating, a weighted switch arm S1 carried by the brush arm was by its inertia caused to rest upon an insulated back contact carried by the brush arm BA1. When the brush arm came to rest, however, in the manner above described, the momentum of the Weighted switch S1 caused it to move forward against its front contact, thereb completing a circuit from the output sidse of the delay network DN1 to the outer brushes of the brush arm and over the speech segments SSM to the trunk D. During the time necessary for the brush arm to rotate until it comes to rest upon the segments corres onding to an idle trunk, the voice currents rom the terminal 1 are prevented from being transmitted by the open switch S1. After the brusharm has come to rest and the weighted switch S1 has completed the talking circuit, the voice currents pass through the delay circuit and over the s ech-segments SS11 to the trunk D.

W ile the brush arm BA1 was rotating with its voice relay VR1 energized, it did not come to rest upon the segments corresponding to an vtrunk which at the moment was engage because all such trunks had their stop magnets energized so that the detents were drawn out of the path of the detent of the voice relay VR1. For example, if we consider the trunk C and refer to the distributor TDS which is shown resting upon the segments corresponding to the stop magnet SMBC, it will be seen that the relay R3., is energized to put groundupon the wire c which energizes the stop magnet SM1c of the distributor TD1. Therefore, the brush arm BA1 could not have come to rest upon the segments corresponding to the trunk C. Furthermore, as will be explained later, there is no possibility that two brush arms of dif- :ferent distributors whose voice relays are at the same moment energized by talking currents will come to rest upon sets of segments corresponding to the same trunk because the brush arms when rotated will always be out of hase with each other.

e have now traced the operation to the point where the'terminal 1 has been connected to the trunk D and the voice. currents are passing over the trunk D. We will now see how the correspondin terminal 1 is connected tothe same t D and no other during the continuance of the rain of voice waves from the terminal 1. he voice currents now transmitted to the trunk D ass over said trunk'to the s eech segments S'm of the receiving distri utor RD1 and also pass to the corresponding speech segments of the distributors of the' other receiving ter- 2) minals. The brush arm BA1 during its continuous rotation has its receiving connection from its outer segments to the hybrid coil HC1 held open by the inertia of the weighted switch S1 so that any speech currents picked 2 upfrom talking trunks as its outer brushes pass over the speech segments corresponding to such trunks are not transmitted to the terminal 1 so long as the brush arm continues to rotate. Each time the'outer brushes pass `over energized speech segments, voice currents pass to the amplifier-detector AD1 and some of the rectified output energy causes voicerelay VR1 to move its detent outward` ly. `The brush arm is not brought to rest, -5- however, upon a set of segments whose speech segments are ener ized, if the corresponding trunk has already een switched into connection with another talking terminal such as the terminal 3', because in that case the cor- 73 responding stop magnet of the distributor RD'1 will be energized under the control of' some other distributor in a manner which will be described later. Furthermore, the brush arm of the distributor RD1 will not be brought to rest upon a group of segments that are not energized by speech currents, because in that case the relay VR1 will no't be energized as the brush arm passes over such set y of segments, and hence its detent cannot enf gage the detent of the stop magnet.

In other words, the brush arm will not come to rest upon the set of segments corresponding to an idle trunk. It can only come to rest upon segments corresponding to a trunk which at the moment is applying speech currents to the speech segments of the set of segments. And it cannot come to rest upon a set of segments corresponding to a trunk which has already been connected to some other terminal. It will come to rest, however, upon the set of segments corresponding to the trunk D because that trunk will not have been connected by any other distributor to any other terminal than the C5 terminal 1 and hence, its stop magnet SMm will be amel-gized a the moment the brush.

arm gasses over the group of segments correspon ing to the trunk- D. As will be more fully explained hereinafter, -all ofthe receiving brush arms which are in rotation have: fixed angular positions with respect to the rotatin shaft which are out of hase with each ot er so that only one brus armwill pass over a Set of energized segments at a time. Furthermore, 'the synchronism' between the rotating shafts at the transmitting end and at the receiving end is such that when the brush arm BA1 at the sending end comes to rest and transmits voice currents over the trunk D, the voice currents will arrive at the receiving end of the trunk D and will be applied to the corresponding speech segments SSH., just before or at the moment the outer brushes of the receiving brush arm BA1 are passing over said speech segments. Consequently, the voice relay VR1 is ener ed and its detent engages the detent of moment is energized. This brings the' brush arm BA1 to rest on the set of segments corresgmnding to the trunk D.

ome o the rectified voice energy now aps..

pearing on the output side of the amplifierdetector ADQ passes to the inner or control se ments CSm and thence to the relay R 1d. This relay is therefore energized and applies ground to the wire that all of the corresponding stop magnets of other receiving distributors are ener 'zed. Stop magnet SMm of the distributor R 1 is not energized, however, as its winding is short-circuited by thecontact between the detent of its armature with the detent of the; voice relay V'Rl. The switch arm now remains at rest on the set of segments corresponding to the trunk D and will remain asso-I If during the time that speech is incoming A from trunk D and the brush arm BA1 is resting upon the segments of the distributor RD1 corresponding to said trunk, the brush' arm of any other receiving distributor passes over the contacts of such other distributor which corresponds to the trunk D, the brush arm of such other distributor will not come to rest even though its voice relay is energized.

For example, suppose the brush arm BA2 rotates over the segments corresponding to the 1 trunk D with the result that its voice operated relay V12/2 is energized at that moment. It

e corre' spondmg stop magnet SMM which at thev izo cannot come to rest because the ound applied to the wire d b the relay 1d of the distributor RD1 will ave energized the stop ma et SMZ., to pull its detent out of the pat of the detent of the voice relay VR2.

It will, of course, be obvious that any brush arm of any distributor will be released as soon as voice currents cease to energize its voice relay. For example, the transmitting distributor TD1 will have its brush arm released as soon as voice currents cease to arrive from the terminal 1 because the voice relay VH1 will be deenergized and its detent withdrawn from contact with the detent of the stop magnet SMM. Similarly, the receiving brush arm BA'1 will be released and start into rotation a ain as soon as voice currents cease to arrive rom the trunk D, for the voice relay VR1 will be deenergized and as a consequence its detent will be withdrawn from contact with the detent of the stop magnet SMM. As soon as the two brush arms commence to rotate the previously energized relays, Rm of the transmitting distributor and R 1d of the receiving distributor, will release and remove ground from the wires d and d', respectively, to release the corresponding stop ma ets of other distributors.

If or inary friction drive arrangements were employed between drive shafts and the brush arms it would be possible for the brush arms of two sending distributors to rotate in phase with each other and in response to voice currents arriving from two sending terminals at the same instant come to rest with their brushes on the segments corresponding to the same trunk. There would then be a possibility that the two brushes on the corresponding air of receiving distributors (which would) presumably be rotating in phase) would come to rest and connect two receiving terminals to the same trunk. This not only would cause a cross connection but might resultin getting the brush arms of corresponding sending and receivin distributors out of proper synchronism with respect Y to each other if no arran ment were provided to prevent this actlon. A receiving distributor would get out of properV synchronous relation to its corresponding transmitting distributor if, under the conditions above mentioned, one of the transmitting distributors was released by the cessation of voice currents from its terminals before the other sending distributor is released. The two receiving distributors which were stopped upon the same trunk would inevitably be released at the same time upon the cessation of talking current from the trunk to which they are connected. The sending distributors would, however, only be held upon the trunk Vso long as talk was incoming from the sending terminals with which the distributors vare associated. Consequently, when all four of the distributors synchronous relation to the correspondm receiving brush arm at the opposite termmal.

The diiculties referred to in the previous paragraph are overcome in accordance with the arrangement disclosed by providing means to assure that when a set of brush arms of distributors at a given terminal are rotated they will always rotate in a fixed angular relationship with res t to the rotating shaft and will be out o hase with each other. This may be accomp ished by means of the arrangement previously described in connection with Fig. 4. In this figure let 20 represent the rotating shaft with which all of the brush arms of the various distributors at a given switching station are associated. Each brush arm is connected to the shaft by means of a ball pressed by a spring 22 which ball rests in a socket in the shaft 20. When the ball is in the socket the frictional engagement between the brush arm BA and the shaft 2() is suilicient to cause the brush arm to rotate. When the brush arm is held by engagement with a detent, as previously described, the ball 21 will ride out of the socket and the shaft will continue to rotate without carrying the brush arm with it.v The sockets in the shaft 20 for the various brush arms of the various distributors will be arranged at different angular positions about the shaft 20 as indicated in dotted lines in Fig. 4 to show the angular position of a second brush arm. Consequently, when any brush arm is released it will remain stationary until the shaft has rotated to bring its own socket into proper relationship, whereupon the ball enters the socket and the brush arm then rotates with the shaft in the same angular position with respect to the shaft which it occupied before it was stopped by engagement with the detent.

Each brush arm, therefore, when rotated must necessarily rotate in a dilferent phase relation with respect to every other brush arm. Consequently, if two subscribers at the sending terminal should both commence talking at the same time, there is no possibility of two sending brush arms stopping upon the segments corresponding to the same subscriber. For example, if the subscribers corresponding to terminals 1 and 2 should both commence talking at once and the brush arm of. distributor TDl is ahead of the brush arm of distributor TD2, the terminal 1 will be connected to the first idle trunk and will lock out the distributor associated with terminal 2 from connection to that idle trunk. The distributor associated with terminal 2 will then select the next idle trunk. If by a similar relationship of distributor arms to driving shaft the receiving distributors of Fig: 3 are rotating out of phase with each other but in pro r synchronous relationship to the correspon ing sending distributors, voice currents will arrive at the receiving end over the trunk connected to the terminal 1 before they will arrive over the trunk connected at the terminal 2, because the connection to terminal 1 was completed before the connection to terminal 2. Since the brush arms of the corresponding receiving` distributors are each in proper synchronous relationship to its corresponding sending distributor, the brush arm of the distributor associated with terminal 1 will come to rest upon the trunk to which the terminal 1 is connected by virtue of the fact that it will be passing over the energized speech segments of such trunk at the moment voice currents arrive over such trunk. Similarly, the brush arms of the distributor associated with the terminal 2 will come to rest upon the segments associated with the trunk which was connected to vthe terminal 2 because the voice currents will arrive from its trunk after the voice currents have arrived from the terminal 1 and will arrive at the moment the brush arm associated withterminal 2 passes over the corresponding segments. This takes place notwithstanding that speech started from terminals 1 and 2 at the same instant. The delay in the arrival of speech at the terminal 2 is due to the fact that an idle trunk was conneced to the terminal 2 after the idle trunk was conA nected' to the terminal 1. v

`By means of the mechanical connection between driving shaft and brush arms above described and with the sockets in the shaft correspondin to different brush arms all arranged in di erent angular positions, it will be evident that when any brush arm is stopped and then again released, it will always start rotating in the same angular position wi'h respect to its shaft that it occupied before it was stopped. Hence if the shaft of a set of sending distributors is in synchronism with a shaft of receiving distributors, each sending brush arm will rotate in proper synchronous relation to each receiving brush arm no matter when it is stopped nor how long after it is stopped it is again released. Thus the possibility of false switching connection being made between two terminals is avoided.

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

What is claimed is:

1. In a signaling system, a pair of switching stations, trunks extending between said stations, a signaling terminal at one station, and means responsive to sound currents incoming from said terminal to select and connect thereto an idle trunk.

2. In a signalin system a pair of switching stations, trunEs exten ing between said stations, a signalin terminal at one station, and means responsive to sound currents incoming from said terminal to select an idle i trunk and maintain said trunk connected to said terminal only during the continuance of sound currents.

3. In a signalin system, a pair of switching stations, trun s extending between said stations, a signaling terminal at one station, and means responsive to sound currents incoming from said terminal to select and connect thereto an idle trunk, and means to release said trunk upon the cessation of sound currents.

4. In a signalin system, a pair of switching stations, trun s extending between said stations, a signaling terminal at one station, and means responsive to sound currents incomin from said terminal to select and connect t ereto an idle trunk, means to release said trunk upon the cessation of sound currents, and means to select and connect to the terminal a new trunk upon the initiation of a newA train of sound currents.

5. In a signalin system a pair of switching stations, trun s extending between said stations, signaling terminals at each station arranged to intercommunicate in pairs between stations, and means responsive to sound currents incoming from one terminal to select and connect thereto an idle trunk, and means to connect said trunk to the corresponding terminal at the other station.

6. In a signaling system, av pair of switching stations, trunks extending between said stations, signaling terminals at each station arranged to intercommunicate in pairs between stations, and means responsive to sound currents incoming from one terminal to select and connect thereto an idle ti'lmk, and means to connect said trunk to the corresponding terminal at the other station, said trunk remaining connected only during the continuance of said sound currents.

7. In a signalin system, a pair of switching stations, tr s extending between said stations, signaling terminals at each station arranged to intercommunicate in pairs be.

tween stations, means responsive to sound currents incoming from one terminal to select and connect thereto an idle trunk, and means to connect said trunk to the corresponding terminal at the other station, and means to release said trunk upon the cessation of said sound currents.

8. In a signaling system, a pair of switching stations, trunks extending between said stations, signaling terminals at each station arranged to intercommunicate in pairs between stations, means responsive to sound currents incoming from one terminal to select and connect thereto an idle trunk, and means to connect said trunk to the corresponding terminal at the other station, means to release said trunk u on the cessation of said sound currents, an means to select and connect to the same terminals a new trunk upon the initiation of a new set of sound waves.

9. In a signaling system, a vpair of switching stations, a group of trunks extending between said stations for transmission in one direction, a. second group of trunks extending between said stations for transmission in the opposite direction, signaling terminals at each station arranged to intercommunicate in pairs betwen stations, means responsive to sound currents incoming from one signaling terminal to select an idle trunk from one group and connect it to said terminal, means to connect said trunk to the corresponding terminal at the other station, means responsive to sound currents incoming from said last mentioned terminal to select a trunk from the other group and connect it to one terminal, and means to connect it to the other terminal.

10. In a signaling system, la pair of switching stations, a group of trunks extending between said stations for transmission in one direction, a second group of trunks extending between said stations for transmission in the opposite direction, signaling terminals at each station arranged to intercommunicate in pairs between stations, means responsive to sound currents incoming from one signaling terminal to select an idle trunk from one group and connect it to said terminal, means to connect the selected trunk to the corresponding terminal at the other station, means responsive to sound currents incoming from said last mentioned terminal to select a trunk from theother group and connect it to one terminal, and means to connect it to the other terminal, said trunks remaining connected only during the continuance of said sound currents. l

11. In a. signaling system, a pair of switching stations, a group of trunks extending between said stations for transmission in one direction, a second group of trunks extending between said stations for transmission in the opposite direction, signaling terminals at each station arranged to intercommunicate in pairs between stations, means responsive to sound currents incoming from one signaling terminal to select an idle trunk from one group and connect it to said terminal, means to connect the selected trunk to the corresponding terminal at the other station, means responsive to sound currents incoming from said last mentioned terminal to select a trunk from the other group and vconnect it to a terminal, means 66 to connect it to the other terminal, and

ing from one signaling Vterminal to select' an idle trunk from one group and connect it to said terminal, means to connect the selected trunk to the corresponding terminal at the other station, means to release said trunk upon the cessation of sound currents from said terminal, means to automatically reselect a trunk from said group upon the initiation of a. new set of sound waves from the same terminal, means responsive to sound currents incoming from said terminal at the other station to select a trunk from the other group and connect it to' a terminal, and means to connect it to the other terminal, means to release said trunk upon the cessation of sound currents from said last mentioned terminal, and means to automatically reselect a trunk from said second group upon initiation of a new set of sound currents incoming from said last mentioned terminal.

13. In a signaling system, a pair of switchin stations, a plurality of trunks extending tween said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, and means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other ation.

'14. n a signaling system, a pair`of switching stations, a plurality of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch', means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, and means to thereupon connect said trunk to the receiving branch of the correspondingterminal at the other station, said trunk remainin connected only during the continuance of said signals.

15. In a signaling system, apair of switching stations, a plurality of trunks extending between said stations, signaling terminals connected to each station and arranged to inliw tercommunicate in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from 5 one terminal in its transmitting branch to select and connect thereto an idle trunk, means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other station, and means to release said 10 trunk upon the cessation of said signals.

16. In a signaling system, a pair of switching stations, a plurality of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate ,in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to 20 select and connect thereto an idle trunk,

means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other station, means to release said trunk upon the cessation of said signals, and means to select and connect a new trunk to said transmitting and receiv: ing branches upon the initiation of a new set of signals to be transmitted in the same d1- rection.

3 17. In a signaling system, a pair of switching stations, a plurallty of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other station, and means to select and connect another trunk between the transmitting branch of said second terminal and the receiving branch of said first terminal upon the initiation of a set of signals at said second terminal. l

18. In a signaling system, a pair of switching stations, a plurality of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs between stations, each termina-l terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other station, and means to select and connect another trunk between the transmitting branch of said second terminal and the receiving branch of said first terminal upon the initiation of a set of signals at said second terminal, said trunks remaining connected for transmission in a iven direction only during the continuance o signals.

19. In a signaling system, a pair of switching stations, a Yplurality of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, means to thereupon connect said trunk to the receiving branch of the corresponding terminal at the other station, means to select and connect another trunk between the transmitting branch of said second terminal and the receiving branch of said first terminal upon the initiation of a set of signals at said second' terminal, and means to release said trunks upon the cessation of signals in a given direction.

20. In a signaling system, a pair of switching stations, a plurality of trunks extending between said stations, signaling terminals connected to each station and arranged to intercommunicate in pairs` between stations, each terminal terminating at its switching station in a transmitting branch and a receiving branch, means responsive to signals from one terminal in its transmitting branch to select and connect thereto an idle trunk, means to thereupon connectsaid trunk to the receiving branch of the corresponding terminal at the other station, means to select and connect another trunk between the transmitting branch of said second terminal and the receiving branch of said first terminal upon the initiation of a set of signals at said second terminal, means to release said trunks upon the cessation of signals in a given direction, and means to select and connect a new trunk for transmission in a given direction inresponse to the initiation of a new set ofsignals in that direction.

21. In a system in which a plurality of trunks extend between two stations and signalin'g terminals are provided at each station for communication in pairs between stations, the method which consists in connecting an idle trunk between a given pair of terminals only during the continuance of sound waves from one of said terminals.

22. In a system in which a plurality of trunks extend between two stations and signaling terminals are provided at each station for communication in pairs between stations, the method which consists in connecting an idle trunk between a given pair of terminals only during the continuance of sound waves from one of said terminals and disconnecting said trunk upon the cessation of sound waves.

23. In a system in which a plurality of les trunks extend between two stations and signalin terminals are provided at each station or communication in pairs between stations, the method which consists in connectin an idle trunk between a given pair of terminals only during the contlnuance of sound waves from one of said terminals, disconnecting said trunk upon the cessation of sound waves, and selecting and connecting between the terminals a new idle trunk upon the initiation of a new set of sound waves.

24. In a system in which a plurality of trunks extend between two stations and signaling terminals are provided at each station for communication in pairs between stations, the method which consists in connecting an idle trunk between a given pair of terminals only during the continuance of sound waves from one of said terminals, disconnecting said trunk upon the cessation of sound waves, and selecting and connecting between the terminals a new idle trunk upon the initiation of a new set of sound waves from the other intercommunicating terminal.

In testimony whereof, I have signed my name to this specification this 13th day of November 1931.

HERMAN A. AFFEL.

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