US2280871A - Control system - Google Patents

Description

April 2 1942- w. w. TUTHlLL 2,230,871

CONTROL SYSTEM Filed Aug. 31, 1940 4 Sheets-Sheet l POL AR/ZED POLAR/ZED POL AR/ZED PERFORA TOR 'AT TOR/VEY 4 W. W. TUTHILL CONTROL SYSTEM Filed Aug. 31, 1940 4 Sheets-Sheet 2 A TTORNEV u mm N Wm m 0 0 V B DON aw. sufiw April 28, 1942.

w. w. TUTHILL 2,280,871 CONTROL SYSTEM Filed Aug. 31, 1940 4 Sheets-Sheet 5 TELEGRAD AR/ZED FIG 3 lA/I/E/V TOR W W 7' U TH/LL 8V9 ggw A TTORNEV PR/N T LOCK-UP April 28, 1942.

w. w. TUTHILL 2,280,871

CONTROL; SYSTEM Filed Aug. :51, 1940 4 Sheets-Sheet 4 FIG. 4

SPEECH CONTROL I TONE TELEGRAPH SIGNALS k-RELUSF OF RELAY 274 ENABLING ar TILE'GRAD ACCORDING TO PRESENT RELEASE or uwewnon. EARL/EST nsur 274 POSS/8L6 ARRIVAL or ENABLING or TELEGRAPH SIGNALS. nucmo ACCORDING TO PRIOR ARRANGEMENTS m/vawro/a r W W TUTH/LL A TTORNEV Patented Apr. 28, 1942 CONTROL SYSTEM Walter W. Tuthill, Jackson Heights, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 31, 1940, Serial No. 354,912

4 Claims. (Cl. 179-4) This invention relates to communication systems and particularly to systems wherein teleraph signals are interpolated in speech during lulls and pauses therein.

In Patent No. 2,238,028, granted April 15, 1941, upon the application of Barney et a1., a device known as a telegrad is fully disclosed. This device converts varying strength alternating current signals into equal length uniform strength direct current signals and is useful at the receiving end of a transmission channel including a mutable link.

The telegrad has features of similarity to the well-known vogad (voice operated gain adjusting device) shown, for instance, in Patent 1,853,974, granted April 12, 1932, to Hogg et a1., Patent 1,936,653, granted November 28, 1933, to Bjornson et al., Patent 2,012,810, granted August 2'7, 1935, to S. Doba, and Patent 2,156,622, granted May 2, 1939, to S. Doba.

The telegrad, however, is designed to be extremely quick acting in comparison to the vogad and comprises means whereby this quick action may be accomplished.

Due to the action of the mutable link and other causes such a transmission channel may at times deliver to the telegrad electrical disturbances, spoken of as noise, of a level high enough to be converted by the telegrad into signals, which will result in false operation of telegraph apparatus at the output of the telegrad.

Heretofore the normal operation of a system employing a telegrad subjected such telegrad to intervals during which only such noise could reach the telegrad with the result that false operation of telegraph apparatus occurred.

Where telegraph signals are interpolated in speech during lulls and pauses therein there is provided at the transmitting end of a transmission channel a transmitting chain of relays responsive to voice control. It is the function of these relays to carry out several switching operations when the voice takes command of the circuit and when the voice relinquishes such command. Various timed operations are provided known as hang-over periods. Thus when the voice relinquishes command of the circuit there is first a transmitting hang-over period during which the remote control of the switching at the distant end is maintained so that if the speech comes on again within such hangover time unnecessary switching operations which otherwise would become too frequent will not be carried out. Following this there is an additional hang-over time provided before the end of which telegraph transmission under the most favorable conditions cannot be started. These hang-over times are reflected in the operation of the receiving chain of relays at the distant end of the transmission channel. There a telegrad disabler relay is included in the receiving chain whose function it is to maintain the telegrad disabled during the operation of the chain. Therefore at the end of the transmitting hang-over period when the remote control of the receiving chain is relinquished by the distant transmitting chain and after the short hang-over period of the complete receivin chain the telegrad disabler relay releases and allows the telegrad to become enabled. Thereafter and until the earliest possible opportunity for the arrival of telegraph signals the enabled telegrad is subjected to any spurious signals caused by noise or otherwise coming in over the transmission channel so that a fair opportunity for false operation of the telegraph apparatus beyond the telegrad is given.

The object of the present invention is to minimize the opportunity for false operation of telegraph apparatus in a communication system employing voice controlled switching means. Accordingly, the telegrad disabler relay is placed at the extreme end of the receiving relay chain where it can be provided with a hang-over circuit whereby the telegrad may be maintained disabled until the earliest possible beginning of telegraph signal reception thus greatly reducing the opportunity for false operation of telegraph apparatus responsive to the said telegrad.

A feature of the present invention is a control means for a receiving telegraph signal circuit which may be accurately operated to enable the said receiving circuit only just before the arrival of telegraph signals.

The drawings consist of three sheets of circuit diagrams and one sheet containing diagrams in the form of graphs. With Figs. 1, 2 and 3 placed together a circuit diagram of one terminal of an interpolated telephone and telegraph system is shown.

Fig. 1 shows the transmitting telegraph circuits;

Fig. 2, partly schematic and partly circuit diagram, shows the telephone and controlling circuits;

Fig. and

Fig. 4 is a pair of diagrams made from graphs of current plotted against time to illustrate the timing relations of certain circuit operations.

3 shows the receiving telegraph circuits;

One terminal of a system is shown but it will be understood that at some distant point a similar terminal is located so that speech coming in over channel 201 will be transmitted from the radio transmitter 222 and its antenna 203 to be received at the said distant point over the antenna 224 and the radio receiver 22-5 for transmission into the speech path at that point corresponding to the channel 201.

While speech is being transmitted from chan nel 201 over the antenna 203, the telegraph transmitting apparatus of Fig. l is inactive and the telegraph receiving apparatus of Fig. 3 at the distant point is similarly inactive. By the same token the telegraph transmitting apparatus of Fig. l at the distant point and the telegraph receiving apparatus of Fig. 3 at the near end, as shown, will be in operation.

In general, speech over channel 221 enters the hybrid coil 205 provided with the usual balancing network 221, passes over path 228 through the network 209 to the voice operated gain adjusting device (termed vogad for short) 211. From the vcgad 2.1 1 speech currents enter the hybrid coil 212- where they spit, part going on to the main speech channel and part entering the syllabic amplifier detector 253 for control purposes. The output of the amplifier detector 213 feeds into the transmitting chain 214 which performs a variety of switching functions, as will be more clearly set forth hereinafter. At present it is sufficient to say that the transmitting chain 2 M clears the way for the speech currents to the antenna 293 and that the distant receiving terminal similarly conditions the receiving circuits thereat for the proper reception of the speech currents. The main portion of the speech currents then pass from the hybrid coil 212 into the delay circuit 215, through a repeater 2 i6, and the first transmitting suppressor 211. Thereafter the speech path is through privacy circuit 218, the second transmitting suppressor 2H1, and another part of the privacy circuit 22!! to the hybrid coil 2231. Speech currents then pass to the hybrid coil 222, thence to the transmitting repeater 223'to the radio transmitter 282.

At the'distant' receiving end, the speech currents transmitted from the radio receiver pass through the receiving repeater 224 into the hybrid coil 225. At this point the control tone which accompanies speech is diverted to the control tone filter 22 5, to the receiving detector 221, which operates the receiving chain 228. This receiving chain responds to the control tone transmitted from the distant end through the operation of the transmitting chain 214 thereat and like the transmitting chain performs a variety of switching functions which will be more fully described hereinafter. At present it is sufficient to say that the receiving chain clears the way for the speech currents to reach the hybrid coil 266 and channel 261. The speech currents leaving the hybrid coil 225 enter the next hybrid coil 229 and thence pass through a part of the privacy circuit 230, the first receiving suppressor 2&1, another part of the privacy circuit 232 to the second receiving suppressor 233. From this point the speech currents pass through the variable suppressor 224, a low-pass filter 225, a volume controller 236, a repeater 231, a network 222, and thence to the hybrid coil 2836 from which they pass over the channel such as 2631 at the said distant terminal.

The functions of these various pieces of apparatus are briefly as follows:

The hybrid coil 2% receives voice currents from the channel 201 and transmits them out .over the channel 298. The hybrid coil 206 also receives voice currents from channel 239 and transmits them out over channel 2131. The function of the balancing network 281 is well known. In this connection it should also be noted that each of the hybrid coils 212, 221, 222, 225 and 229 are provided with appropriate balancing networks. The networks 289 and 238 are provided to perform certain functions necessary in commercial telephone circuits to compensate for the differences in transmission when the channel 201 is connected to (hfferent types of telephone circuits. They play no particular part in the present invention as their adjusting circuits are not shown but they are included in the schematic part of this diagram in order to render the diagram as complete as possible. The vogad 21! is a means for adjusting the gain applied to the voice currents incoming thereto so as to provide a uniform level of output. The hybrid coil 212 allows a small part of the voice currents to be taken off to the syllabic amplifier detector 213 without causing distortion in the voice currents flowing from the hybrid coil 212 to the rest of the circuit. The delay circuit 15 is an arrangement by which voice currents are delayed to allow time for the transmitting chain 21 1 to properly perform its functions before the voice currents are finally delivered to the antenna 203. Since these delay circuits entail certain loss in transmission, amplifying means are associated therewith in the form of a repeater 216 which is shown as a one-way amplifying repeater. The first transmitting suppressor 211 and the second transmitting suppressor 219 both act to block speech currents therethrough when the relays of the transmitting chain 214 are in the position shown. When, however, the transmitting chain is operated both transmitting suppressor 21'! and transmitting suppressor 219 give a clear path for the transmission of voice currents. It is necessary to use a blocking path at each terminal of the privacy system circuit 258, this being a controlling agency for the other part of the privacy system 229. These two units 218 and 220 are included to render the speech between the antenna 223 and the distant antenna 204 unintelligible but do not form any essential part of the present invention being included again for the purpose of rendering the schematic layout as complete as possible. The function of the hybrid coil 221 is to transmit to the hybrid coil 222 either speech coming from the privacy system unit 228 or telegraph signals coming from Fig. 1 above. The function of the hybrid coil 222 is to pass on to the transmitting repeater 223 both the output of the hybrid coil 22! and the control tone originating from the oscillator 24? This oscillator is a source of alternating current of a frequency just outside the voice range so that it may be eifectually filtered out at the receiving end without disturbing the voice currents entering the receiving circuit thereat.

Current from the oscillator 24E! enters the control tone enabler 24!, which is under control of the transmitting chain 214, as will appear hereinafter. When the voice takes command of the transmitting chain 214 and certain relays in the telegraph transmitting apparatus of Fig. 1 are properly operated, the control tone enabler 241 will allow alternating current from the source 2 52 to enter the control tone compressor 242 and from this point the control tone will be passed through the filter 243 to the hybrid coil 222. The effect, therefore, is that when the voice takes command of the transmitting chain 214, control tone at full volume will be delivered to the hybrid coil 222. A short time thereafter, as measured by the delay circuit H5 and controlled by a connection in the voice path between the first transmitting suppressor 2" and the first unitv of the privacy system 218, the control tone compressor will operate to reduce the volume of the control tone being delivered to the hybrid coil 222.

The transmitting repeater 223' is a well-known type of one-way amplifier. The radio transmitter 202 and its associated antenna 263 need no special description. Likewise, the radio receiver 205 and its associated antenna 204 need no special description. The repeater 224 is, like the repeaters 216 and 223, a one-way amplifying device. The hybrid coil 225 receives the output of the radio receiver 205 and allows part of this output to flow to the control tone filter 226 which delivers to the receiving detector 22! only the control tone.

The hybrid coil 225 also delivers to the next hybrid coil 229 the speech currents, .the accompanying control tone being filtered out later. Hybrid coil 229 acts during the transmission of speech currents to deliver the speech currents which are transmitted from the radio receiver 205 to the privacy system unit 230 and the various circuit units thereafter. During intervals of telegraph transmission the hybrid coil 229 delivers the output of the radio receiver 295 to the telegraph receiving apparatus of Fig. 3.

The privacy system units 230 and 232, like the privacy system units 220 and 2| 8, are used to insure secrecy in the transmission of intelligence by translating for delivery to channel 20] the otherwise unintelligible transmission from r the antenna 203 to the antenna 204. The first receiving suppressor 23l and the second receiving suppressor 233, both operate under control of the receiving chain 228, operate to block the speech path during those intervals when the control tone is absent from the transmission being received by the receiver 205. When control tone is present as an indication that speech is present, the receiving chain 228 takes the position shown by the various relays and the receiving suppressors 23| and 233 give a clear path for speech currents toward the hybrid coil 206 and the channels 20I. The variable suppressor 234 is a device used to cause the transition from speech to silence and from silence to speech to be slow so that clicks and unpleasant operation of the circuit will not disturb the listener. The low-pass filter 235 effectually blocks any control tone which may have accompanied speech to this point and allows only the speech to go into the volume controller 236.

At this point it should. be noted that between the low-pass filter 235 and the volume controller 236 there is a connection to the receiving detector 221. Thus when the voice takes command at the distant transmitting end, control tone from the oscillator 240 is transmitted by the radio transmitter at full volume, and this will enter the control tone filter 226 and the receiving detector 221 to insure proper operation of the receiving master relay within the receiving chain 228. By the time that the voice arrives the receiving chain will have conditioned the receiving circuit, particularly by operating the first and second receiving suppressors 23| and 233 and the variable suppressor 234 so that as the control tone is reduced in volume through the action of the control tone compressor 242, voice currents from the connection between the low- pass filters 235 and 236 will reach the receiving detector 231 to augment the operation of this device and insure the proper and continuous operation of the receiving chain even during periods when fading or other disturbances in the mutable link cause the received control tone to drop to a value where the continued operation of the receiving chain might be unsatisfactory.

That part of the circuit between and including radio transmitter 202 and radio receiver 205 is spoken of as a mutable link since it comprises a signaling channel capable of or liable to change from internal or external cause which may give rise to interfering energy or more specifically, subject to noise, fading or change of attenuation. It is to be understood, however, that the present showing is by way of example and that the term mutable link does not necessarily mean that a space radio link is invariably involved but that the term is broader in its meaning and includes any channel liable to change from internal or external cause.

The volume controller 236 is a device generally under the supervision of a technical operator for controlling the volume as indicated by a monitoring device not shown connected between this unit and the receiving repeater 231. The receiving repeater 23'! is like the other repeaters 256, 223 and 224, a one-way amplifying device.

The syllable amplifier detector 283 is a device which will be unoperated by the maximum noise which may be expected on the transmitting circuit but will be operated quickly by speech signals of both high and low amplitudes. It is connected to the hybrid coil 212 and delivers its output to the receiving chain 2 i 4.

If the receiving chain 223 is in the position shown the amplifier detector in will be enabled. If at this time voice currents come in over channel 28d their effect will be to operate the amplifier detector H3 and thereupon operate the transmitting chain 2 4.

The transmitting chain comprises a transmitting master relay 25%) and a chain of relays 25l, 252, 253. 25 i, 255 and 256. The transmitting master relay 553 responds directly to the amplifier detector M3. The relays 253 and 25! to- ,ether provide an accelerating circuit for the sure and speedy operation of the remainder of the chain of relays. It will be noted that the lower windings of both relays 25d and 25! are included in a series circuit which extends from ground connected also to the armature of relay 250 through the lower windings of relays 25D and 25! and thence to a resistance 250 and battery. However, the connection between the lower winding of relay 25! and the resistance 25%! extends to the back contact of relay 250 which, as before stated, is connected to ground. Therefore, the lower windings of relays 259 and 25! are normally short-circuited. When relay 250 operates, then the instant that the armature leaves its back contact the circuit from ground through the resistance 258 to battery is rendered effective and the lower windings on these relays are so designed that the current flowing in this circuit will cause the relays to attract their armatures strongly and with the utmost speed. When relay 25! moves its armature into connection with its front contact, the two lower windings of these relays are again short-circuited but by that time the relay 255 will have moved its armature to its front contact and relay 254 will ave become fully operated. Relay 25l is now held operated in a circuit from ground, the armature and front contact of relay 255, resistance 259, resistance 25%, the Winding of relay 25!, resistance 2 i to battery.

It. should be noted that when under influence oi the amplifier detector M5 the transmitting master relay 25.5 becomes deenergized that the armature of relay 255 will reach its back contact and again establish the original circuit for shunting the two lower windings of relays 255 and I before relay 25I can release its armature. Relay 25!. is known as the transmitting voice hang-over relay and through the operation of the circuit including condenser 2-52 and resistance 255 this relay is caused to hold its armature operated until condenser charged. By the proper selection of the values of resistance 25a and condenser 252, the hangover period by which the release of relay 25I is delayed beyond the release of relay 255 may be adjusted to any desired value.

Thus the accelerating circuit operates only on the forward operation of these relays 255 and MI and plays no part in the release thereof.

The operation of relay 25! causes the operation of relays 252 to 2.53, inclusive. Relays 252 to 255, inclusive, have their windings in a series circuit extending to the back contact and armature of relay 25! and from this point extending also through resistance 253 to battery. Since the armature of relay 25! is grounded, the circuit through the windings of relays 252 to 255 normally is shunted. However, as soon as the relay 25! moves its armature from its back contact, the circuit through the resistance 253 will become effective and relays 252 to 255 will immediately become operated. Through the operation of relay 255, relay 255 is operated.

Relay 252 in its normal position affects the first transmitting suppressor 2!! to block voice currents delivered to it by the repeater 2H5. Upon its operation, however, relay 252 changes this condition so that the first transmitting suppressor til now enables the free transmission of voice currents. Relay 253 is the privacy relay and this causes certain switching functions to take place when speech is to be transmitted out over antenna 253. The privacy relay 253 also functions on its front contact to operate the transmitting signal relay 255 and thus the signal lamp 285 to indicate that the transmitting chain is in operation. The relay 254 controls the second transmitting suppressor H9 and. relay 255 functions to cause the operation of the transmitting telegraph enabler relay 255. This relay is provided with a, hang-over circuit comprising the resistances 255 and 251 and the condenser 258 so that the transmitting telegraph enabler relay does not become released for a given period after the remainder of the transmitting chain has released.

It has been noted briefly hereinbefore that the receiving detector 221 is first operated by control tone through the filter 22s at comparatively high volume and later, after the receiving chain 228 has operated, is then controlled by both the corn trol tone at lower volume through the filter 225 and by voice currents coming in over a connection between the low-pass filter 235 and the volume controller 235. The receiving detector normally holds thecontrol master relay Z'lfi op- 252 can become sufficiently erated and when the receiving detector responds to these incoming control tone and voice currents, it allows relay 275 to become deenergized. During the normal condition, then, relay 275 is operated and the chain of relays controlled thereby is in the position shown. Upon the release of relay Zli a circuit is completed from ground, the armature and back contact of master relay 2'50, resistance Eli, resistance 212, the windings oi relays 2'13, and 275 in series, resistance 25! to battery. Upon the operation of relay 275 a connection is established from ground, armature and front contact of relay 215, resistances 28I and 282 and thence through the windings of relays 2%, ill, 2N3 and 2'19, resistances 2E5, 281, relay 2%, resistance 255 in series to battery. Resistances 2H and H2 and the condenser 28!] form a hang-over circuit so that it is not for a given period after the master relay 2?!) has again operated that relays 2'i3 to 21.9, inclusive, may release their armatures. In addition, the resistances 23!, 282 and the condenser 253 form a hang-over circuit for relays 215 to 275, inclusive, and relay 2M so that it is not for an additional period after relays 2 13' and 215 have released that relays 2'55 to- 279 and 2H will release. Furthermore, relay 2M has an individual hang-over circuit consisting of the resistances 28"! and 288 and the condenser 289 so that of all the relays of the receiving chain relay 214 is the last to release for a purpose which will presently appear.

Relay 2'53, known as the receiving suppressor relay, in releasing changes the circuits ofthe variable suppressor 234 so as to allow what may be termed a gradual opening up of the voice path. Thereafter, in a time interval as measured by the hang-over circuit of resistances 28I and 282, and condenser 283, the receiving suppressor'relays 2'6'6 and 219 will cause the first and second receiving suppressors 23I and 233, respectively, to fully open up the voice channel to allow voice currents to flow toward the hybrid coil 2%. The telegraph relay 214, known as the receiving printing master relay, controls the printer circuit in Fig. 3. The receiving echo hang-over relay 2' controls the amplifier detector 2| 3 at the same terminal and the vogad disabler relay 2'18 controls the vogad 2| I sothat while speech is being received at the transmitting terminal, the vogad 2 will be unable to transmit outgoing and, therefore, interfering speech. Relay 219 when released causes'the operation of relay 284 and in turn the glowing of lamp 285, as a signal that the receiving chain is effectively operated.

The transmitting telegraph apparatus consists, generally, of a pair of tape transmitters I and I56. Each of these transmitters has a series of five contacts operating between a spacing battery lead It)? and a marking battery lead I08 and affecting in turn, the segments III to I20, inclusive, of the multiplex distributor. This latter piece of apparatus consists, in general, of a motor and synchronizing equipment Ill] operating a shaft I09. This shaft has upon it a number of brushes l2l, I22, I23 and I24. The brush IZI as it passes successively over the segments III to I28, inclusive, connects these segments to the ring I25 which is connected through either the armature and back contact of relay IE5 or the armature and back contact of relay I21, thence through the back contact and armature of relay I53 and the winding of the telegraph transmitting line relay I28 to a point on a potentiometer consisting of the resistances I29 and I35 whereby the relay I23 will respond to either marking or spacing potential and thus operate its arma ture accordingly. When relay I28 is operated by a spacing signal it closes a circuit through its armature and contact to render the telegraph tone enabler I3I ineffective to transmit telegraph tone from the source I32 to the hybrid coil 22I. When the relay I28 is operated by a marking signal it opens this circuit which affects the telegraph tone enabler I3I in such a way that alternating current from the source I32 freely passes to the hybrid coil 22I and thence out over the radio transmitter 202.

It should be noted that when the transmitting chain 2I4 is operated and, consequently, relay I03 is operated, that a connection is extended from spacing battery lead I01 through the front contact and armature of relay I03 to the winding of relay I28 to hold this relay spacing and, therefore, continuously to block the transmission of telegraph tone from the source I32 to the hybrid coil 22I.

The function of brush I22 is as follows: If the transmitting chain operates at any time before brush I22 comes in contact with segment I33 or segment I34, then relays I02 and I03 will be properly operated and further transmission of telegraph signals interrupted and the stepping of the tape magnet prevented. If, however, the operation of the transmitting chain 2I4 occurs while brush I22 is on either of these segments I33 or I34, a connection will be extended from battery, ring I35 over brush I22 to segment I33 and thence through the windings of relays I04 and I00, the back contact and armature of relay I02 to ground. This causes the circuit for the operation of relays I02 and I03 to be opened to prevent the disabling of the telegraph apparatus for this very short interval. This arrangement is provided so that if the voice takes command of the circuit at or during the transmission of the last pulse of a telegraph code, this last pulse may be allowed to be transmitted without interruption.

The function of brush I23 is as follows: The segments and rings of this multiplex distributor are developed for the sake of clarity and the brush I23, now moving downwardly, has reached the point where transmission of the signals from the tape transmitter I06 has been completed. Brush I23 now establishes a connection from ground, ring I36, brush I23, segment I31, back contact and outer right-hand armature of relay I38, winding of stepping magnet I39, right-hand contact and armature of relay I40 to battery. If relay I40 is on its right-hand contact, as it should be while this apparatus is operating normally, and there is a, sufficient supply of tape for use by the transmitter I06, then the magnet I39 will operate and advance the tape to the next punched character. As brush I23 advances it next comes into contact with segment I4I where a connection is established from ground, ring I36, brush I23, segment I4I, the contacts of the taut tape switch I42, which will be closed as long as there is sufficient tape in this transmitter, to the lefthand winding of relay I38. This connection also extends in parallel through the normal contacts and the inner right-hand armature of relay I38 through the right-hand winding of this relay, and these windings being opposed no operation of the relay I38 will occur. If, however, upon the operation of magnet I 39 the taut tape switch I42 had operated, then only the right-hand winding of relay I38 would have been energized and this relay would then have operated and locked through its inner right-hand armature to ground.

This condition would have persisted until the taut tape switch I42 closed its contacts again and brush I23 made contact with segment I4I whereupon the relay I38 would have been automatically released.

During the time that relay I38 is operated each of the segments I I6 to I20, inclusive, would have been connected through the front contacts and left-hand armatures of relay I38 to marking battery, so that a signal consisting of five marking pulses would have been repeatedly sent each time the brush I25 passed over the segments II6 to I20, inclusive.

When brush 223 advances to segment I43 a connection is momentarily established from ground, ring I36, brush I23, segment I43, the lower winding of relay I40 to battery. This tends to drive relay I40 to its right-hand contact where it will remain unless some other circuit is closed to change this condition.

As brush I23 advances further it first causes the operation of stepping magnet I44 in a similar manner to the operation of stepping magnet I39 and attempts to operate the relay I45 and finally closes a circuit to drive relay I46 to its right-hand armature.

The function of brush I24 is as follows: If durring the time that brush I24 is on segment I41, relay I02 becomes operated, then a circuit will be established from ground, the armature and front contact of relay I02, ring I46, brush I24, segment I41, the upper winding of relay I46 to battery. Relay I46 will thereupon be driven to its left-hand contact where it will remain until brush I23 drives it back to its left-hand contact. During the time that relay I46 is on its left-hand contact it will cause the operation of relay I26 in an obvious circuit and thereby open the transmitting circuit which operates the telegraph transmitting relay I23. When brush I24 reacl1- es the lower segment I49 it will cause the relay I40 to move to its left-hand contact whereupon the relay I21 will be operated and complete the opening of the circuit for relay I28. It will be noted that each of these relays I40 and I40 will be periodically returned to its right-hand contact at the ending of the period of activity of the other circuit, but if the telegraph transmitting apparatus is now rendered ineffective, the relay will return to its left-hand contact immediately thereafter and before any signals can be effectively transmitted.

It should be noted before leaving the descrip tion of the transmitting telegraph apparatus that if both the taut tape switches open the lefthand windings of relays I38 and I45, respectively, that the contacts and the left-hand armatures of relay I45 are connected to spacing battery so that first a series of five marking impulses and later a series of five spacing impulses will be transmitted. This provides for an occasional transition between a spacing and a marking impulse for the purpose of correcting the distributor speed at the distant end.

When the receiving chain 223 is in its normal unoperated condition then the telegrad 300 will be enabled. This will render the telegrad effective to operate the receiving telegraph apparatus. At this time telegraph signals being received by the radio receiver are passed into hybrid coil 229 and thence into the band-pass filter 30I from which they are delivered to the telegrad 300. This results in the operation of relays 302, 303 and 304 to their marking contacts for each marking impulse delivered to the telegrad 300. Re-

lay 332 is known as the receiving telegraph. line relay and for each marking impulse it establishes a ground connection to the ring 305. Relay 304 is known as the corrector relay. Upon each spacing impulse this relay will cause its condenser 3536 to be energized and upon each marking impulse this relay will deliver the condenser discharge into ring 331. Relay 333 is known as the auxiliary relay and operates on each marking impulse to drive either relay 333 or relay 339 to its left-hand contact, respectively.

The receiving telegraph apparatus consists, generally, of two printers are and 3H and a multiplex distributor comprising a motor and oer-- tain synchronous equipment 3I2 operating a shaft 313 carrying brushes M4, 315, 313 and 311.

As brush 3M moves downwardly it connects the ring 335 through segments 3i8, 319, 323, 32! and 322 to the selecting magnets of printer 3H and thereafter through segments 323, 324, 325, 326 and 321 to the selecting magnets of printer 310. Thus for each marking impulse one of the selecting magnets of printer 3 or printer 3N! is operated.

Brush 3E6 is moving downwardly makes contact with segments 323 and then 323 while brush 3M is traversing the connections to the selecting magnets of printer 3. The segments 328 and 323 are associated with printer 353. The

connection to segment 328 establishes a circuit from ground, ring 330, brush 356, segment 328, armature and contact of relay 338 to the printing magnet 33!. Thus the selection set up on printer 310 is rendered effective by the printing magnet 33% after the brush 3 l 4 has completely traversed the segments 323 to 321 and is now engaged in passing over the segments 318 to 322. As the brush 313 advances it makes a connection from ground to segment 329, which leads to the lower righ-hand set of contacts of key 332, for

tends a battery connection to the two windings of the relay 339 through the rectifiers 331 and 338. If this telegraph receiving apparatus is now properly in operative condition there will be an open connection to the upper winding of this relay at the armature and contact of relay 333. Any marking impulse coming in at this time will be rendered effective by the auxiliary relay 303 to keep relay 333 on its left-hand contact and thus render the printing magnet effective. If, on the other hand, the receiving chain 223 is operated by voice currents then relay 333 will be released and ground on the armature of relay 339 will cause relay 339 to be driven to its other position where the circuit for printing magnet 3-33 is opened. Similar action of relay 333 will take place when the brush 311 traverses the segment 341.

It will also be noted that when the relay 333 is operated, as when the receiving chain 228 is in its normal position, thus denoting the fact that the receiving telegraph apparatus is effective, that relay 343 will be operated. Relay 340 plays a particular role with relation to the key 332.

If the distant transmitter corresponding to transmitter 136 operates its taut tape switch so as to send out a series of five marking impulses, then the receipt of these five marking impulses by the printer 3H] results in a thumping of the teletypewriter apparatus without the production of any printing. If this becomes annoying to the operator then the key 332 may be moved to its right-hand position. Thereupon a circuit will be established from battery, the upper right-hand contacts of key 332, the winding of relay 342, the lower right-hand contacts of key 332 to the segment 329 and when brush 383 makes contact with segment 329 a connection is extended to ground on ring 333. This causes relay 342 to operate and this relay locks up to battery on its inner right-hand armature. Relay 342 is sufficiently slow in releasing so that it will remain locked up in a manner now to be described. Upon the first operation of relay 322 a circuit for the operation of relay 333 is closed at the front contact and outer right-hand armature of relay 342. This relay now disconnects the segments 323 to 321, inclusive, from the selecting magnets of the printer 3m and extends them to conductor 344 which, with the left-hand contacts of key 332 in their normal position, extends the ground connection each time the brush 3 l 4 connects with a segment 323 to 321, inclusive, to the winding of relay 342 to maintain this relay operated.

If at the distant end the taut tape switch should return to normal then ground impulses will not be supplied to the winding of relay 342 at sufficient intervals to keep this relay operated and it will therefore release and by releasing cause relay 333 to return to normal, so that the printer 3H! again becomes effective. If during the time that relay 322 is locked up the receiving telegraph apparatus is rendered ineffective by the operation or" the receiving chain 223, then relay 3% returns to normal and this maintains relay 3&2 locked up until the telegraph apparatus is again rendered effective through the operation of the receiving chain 223.

The relay 332 may be unlocked at any time by moving the key 332 to its left-hand position.

As brush 355 moves it alternately makes contact with segments connected to either conductor These conductors are connected to difierent windings of the connector relay 341 and therefore the discharge of the condenser 336 will tend to operate the relay 331 in one direction if the motor 3i2 is running fast or operate the relay 341 in the other direction if the motor 312 is running slow. The correcting means is Well known and will not be further described except to note that a device 368, which will indicate fast or slow operation, is inserted at this point to indicate that correction may be properly made.

Referring now to Fig. 4 it will be noted that two sets of graphs of current plotted against time are shown. On line 433 as a base line are shown speech current, control current and telegraph current in proper time relation at the transmitting end, that is, speech currents are shown along the line 433 until the vertical 331 is reached. This line represents the time at which speech ceases and the tim therefore at which the syllabic amplifier detector 2 l 3 releases the transmitting chain 214. Due to the transmitting hangover time provided by the slow release of relay 25l through the agency of the hang-over circuit consisting of resistance 23% and condenser 232, the control tone enabler 241 will continue to allow control tone from the source 243 to be transmitted until the time represented by the vertical line 4132 is reached. Ther after a period which along the horizontal line 4% appears to be blank is provided by the slow release of the transmitting telegraph enabler relay 256 through the agency of the hang-over circuit provided by the resistance 261 and condenser 268. This extends to the time marked by the vertical line 403. This line then represents the earliest possible time at which telegraph signals may be transmitted.

The second horizontal line 404 represents the action in the receiving circuit. Speech it will be noted will be received up to the time denoted by the vertical line 4M and control tone will be received up until the time denoted by the vertical line 402. Heretofore the telegrad disabler relay 214 was placed in series with and between the relays 213 and 215 and hence its release was controlled by a slight hang-over provided by the resistance 2'12 and the condenser 280. The time at which this relay therefore released according to prior arrangements is denoted by the vertical line 405. This leaves a space of some considerable time between the vertical time 485 and the vertical time 403 which denotes the earliest possible arrival of the telegraph signals. During this time the receiving telegraph circuit from the line to the printers is open to noise operation and if the action of the mutable link is particularly severe may result in false operation of the printers.

In accordance with the present invention the telegraph disabler relay 2' is placed at the extreme end of the receiving relay chain 228 and provided with an extra hang-over means consisting of the resistance 28'! and condenser 289. This shifts the release of relay 214 to the time denoted by the vertical line 463 so that the enabling of the telegraph will not be accomplished until the earliest possible time at which telegraph signals might arrive.

What is claimecl is:

1. In a communication system wherein telegraph signals are interpolated in voice current transmission during lulls and pauses therein, a transmission channel, voice controlled means at the transmitting end of said transmission channel comprising a transmitting chain of relays for performing interpolating switching operations, one of said relays exercising a remote control over a receiving chain of relays at the receiving end of said transmission channel, another of said relays in said transmitting chain operating to control the transmission of telegraph signals, said last relay being provided with a hangover circuit to time the earliest possible start of telegraph signal transmission a predetermined time interval after the said first relay has relinquished its said control over said receiving chain of relays, telegraph signal responsive means at the receiving end of said transmission channel, said receiving chain including a relay for enabling said telegraph signal responsive means, and a hang-over circuit for said enabling relay arranged to prevent the enabling of said telegraph signal responsive means until the said time fcr the earliest possible start of telegraph signal transmission.

2. In a communication system wherein telegraph signals are interpolated in voice current transmission during lulls and pauses therein, a transmission channel including a mutable link, voice controlled means at the transmitting end of said transmission channel comprising a transmitting chain of relays for performing interpolating switching operations, a first of said relays exercising a remote control over a receiving chain of relays at the receiving end of said transmission channel, a second of said relays in said transmitting chain operating to control the transmission of telegraph signals, said second relay being provided with a hang-over circuit to time the earliest possible start of telegraph signal transmission a predetermined time interval after said first relay has relinquished its said control over said receiving chain of relays, telegraph signal responsive means at the receiving end of said transmission channel having a sensitivity rendering it capable of responding to serious spurious disturbances originating in said mutable link, said receiving chain including a relay for enabling said telegraph signal responsive means and means for minimizing the effect of said spurious disturbances upon said telegraph signal responsive means comprising a hang-over means for said enabling relay for synchronizing its said enabling action with the action of said second of said relays in said transmitting chain.

3. In a communication system wherein telegraph signals are interpolated in voice current transmission during lulls and pauses therein, a transmission channel including a mutable link, voice controlled means at the transmitting end of said transmission channel comprising a transmitting chain of relays for performing interpolating switching operations, a first of said relays operating to connect a source of control tone to said transmission channel for transmission thereover, a second of said relays in said transmitting chain operating to start and stop the transmission of telegraph signals over said channel, said second relay being provided with a hang-over circuit to time the earliest possible start of telegraph signal transmission a predetermined time interval after said first relay has disconnected said source of control tone from said channel, a receiving chain of relays at the receiving end of said transmission channel responsive to control tone for performing interpolating switching operations thereat, telegraph signal responsive means at the receiving end of said transmission channel having a sensitivity rendering it capable of responding to spurious disturbances originating in said mutable link, said receiving chain including a relay for enabling said telegraph signal responsive means and means for minimizing the eifect of disturbances arising in said mutable link on said telegraph signal responsive means comprising a hang-over circuit for said enabling relay arranged to prevent the enabling of said telegraph signal responsive means for a period corresponding to said hang-over circuit time of said second relay in said transmitting chain.

4. In a communication system wherein telegraph signals are interpolated in a voice current transmission during lulls and pauses therein, a transmission channel including a mutable link, voice controlled means at the transmitting end of said transmission channel comprising a transmitting chain of relays for performing interpolating switching operations, a first of said relays operating to connect a source of control tone to said transmission channel for transmission thereover, a voice current delay circuit for delaying the transmission of voice currents over said channel to give said control tone a time preference in transmission over said channel, means responsive to said delayed voice currents for reducing the volume of control tone transmitted over said channel under control of said first relay, a hangover circuit for said first relay for maintaining the flow of control tone over said transmission channel for a predetermined period after the stoppage of voice currents, a second of said relays in said transmitting chain operating to start and stop the transmission of telegraph signals over said channel, said second relay being provided with a hang-over circuit to time the earliest possible start of telegraph signal transmission a predetermined time interval after said first relay has disconnected said source of control tone from said channel, a receiving chain of relays at the receiving end of said transmission channel primarily responsive to control tone and secondarily 10 sitivity rendering it capable of responding to spurious disturbances originating in said mutable link, said receiving chain including a relay for enabling said telegraph signal responsive means and means for minimizing the effect of disturbances arising in said mutable link on said telegraph signal responsive means comprising a hang-over circuit for said enabling relay arranged to prevent the enabling of said telegraph signal responsive means for a period corresponding to said hang-over circuit time of said second relay in said transmitting chain.

WALTER W. TUTHILL.

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