US2363671A - Telephone system - Google Patents

Description

Nov.28,-1944. A, HUBBARD 2,363,671

TELEPHONE SYSTEM Filed Dec. 51, 1942 5 Sheets-Sheet l HWEA/TO/ F. A. HUBBARD A T TOD/VF V Nov. 28, 1944. F. A. HUBBARD 23,353,671

' TELEPHONE SYSTEM J Filed pee. 31, 1942 5 Shets-Sheet 2 MAI/EN TOR F A. HUBBARD ATTORNEY I Nov. 28, 1944. U BARD 2,363,671

TELEPHGNE SYSTEM Filed Dec. 31, 1942 5 Sheets-Sheet 4 F/GJO was /00 INVEN 70/? F. A. HUBBARD A TTOR/VFV I Patented Nov. 28,1944

r 2,363,671 TELEPHONE SYSTEM Francis A. Hubbard, Maplewood, N. J.,a.ssignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporationof New York Application December 31, 1942, Serial No. 470,724. to

o e o 14 Claims. l 'I' his invention relates to signaling and communication systems. and particularly to telephone systems in which automatic switches used in the establishment of telephone connections are controlled by means of alternating current.

Systems have been proposed, heretofore in which the designationsof called: lines are transthe first or the second of the three condensers mitted from one pointft'o anotherby'means of alternating "currents "of different frequencies transmitted singly or in combination characterizing the different digits or other characters of a wanted line designation. In Patent No. 2,164,- 335, is'suedJuly 4; 1939, to R. C. Mathes,.there is disclosed a system of this general character in which a harmonic generator is employed at the In the proposedtransmittera} resonant sup pression circuit is provided comprising two don-Q ble' wound retard coils each having its windings connected in series opposition and three fcondensers. One coil may be tuned to either of two frequencies a or b by the connection of either to the mid-point between the windings by the operation of a first or second switch element, and the second coil may. be tuned to the frequency 0 by the connection of athird condenser to the mid-point between its windingsby the operation of a third switch element. Preferably the switch elements are of the timed mercuryjcontact type subscribers station which is activated by ourrent of a fundamental frequency generated at the central ofiiceto produce .harmonicsof this fundamental frequencyand in which the subscriber l is" provided with means. for selecting certain of r the generated harmonics to characterizethe digits of a telephone designation and to cause the selected harmonics tobe.suppressed to. control the operation of automaticfswitches. A further improvement on the: system disclosed in the patent to Mathes just referred tois disclosed in Patent N0. 2,201,296issued May 21, .1940, to A. A.

Lundstrom and E. L. Norton.

It isthe' object of the presentinvention to further improve systems of this type. whereby a smaller number of generated harmonics are utilized to characterize the digits. of a telephone designation.

and are selectivelyoperable once during the down-stroke of a key-set keyand are selectively operable again during" the up or return stroke oflan operated keyin accordancewitha predeterminedcode; v. v v r A code may be so selected with respect to the standard arrangement of thekeys in the keysetas indicated. in a table appearing hereinafter that every key suppresses a single harmonicron the down-stroke. and. that no. two, adjacent keys arranged either vertically or horizontally sup press the same harmonic onthe down-stroke. wIl'l accordance with the-code all. keys but theukey for the digit ,0 suppresses a singleharmonic on i l its up-stroke, the keyforthe digit O suppressing "It is a further object of. the present invention to enable a wider spacing of the utilized harmonics iwithout increasing the outside frequency rangewhereby a greater discrimination. by the receiving channels is secured or a narroweroutside frequencyrange of. the harmonicsmay be employed whereby the difference in attenuation betweenthe highest and lowest frequencies is In accordance,w ith one embodiment of themvention. these objects are attained by the provision of mechanism in a call transmitterof the general type disclosed in the Patent No. 2315 344 granted March 30, 1943, in the name of R. F. Mallina whereby the operation of any one of the ten; keys ofthe key-set is effective upon the down-stroke to selectively suppress one ofthe harmonics which characterizes the digit corresponding to the depressed key andtagain upon the up-stroke of the operated key to suppress one, or more harmonics which characterize the digit .55

corresponding to the operatedjkey.

two harmonics simultaneously on its up-stroke.

The seriallyconnected suppressionfc-oils are connectable to the, tip conductor-of the .substation line through a fourth. condenser by an offnormal switch of the timed mercury contact type. Thiscifi-normal switch is momentarily operated during the down-stroke movement of anygkey and is again momentarilypperated during the up-stroke movement of the operated key to transfer the substation line from the substation subset to the harmonic generator coil of the. call j transmitter. By connecting this condenser in se ries withthe generator coiland suppression coils, the off-normal switch when operated, opens the direct current path at the substation whereby central office equipment may be signaled and conditioned to receive voice frequency signals thus "eliminating certain 'difficulties that have heretofore appeared tobe inherent inthe sys temsof this type hereinbefore proposed, by entirelyseparating the signalingcondition from the normal talking condition, eliminatinginterference between the two and by providing a positionsignal to activate the receiving channel,

. The production of two signal impulse conditions by the call transmitter foreach keyeddigit wwi sponse to the suppression of one of the three frequencies suppressed upon the down-strokeof an operated key, and the other group being associated with the three receiving channels following the termination of the first impuiseof .a digit sig-= ing 3 is attached. Secured to the base I is a mounting plate 4 having upturned ears 5 and 6 for supporting a shaft 1 on which the key member Kl to Kill, inclusive, are pivotally mounted;

an upturned and then inturned bracket 8 upon which the off-normal switch assembly 9 and the suppression switch assembly I are secured by the screws ll; an ear I2 for supporting one end of the pivot screw l3 upon which the armatures of the switch assemblies 9 and "1C are pivoted; an upturned and then inturned bracket l4 upon "which the suppression switch assemblies IDA and nal so that relays of such group are selectively operablein response to the suppression of one 'or more of the three frequencies upon the upstroke of the operated key. Thus upon the terur na ion of the wo impulses .of a digi nal a re ay. of the first .sreupand one or two rel ys of thel eccnd group w ll m in ope to 9 trol the setting of a digit register of the sender. For a clearer understanding of the invention reference may be had to the following detailed descr ption t ken in connection with the accompan in d awin s n Which;

Fig, 1 is a left side elevation view of the telephone call t fiansmitter' mbodying the invention, the casing being shown with a portion broken away to disclose the frequency suppression switches and the key-controlled operating mechanism therefor;

,Fig. 21$ 3 top plan View of the callv transmitter with a portion of the casing broken away;

Fig. 3 is a right side elevation view of the call transmitterthe casing being shown with-a portionbroken away to disclose one of the frequency suppression switches and operating mechanism therefor Fig. is an enlarged side elevational detail view of the frequency suppression switch disclosed in Fig. 3; r

Fig. 5 is, an enlargedend view of an assemblage of'a suppression switch and the off-normal switch; I

s Fig. 6 is a detail View of the end of the operating levers associated with the suppression switch disclosed in Figs. 4 and 5; i

Fig. 7 is a detail view of the end of the offnormal switch operating lever associated with the oiif-normal switch disclosed in Fig. 5;

Fig. ,8 is a detail view, partly in cross-section, of" one of the mercury contact Switch elements a so i edw th h uppression switches and off- ,swi c and i s-: l9 and 11,. taken together, show a tele phone syst min accordance with the pres t i vention. and in which. the call transmitter dis-. lose in Fi s 1. t 8, inclusive, s empleyedz Fig. 9 .sh wing the. substation. circuit in which the; call transmitter is, installed, a diagrammatic illn strationof allnefinder; first selector, a. sender link comprising a run fln erand sender selector and aportiqh of the, circuits of a; central office send F sshamin t e re ivin channels of thesender, the; recording relays and other contror relays and Fig. 1 1 showing certain of; the sender refisters; and progress; relays associated there.-

I 16- i tra mitter of the invention as shown; in. Figs; 1-, 2: and, 3, a base If? is provided" a n upturned edges 2 to which a molded casbracket. i For camm'ing the armature 36 away from the polar'ends of the pole- pieces 32 and 33, the ho-ri-q .lllB are secured by the screws l5; the ear I6 "for supporting one end of the pivot screw l1 upon 'wh'ichthe .armatures of the switch assemblies IBA and 1B are. pivoted; and an upturned plate Each of the key members Kl to KIU, inclusive,

is normally and yieldably maintained in the posiin different combinations upon the depression of the key'members. These bars are normally and yieldably held in the positions disclosed in Fig. l by retractil-e springs 20 which are hooked at one of their ends to the upper edge of plate l8 and at their otherends are hooked to lugs 2| of lever members '22, 23, 24, 25, 26,-and 21 which are secured to the U-bars B1, B2, B3, B4, B5, and

B6, respectively as by rivets 28.

A U-shaped off-normal bar B1 is also pivoted on shaft 1 and held in operable relation with each of the ten' key members K I to Kit inclusive, by a retractile spring 29 hooked at one of. its ends to a lugon the lever 30 secured to the bar B! as by rivets 3| and at the other of its ,ends to the plate 18. control the off normal switch assembly 9 once when any key of the key-set is operated in a down-stroke and. again when the operated key is. released in an up-stroke.

The off-normal switch assembly 9 comprises two parallelly disposed pole-pieces 32' and 33 clamped by the clamping screws l I, previously referred to, to the pole-pieces of. a permanent magnet 34 as bestshown in Fig. 3. The pole-pieces are provided near their outerends with aligned holes in which is supporteda switch element 35 of the mercury contact type. A switchel'ement of this type is disclosed in Patent No. 2,295,602, granted September '15, 1942, to C. E. Pollard, Jr; Cooperating with the polar ends of the pole pieces is a soft iron armature 36. The armature is channel-shaped, theflanges 31 and 38 thereof having aligned holes'therethrough near their lower ends through which the pivot screw I3 extends and on which screwthe armature is pivoted} The inner end of the pivot screw is threaded inter 31 of the armature 36 and at its other end tothe entension M of the bracket 8' which extens1on 1sbent inwardly at; right angles. to the zontal of lever 30', which lever is secured. to

the off-'nonnal' bar'Bl, extends beneath the pole-I The lever 30 is effective to ascac'zr piece 33 with its tip 42 engaged in the. opening 43 in the armature 36 and abovethecamming mercury between the upper edges of the guide portion 44 thereof. The shape ofthis camming portion is best disclosed in connection with the armature 51 of the switch assembly IOC disclosed inFig. 4. When the end of the lever is depressed the camming end of such lever en ges with the camming portion 44 of the armature and cams the armature 36. away from the polar ends ofthe pole- pieces 32 and 33, but when the end of lever 39 is fully depressed, inwhich position the camming end 42 thereof will be below thecam portion 4440f the armature and within the opening 45 in the armature, the spring 40 and the attractive force of the permanent magnet 34 will draw the armature again into engagement with the polar ends of the pole-pieces. Similarly, in the return movement of the lever 30 when the depressed key-set keylis released, the camming end 42 of such lever moving upwardly over the camming portion 44 of the armature again moves the armature away from the pole-pieces until the timing end 42 reenters the opening 43 in the armature. 1

i The mercurycontact switch element 35 of the off-normal switch assembly, as bestdisclosed in i Fig. -8, is, as previously stated, of the type disclosed in the patent to Pollard hereinbefore referred to and has an envelope 45 of glass or other suitable material within which is a guide sleeve '41 entirely open at its upper end and partially closed at its lower end to add rigidity thereto and supported on and secured to the upper end of the terminal wire 48. The wire 48 is sealed through the bottom of the envelope 46. The guide sleeve 41 is made of a material such as nickel which is wettable by mercury. Sealed through the upper end wall of the envelope are two parallelly disposed contact members 49 and 5i] having their ends which extend into the envelope bent at right anglestoward each other to form two stationary contact portions 5| and 52,the upper one 52 of which serves as a front contact and the lower one 5| of which serves. as a back contact. The contact portion 52 is wide but the contact portion 5| is narrow. Movable within the guide sleeve 41 is a cylindrical tubular armature 53, the ends of which are entirely open. The armature ismade of magnetic materialbut its surfaces are such that they are readily wettable by mercury. Secured to the inner surface of the armature and movable therewith is a contact member 54 which may be formed by doubling a length of wire, bending the looped end at right angles and flattening the same to provide awidened contact portion 55 i for engagement with the contact portions 5| and 52 of the back and front contact members 49 and 50. X A contact of this type has the property of conducting mercury along the capillary' ducts formed therein to its upper contact portion from which a small amounto-f mercury is transferred 4 to the surfaces of the contacts with which it cooperates. v To complete the switch element a measured amount of mercury56 is depositedin the bottom of the envelope which envelope is then evacuated, refilled withta gas such as hydrogen to a required operating pressure and then sealed. The meronly in the envelope rises within the guide sleeve 41 and within the tubular armature 53 to the position illustrated in Fig. 8 and the mercury is also conducted by the capillary action of the inner surface of the guide sleeve 4'! and the outer surface of the armature 53 to fill thespace bee When the armature 36 of .theoff-normal assembly is cammed away from engagement with sleeve 41 and the armature 53 and the surface tension of the mercury within the armature exerts a downward pull upon the armature to normally hold the contact portion 55 firmly against the contact 5| of the back contact member 43."

The mercury within the armature also engages the lower end'of the contact member 54 whereby mercury is conducted along such member to its upper contact portion 155 and in the normal position of the armatureto the contact portion 5| thereby establishing a mercury contact between the contact members 55 and 5!. i a a the pole- pieces 32 and 33 all of the flux generated by the permanent magnet 34 is permitted to through the armature 53 ofthe switchelement and the armature rises within the guide sleeve 41:

to center itself within the magnetic field thus created, but will be restrained in its movement i the contact portion 55 of the contact member 54 quickly out of engagement with the contact portion 5| of the back contact member 49 and into engagementwith the contactportion 52 of the front contact member 50." Mercury adhering to the contactmember 55 is now transferred to the front contact member mercury therewith.

Since the armature 36 is cammed away from the pole- pieces 32 and 33 only momentarily, it is quickly restored to establish a low reluctance shunt of the armature 53 of the switche'lement whereupon the magnetic pull on thearmature 53 is reduced permitting the surface tension of the mercurypool to pull" the armature 53 back into its normal or retracted position but sincethecontact areas of the contact portions 52'and 55 are both relatively large, the film of mercury between them will persist unbroken due to the mercury being drawn into thefilm up the ducts of member 54 while the armature 53 moves in its retractive' movement under the influence of its weight and the surface tension of the mercury pool, until the film'finally breakswhereupon the contact portion 55 snaps quickly into engagement with 1 the contact portion 5| of the back contact member49.- This switch elementtherefore effects a quick make and a slow break of its front contact closure which break should be in the order of 30 i or .40 milliseconds and a quick break and a slow i make of its back contact closure. The off-normal switch assembly is effective to transfer the substation line from the telephone set to the harmonic generator andsuppression coils of the call i transmitter as will be later described.

tween such surfaces. The surface tension, of the 7 5 The suppression'switch assemblies IBA, I03

and IE0 are similar in construction to the offnormal switch assembly 9 just described except,

for the construction of the camming' ends of their associated operating levers 22, 23, 24, 25, 26; and 21. The armature 51 of the switch assembly IBC is pivotally supported on the same pivot screw I3 upon which thearmature 35 of the off-normal switch assembly 9 is pivoted; the two armatures switch 52 to establish a film of being: suitably spaced apart by the spacer 58 supported on the pivot screw I3. andinterposed between the armatures. The suppression switch assemblies IDA and MB have their armatures 59' and 60 pivotally supported on the pivot screw H which. extends through the ear I6, through aligned holes in the flanges of the armatures and into a threaded hole in the side plate BI- which. supports one end of the key-set.

7 Each of the suppress-ion switch assemblies is so arranged. that its switch element may be operated either in response to the depression of a key-set key, in response to the'releasing movement of an operated key or in response to both movements of the key, dependent upon the impulse code employed. For controlling the operation of these switch assemblies two operating levers are associated with .each assembly, levers 26 and 21 connected to U-bars B5 and, B6, respectively, being associated with assembly IIlA, levers 24' and 25 connected to U-bars B3 and B43 respectively, beingassociated with-assembly MB, and levers 22 and 23% connected to U-bars BI and B2, respectively, being associated with assembly II'IC.

Referring now to Figs. 4 to 6, inclusive, the lever 23 has a cam member 62 pivotedat 63 to the end thereof, the tail portion 64 of such member being normally held by the leaf spring 65 against the stop pin 66, also secured to the lever 23. The leaf spring 65 is provided with two parallelly disposed ears 6'! bent atright angles thereto and positioned on; either. side of the upper edge of the lever 23 by which the spring is riveted to the lever. I

The outer end of the camming portion 62 normally extends through the opening 6-8 in the armature 5'1 of the assembly I-OC above the upper camming surface of the cam portion 69 of the armature. When the cam member 62 is moved downwardly by the lever 23 upon the depression of a key of the key-set, such member engages the upper edge of the cam portion 69 and the member therefore tends to rotate in a counter-clockwise direction. Since, however, the cam member 62. is prevented from rotating in a counter-clockwise direction by the stop pin 56, the member is effective in its downward movement to cam over the cam portion 69 and thereby move the-armature 51 from its bridging engagement with the pole-pieces I and II of the switch assembly IUC. The armature of the switch element of such assembly is thereupon quickly moved to a position in which its movable contact is disengaged from its back contact and is engaged with its front contact. As the member 62 continues its downward movement it moves pastthe cam portion 69 of g the armature 51 into theopening 12 thereby permitting the springylfi to reengage the armature 51 with the pole-pieces) and II whereupon the armature of. the associated switch element is restored to normal to move its movable contact out of engagement with its front contact and into engagement with its back contact.

When the depressed key is released and lever 23. is permitted tov rise, the end of cam member 62- carried thereby engaging the lower edge of the cam portion 69 of the armature the cam member 62 I rotates in a clockwise direction against the aeeaevr closed Fig. 6 Normally, this cammember 13* extends throughtheopening 68 in thearmatension of leaf spring 65. without causing the I armature to be cammed out of its normal position. Therefore, the associated switch element is not operatedupon the releasing or upward movement with the same switch, assembly WC has its cammember [3 reverselypivoted to the lever as disture- 51 and when the lever 22 is depressed'in response to the depression of akey-set key, the member I3 is moved downwardly into engage ment with the upper surface of the cam portion 69 of the armature, and such member rotates in. a counter-clockwise direction against the tension of the associated leaf spring 14 without cammin-g the armature away from the ends of the polepieces I0 and I I, until it snaps off of'the cam per-i tion 69 and remains positioned in the opening T2 of the armature'when theoperated key is fully depressed. 7

When the depressed key is released and lever 22is permitted to rise; the cam portion 1s engages the lower surface of the cam portion 69 andtherefore tends to rotate in a clockwise direction;

' apparent that the depression of lever 23 is effective to cause the functioning of the switch element of the assembly- I'DC only during the depression movement of the lever 23and that the depression of lever 22 iseffective to cause the functioning of the-switch element of the assembly ,IilC only during the return movement of lever" 22. The switch assemblies IOA and IOB are oper able in a similar manner by their associated levers.

'The U -bars BI, B3 and B5 through their associated levers 22, 24 and 26'may be considered as rip-stroke barsrand the U-bars, B2, B4 and B6 through their associated levers 23, 25 and 21' may be considered down-stroke bars.

To illustrate the manner in which the call 9 transmitter functions it will be assumed that the key member KI for transmitting, impulses of a code for the digit 1 is depressed. By reference to the following table it will be noted that for" the digit 1 it is necessary to operatethe switch assembly IUA to suppress frequency a during the down-stroke of the key KI nd to again operate the switch assembly IDA to suppress the fr equency a during the up-stroke of key KI whereby.

two suippressions of frequency a are effective at the central ofiice sender. To accomplish this, the; under-surface of the key member Kl is provided with an extension I6 which engages the l pp r edges of both U-bars B6 and B5 so that; upon the down-stroke of the key member both of these" U-bars are depressed. The depression of the. U-bar B6 through the-associated lever 21 causes a timed operation of the switch element of the switch assembly IDA andthrough the off-normal bar 31' and associated lever 36. causes a timed] operation of the switch element 35 of the off-I normal switch assembly 9 whereby the frequency a. is momentarily suppressed.

The depression of the U-bar B5 is not effective,

through its associated lever 26 to operate the switch assembly [0A during the down-stroke movement of such U-bar and lever but when the depressed key is released and the depressed U-bars B6 and B5 are returned to normal by their associated springs 29, the lever 26 is effective to,

again operate the switch element of theswitch assembly IOAand at the same time the up-stroke of the operated off-normal bar BI- under the influence of the retractile spring 29 causes the operation of the switch element 35 of the offnormal switch assembly9 whereby the frequency a is again suppressed for ashortinterval.

The keys KI to KIO; inclusive, of the key-set are so designed thatthey are efiective to operate the U-barsBI to B6,inclusive, and the suppression switch assemblies IOA, I03 and I to control the suppressionof frequencies a, b and c finder LF to hunt for and establish a connectionwith the calling line, after which the line finder-first selector link becomes associated over the sender link SL with an idle sender. Upon the association of the sender with the substation a circuit is established from battery over brushes of the trunk finder TE and sender selector SS, conductor 900 and windings of relay I000 I to ground. Relay I000 operates and closes an 0bin themanner indicated inthe following table: vious operating circuit for relay I002. Relay I002 Key K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 U-bars operated. B9, B5 B2, B1 B4, B3 B2, B3 B6, B1 B2, B5 B4, B5 B2, B1, B3 B4, B1 B2,,Bl, B5 Switch operated on, down: 3 I I stroke 10A 10C 10B 10C 10A 10C 10B 10C 10B 10C Switch operated on 'up- I I I I stroke 10A 100 I 10B 10B 10C 10A 10A 10C The call transmitterIof Figs. 11 to. 8, inclusive,

is applicable to a wide variety of types of idial switching systems andtparticularly to those of the I type in which register mechanisms are employed at the central office for. registering the designations transmitted for controlling the sclective operation of automaticswitches to complete connections. Accordingly, the system upon operating connects ground over its right contacts to off-normal ground conductor I003, to provide locking ground for other relays of the sender and over its left contacts and conductor circuit is established therefrom over the left back chosen to illustrate the invention is one injxwhich l the central ofiice is equipped I with! automatic switchesof the panel type and with register send! ers for registeringthe designations transmitted to the central ofiice from subscriber stations. It

will be obviousIthat other forms of switches may be used for establishing connections such as I switches I of the well-known step-by-step and crossbar types. I I. 1 l I Referring to Figs. 9, 10 and 11 of the draw ings, a subscribers line is shown appearing inthe contact bank of the linefinder LF. The line are necessary for an understanding of the present invention. The number of registersemployed in these senders will, of course, vary with the requirements of the'exchange area. In some of the" larger areas ofl'lce codesrequire two or three office code digit registrations and the numerical part of the designations usually requires four registrations. In the present disclosure three office code digit registers A, B and C are shown inFig. l1 and the' units numerical register U is also shownfitbeing understood that the thousands, hundreds and tens numerical registers would be ,provided and inserted between theunitsregister U and the ofiice code digit register C. These registers each comprise five register relays which are selectively operated under the control of the siX recording relays AD BD, CD, AU, BU and CU and thefrequen'cy receiving channels Fa, Fb, Fc of Fig. 10. I I

It will be assumed that to initiate a call at the substation illustrated in Fig. 9 the subscriber removes the handset H of the substation instrument from the cradle Iwhereupon a'circuit is established over, the substation line to the central 'ofiice which is instrumental in causing the line-,

contact of relay I009, conductor IOI0 to battery through the winding of progress relay H06, whereupon relay I I06 operates and locks in a circuit from battery through its winding and the winding of progress relay II01, over the outer left front contacts of relay I I06, and over the back contact of progress relay II I I to ground on conductor I003. Relay IIOI does notoperate in this locking circuit sinc itswinding is shunted as long as ground remains connected to conductor I M 0. When relay [I00 operatesa circuitisalso establishedfromground on conductor I003 over theback contact ofI relay III I, the outer left contacts of relay H06, conductor IOII and to battery through the rightnormal contacts and Winding of relay I009. operates, locks overfits right alternate contacts to ground on conductor I003 and at its back contact removes ground from conductor I M 0,

whereupon relay II 0-! I operates in the locking circuitofrelay H06; prepares operating circuits for relays H00, IIOI, II02, II04'and H05 of the first code digit register A over conductors I030, I03I, I032, I034 and I035; and at itsright contactsconnects ground to conductor IO0I to shunt the rightwinding of relay I000 whereby the cur- I rent flowing, over the operating circuit of relay IO0Iis increased as a signal to the line finderselector link. I I

, Relay 90I, upon operating, connects the winding of battery feed relay 902 to the calling line substation over a circuit which may be traced frombattery through the left winding of relay sender selector SS, brush 904 of the trunk finder TF, contact of sequenceswitch cam 905, brush 906 of line finder LF,thering conductor of the calling line, switchhook contacts 901, the back contact of the oir-normal switch assembly 9,

through the transmitter 908, the left winding of ring contacts'ofrelay I; the right winding of I relay 902and the normal contacts of relay BM to ground through the secondarywinding of the dial tone coil 9I5.I Relay 902 operates over this Relay I009 thereupon 902, the left contacts of relay 90I, brush 903 of,

circuit and, dialing tone is applied thereover to apprise the calling subscriber that he may proceed to key upthe digits of the desired telephone number. Relay 902, upon operating, establishes an obvious'circuit for relay 9I6 which also operates to prepare an operating circuit for relay 9 I4 and relay 902 establishes a circuit from ground over its left contacts, conductor 9I'I, over the upper normal contacts and through the winding of relay I005, and through resistance i001 to battery and, in parallel therewith, through the winding-of relay I009 and resistance I000 to battery. Relay I005 operates and looks over its upper alternate contacts to ground on conductor. 1003, but the winding of relay I096 being shunted so long as groundis applied to conductor 9.I I, does not operate. The closure of the lower front contact I005 is without function at this time.

,In response to the reception of dial tone, the

calling subscriber proceeds to key up the digits of the wanted line number which numberjit will be assumed is CHE-1067. j When the key K2, which in addition to the digit value 2 has the letter designations ABC; is depressed to transmit signal impulses for the firstco'de letter C, the off-normal 'sfw'itch assembly 9 is momentarily operated and then released during the down-stroke of the key and in the interval that them-ovable contact of such switch assembly is in engagement with the front contact thereof, the suppression switch assembly WC is momentarily operated. Again when thedepressed 'key is released, the off normal switch 'assembly 9 is momentarily operated and released and'during the interval that the movable contactof suc-lrassembly 'is'in engagement with the front contact thereof, the suppression switch assemblyl 0C is again momentarilyoperated for 'a purpose to be later described.

' l he movement of the movable contact of the off-normal switch assembly 9 from its back or normal contact position disconnects the subset transmitter 908 from its bridged connection across the substation line and the engagement of the movable con-tact with the front contact, connects the harmonic generator 921 in series with,

the suppression'coils 922 and 923 and'condenser 9I8 across the line. There being'no direct currentbridge across the substation line at the substa tion so long ast he movable contact of the off-normal switch assembly!) is out of engagement with its back contact, relay 902 of the sender releases in turn opening the circuit of relay'9I6 and removing ground from conductor 9H. Relay '9I6, however, being slowto release does not-release during the interval that the movable contact of the off-normal switch assembly is disengaged from its back contact. With relay 902 released and relay 9I-6 operated, an obvious circuit is established for relay '9I-4 which operates and at its contacts disconnects the secondary windingofuthe dial tone coil 9I5 from the calling line loop to discontinue the application ofjdialtone current thereover and connects direct ground to thecalling line loop. The removal of ground from conductor 9I-1 removes 6 ass ntcircuit traced fromthe sender to the tip cond lator-Diane calling line, through-condenser 9I8, coils 923 and 922, the two windings ofeach of which coils are wound to be series opposing, through the coil ofthe harmonic generator 92I, over. thefront. contact of the off-normal switch assembly 9, over the switchhook contacts 901 over the ring conductor of, the calling line and thence over the circuit previously traced tothe thereupon travel back to the central oflice where they passthrough the base'frequ'ency elimination filter 9I9, shielded transformer920, through circuit X and thence through the primary windings of the input transformers associated with the receiving channels Fa, Fb, Fc and V. 7

Associated with each input transformer such as l0l 3, is'a frequency receiving" channel'con-l sisting of a secondary winding of such transformer,=a seriestuned circuit IOI4, a single vac- .uumtu-be such as I0 I 5 with a feedback through the copper-oxide units, such as IIII6, and a relay, such as I0'I'I. Initially the vacuum tube is biased nearly to cut-off. A small received signal is amplified and fed back through the condenser :IOI8 and the copper-oxide units -I0I6 to charge up the condenser I019. This condenser is poled to reduce the negative bias on the grid of the tube I015 with the result that the gain of the tube is increased and the amount of voltage on the grid is increased further. The final result is that a .relativeiy'smallzsignal su'ilicie'nt to .produce a sharp rise in plate current through the winding of relay MIT. The sensitivity of each individual channel is adjusted by means of the variable resistance, such as I020. This method of controlling the sensitivity by changing the alternating current feedback-does not affect the tuning-of the channel. From the foregoing. it

will be apparent that each relay such as IOI'I of each channel will respond to a single frequency with a relatively high discrimination against the others.

In the present description, it will be assumed that the first :channel Fa is tuned to the a frea quency harmonic generated bythe coil 921 of 700 cycles; the second channel Fb is tuned to the b frequency harmonic of 1:100 cycles and the third channel F0 is tuned tothe 0 frequency harmonic of 1500 cycles. .Since all harmonics of the base frequency are transmitted back over the line by the generator 924 before any one-of the suppression-switches has had time to function, the channels' all initially respond and their associated channel relays -I'0I-I I023 and I024 are all operated. With these channel relays all operated, a

a series circuit is established over their front consion coil 923 overithe front contact of the switch :IDC andtover the front contact of switch 9 and thes'wit'chhook contacts 901 'to the ring side of the line whereby the condenser Cc is elfective to suppress the frequency o I of 1500 cycles, whereuponIrelay lfll'hofthereceiving channel E'c releases,relays I023 and I024, however, remain:

ingoperated. Relay IOI'I, upon releasing, opens I which releases, after an interval. I I I ;Relay LOH upon releasing and before relay over the contacts of relay I026, the back contact of relay IOI'I, the middle right back contact of transfer relay I02 I, through the winding of re-, cording relay CD to battery. RelayQD, thereat its front contact thecircuit of relay I026 I026 releases, establishes aIcircuitIfrom ground upon operates, looks over its inner left contacts i to ground over the back contact of release relay I022, and at its outer left contacts prepares a circuit forrelay I02I. Upontheterminationof the signaling period, when the off-normal switch assembly 9 reestablishes the direct currentbridge atthe substation through the subset-transmit ter, relay 902 reoperates-t o establish t e circuit offrelayllfli and to reconnect groundtto con-J ductor 9|! whereupon such ground is extended over the upper front eontact of relay I006 to a c is; suppressed resulting in the releaseof channel relay I0" and the release of relay I026.

During the releasingtime of relay I026 and with transfer relay I 02I operated, a-circuit is established from ground over the contacts of relay I026, the back contact of relay IOI'I, the middle right front contact of relay I02I to battery through the winding of recording relay CU. I Relay CU, upon operating, looks over its left contacts to ground over the, back contact of relay When the offenormal switch assembly 9 again releases, relay 902 ,reoperates and causes the reoperation of relay I005, over the circuit previously traced. With relay I005Hoperated and relay I006 unoperated, a circuit is established from ground: over the lower front contact of relay I005, the lower back contact oflrelay I006, the

right back contact of relay AD, the No. 2 right back contact of relay BD, the No. 2 right front contact of operated relay CD, the No. 2 right back contact of relay AU, the No. 3 right back 1 contact of relay BU, the No. 5 right front conpoint between the Winding of relay I005 and re- I sistance I001. Relay I005 being now shunted releases IRelayI I006 is, however, maintained operated-following the release of relay I005 over a circuit from ground on conductor;0l1, over the upper normal contacts of relay I005, through the winding of relay'I006 and resistance I008 tobatterylff With relay I005 released and relay I006 operated, the-circuit of relay I02I is now completed fromground over the lower backIcontact of relay I005, the innerlower front contact of relay I006, the outer leftIcontacts of relay CD to battery through. the winding of relay I02I; Relay I02! now operates,,locks over its inner right front contact to ground over the right back contact of relay I022; at its back contacts disconnects the windings of recording relays nd CD from the contacts of the channel relays] I023, 1024' and I0II,Y respectively; rconnects the windings of recording relays AU, BU

and CH with the contacts of the channel relays allofI which are at thistime operated andat its outer right front contact prepares a circuit for relay I022. When the off-normal switbhassem- I bly 9 restores toits normal position thus discon necting the harmonic generator from thesubstation line, the frequencies .a, band 0 are no longer generated and. transmitted to the receiv ing jcl iannels of the sender and channel relays I023, I024 and ljflll thereupon'fall; release, but

relay I026 being now released, the channel relays are ineffective I to establish circuits for e the recording relays s I s i I During theretur orjup-stroke movement of the operated key K2, the off-normal spring as sembly 9 is again operated and released and during that interval, the suppression switch assembly IBC is againIoperated and released to "again suppress the frequency 0. During, the in terval that theIdirect current loop at the sub- I relaysfalloperated, relay I026 again operates. in responsefto the momentary operation of the tact of operated relay CU, conductor I032,the No.v 3, left contacts of progress relay IIO'I to battery through the right winding ,of relay H02 of the A code ,digitregister Relay II02 thereupon operates and looks over its left winding and left contacts to-ground onwconductoz-I I003 and with theremaim'ng relays LIIOI, pI I04, [I05 and I I00,

of the A register unoperatedserves to register thefirst office code letterC. {The removal of the I harmonic generator from the calling line when the off-normal switch assembly is fully restored causes the releaseof all, of the ,channel relays I023,I024and|0l1.

A c'ircuitis also establishedhupon the operation of relay I005 from ground over its lower, front contact, the lower back contact of relay I006, over the outer right front contact of relay II02I to battery through the winding ofrelay I022 which operates after anIinterval sufficient to insurethat the digit signals recorded by the operation of recording relays have been effective to cause the registration thereof in a digit register of the sender; atits Ibackcontact opens the locking circuit of the-operated recording relays, in the case assumed relays CD and CU which thereupon release; opens the locking circuit of transfer relay I02II which-releases; and at its front contact establishes Ian obvious circuit for relayl025. Relayl025 operates, locks over its front contact to off-normal ground on conductor I003, and at its left contacts prepares a circuit for ,operatingthe progress relay III6. When relay I02I releases, relay) I022 also releases,

When: the subscriber depresses the key K4 for the second oilice code letter-H which has a numerical value; of (l; the off-normal switch as sembly9 is operated momentarily to open the direct current loop at thesubstation and to connect the harmonic generator 92L to the substation line. Duringthe ,interval that the switch is thus operated, the frequency suppression switch I00 is momentarilyoperated. With the generator connected to the line, all of the chan-I nel relays I023, IBM and Hill operate, followed by the operation of relay I026 and when the switch is momentarily operated to sup press frequencyc ,channel relay IOI I releases in turn causing the release of relay I020. Dur

ing the releasingtimeof relay I026 and with suppression iswitcli assembly IOC, the frequency 715 transfer relay I02! now released, a circuit is established from ground over the contacts of re1ay I 026, the back contact of relay IOII, the

operated and relay I025 operated, a circuit :is'

established 'from ground over the lower :front contact of I relay 1-0 05, the lower ffront contact of cassava 'tery through the winding or recording rilay'iBU.

Relay upon-operating looks over its left com tacts under thec'ontrol of relay 'I 02-2.

When the oiT -normal switch assembly is again restored, the harmonic generator 021 is disconnected from the substation line resultin in the release -of all or the channel relays W023, I020 and 00H and th direct current loop is reestablished at the substation, resulting inthe reoperaitlon of relay -902, followed by the reopera tion of :relay "I005 as previously described. With relay I005 operated, and relay -I'0'06 unoperat'ed,

relay I006, the left contacts of relay I1I25,-c'onductor I012, the. right front contact of progress relay '1 I00 to battery through the {winding of progress relay I II B. 'Rel'a'y' Il lfi operates and locksthrough its winding and the 'wm'ding of progress relay @I I'l over the left contacts of relay fIIIiIB and the back' contact of progress relay N27 to groundon conductor 1003. Relay 1:110 being shunted-soaring :as ground remains "connected to conductor -12 does not operate.

1 When the on-normal switch assembl 0 is restored, the transmission of harmonic "frequenciesby generator '92I :eeasesLandall of the operated channel relays 1023, M024 and lfl-l 'l release and the direct current-loop is reestablished at the 'substation resulting in the reoperat'ion "of relay -902 and the reconnection ofgroun-d to conductor 9II. As before described, relay I006 -is now held operated tothis ground 'and-rel-ay 4005 is shunted and releases. With-relay l005 release'd and relay I006 operated, the *c-i'rcuit of -tr-ansfe'r relay I02 I previously prepared through the operation of recording relay CD is completedand relay'I02I operates and locks as previously-described under the control er relay 1022. Relay I005, upon releasing, also removesgroundirom conductor I-0I'2 whereupon progress relay II I1 operates in the "locking circuit of relay III B;

connects the windings of the relays or "the code digit register to L conductors I 031, I 032, 1030, I035 and 103-0, extending to cont-acts of the *recording relays, and 'at its back contact opens the locking circuit of relays I I 0 0-and I' I G'I which now release since their operating "circuit was opened upon the 'prev-ious-"operationof relay I000.

Uponthe up- 'strolce of the depressed --key "K4, the off-normal switch assembly 9 is again momentarilyoperated to open the direct-current loop at I the substation and to connect the harmonic generator 92I to the suhstatic'm line; With the a circuit is established from ground over"'-the lower none contact-of relay 0005, the lower back contact-or relay N106, the right back contact of relay AD, the No. 2 back contact of reIayBD,

the N0. 2 right front "contact of relay CD, the No. 2'=rightback contact of relay AU, the "No.3 right from; contact -of relay BU, the No. 4 right back-contact -of -'relay-'CU,--conductor I030, over the No. 4 1e'ft contacts of relay IN 1 through the winding or relay --I I I! of the oflice code register B to battery. Relay "I H 4, upon-'oper'ating locks over its left winding and left contacts to ground =on conductor I003 and with the ;remaining relays of the B register *unoperated, serves to register the second "ofiice code -letterH. The operation of relay I005 with relay' "I000 unoperated, also establishesthe previously traced circuit of relay 102-2 which operates after'aninterval to cause the release of the operated re"- cor'din'g relays CD :and EU and the release of the transfer relay I02I. leases,-'relay' I022 alsoreleases. I

*Wheh'the subscriber'depresses the key K3 "for thethird ofiice code digit 3, the. off-normal switch assembly is operated 'momentarily 'to open "the direct "current 'loop at the substation and connects the harmonic generator 9'2I to the sub: station line. During the interval'thatjtheswitch is thus operated, the-frequenc suppression'switch I 03 is -momentarily operated. With the "generator connected to the-line, all of the channel "regenerator reconnectedto the'line, the -receiving 7 channels 'of the sender all respond "toth'egenthe back contact 'of switch 10A to the ring "side of the line to suppress th frequency-b whereupon the channel relay I024 releases'followedhy the release of relay I020. With'transfer relay I02I now operated, a circ'uitisestablished 'during the releasing time of re1ayI020 from "ground over its contacts, the'bac'k contact of relayiOZI,

the inner leftiront "contact of ma -"I 021'hatlays 1023, 1-024 and -IOI'-'I operate'followed 'bythe operationo'f relay I026 andwhen the switch 103 is momentarily operatedto suppress the'frequency b, channel relay 'I024're1ea'ses'in turn causingrthe release of "relay "I026. During "the releasing time-of relay I026 and with transfer relay -I02I now released, a circuit is-establi'shed from ground over the contacts of 'relay I 0 26, the back contact of relay I024, thednnerleftbabk contact of relay I02I to battery through the winding'o'f therecordihg rela *BD. Relay"BD,.upon operating, locks under'the'control ofrelay' I022 and prepares a circuit for relayfl'02l as previously described. 'When the line loopls opened atthe substation by the oifenorma'li'switch assembly 9, relay 002 releases and by removing ing of progress relay "l -I20. Relay I I26 operates and locks through its winding and'the winding of progress relay -'I-I2I"-'ovei"the left contacts ofree' lay I 'and'to ground'on conductor I003, over the back contact of the progress 'relay"(not. shown) associated with'th thousands "digitreg- I isterand corresponding "to "progress "relay "H21;

When 'relay 'I 02'I re- Relay II 21 being shunted does not operate so long as ground remains connected to conductor IIII2. I I I When theoif-normal switch assembly 9 isrestored, the transmission of harmonic frequencies by the generator 92I ceases andall of the operated channel relays I023, I024 and I" release and the direct current loop is reestablished at lay 902 and the reconnection of ground to conductor 9 I I. As before described, relay I006 is now held operated tothis ground and relay I005 is shunted and releases.

' and at its right back contact opens the locking circuit of progress relays III6 and III! which.

now release since their operating circuitlwas opened upon the removal of ground from conductor IOI2. r

Upon the up-stroke of the depressed key K3, the ofi-normal switch assembly 9 is again mo- ,mentarily operated to open the direct current loop at the substation and to connectthe har .902 releases removing ground from ground conductor 9I'I whereupon relay I006 releases as previously described. During the interval that the ofi-normal switch iSthllS operated, the frequency suppression switch assembly IOB is momentarily operated to suppress the frequency b'whereupon the channel relay I024. releases, followed by the the substation resulting in the reoperation of rerelease of relay I026. With transferrelay I 02I now operated, a circuit is established during the releasing time of relay I026 as previously described through the winding of recording relay BU. Relay BU, upon operating, locks overits left contacts under the controlof relay I022.

When the off-normal switch assembly 9 is again restored, the harmonic generator 92I disconnected from the substation line resulting in the release of all of the channel relaysl023, I024 and I0" and the direct current loop is established at the substationresulting in, the re operation of relay 902 followed by the reoperation of relay I005 as previously described. With relay I005 operated and relay I006 unoperated a cir-- cuit is established from ground over the lower front contact of relay I005, the lower back contact'of relay I006, the rightback contact of relay. AD, the No. 3 right front contact of relay BD, the No. 3 right back contact of relay CD, theNo. 3 right back contact of relay AU, the No, 5right front contact of relay BU, the No. 6 right back lishedfrom ground applied over the right back tactof relay BD, the No. 4 right back contact of relay CD, the No. 7- right from contact of relay BU, the No. 5 right back contactof relay CU, conductor I032, theNo. 3 left contacts of I progress relay N21 to battery through the right winding of relay I I22 oftheC code digit register. Relays II2I and H22, upon operating, lock over their left windings and left contacts to ground on conductor I003 andwith the other relays of the C code digit registerunoperated, serve to registe the third office code digit 3. I I The operation of relay I005 with relay I006 unoperated, also establishe the previously traced circuit of relay I022 which operates after an interval tocause the release of the operated record- I ing relays BD and BU and the release of transfer relay 102i I followed by the release of relay I022.

In asimilar manner in response to thekeying of the thousands numerical digit 1, the frequency a is suppressed once in response'to the operation of the switch assembly IOA upon the depression of the key KI and again upon the release of such key, resultingin the operation of recording relays AD and AU. In response to the keying of the hundreds digit 0,the1 frequency e is suppressed upon the depressionof. the key Kl0 through the keying-of the tens digit 6, the frequency 0 is suppressed upon the depression of the keys K6 through the operation of the switch assembly IIIC and thefrequency a is suppressed upon the release of the depressed key upon the operation of the switch assembly IOA resultingin the opera: tion of the recording relays CD and AU and in responseto the keying of the units digit 7, the frequency b is suppressed upon the suppression of the key Kl through the operation of the switch assembly [03 and the frequency ais suppressed uponthe release of the depressed key through. the: operation ofjthe switch assembly IOA. operates it connects the mid-point between; the windings of coil 922through condenser Co to the ring side 3 of the line and renders switch 103 ineffective. I I

With recording relays AD and AU operated in response to the keying of the thousands digit 1, I

Contact of relay on, the No. 1 right front contact of relay AU, the No. 2 right back contact of relay I BU, the No. 6 right back contact of relay BU to conductor I03I andthence over the No 2 left contacts of an operated progress relay; similar .tO-relay I|0I but associated withthe thousands digit register, to battery through the winding of a 'relay of that register, corresponding torelay,

IIOI, whereby such relay operates and locks-and with the other relays of such register unoperated, I registers the thousands digit I 1. 4 I

With recording relays CD, AU and CU operated, in responseto the keying of the hundreds digit 0, then when ground is applied to the right armature of relay AD, a circuit is estabsished over the right back contact of relay AD, the bio. 2 right back contact of relay BD, the No. 5 right contact of relay AD, the No. 4 right front con- I It is to be noted 'thati'when switch I0A front contact of relay 'CD, the No. 5 right front contact of relay AU, the No. 4 right back contact of relay BU, the No. 3 right front contact of relayCUto conductor I030 and thence over the No. 1 left'contacts of an cperated'progress relay, similar to relay .IIfl'I but associated with .the hundreds. digit register, to batterythrough a winde ing of arelayof that register corresponding to relay I I00, whereupon such relay operates and locks to register the hundreds digit 0.

With recording relaysCD and AU operated, in response to the keying of the tens digit 6, then when ground is applied to the right armature of relay, AD, a'first circuit iscompleted over the right back contact of relay AD, the No.2 right back contact of relay BD, the No. 2 right front contactof relay CD,,the No. 2 right front contact of relay IAU, the No, 2 right back contact of relay the No. 6 right back contact of relay CUfcoriductor I03I and thence over the No. 2 left contacts of an operated progress relay, similar' tojre'la'y H01 but associated with the tens I digit register to battery through the winding of aremy of'su'ch registercorresponding to relay Ill! I, whereupon such'relay operates andlocks. A j'circuitis also established from ground applied oVjerthe right back contactof relay AD, the No. 2 right back co n'tact of relay BD, the No. 5 right front contact ofrela CD, the No. 5Qright front contact ofrelay AU, the No; 4 right back contact of'relay BU,'the' No. 1 right back Contact of relay CU, conductor I035 and thence over the No; 5 left contacts'of an operated progress relay, similar to relay I I! but associated with thetens frontcontactofsrelay 'BD, the No. 4 right back contact of relay CD,.the N o. 4 right front contact of'relayAU, the No.6 right back contact of relay BU, theNo. right back contact of relay CU, overconductorlflfl and thence over the No. 3 left contacts of, the operated progress relay IIG'I to battery through the right winding of relay I I62 of the units digit register U. A second cir- 'cuit is also completed over the right back contact of relay AD, theNo. 3 right front contact of relay BD, the No. 3 right back contact of relay CD, the No. 3 right front contactof-relay AU, the No. 4 right back contact of relay BU, the No. 1 right back contact of relay CU, over conductor I035 and thence over the No. 5 left contacts of relay II 6''! to battery through the right winding of relay H65 of the units digit register U. Relays H62 and H65, upon operating, lock over their left windings and left contactsto ground on conductor I I I303 and with the other relays of this register unoperated, serve to register the units digit '7.

'QAllof the digits of the wanted line number keyed by the subscriber are now registered in the sender and the sender may proceed to control selector switches to extend a connection over the district selector S and other selectors (not shown) in accordance therewith after which the sender link SLis released to release the sender to make it available for other calls.

In the preceding discussion, the keying and registration of letters or digits having the digit values'l', 2, 3,4, 6', *7 and0 have been discussed;

If the digit 5 is keyed by the operation of key K5,

then upon the depression of the key, switch assembly WA is operated to suppress the frequency a and upon the release of theldepressed key, the i switch assembly IIlC is 'operatedlto suppress the frequency 0 resulting in the operation of the recordingrrelays AD and CU. With these relays operated, then when ground is app-lied to the right armature of relay AD,-a circuit is completed over the right frontcontact of relay AD, the No. 1

right back contact of relay BD, the No. 1 right back contact of relay CD, the No..1 right back contact of relay AU, the No. 1 right back contact of relay BU, the No. 1 right front contact of relay CU to conductor I035 to cause the operation of the relay of a register, such as relay I I05 of the first code digit register A.

If the digit 8 is keyed by the operation of key K8, then upon the depression of the key, the switch assembly IOC is operated to'suppress the frequency 0 and upon the release of the depressed key, the switch assemblies IOB and I0C are operated to suppress the frequencies b and 0 'resulting in the operation of recording relays CD,

BU andCU. With these relays operated, then 7 when ground is applied to the right armature of relay AD, a first circuit is completed over the right back contactof relay AD, the No. 2 right back contact of relay BD, the No. 2 right front contact of relay CD, the No. 2 right back contact of relay AU, the No. 3 right front contact of relay BU, the No. '6 right front contact for relay CU, to conductor I'03'I. A second circuit is corn pleted over the right back contact of relay AD, the No. 2 right back contact of relay BD, the No. 5 right front contact of relay CD, the No. ,5- right back contact of relay 'AU, the No. 6 right front contact of relay BU and the No. 5 right front con-v tact of relay CU to conductor I032 and a third circuit isestablished over the rightfront contact of relay AD, the No. 2 right back contact of relay BD, the No. 2 right 'front contact of relay CD, the No. 2 right back contact of relay AU, the No. 3 right front contact of relay BU and the No. 2 right front contactof relay CU to conductor I035, With ground applied to conductors I03I, I032 and I035, relays of a digit register, such as relays I IOI, H02 and I I05 of the first code oligitregister A, are operated to register the digit8.

If the digit 9 ispkeyedby the operation of key K9, then upon the depression of the key, the switch assembly 'IIlB is operated to suppress the frequency'b and upon the release of the depressed the armature of relay AD, 2. first circuit is com-1 pleted over the right back contact of relay AD, the No. 3 right front contact of relay BD, the "No. 3 right back contact ofrelay CD, the No. 3 right back contact of relay AU, the'No. '5 right back contact of relay BD, the 'No. '4 right back contact of relay CD, the N014 right back contact of relay AU, the No. 7 right back contact of relay BU and the No. 7f right front contact or relay CU to conductor I035. With ground applied to conductors I034 and I035, relays of a digit register,

such as relays I I04 and I I05 of the first code" ascaevr digit register A, are operated to register the digit 9. i

quency in saidline, means at the central oflice selectively responsive to the harmonics generated at said station, a plurality of keys at said station each havinga downand an up-stroke and means controlled by said keys for selectively suppressing one of said generated harmonics during the down-stroke of a key and for selectively suppressing one or more of said generated harmonics during the up-stroke of the operated key.

2. The combination in asignaling system of a line having a station thereon, a source of alternating current ofa base frequency at the central ofiice, means for connecting said source to said line to supply current thereto; a harmonic generator at said station responsive to current from said source togenerate harmonics of the base frequency in said line, means atthe central ofiice selectively responsive to the harmonics generated at said station, a pluralityof keys at said station each having a downand an up-stroke and means controlled by said keys for selectively suppressing one of said generated harmonics during the down-strokeof a key and for selectively supsaid generated harmonics during the down-stroke of akeyfi an'd for including variable amounts of said reactance in circuitwith said generator for selectively suppressing one ormore of said geno'perated'fkeyp l l -'-5 The'combination:in a. signaling system of a erated harmonics during the up-stroke of the line having a station thereon, a source of alternating currentof a base frequency at the central ofiica means forconnecting said source to i said line to "supply current thereto, a harmonic generator' atsaid station responsive tocurrent from said source to generate harmonics of the base frequency in said line, means at the central oifice selectively responsive to the harmonics generated at said station, a tuning circuit at said station including a. variable reactance associated with said generator, a plurality of keys at said station havinga down and an up-strokeand a: pluralityof switch elements controlled by said keys-for includingvariable amounts of said re -3 actance in circuit"with' said 1 generator for selectively suppressing one of said generated harmonics during the down-stroke of a key and for includingvariable amounts of said reactance in circuit withsaid generator for selectively suppressing one ormore ofsaid generated harmonics duringthe up-stroke of the operated key..

l 6. The combination in a signaling system of a line having astation thereon, a source of alternating currentof a base frequency atthe central :ofiice, means for connecting said source to said pressing one or two of said generated harmonics during the upv-stroke of the operated key.

3. The combination in a signaling system of a line having a station thereon, a source of alternating current of a base frequency at the central oifice, means forconnecting said source to said down-stroke of any operated key and again during the up-stroke of such operated key, means controlled by said switch for connecting said harmonic generator; to said line for atimed interval and means controlledby said keys for selectively suppressing one of; saidgenerated harmonicsduring the operation of said switch in response to the down-stroke of an operated key and for selectively suppressing one or more of said generated harmonicsduring the operation of said switch in response to the up-stroke of an operated key. l

4. The combination in a signaling system of a line having a station thereon, a sourceof alternating currentof a base frequency at the central ofiice, means, for connecting said source to said line to supply current thereto, a harmonic generator at said station responsive to current from said, source to generate harmonics of the base frequency in said line, means at the central office selectively responsive to the harmonics generated at said station, a tuning circuit at said station, including a variable reactance associated with said generator, a plurality of keys at said station having a down and an up-stroke and means controlled by said keys for including variable amounts of saidreactance in circuit with said generator for selectivelysuppressing one of line tofsupply currentthereto, aharmonic generator at said station responsive to current from said source to generate harmonics of the base frequency insaid line, means atthe central office selectively responsive to the harmonics gen erated at said station, a tuning circuit at said station including a variable reactance associated withsaid generator, a pluralityof keys at said station each having a down and an u'p-stroke and a pluralityof switch elements controlled by pressing one or more of said generated harmonics during the up-stroke of the operated key, two of said switch elements being connected in series,

relation "whereby ,if both of them are simultaneously operated by the erroneous operation of two keys the circuitclosureof one of said two switches is nullified.

7. The combination in a signaling system of a line having a station thereon, a source of alternating current of a base frequency at the central oflfice, means for connecting said source to said line to supply current thereto, aharmonic generator at said station responsive to current from said source to generate harmonics of the base fre quencyfin said line, means at the central oflice selectively responsive to the harmonics generated at said'station', a tuning circuit at said station including a variable 'reactance associated with said generator, a plurality of keys at said station each having a down and an up-stroke and a plurality of timed switch elements controllable by said keys for including variable amounts of said reactance in circuit with said generator for selectively suppressing one of said generated harmonies for a timedinterval during the downstroke of a key and for including variable amounts of said reactance in circuit with said generator for selectively suppressing one or more of said generated harmonics for a timed interval during the lip-stroke of the operated key.

, 8. The combination in a signaling system of a. line having a station thereon, a source of alternating current of a base frequency at the central onice, means for connecting said source to said line to supply current thereto, a harmonic generator at said station responsive to current from said source to generate harmonics of the base frequency in said line, means at the central office selectively responsive to the harmonics generated and a plurality of timed switch elements controlled by said keys for including variable amounts of. said reactance in circuit with said generator for selectively suppressing, one of said generated harmonics for a timed interval during the down-stroke of a key and for includingvariable amounts of said reactance in circuit with said generator for selectively suppressing one or more of said generated harmonics for a timed interval during the up-stroke. of the operated key. 9,. The combination in a. signaling system of a line having a station thereon, a source of alternating current of a base frequency at the central oflice, means for connecting said source to said line to supply currentthereto, a harmonic generator at said stationresponsive to current from saidsource to generate harmonics of the base frequency in said line, means at the central ofiice selectivelyresponsive to the harmonics generated at said station, a tuning circuit. at said station including a variable reactance associated with said generator, a plurality of keys at said station each having a down and an up-stroke, a plurality of switch elements for including variable amounts of. said reactance in circuit with said generator and selectively operable to suppress different generated harmonics, a pair of bars associated. with each of said switch elements,

means controlled by the operation of the first bar of any pair for operating the associated switch element, means controlled by the release of the second bar of any pair when operated for operating the associated switch element and means controlled by said keys for selectively operating and then releasing said bars to cause the selective operation of said switch elements whereby one of said generated harmonics is suppressed during the down-stroke of a ke and one, or more Of said harmonics is or are suppressed during the up-stroke of the operated key.

10. The combination in asignaling system of a line having a station thereon, a source of alternatlng current of a base frequency at the central o-flic'e, means for connecting said source to said line to supply, current thereto, a harmonic. generator at said station responsive to current from said source to generate harmonics of the base frequency in said line, meansat the central office,

selectively responsive to the harmonics generated at said station, a tuning circuit at said station including a variable'reactance associated with said generator, a plurality of keys at said station each having a down and an up-stroke, a plurality of switch elements for including variable amounts of said reactance in'circuit with said generator and selectively operable to suppress difierent gen-'- erated harmonics, a pair of bars associated witheach of said switch elements, a cam member connectedto the first bar of each pair for momentarily operating the associated switch element only upon the operation of said bar, a cam mem-, ber connected to the second bar of each pair for momentarily operating the associated switch ele-- merit only upon the release of such bar and means controlled by said keys for selectively operating and then releasing said bars to cause the selective operation of said switch elements whereby one of said generated harmonics is suppressedduring the down-stroke of akey and one or more of said harmonics is or are suppressedduring the upstroke of the operated key v 11. The combination in a telephone system of a line having a station thereon, a source of alternating current of a base frequency at the central ofiice, means for connecting said source to said line to supply current thereto, a harmonic gen erato-r at said station responsive to current from said source to generate harmonics of the base frequency in said line, means at the central ofiice responsive respectively to the harmonics generated at the station, a plurality of keys at said station each having a down and an rip-stroke, means controllable by said keys for selectively suppressing one of said generated harmonics during thedown-stroke of a key and for selectively suppressing one or more of said generated harmonies during the up-stroke of the operated key, two groups of recording relays at the central of fice, each group comprising as many relays as there are harmonic responsive means and means controlled over said line for rendering a relay of the first group responsive to said responsive means upon the suppression of one of said hermonies during the down-stroke of an operated key'and for thereafter rendering one or more relays of the second group of relays responsive to said responsive means upon the suppression of" one or more of said harmonics during the upstroke of an operated key s 12. The combination-in a telephone system of a line having a station thereon, a source or alternating current of a base frequency at the central oflice, means for connecting said source to saidline to supply current thereto, a harmonic generator at said station responsive to current from edv at said station, a plurality of keysat said 'station each having a down and an upstroke, means controllable by said keys for selectively suppressing one of said generated harmonics. during thedown-stroke of a key and for selectively sup-1 pressing one or more of said generatedharmonics, during the up-stroke of theo-perated key, two

groups of recording relays at, thecentral office,

each. groupcomprising asv many relays as there are harmonic responsive means, means controlled,-

the suppression of one of said harmonics duringthe down-stroke of an operated key and for thereafter rendering one or more relays ofthe second group responsive to saidresponsive means upon the suppression of one or more 01- said harmonics during the rip-stroke of an operated key, a plurality of registers and means for successive-- ly setting said registers'in'accordance with successive joint settings of said groups of recording relays. V i e t of said line for generating current of aplurality of said groups of relays with said responsive means and means controlled over said line for controlling saidtransfer relay for rendering one of said,

groups of relays responsive to said responsive means to register the first impulse of a transmitted digit signal and for thereafter rendering the other of said groups of relays responsive to said responsive means to register the other impulse of the same digit signal. l

14. In a telephone system, a calling line, a central oflice, means for extending a connectionfrom said line to said ofiice, means at the substation of said line for generating current of a plurality of different voice frequencies, means for transmitting over said line two impulses of selected voice frequencies in accordance with any of ten digit values, means at said'central oflice responsive respectively to said different voice frequen-' cies, two groups of recording relays, each group comprising as many relays as there are frequency responsive means, a first and a second counting relay, means controlled over said line for operating said first counting relay prior to the trans mission of th first impulse of each digit signal,

for operating said second counting relay during the transmission of said first, impulse, for releasing the first counting relay priorto the transmission of the second impulse of each digit signal and for releasing said second counting relay duringthe transmission of said second impulse, a transfer relay for associating either of said groups of recording relays with said responsive means, an operatingcircuit for said transfer relay effective upon the release of said first counting relay while said second counting relay is still operated and means for releasing said transfer relay effective upon the subsequent release of said second counting relay and the reoperation of said first counting relay, whereby one of said groups of relays is rendered responsiv to said responsive means to register the first impulse of a transmitted digit signal and the other of said groups of relays is thereafter rendered responsive to said responsive means to register the other impulse of the same digit signal.

' FRANCIS A. HUBBARD.

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