USRE21778E - Transmission system - Google Patents

Description

April 22, 1941. PQTTS Re. 21,778

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N I r 5 $5 Qh NQ gqG J-mab [My 9 M 0 0 mp m 0 W Reicsued Apr. 22, 1941 UNITED STATES PATENT OFFICE TRANSDHSSION SYSTEM Louis M. Potts, Evanston, 111., asslgnor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York 167 Claims.

This invention relates to systems for the transmission of intelligence, and more particularly to systems in which transmission is effected by varying or modifying the flow of electric currents.

It is an object of the invention to improve systems of this general character by increasing the speed of transmission, and by increasing the efficiency and serviceability thereof.

Another object of the invention is to enable a comparatively large number of channels of telegraph transmission over the same electrical transmission circuit.

A feature of the invention relates to the provision of means whereby the ordinary equipment employed in telephone exchange systems may be employed for the transmission of a large number of telegraph messages.

Another feature relates to a system in which a comparatively large number of outlying telegraph subscribers are enabled to transmit messages through the use of currents of relatively low frequency of intelligence variation over telephone lines to a central office where said currents are translated by successively increasing frequencies into a single current of relatively high frequency of intelligence variation, which is then transmitted over a telephone circuit to a distantcentral omce where it is retranslated and separated into the several messages which it represents.

Another feature relates to a telegraph distributing mechanism which is capable of receiving a. plurality of simultaneous messages each represented by code impulses of a low frequency, combining these into a number of groups each represented by currents of a. higher frequency, repeating the combining operation and with each repetition decreasing the number of groups and increasing the frequency until all channels in which the individual messages originate are combined and represented by a single current of high frequency for transmission over the line.

Another feature relates to a distributing mechanism arranged to receive a large number of messages represented by code combinations of current which may be transmitted promiscuously with respect to each other and to distribute to a single line in a definite order, which may be determined by the grouping of the channels in which said messages originate, current impulses representing all oi. theorigina-l messages.

' Another feature of the invention relates to a distributing mechanism which is capable of receiving from a single line a succession of current impulses sent at a high rate and representing a large number of messages originally translated into a given code, and to distribute to a plurality of channels or subscribers lines at a relatively low rate of transmission the various impulses representing the messages intended for each of the successive lines.

Another feature of the invention relates to an arrangement whereby a plurality of telegraph messages are combined and represented by a single current of high frequency which serves to modulate a carrier current, together with means for transmitting over a single carrier telephone channel currents having frequencies within a desired band which are demodulated at the receiving end to give a current representing the transmitted messages, which is in turn separated by a distributor into the various messages which are thereupon distributed to the proper lines.

A feature of the original invention not claimed herein is a relay arrangement responsive to impulses of one frequency received over a circuit to deliver to another circuit impulses of another frequency, this being claimed in Patent 1,882,892, granted October 18, 1932.

A still further feature relates to a telegraph distributor for use in a system of this character comprising an arrangement of thermionic relays.

Other features relate to various subcombinations of and features of the apparatus and circults disclosed for carrying the foregoing obiects into effect such as a mechanical signal storing pulse lengthening and signal regenerating device; a start-stop mechanism controlled by the thermionic relay distributor; features of the system by which code impulses from the multiplicity of start-stop lines are relayed over a multiplex line on a time-division basis; features of the system by which the messages derived from the multiplex line at the receiving end are separated and relayed at the receiving end and each provided at the relaying point with start and stop pulses for each code combination; features of the cord circuits for connecting the subscrlbers or outlying station lines to the main transmission channel features of the subscriber arrangement; and features of the thermionic relay distributor.

Referring to the drawings, Figs. 1 to 6 when taken in order disclose the equipment pertaining to six originating lines, the outgoing distributor at a central office, an interofiice telephone transmission iine, the incoming distributor located at a distant central omce, and six receiving lines; only one originating line has its equipment show completely.

shown a frequency changer consisting of thermionlc relays.

Fig. 3 shows a telephone trunk interconnecting two central oflices and arranged for the transmission of currents of ordinary telephone frequency and also of carrier frequencies.

Fig. 4 shows the incoming end of the line at the distant central oflice. At the left of Fig. 4 is shown a synchronizing circuit consisting of thermionic devices. At the right of this figure is shown a thermionic relay distributor.

Fig. 5 at the left shows a a frequency changer made up of thermionic devices. At the right this figure shows another portion of the distributor consisting of polarized relays.

Fig. 6 illustrates a portion of the central ofiice distributor consisting of ordinary relays and arranged to serve six Outgoing telegraph subscribers lines.

Figs. 7 and "l comprise a diagram showing the application of this invention to a telephone exchange network.

Fig. 8 is a diagram showing the manner in which the several subscribers lines terminating in two telephone exchanges are grouped to secure the multiplex telegraph operation.

Fig. 9 illustrates one of the thermionic devices employed in the distributors.

Fig. 10 is a top plan view showing a portion of the start-stop translator employed for controlling one channel of the multiplex system, by one start-stop line.

Fig. 11 is an end view looking in the direction of the arrows li-ll in Fig. 10, with the parts in a position to show the action of one impulse controlling the setting of a storing rod.

Fig. 12 is an end View looking in the opposite direction of Fig. 10.

Fig. 13 is a detail showing one clutch for signal reception.

Fig. 14 is a detail showing another clutch for signal transmission.

Fig. 15 shows the general plan of oiisetirg the selecting rods and cams.

Fig. 16 is a detail taken along the line l6l6 of Fig. 10.

Fig. 17 is a detail showing the manner in which the selecting rods are positioned.

Fig. 18 is a top plan view showing a portion of the start-stop translator for delivering multiplex signals to the start-stop lines.

Fig. 19 is an end view taken along the line IQ-IS oi Fig. 18.

Fig. 20 is an end view looking in the other direction of Fig. 18.

Fig. 21 is a detail showing the manner in which the selecting rods are positioned.

General description of the system The multiplex telegraph system disclosed herein is designed particularly with the object in view of utilizing ordinary telephone equipment and circuits for the transmission of messages. It may be assumed, for example, that in a telephone exchange area many telephone subscribers will desire printing telegraph service as well. Each of these subscribers may have installed a printing telegraph equipment consisting of any suitable sender and receiver for five-unit code which may at will be associated with the telephone line leading to the central ofllce. Wheneverv the subscriber wishes to transmit a telegraph message, he calls the central ofilee operator in the usual manner and requests connection to a distant oflice, which may be in some other city, through which access may be had to the particular line to which he wishes to transmit the message. In response to this request the operator, by the use of one of her cord circuits, extends the calling subscribers line to a distributing equipment located in the central oflice and in turn connects, or causes to be connected, this distributing equipment to a trunk outgoing to the desired distant ofiice. At the distant ofiice the necessary information is given to the operator, who thereupon connects the trunk to an incoming distributing mechanism and in turn connects, or causes to be connected, the distributing mechanism to the desired outgoing subscribers line. Thereupon, the calling telegraph subscriber may transmit the message by means of the keyboard. This message is received by the distributor at the first central ofiice which distributes it in the proper sequential manner to the outgoing trunk over which it is transmitted to the distant office. At the distant oiiice the message is received by the incoming distributor which, in turn, distributes it to the called telegraphsubstation where it is recorded on a printer or other suitable receiving device.

Referring particularly to the diagram of Figs. 7 and '7, there are shown two combined telephone and telegraph subscribers stations, Hill and HIT, which terminate in the first central oflice at the operators position 132. These subscribers may, of course, converse with each other or with any of the other subscribers terminating in this ofiice by means of their telephones I06 and 109, which are normally connected through keys or other switching devices to the respective lines H0 and HI. Moreover, if the subscriber at station Illll wishes to send a telegram to the subscriber at station 101, he calls up the central oillce and the operator thereat connects his line to the called subscribers line by inserting one plug of her cord circuit ill in the jack N2 of the calling line and the other plug in the jack H3 0! the called line H I. As soon as the called subscriber is advised that a telegram is to be sent, he shifts his key IN to connect the line lll directly to the telegraph equipment.

At each station there is provided a suitable device such as a buzzer which operates in response to current received from the central oilice. This buzzer may be designed to vibrate at the rate of say 800 cycles per second, thus setting up in the line a current of a frequency which may readily be transmitted through the ordinary telephone equipment, this frequency being well within the voice range. Also at each subscribers station there is provided a relay 104 which is designed to operate in response to alter nating current of a given frequency for controlling the printer or other recordin device.

The calling subscriber thereupon manipulates his keyboard whereby a sending contact, such as the contact I03, completes a circuit for the buzzer relay 105 in the proper manner to send the impulse codes representing the characters of the message. At the called station, a relay or other device I33 responds to these code impulses of alternating current to operate the telegraph receiving device I08, such as a printer.

In order that the current upon the subscriber's line may be zero during idle periods a no-current stop pulse and a current start pulse are used in the start-stop telegraph printer.

1!, on the other hand, the calling subscriber at station IMI wishes to send a message to a subscribers station I3I (see Fig. "1) appearing in a distant central oflice, it will be necessary for him to make use of a central ofllce trunk. Upon receiving his request, the operator at the position I32 extends his line by means of his cord circuit over a connecting circuit, one end of which tenninates in the jack I I5 and the other end of which terminates in the out-going distributor H6. Moreover, the distributor H6 is connected to the outgoing line I2I by means of a cord circuit H8, one plug of which is inserted in the jack I I1 and the other in the jack H9. This cord circuit H8 may be at the position I32 or it may be located at another operators position in the same exchange, or the outgoing distributor may be connected permanently to the outgoing end of the trunk I2l. The operator at the first exchange now instructs the operator at the distant exchange who extends the trunk I2l by means of the cord circuit 124 to the incoming distributor I26. This is accomplished by inserting one plug of the cord in the jack 122 and the other plug in the jack 125. Lastly, the distributor I26 is connected by means of a cord circuit I28, one plug of which is inserted in the jack I21 and the other in the jack I29, to the line I30 which has been called by the subscriber at station I00.

If desirable two main lines I2I may be used for opposite direction of transmission instead of one to decrease the possibility of interference between messages sent in opposite directions.

The calling subscriber now sets up the code combinations on his keyboard which are transmitted over the line IIIII to the central office on the start-stop principle. These impulses being made up of 800 cycle alternating current, cause the operation of an alternating current relay 23 at the central ofi'lce which operates the start-stop distributor 42 which receives and stores the code combinations. are received and temporarily stored in the startstop distributor, are fed into the synchronous multiplex distributor in their proper order together with similar combinations from a plurality of other incoming lines, and thereupon transmitted over the interoflice trunk I2l to the distant ofllee. At the distant omce they are received by the synchronous multiplex distributor 126 and distributed in proper order to the start-stop distributors. The message being transmitted from the station I00 is received by the start-stop distributor I50 shown at the distant office and transmitted over the line 130 to the called station I3I, where it operates a receiving device such as a printer I34.

It may be desirable to provide for two-way back and forth communication between subscribers lines involving the multiplex apparatus. To this end, each central oilice is equipped with a plu-' rality of receiving multiplex distributors I52, as well as a plurality of sending distributors IIB. Likewise, the terminating office is equipped with a plurality of sending distributors I53, as well as the receiving distributors I26. A pair of distributors including a sending distributor H6 and These code combinations, which a receiving distributor I52 may be provided with a half-repeater, including the relays 23, 3, etc., whereby signals transmitted from the substation Hill to the substation I34 are repeated to the multiplex distributor IIG; whereas signals transmitted from the station I34 to the station Iflll are translated to start-stop code and distributed by the distributor I52 to the called line, all without interference. Likewise, at the distant terminal, signals coming from the station Illfl are translated to start-stop code distributed by the distributor I26 and by means of a half-repeater delivered to the called station I34. When the station I31 desires to communicate, the distributor I53 receives the signals and transmits them to the central office at the distant end. This provision is made in order that two subscribers may communicate with each other without establishing successive connections.

For the purpose of establishing a connection in order that the called station I3I may communicate with the calling station Illil, the operators at the central ofiices employ the cord circuits TGI and IE3.

In order to conveniently explain a system of this character, certain assumptions will be made regarding the number of subscribers lines involved, the number of channels that may be combined in a single transmission line, also with respect to the speed of transmission. For example, it may be considered that the out-going or sending end of the system may be made up of 96 different telegraph subscribers stations each constituting a separate channel-for communication, and that at the incoming or receiving end of the system there are 96 called telegraph lines with provision whereby each of the 96 calling lines may send messages simultaneously to respective ones of the 96 called lines, all over a single transmission circuit. Referring particularly to the diagram in Fig. 8, 96 calling subscribers lines 800 may appear in jacks at the operators switchboards in the first central oflice. Also appearing in the operators switchboards are the jacks of 96 different telegraph channels Blll. By means of cord circuits H8, etc., the operators may connect any of the 96 subscribers lines to any one of the 96 different channels.

Each individual calling line may transmit telegraphic messages by means of code combinations of current sent at a relatively low frequency. For this purpose, sending current of the order of 10 or 20 code impulses per second may be employed. These character code combinations are transmitted by start-stop apparatus from the subscriber's station to the central oiiice as groups of 800 cycle waves.

In order to secure multiplex operation at the central oflice, the 96 channels I are divided into 16 different groups of 6 channels each. For instance, the first 6 chanels 805 constitute one group and terminate in a single low speed distributing mechanism BIG. The second, third, and fourth groups of channels B, 801 and B08 terminate, respectively, in individual low speed distributors ill I, BI2 and 8l3. In a similar manner, the remaining 12 groups of 6 channels each are assigned to individual low speed distributing equipments. Each of these low speed distributors, such as the distributor 8H! which is shown in detail in Fig. 1, consists of a plurality of relays forming a distributor I20 (Fig. 1)

Each of the six incoming channels terminates in a translator unit. The signals may be transmitted from the subscribers station to the central oflice by the usual seven-unit start-stop signals comprising five current impulses and a start and a stop impulse. The translator unit receives and stores these signals under control of the alternating current relay 23 (Fig. 7). It delivers them to the low speed distributor 8"! in the proper order and in the proper phase position.

By means of the distributor M6, the signals in all of the first 6 channels 885 are directed over a single channel 8I5 which leads to a second distributing unit ill of relatively higher frequency. The current in the channel 848, which represents the message signals in all 6 channels 885, is 01' a greater impulse frequency than the original sending current and may be of the order of 60 impulses per second. In a similar manner, the signals in the second, third and fourth groups of channels 888, Bill and 888 are combined and directed over the respective single channels BIB, 8H and H8 at 60 cycles per second. In a similar manner, the signals in each of the succeeding groups of channels are combined and directed over a less number of channels to the distributing elements BIB, 828 and 82L Thus the message signals in the 96 channels which originate by means of current of frequency of i impulse cycles per second, are combined in the first stage distributing mechanisms into 16 dim-rent groups each represented by a current of 60 impulse cycles per second. These 16 groups of channels are then directed to four distributing mechanisms M4, 8'9, 828 and 82l as explained.

The distributor 8H, for example, which is designated I38 and shown in detail at the right of Fig. 1, consists of a plurality of polarized relays. The function of this distributor is to receive the signals transmitted over the channels M5, 816, 8|! and M8 by means of 60 impulse cycle current, and to combine these signals and redistribute them over the single channel 822 by means of a current having a still higher frequency, such as 240 impulse cycles per second. Similarly, the distributors M9, 820 and MI combine the signals in four diiferent channels and transmit them over the single respective channels 823, 824 and 825 by means of 240 impulse cycle current to a single distributing mechanism 828. The distributing mechanism 826, which is designated 288 and is shown in detail at the right of Fig. 2, consists of a plurality of therminoic or vacuum tube relays and its function is to combine the signals in each of the four channels 822, 823, 824 and 825, incoming at 240 impulse cycles per second, into a single channel 821 by means of a current of still higher frequency such as 960 impulse cycles per second.

Thus the signals incoming over 96 different lines simultaneously, originating at a. relatively low frequency of sending, are combined by means of the distributing apparatus shown and transmitted over the line 821 at a comparatively high frequency.

A better understanding of the manner in which these signals are combined will be had after considering the detailed description oi the apparatus given hereinafter. For the present it may be explained, however, that assuming the Baudot 1r five-unit code as the method of transmitting messages, the distributing apparatus is so arranged that impulse times or units of time for transmission of impulses are assigned in sequence to distributors 8l4, BIS, B28 and "I; successive unit times for each distributor 814 are assigned to its subdistributors lllll, 8, M2 and M3; and successive unit times for each distributor 818 are distributed to each of the group of lines 885.

Thus the assignment 01 one unit time to each line requires 24 cycles oi distributor I28, 6 cycles of each distributor 8, etc, and 1 cycle oi each distributor 8", etc. Thus the first 96 intervals for transmission over the line 821 account for the first unit of the five-unit code in each of the 96 channels. Repeating this cycle of operations, the remaining four units or the character are accounted for in the four succeeding transmission groups of 96 intervals each.

At the distant central oiiice the called telegraph subscribers lines 828 terminate, of which there may, for example, be 96. There are also 96 channels 888 at the distant central oflice arranged in 16 groups of 6 channels each. The first four groups 83!, 832, 888 and 834 appear in individual distributing mechanisms 835, 838, 881, and 838. Similarly, the remaining groups appear in other individual distributing devices. The distributing device 838, for instance, consists of a plurality of simple relays such as is designated 424 and shown in Fig. 6 and serves to distribute the message signals for the first 6 channels to start-stop translators.

The operator. by means of cord circuits 838, 848, 8", etc., may connect any of the called telegraph lines to any one of the 96 channels. Thus the signals received by the distributing mechanisms, 835, 836, 881, etc., are distributed over the proper individual channels to ordinary start-stop distributors, which in turn function with the start-stop distributors at the called telegraph stations to cause the operation of printers or other recording devices.

The low frequency distributing mechanisms 835, 838, 821, etc., are each connected by a single channel 842, 843, 844 and 845 to the distributor 846 which operates at a higher frequency. This is shown in detail in Fig. 5 and designated 423. Likewise, the remaining three groups or low frequency distributors are connected over single channels to the three distributors, respectively, 841, 848 and 848. These four distributors 846, 841, 848 and 849 are connected by single channeds each to the single distributing device 858 (designated 422 in Fig. 4) which operates at a still greater speed.

Thus the signals received over the line 821 by means of a current of 960 impulse cycle frequency are divided into four groups by the distributor 858 and sent over the four channels I, 882, 858 and 884 by means of current of 240 impulse cycles frequency to the distributors 846, 841, 848 and 848. Each of these latter distributors, such as the distributor 846, further subdivides the signals received and directs them over four separate paths 842, 843, 844 and 845 by means of 60 impulse cycles frequency to the distributors 885. 888, 821, and 838. Finally, each of these latter distributors, such as the distributor 835, divides the signals received and directs them over the 6 different channels by means of a current having a frequency of 10 impulse cycles per second.

These ten-cycle frequency impulses of current operate the translator at the central oflice. The signals are stored in the translator and are retransmitted in the form 01' seven-unit start-stop code signals to the subscriber's station where they are recorded in a well known manner.

Inasmuch as 96 diflerent messages may be sent over a single transmission line 821 at the same time, it becomes necessary to preserve a systematic and orderly assignment of the 96 different channels at the outgoing and incoming ends. This is taken care of by the operators at I lustrated schematically in Fig. 1.

the distant central offices who may communicate with each other in any suitable way, such as by the usual order wire which exists as a part of the regular telephone equipment. For instance, if a calling subscriber 855 desires to send a telegram to a called subscriber 056, the operators may assign any channel identified as the first channel for this purpose. In this case, one of the cord circuits 802 is inserted in the jack of the calling station 355 and the other plug inserted in the jack 051 relating to the first channel. At the distant central ofllce the operator inserts one of the plugs of her cord circuit 330 in the jack 050 of the first channel and the other plug she inserts in the jack 359 of the called telegraph subscriber's line 856. In this manner, 95 other calling and called stations may be assigned to the remaining 95 channels.

Any number of multiplex lines of this kind may be connected in tandem through ordinary telephone switchboards to provide a long distance circuit. The only condition necessary for such a connection is that all of the multiplex channels, regardless of the multiplicity, shall operate be tween two limiting speeds, for example, 40 and 41 words per minute. All substation transmitters should be so adjusted that they cannot transmit over a certain limit, as, for example, 39 /2 words per minute. and all receivers so adjusted that they will receive up to a given limit, as for example, at least 42 words per minute.

Referring to Figs. 1 to 6 inclusive, a brief description will now be given of the apparatus. At the left of Fig. l is shown at 22 one of a plurality of incoming. signal channels such as the one associated with Jack 058 of Fig. 8. The circuit leads to an alternating current relay 23 which is designed to maintain its contacts normally closed and responds to current of a given frequency. such as 800 cycles per second, to open and hold open its contacts during the time that current is flowing. Associated with the channel 22 is a start-stop translating mechanism 42 which, for the sake of convenience, has been il- This startstop mechanism is connected to a signal-receiving relay 43 which responds in the usual manner to open circuit conditions to cause the distrlbutor 42, by means of the receiving magnet combinations representing the characters re ceived and control the sending contacts I in accordance therewith, one contact being assumed to be connected to a current source of suitable potential. The start-stop translator I2 is associated with the relay distributor I20 by means of the circuit 45. which includes the start magnet 00 of the start-stop translator. The circuit 40 is so connected to the distributor I20 that the magnet 06 is operated at a given point in the cycle of operation of the distributor I20 in order to start the start-stop translator. at the proper instant. Similarly. five other channels are connected to the translator I20 at five different symmetrically spaced points. By this arrangement the 6 start-stop translators representing the 6 channels associated with the distributor I20 are started in operation in, a definite sequential order under the control of the distrlbutor I20, each beginning to operate at a different point in the cycle oi operation of the dis-' tributor I20. Hence the signals stored in the distributors 42 are fed into the distributor I20 in a definite sequential order. This same ar- 15 groups 01 channels. The signals from the start-stop distributor 42 are delivered to .he relay distributor I20 by means of the usual sending contact 41 which is operated in a code-wise manner by the storing means of the start-stop translator. The timing is to be such that contact 41 of a particular channel is controlled (either open or closed) at the precise instants (with a suitable margln) a path through distributors I20, I30 and 208 is closed for the particular channel assigned to this contact; the position of the contact 41 of this channel at other tiilles is immaterial.

Relays I to 5, and I2I to I26 are arranged to operate and lock in pairs, each pair causin the release of a preceding pair. The operating circuits are closed by the polarized relay 9. Relay 9 is in turn operated by relay 1, which is operated periodically by the distributor I30.

The distributing mechanism I30 consists oi four pairs of polarized relays II, I2, I3, I4, I3'I, I32, I33 and I30, together with an operating relay 4 and a distributing relay I5. The relays I, B, 9 and I0, which are also polarized, serve to interconnect the distributing mechanisms I20 and I30. These relays, together with the other polarized relays shown in other parts of the disclosure, are so arranged that the armature always stays In the position in which it was last attracted; one winding serves to attract the armature in one direction, whereas the other winding serves to attract it in the opposite direction. The four pairs of relays II, I3l, and I2, I32 and I3, I33 and I0, I31 are arranged in counting relation to be operated from the contacts of relay III.

Assume relays II and I3I and relays I2 and I32 are operated and the other relays of the distributor are unoperated. Relays I3 and I33 operate and relays II and I3I release on the next step, and on the next succeeding step relays I4 and I34 operate and relays I2 and I32 release. This process continues as long as relay 4 receives impulses.

The relay I is arranged to operate through its lower winding who-never the second pair of relays I2 and I32 are energized, and through its upper winding whenever theiourth pair It and I34 are energized. In other words, the relay I operates once in each direction for every cycle of the counting relays I30. Relay I on closing its lower contact, charges the condenser 5 either with a positive or a negative charge depending upon the position of the armature oi relay 0. When relay I next closes its upper contact, the condenser discharges through the windings of relays 0, 3 and I0, serving to operate these relays to their other position.

Relay 0 operates in one direction durin one cycle of the distributor I30, and in the other direction for the next succeeding cycle.

The relay 0 on each operation causes an operating circuit for a pair of counting relays or the distributor I20. Thus it will be seen that the rate of operation 61' the counting relays I20 is reduced as compared with the rate at which the counting relays I30 are operated.

Thus, i'or each cycle of operation of distributor I30, distributor I20 is operated one step and distributor I30 must complete six cycles while distributor I20 completes one cycle.

All of the code impulses representing messages in the six channels leading to distributor I20 are directed through contact: of the relay I0,

range'ment 15 provided ior each of the remaining over conductor Iii. to the contact oi relay l.

In a similar manner, the impulses for three other groups of six lines each are directed over conductors ill to the contacts of relays i2, i2 and M, respectively. The armatures these relays H, l2, l3 and ii are connected to contacts of the relay i5, whereby all impulses representing the messages in four different groups may be directed to the single conductor 0.

The last stage of the distributor consists oi a distributing mechanism 208 which is made up of a plurality of sets oi thermionic relays. These relays, which will be described in detail hereinafter, consist of vacuum tubes each having a filamentary cathode, an anode and various windings which in the most general case include starting, locking and releasing windings. They are sensitive and accordingly may be operated at a high rate of speed. The thermionic relays are arranged in a counting relation similar to the relays 'shown in Fig. 1 and are operated cyclically by alternating current generated by an oscillation generator 202. The generator 202 consists of an ordinary three-electrode vacuum tube V which supplies space current to the middle winding of the induction coil T. The left winding of the coil supplies current to the input side of the tube. the frequency of which may be adjusted by the inductance and capacitance shown in the input circuit. The right winding of the coil T is included in series with the operating windings 200, I99, 204 and 203 of the relays 00, 3'9, 38 and 31. respectively.

The operating windings of these relays are so arranged that when current flows in one direc- 'is flowing in a given direction, one relay will be closed and the other relay open. Similarly, the relays 31 and 30 are arranged to operate and release alternately. The polarizing windings 2M. I98. 209 and 2i0 are shown associated with their respective relays.

The relays oi the distributor 208 are arranged in four sets. each'set constituting a vertical row.

That is, the relays 33, 20 and 25 constitute the first set; relays 34, 30 and 26 the second set; and so on. Relay 33 is provided with a polarizing winding I90, an operating winding I06. :1. release winding I82, and a locking winding I94. In like manner. the relays 34, and 36 are similarly provided. Relay 23 has an operating winding H4 and a polarizing winding H8. The same is true of relays 30, 3i and 32. Likewise. the relay 25 i provided only with an operating winding I66 and a polarizing winding I10, which is also true of the relays 26, 21 and 28. For each closure of the relays 89 and 40, the succeeding one of the relays 33, 34, 35 and 36 is operated. The operated relay looks through its locking winding, causing the operation of the two associated relays in the same set. Also. at the time one of the relays 33, 34, etc., is operated, the second. preceding relay which has been previously operated is released. This rotating action continues under the control or the oscillation generator 202.

Since the stepping rate or the distributor 200 is higher than is required for the distributor I30. 8. frequency changer 2 is inserted to reduce the speed of operation of the distributor I80. The frequency changer 2 consists of four pairs of thermionic relays. The relay I" is provided with an operating winding 2". a polarizing winding i5i, a locking winding I00, and a release winding I41. The same is true of the remaining three relays I36, I31 and IIB. The relay It has only an operating winding I43 and a polarizing winding I39, and this is also true of the relays i1, i8 and I9.

Interacting between the high speed distributor 208 and the frequency changer 2 is a device consisting of two thermionic relays 20 and 24, each of which has a polarizing winding, an operating winding, and a release winding. The re lays 20 and 24 are so connected to the distributor 203 that one relay-operates and the other releases when relay 34 closes. When relay 30 closes, the reverse action takes place with relays 20 and 24. Thus the relays 20 and 24 each operate and release for each rotation of the distributor 20B. Relays 20 and 24 govern the counting operation of the relays of the frequency changer 2ii. These relays 2i] determine the operation of the polarized relays i5 and I.

As the distributor 208 rotates under the control of the oscillator 202, the relays 25, 2B, 2! and 28 are sequentially closed and opened at a definite rate per second. During the closed period of relays 25 jointly and 38, all message impulses on the conductor 8 are delivered through the relay 30 to the single path 2I3. Similarly, during the closed periods of relays 26. 21 and 28. all message impulses flowing in the conductors 4i 9. 020 and MI are delivered through relays 26. 21 and 20 and either through the relay 3! or the relay 38 to the single path 2l3.

The path U3 is connected to the transmission line 226 by means of a connecting or cord circuit 206, the plugs of which are inserted in Jacks 205 and 201. At the distant central oflice, the transmission line 226 is connected with the path 252 by means of the connecting circuit 2, the plugs of which are inserted in Jacks 230 and 232.'

The transmission line 226 may be of the known character used for multiplex carrier teiephone transmission. Accordingly, there is provided at the outgoing end. an oscillation generator 22i for generating a high frequency carrier current suitable for transmission overthe line 226. A modulator 220 of any known type. such as a vacuum tube modulator, is employed for modulating the high frequency carrier current produced by source 22i in accordancewith the.

telegraph signals received over the path 2|! from the distributor 208. The modulated carrier current may then be amplified by an amplifier 222 01' any known design and passed through a highpass band filter 223 to the transmission line228.

At the receiving or distant station the high frequency modulated. carrier current is passed by the high-pass bandfilter 221 to the demodulator 228. The demodulator 220, which may also be or any known-construction, demodulates the carrier current and delivers the detected tele-.

leading to the distributing mechanism in the incoming oiilce.

If desirable. the transmission line 220 may also be arranged to transmit ordinary voice frequency telephone currents without interference. This is accomplished by employing low-pass band filters 224 and 233. These filters are designed to pass the comparatively low frequency voice currents but to exclude the high frequency carrier telegraph currents. By making suitable connection with the jacks 225 and 234, ordinary telephone conversations may be held over the transmission line 228.

At the receiving oifice, the distributors 422, 423 and 424 are similar in function to those shown at the sending ofiice and serve to receive the signais of all 96 different channels and distribute them to the corresponding called telegraph subscribers lines.

The distributor 422, which operates at high speed, corresponds to the distributor 200 at the sending end and is made up of a plurality of sets of thermionic relays. However, instead of having four sets of relays as in the case of distributor 208, the distributor 422 is provided with eight sets, these sets occurring in vertical rows. The reason for having eight sets instead of four is to facilitate the maintenance of synchronism between the equipment at the sending end and at the receiving end. Another reason is that, with proper phase relation within a signal impulse period, a central and hence more reliable portion of impulses may be used for signal reception. The relay distributor 422 is driven by an oscillation generator 252 which comprises a vacuum tube X having input and output circuits associated with the inductance Y, together with an inductance and capacity in the input circuit for securing the desired frequency. It is found that synchronism may be maintained conveniently by driving the oscillator 252 at a frequency which is double the frequency of the oscillation generator at the sending end. Accordingly, twice the number of such relays are needed for the distributor 422 in order that the frequency changer 425 may be driven at half the speed of the distributor 422, or, in other words. at a speed equal to the speed of sending at the transmitting station.

The first set 01' relays in the distributor 422 consists of relays 240, 250, 13, 12 and and ii. Similarly. the third, fifth and seventh sets of relays consist of as many as the first set. The

second set of relays, however, consists of only two, namely, the relays 2 and 60. In like manner, the fourth, sixth, and eighth sets each have two relays. The relay 340 has an operating winding 322, a polarizing winding 34!, a release winding 224, and a locking winding 3I6.

Each of the relays 24L 342, 342, 244, 345,340 and 341 have similar windings. Relays 250 and 13 are each provided with an operating winding 208 and 604, respectively. The same is true of relays 00, Ni, Si, 262, 02, 262, 02, 15, 11, 19, 12, 14, 16 and 10. Although the polarizing windings are not shown for several of these latter mentioned relays it is to be understood that these windings will be provided to maintain the relays normally open. When relay 242 is operated, relay 250 is operated and relays 12 and 13 are prepared tor operation; which of 12 and 12 will be operated depends on which of and 50 is operated and this in turn depends upon whether a marking or spacing signal has caused one or the other of 425 or 420 to be operated.

The distributor 422 is driven by the oscillator 252 under control of the thermionic relays 09 and 60. Upon the occurrence of an oscillation in the output circuit of the generator 252 one of the relays, 59 for instance, is closed and the other relay 6!! is held open. Upon the next oscillation, the reverse process takes place, namely, the relay B9 is opened and the relay i0 is closed. This continues, the relays alternating throughout each successive cycle of the current produced by the generator 252. Upon each closure of each of the relays B8 and 09, a succeeding one of the relays 340, 34!, 242, etc., is operated and a second preceding if is released. Therefore, it will be noted that a succeeding one of these relays operates upon each half-cycle of the current produced by the generator 252. It will also be noted that the relays I3, 15, 11 and I9 and also relays I2, 14, 16 and 18 are conditioned for operation at the rate of one pair of relays per cycle of the oscillatory current. Also included in the output circuit of the generator 252 is a relay 61, which is conditioned to pass current in a given direction once per cycle and accordingly is closed once during each cycle of the current. The relay 61 supplies voltage to the relays 65 and 56, one of which latter relays is operated in response to incoming signals, as will be explained hereinafter, for determining the operation of one or the other of each of the pairs of relays and 8|, 82 and 83, 84 and 85, B6 and 81. Relays 80 and BI, when operated, complete a circuit through the winding of the polarized relay 94 to determine its operation in one direction or the other according to which oi the two relays was closed. Relay 94 determines the application of plus or minus battery to some polar relay of the set I02, etc. In similar manner, the remaining three pairs of relays 02 and 83, 84 and 05, etc., determine the operation of three other relays similar to the relay 94.

The second portion of the main receiving distributor consisting of distributor 423 consists of four pairs of polarized relays 98 and 390, and 399, I00 and 400, and IM and 40!, together with four polarized relays I02, I03, I04 and I05. The relays 98, 398, etc., are operated in sequential fashion by means of the frequency changer 425. The frequency changer 425 is made up of four sets of thermionic relays which are driven in a cyclical manner by means of the two relays 02 and 09. The relays 80 and 89 have their operating and releasing windings connected to two different points in the distributor 422. Thus for each rotation of the distributor 422, relays 00 and 89 are each operated to determine the sequential operation of the relays of the frequency changer 425; The frequency changer 425 has two of its relays 280 and 202 connected to windings of polarized relays 25 and 50. By this means the relays and 00 are operated once in each direction for each rotation of the frequency changer 425.

The relays I02, I03, I04 and I05 are selected sequentially, however, by the counting operation of the relays 90, 390, etc., and are operated in either one or the other direction by circuits closed through the contacts of relays 94 and 25, according to whether there are signals in the conductors 426 or 421. The relay I02, when operated in either one or the other direction, applies either positive or negative current to the conductor 42!. The signals thus produced in the conductor 42! are directed through one or the other of the contacts of relay I06 to the contacts of the relays of the distributor 424. In a similar manner, the relays I02, I04 and Ill receive signals from contacts of relay 94 and in turn apply plus or minus battery to the conductors 430, each of which leads to the armature of a relay similar to relay I06 associated with three distributing mechanism similar to the mechanism 424.

The distributing device 424, similar to the distributor I20 at the sending station, consists of six pairs of simple relays. These relays are arranged in counting relation to each other and are operated and released sequentially at a given rate which is a function of the rate of rotation of the relays of the distributor 422. In 96 unit signal periods or 192 half periods the distributor 424 passes through a complete cycle, and distributor 423 and other similar distributors pass through 6 complete cycles. For operating the relays 424 in sequential manner, polarized relays I01, I80 and IBI are provided. The relay I'I operates to close its upper and lower contacts once for each rotation of the distributor 423. On closing its lower contact, the relay 01 permits the condenser 43I to charge either positively or negatively according to the position of relay I80. On subsequently closing its upper contact, relay I07 closes an operating circuit for relays I80, IBI and I00 which operate in a direction depending upon the nature of the charge which the condenser 41 discharges through their windings. For each operation of relay II in either direction, a pair of the counting relays I03, 408 and I09, 409, etc., are energized and a preceding pair are released.

The signals occurring in the conductor 429 are directed through contacts of relay 06 to the closed contacts oi relays I08, I09, IIO, etc. Whenever marking signals are present in conductor 423 at the time relay I06 closes its upper contact and relay I00 is operated, these signals are directed over the path 432 to the windings of the polarized relay II4. Relay II4 completes a circuit through the windings of polarized relays H5 and H6 and through the code magnet 564 of the start-stop translator associated with the channel identified by the relay I00. Likewise, the signals intended for the following five channels are directed through contacts of the relays I09, H0, etc., to the respective conductors 434.

In order that synchronlsm may be maintained between the sending and receiving ends, means is provided for adjusting automatically the speed of the oscillator 252 whenever it varies from the frequency established by the oscillator 202 at the transmitting station. For this purpose, the thermionic relays 239 and 238 have their operating windings 246 and 241 included in series with the output circuit of the oscillator 252. Accordingly, these relays will both be operated once for each cycle of the oscillatory current 252.

The signals, after detection and amplification, delivered to the conductor 253, are directed to the operating windings of the thermionic relays 435 and 436. The relay 435 is so arranged that the polarizing and operating windings both act in the same direction. The polarizing winding is adjusted so that it almost opens the relay normally. Thus when a slight current is flowing through the operating winding, the relay will open. Conversely, the operating and polarizing windings of the relay 436 are in opposition to each other and the polarizing winding is adjusted so that it is just strong enough to hold the relay open. Accordingly, a small amount of current through the operating winding will close the relay. Accordingly, whenever a signal occurs in the conductor 253, the relay 435 opens and relay 436 closes. In this condition, current flows through the left winding of the transformer 235 in a given direction. Following the signal when an absence of current occurs, relay 430 opens and relay 435 closes. This reverses the direction of the current through the winding of the transformer 235. Thus for each signaling current impulse, there is a reversal of the direction through the left-hand winding of the transformer 235. Accordingly, an alternating current is induced in the right-hand winding of the transformer, the direction of which alternates through the operating windings 242 and 243 of the thermionic relays 230 and 231. This current is composed of short pulses separated by much longer intervals of no current.

The frequency of the current produced by the oscillator 252 is twice the frequency of the incoming signals from the transmitting station. Accordingly the relays 230 and 230 will open and close at twice the rate of the relays 236 and 231. These relays are adjusted in such manner that when the transmitting and receiving stations are in synchronism the closed period for each of the relays 236 and 231 occurs between the closed periods of the relays 230 and 239.

When condenser 430 is out of the circuit, the frequency of -the oscillator is slightly greater than that of the incoming signals; and when the condenser is in the circuit, the frequency of the oscillator is slightly less than that of the incoming signals. While switching condenser 430 in and out at rapidly recurring intervals, the intervals may be so regulated in lengths that the average frequency of the oscillator will be exactly the same as that of the incoming signals. The relays 236 and 23l close for very short intervals for each reversal of the current in line 253. This short impulse is delivered by relay 230 or 230 into the winding 250 or 25I of relay 240, depending upon the phase of the oscillator with respect to the incoming signals. For a certain interval pulses will go through relay 23B and for a certain interval through relay 238, and condenser 438 will be in and out of the circuit accordingly. If any factor allects the rate of the incoming signals or the rate of the oscillator, the relative length of the two sets of intervals will automatically readjust itself to maintain synchronism. By this means is the average frequency of the oscillator made twice that of the signals, to maintain a substantially fixed phase relation.

In order that a better understanding may be had of the cooperation between the difl'erent stages of distributors, certain assumptions will now be made regarding the speed at which these mechanisms are driven. These speeds are purely relative and may be of any value so long as the whole system is varied in the same ratio. Assume that the oscillation generator 202 generates alternating current having a frequency of 960 cycles per second. This means that the direction of the current changes twice during each cycle, or 1920 times per second. Accordingly, the control relays 39 and each close once and open once during each cycle, giving 1920 closures per second. Since one of the relays 33. 34, 35 and 36 operates for each operation of one of the relays etc., of the distributor 208 will operate at the rate of one relay in each /1920 of a second.

The relays 20 and 24 are so connected to the distributor 208 that each of these relays operates 39 and 0, the relays 33, 34, 35, l

'the distributor 422.

and releases once during a complete cycle of the distributor 200, or, in other words, during each interval of /480 Of a second. For each operation of the relays 20 and 24, a set of the relays of the frequency changer 2 is operated. Therefore, in order to operate all four of the sets of relays of the frequency changer 2 I I, it will be necessary to operate each of the relays 20 and 24 twice. Accordingly, it requires 1th] of a second to complete a cycle of the frequency changer 2.

The frequency changer 2" is so connected to the polarized relay 4 I4 that this relay is operated once in each direction for a complete cycle of the changer 2, giving two operations of the relay H4 in of a second. Since it is necessary for the relay 4 to operate four times to complete a cycle of the distributor I20, said distributor requires of a second per cycle. Due to the manner in which the relay I is connected to the distributor I30, said relay operates once in each direction for each cycle of said distributor. Inasmuch as the relay 9 operates once for every two operations of the relay I, it follows that each of the counting relays I, 2, 3, 4, etc., of the distributor I requires two operations of the relay I. Accordingly, for each cycle of the distributor I30, a pair of the counting relays I20 will be operated. This means that the distributor I20 requires & of a second per cycle.

From the foregoing assumptions, it will be seen that the start-stop distributors 42 associated with each of the 96 sending channels may be arranged to send other code impulses to the 16 different distributors I20 at the rate of 20 impulses per second. These impulses are delivered in the proper sequential order to four separate second-stage distributors I operating at a high rate of speed. The impulses from the four distributors I30 are delivered in proper sequential order over four separate conductors M8, M0, 420 and 42I to the single third-stage distributor 200, which operates at a still greater speed and distributes all impulses from 96 different channels in the proper sequential order to the input circuit of the modulator 220 in order to modulate the high frequency carrier current for transmission over the signal line 226.

If desirable, the speed of all four distributors I30 may be governed by the single frequency changer 2I I. This may be accomplished by mull tipling each pair of leads 516 to 500, inclusive, from the changer 2I I to separate distributors I30, the connection being taken off at the proper point to give the correct phase relation for each distributor. going to distributors and D.

At ,the receiving central oflice, it may be assumed that the oscillator 252 generates an alternating current at a frequency of 1920 cycles per second. Accordingly, the relays B0 and B9 operate and release once per cycle. This means that the relays of the distributor 422 operate at the rate of two relays per 3 of a second. In other words, it requires Vim of a second for each cycle of the distributor 422.

The distributor 422 is so connected to the frequency changer 425 that two sets of relays of the changer 425 are operated for each cycle of This means that the frequency changer 425 requires ,5 of a second for each cycle. The changer 425 is in turn so connected to the polarized relay 90 that this relay performs an operation in each direction for each cycle of the changer 425. Accordingly, the disl30 designated A, B, C

In Fig. l the leads are designated as tributor 422 requires of a second for each cycle of operation.

Similar to the manner in which the relay I01 is connected to the distributor 422, this relay operates once in each direction for each cycle of said distributor d, accordingly, the final distributor 424 requires 2 of a second for each cycle.

It follows iron these assumptions that the multiplex distribu -or apparatus at the receiving central office is c: pable of distributing code impulses to each of ihe 96 separate receiving channels at the rate of 20 impulses per second.

The assumptions made for the speed of operation of the equipment shown are arbitrary and that this equipment may be driven at higher or lower speeds according to the requirements.

At the receiving end of the multiplex system, a. phasing arrangement is provided. This consists of the keys 440, I and 442, which in reality may be assembled to constitute a single key. The function of the phasing key is to arrest the operation of the distributors 422, 422 and 424 and cause these distributors to start in operation at a definite point in their cycles which will be exactly in synchronism with the rotation of the corresponding distributors at the transmitting station. A more detailed explanation will be given of the phasing operation hereinafter.

Description of the thermionic relays As already explained, certain of the distributing mechanisms are composed of thermionic relays. One of these relays is illustrated somewhat in detail in Fig. 9. It consists of an evacuated vessel 443 within which is enclosed a thermionic cathode 444 which may be heated by a suitable source of electric current. For convenience this heating source has not been shown throughout the drawings. Also within the vessel 442 and surrounding the cathode 444, is an anode 445 cylindrical in shape. This anode may comprise a solid metal cylinder or it may be made up of a cylindrical cage of spaced metallic members. Surrounding the glass vessel 443 are a number of coils 446, 441 and 440 designed to carry electric currents. If a potential difference is applied across the terminals 449 and 450 with the cathode heated, an electric current will flow due to the discharge of electrons into the evacuated space. By energizing one of the windings 446 with electric current of the proper value and in the proper direction, the stream of electrons flowing between the electrons may be so controlled and restricted that no current flows in the circuit 449, 450. By passing an electric current through a second one of the windings 441 as an operating winding in the proper direction, the polarizing effect of the first winding 446 may be overcome, whereby current again flows in the circuit 449, 450. Once the circuit is closed, it should be maintained in a closed condition by the flow of current through the locking winding 440. The effect of this locking winding is to counteract the polarizing winding 446, whereby the current flowing therethrough is sufficient to maintain the electron flow between the electrodes of the tube. For a further description of relays of this type, refe ence is made to the patent to A. W. Hull, No. 1,387,985, granted August 16, 1921.

Detailed description of the start-stop distributors A detailed description will now be given of the start-stop distributor which receives startstop impulses from a subscriber's line and de

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