US2437027A - Time division multiplex communication system - Google Patents

Description

- March 2. 1948.

J. H. HOMRIGHOUS TIME DIVISION MULTIPLEX' COMMUNICATION SYSTEM 3 Sheets-Sheet 2 Filed Jan, 12, 1943 March 2, 1948. J, I-IOMRIGHQUS TIME DIVISION MULTIPLEX COMMUNICATION SYSTEM Filed Jan. 12,1943 3 Sheets-Sheet 3 0 l fl HM H M 7 8 R %R m QRWIQ EM E E A W W 0 0 O P .P P QM. Km 1 I P WM 0 v I H u I: I J a 4 5 .P. P E Q w O OM D m M A E E E E 2 .M R R Hm 3 1 1|. v A H P m ammm P 9 m WA mxu m MS N I\ 6 F I L a O .UT 0. o m TD s N F m 0 R a L a m a v P. R .M w FA E l 7 R w H PV Patented Mar. 2, 1948 OFFICE TIME DIVISION MULTIPLEX COMMUNI- CATION SYSTEM John H. Homrighous, Oak Park, Ill. Application January 12, 1943, Serial No. 472,105

12 Claims.

This invention relates to improved methods and systems for transmitting a number of messages simultaneously through a single transmission channel.

One of the main objects of my invention is to provide a system for intermittently transmitting two or more like or different messages, such as, sound, pictures, telegraph, written or coded signals over a single carrier. I

Another object of my invention is to provide an improved means whereby signals representative of difierent messages may be recorded and reproduced at a difierent speed for the intermittent transmission and reception of the different message signals over acommon path.

Message in this specification is to be understood to include any intelligence represented by sound, picture, or code signals.

Several methods for transmitting a number of messages on a single carrier have been devised. These systems employ mechanism such as, electromagnets or rotating devices which have a definite operating time, thus limiting the number of messages that may be transmitted intermittently over a single carrier. In one method of my present invention I provide electronic devices having no mechanical moving parts for controlling the intermittent transmittal of two or more diiierent messages. In this system the fragments of each message may be separated and again joined at a very rapid rate. In a second method equal portions or fragments of signals representative of two messages may be recorded and reproduced at a greater speed so that both messages may be transmitted in successive rotation over a common path.

In this invention I also employ a new electron tube which I choose to call an on and on electron relay. This tube will open or close a circuit, that is, it opens or closes the electron path within the tube, giving a very sharp cut ofi.

Other objects and advantages of my invention will appear from the following description, taken in connection with the accompanying drawings, in which:

Figures 1 and 9 are simplified diagrammatic views of a radio transmitting station and a radio receiving station respectively, illustrating the principles applied in this invention.

Figure 2 is a detail view of the oft and on electron relay tube.

Figure 3 is a detail end view of the tube in Figure 2.

Figure 4 shows a circuit arrangement for the on and on electron relay tube.

Figure 5 is a diagrammatic arrangement of the message distributor and associated circuits illustrated in Figure 1.

Figure 6 is a detail view of the message recording and reproducing mechanism shown in Figure 1.

Figure '7 is a detail View of a sound track film used in Figure 6.

Figure 8 is a detail view of the scanning device used in'Figure 6.

Figure 10 is a diagrammatic arrangement of the message distributor and associated circuits illustrated in Figure 9.

Figure 11 is a detail view of the message recording and reproducing mechanism shown in Figure 9'.

Figure 12 is a detail view of a sound track film used in Figure 11.

Figure 13 is a detail view of the scanning device used in Figure 11.

In Figure 1, the numerals l and 2 designate microphones and 3 designates a microphone or a telegraph instrument where electrical signals are developed and supplied to the amplifiers d, and 6 respectively. These signals are fed intermittentiy to the modulation amplifier l.

A carrier wave is provided by an oscillator 8. In the power amplifier 9 this carrier wave is modulated by the sound and telegraph signals and also by synchronizing signals or impulses from the message distributor apparatus Iii through the modulation amplifier I. The signals from the power amplifier 9 are supplied by a connection II to the antenna l2.

Sound signals, telegraph signals, and control signals may be transmitted on the same carrier. While Ihave shown electrical signals from three separate communications modulated on a single carrier, it is to be understood that the signals from several more separate communications may be intermittently modulated on a single carrier where the rate of change from one message to another message is of a greater frequency than the electrical signals produced by sound and the intermittent fragments of the messages are only for a short interval.

In transmitting only two messages a somewhat slower rate of change from one message to another message may be employed and each fragment or intermittent part of a, message may be recorded and reproduced at a greater speed for transmittal so that both messages may be alternately modulated on a carrier without the loss of any part of the message. In order to accomplish this feature the electrical signals from the amplifiers and 6 are applied through switches l3 and M to the recorders or glow lamps l5 and It for registering variable light intensities forming separate sound tracks on a movable memory or fluorescent film. The variable light intensities registered on the film are separated into equal part in the interval reducing mechanism I1 and reproduced at one half their normal interval at E8 and it" where they are fed to the amplifiers l9 and 2i! and then applied to the modulation amplifier 7 through the switch 2|.

Figures 2 and 3 show a new ofi and on electron relay tube used in Figures 5 and 10 to govern the beginning and the ending of the several parts of a message. This tube comprises an evacuated envelope or glass bulb 22 containing an indirectly heated cathode 23, two ray control electrodes 24 and 25 of narrow material located on opposite sides and parallel to the cathode, two anodes 25 and 2 located on opposite sides of the cathode and in alignment with the control electrodes 24 and 25. The anodes 28 and 29 located adjacent to the anodes 26 and 21 are connected together inside the bulb. The several tube elementsare mounted on and held in proper position by the insulating member 35. The member Sills secured by small rods 3! and 32 to the tubular glass stem 33. On the under side of the insulating member there maybe a metal shield 34 connected to the cathode 23 and indicated by the dotted line in Figure 3. A metal shield 35 may also be placed over the top and connected to the lower shield by the rods 36 and 3! extending on the outside of anodes 25 and 29 as shown in Figure 3. These shields maintained at cathode potential will confine the electrons to the anodes. Conductors from the individual tube elements, three from the anodes, two from the control electrodes, and two from the filament are extended through the glass stem 33 to the base of the tube where they are brought out through the glass bulb and terminated on base pins extending from the tube base.

Referring to Figure 4 the operation is as follows, the anodes 25 and 27 are maintained at a higher positive potential than the anodes 28 and 29. The control electrodes 24 and 25 are operated at a variable or adjustable positive potential. Assuming that the control electrode 24 is at approximately the same potential as the anode 26 and control electrode 25 is at a much lower potential than the anode 2?, then electrons will flow from the cathode 23 to the anode 25 through the load resistance 58. The electrode 25 being at a lower potential than the anode 21 will prevent or shield the electrons from reaching the anode 21. Then an increasing potential on the grid of tube 38', such as is produced by a saw tooth wave generator, will cause the potential on the control electrode 24 to become less positive which will deflect or shield the electrons from the anode 25 causing a sharp increase in potential across the load resistance 35 which may be used for many purposes, such as, controlling the energization of a relay, or triggering a tube to discharge a condenser, The increase of potential at load resistance 33 may be applied through a portion of resistance 39 to the second control electrode 25 increasing its potential sufiiciently to cause the electrons to fiow from the cathode 23 to the anode 2'! which will cause a sharp voltage drop in its load resistance 45] which may be utilized to control other circuits.

As the voltage on grid of tube 38' decreases or when the saw tooth voltage is triggered the potential of the electrode 25 is restored to its less 4 positive condition and the potential of the electrode 24 is restored to its more positive condition. The above operation will be repeated for each wave in a series of saw tooth waves applied to the grid of tube 33' to be more fully explained later.

Thus from the above description it will be seen that this off and on electron relay device opens or closes an electron path through the tube, thereby giving a quick cut-off or abrupt current change.

Referring to Figure 5 the apparatus H] for collecting the fragments of several messages so that they may be transmitted on a single carrier comprises a condenser d1 charged through an adjustable resistance 42 from a positive potential source as indicated. By movement of the switches 43 and Ml another condenser 55 may be charged through resistance .5 from a high positive potential source to change the interval for the voltage to build up to a certain value. Charging current control may also be obtained by varying the resistances through the movable contacts All and 48 to give close adjustments. The condenser M or 45 may be discharged through the trigger tube 49 when the voltage builds up to a predetermined value to be explained later. The condenser t! or $5 may be repeatedly charged from the source of potential and discharged through the trigger tube 39 to produce successive saw tooth voltages or saw tooth waves in a manher well known to those skilled in the television art.

When the condenser 61 or 45 becomes charged, depending upon which switch contacts are closed, the saw tooth voltage wave in the plate circuit of tube 45 is impressed on the grid 59 of the multi-unit amplifier tube 5! through an adjustable contact 52 on the voltage dividing resistance 53, and by the adjustment of contact 52 the amplitude of the saw tooth wave may be controlled. The outputs of the amplifier tube 5i supplied to the load resistances 55 and 55 will gradually increase the potential on the grids 56, Hand 58 of tubes 59, 50 and 5! respectively. Tubes 59, 55 and 5! are biased so that maximum current through their load resistances will be at difierent intervals for a gradual increase of potential on their grids. That is, tube 55 is biased so that the current through the load resistance 62 will be approximately maximum value after a short interval of time with no appreciable "change of current in the tubes and 5! during this interval. In tube 50 having a greater negative bias, current will become approximately maximum value through its load resistances 63 after a greater interval of time, and in tube 5i, having the largest negative bias, the current through its load resistance 55 will become maximum value a short interval of time after the peak value of current fiows through the preceding tube 55. These tubes or the bias on the tubes may be arranged to give any desired interval of time before reaching their maximum current flow, or maximum potential drop through their load resistances. Also other tubes may be added at 55 to give a greater number of intervals of the time for the duration of one saw tooth voltage wave.

The large current through the load resistance 52 causes a voltage drop to be applied to the control electrode '57 of the oil and on electron relay tube 68. This change lowers the potential on the electrode 6! below the potential on the anode 59 which causes, first/an increase of potential on control electrode I through a portion of the resistance II and adjustable contact I2. The increase of potential on electrode I0 to approximately the same potential as that of anode I3 will permit the electrons to flow from the cathode to the anode I3 causing a drop in potential in the load resistance 74 which is applied to the grid I5 of tube 4 thus blocking the electrical signals from the microphone I during the time current is flowing through the load resistance 14; second, the potential change on electrode 61 causes the deflection of the electrons from the anode 59 thus raising the potential at the load resistance I6 which is applied to the grid 11 of the amplifier tube 5 rendering this tube operative to the signals produced by the microphone 2.

A short interval after the current in tube 59 has reached its peak value the amplifier tube 60 will function to increase the current flow in load resistance 63 and reduce the current flow in resistance 64 thereby lowering the potential on the control electrode I7 and increasing the potential on the electrode I8 of the off and on relay tube I9. This tube will produce an increase of current in load resistance 80 to cause a decrease of potential on the grid 8I of tube 5 thus rendering this tube inoperative to the electrical signals from the microphone 2, and at the same time by the decrease of current in load resistance 82 it will increase the potential on the grid 83 of tube 6 rendering this amplifier responsive to the electrical signals produced by the telegraph instru ment 3.

The signals from the telegraph instrument 3 i will continue until the current in tube BI reaches approximately its peak value, whereupon the voltage drop developed across the load resistance 65 and applied to the control electrode 84 of tube 85 will prevent electrons from flowing to the anode 86, thus increasing the potential on the control electrode 81, which will produce a voltage drop at the load resistance 88 which is applied through coupling condenser 89 to the grid 90 of the modulation amplifier 1 to develop a high amplitude signal or synchronized pulse to control the receiving stations to be explained later. The high positive potential developed at the load resistance 9| is applied through coupling condenser 92 to the grid of the trigger tube 49. This high potential pulse causes tube 49 to become conductive thereby discharging the'condenser M and restoring the apparatus and associated circuits to their normal condition or starting point to thereafter continually repeat the same operations. The anodes of the different amplifiers 4, 5, and 6 are connected in parallel through condenser 93 to the grid 90 of the modulation amplifier I. Thus by rendering the individual amplifiers inoperative for certain definite periods of time the electrical communication signals may be intermittently modulated on a single carrier.

From the above description it is shown that the message distributor divides and collects parts of different communications and modulates them intermittently on a carrier; this system is not limited to three communications but there may be more depending upon the frequency of the saw tooth wave generated, which may be several times higher than the frequency of speech communication.

With reference to Figure 6 I have shown mechanism for increasing the frequency of signals such as those developed by the microphone or telegraph instruments by first recording them on a moving film having a c ting of fluorescent material and then reproducing these signals by mechanism or a scanning device moving in the reverse direction. Instead of the film, wires may be employed with magnetic devices for recording and reproducing the signals. The film 94 may be of translucent material provided with a coating of fluorescent material activated by light from a conventional glow lamp or a lamp may be used with ultraviolet light predominating. In place of the glow lamp a light valve similar to that shown in my application Serial #306,537, filed November 28, 1939, now Patent No. 2,309,393, issued Jan. 26, 1943, may be used.

The reducing mechanism consists of a container or a light proof box 95 shown with one side removed for clearness, having an endless film 94 coated with fluorescent material and arranged to be rotated downward past the recorder or glow lamp I5 for recording a message on the film. Another glow lamp I6 is behind the glow lamp I5 in Figure 6, and, illustrated in Figure '7. This lamp is for recording a. second message on the film 94. As previously explained in connection with Figure 1 the microphones 2 and 3 through the amplifiers 5 and 6 and switches I3 and I4 may actuate the glow lamps I5 and I6 respectively in accordance with the messages to be transmitted. The glow lamps l5 and I6 may be provided with caps each having a very narrow slot exposed to the film for recording the changes of light intensities on the film in the form of variable intensity sound tracks or variable brilliancy of the fluorescent material as illustrated at 96 and 91 in Figure '7..

Back of the film 94 is a scanning mask screen 98 arranged to be rotated in the opposite direction to that of the film and provided with small projecting light valves IN and I02 having a narrow slot to project only parallel rays of light toward the film. These light valves or light ray control members I04 and I02 are rotated one at a time past the lamp 99.

The film and scanning screen may be divided into sections or framesas shown by the horizontal lines I00 in Figures 7 and 8. The light valve- IOI projecting light to one sound track will appear in every other frame in the scanning screen, and the light valve I02 for the other sound track will appear in alternate frames or fields.

The lamp 99 and lens I03 are located in a separate light proof compartment being approximately the height of one frame. As the film is moving downward and the scanning screen is moving upward at the same time, light from the lamp 99 will be projected alternately to the sound tracks 96 and 91 to increase or intensify the variable glow in the fluorescence material so that light rays alternately reflected by the mirrors I04 and I 05 from the sound tracks may actuate the photo cells I 8 aind I8 respectively.

The motor I06 drives the sprocket wheel I01 to rotate the film in a clockwise direction. The sprocket wheel I08 is driven by the wheel I01 but in the opposite direction. One complete revolution of the sprocket wheel moves the film a distance of four frames. Therefore some means for synchronizing the movement of the film with the frequency of the saw tooth wave must be provided. In order to accomplish this feature I provide a relay I09 located in the box 95 and operated at the same time that the message distributor mechanism I0 is restored to its starting condition to govern the movement of the scan ning screen.

As previously explained in connection with Fig 7. ure 1, when transmitting only two messages, a slow rate of change from one message to another message may be employed. That is, the frequency of the saw tooth wave may be adjusted by the switches 53 and M and the associated resistances to produce any desired frequency such that will conform to the movement. of the film which may be maintained at substantially the speed of television pictures or approximately thirty frames per second.

Tubes 59 and 83 will be inoperative by opening the switches Hi and Hi when using the film for reducing the interval of the parts or fragments of messages.

The film is rotated inside the box 95 for ageing or for restoring it to its normal conditions. The fluorescent material coating may have a short decay time and the film may be run over idle pulleys to give greater time before being again exposed to the glow lamp.

The operation is as follows: The positive pulse that triggers the tube 49 Figure 5 is also applied to the grid of tube Hi1 through the switch I. The switch ill is thrown to the off position when the reduction mechanism I1 is not employed. This impulse supplied to the grid of tube iiil permits sufficient current to flow through relay Iilb for operating its armature to move the pin ii 2 out of engagement with the pin H3 in the sprocket wheel N18. The scanning screen 98 is driven at such speed that the screen will travel the distance of two frames in slightly less time than the duration of one saw tooth voltage wave. In that case the pin H3 in sprocket wheel I08 would engage the pin H2 on the armature of relay we thus holding the scanning screen momentarily through the friction clutch indicated by the circle II t. The operation of the relay I09 disengages the pins and permits the scanning screen to move again the distance of two frames whereupon the pin H2 will momentarily engage the pin i I5. Thus the movement of. the scanning device will be automatically synchronized with the saw tooth voltage waves.

With reference to Figure 9 showing a receiving station, the antenna i2ii receives the carrier signals from the transmitter antenna I2 and transfers them to a radio frequency amplifier I2i. An electrical oscillator I22 reacts with these signals in the first detector stage I23 on the super heterodyne principle to produce an; intermediate frequency which is supplied to the intermediate stage I2 3. After suitabl amplification the sound signals and the synchronizing signals are de tested at 25 and the sound signals are supplied to the power amplifier I26, I21 and I2$one at a time. Aftersuitable amplification lnthese power amplifiers the sound signals may be sup.- plied to loud speakers 629,138 and Fail, or a telegraph instrument may be employed at I3 I.

The control or synchronizing signals are applied to the synchronizing frequency amplifier $32 and after suitable amplification they are. supplied to the message distributor I33 to control the periods of the saw tooth voltage waves developed therein to be explained later.

Sound signals, telegraph signals and control signals may be detected at I25. While I have shown three separate paths for the reception of communication signals, several more separate communications may be intermittently received where the rate of change from one message to another message is very high. In the reception of only two messages where the normalinterval for each message has been reduced and it is required 8, that these messages be expanded for conveying intelligence, then the sound signals from the detector I25 are applied through switches I35 and I35 to the recorder or glow lamps I36 and I31 for registering variable light intensities on a movable memory or fluorescent film. The variable light intensities registered on the film are separated into equal parts in the interval expanding or recording and reproducing mechanism I38 and reproduced at I39 and it as electrical signals and at their normal interval where they are fed through switches I I8 and I [9 to the amplifiers l2! and I28.

Referring to Figure 10 the apparatus I33 for separating the fragments of several messages into separate and distinct messages similar to the apparatus It at the transmitter, comprises a condenser I SI charged through an adjustable resistance M2 from a positive potential source as indicated. By movement of the switches I43 and I44 another condenser I45 may be charged through resistance I46 from a high positive potential source to change the period for the voltage to build up to a certain value. Charging current control may also be obtained by varying the resistances through the movable contacts I41 and I48 to give close adjustments. The condenser MI or MS may be discharged through the trigger tube Hi9 when the voltage builds up to a predetermined value to be explained later. The condenser IM or 55 may be repeatedly charged from the source of potential and discharged through tube Hill to produce a series of saw tooth waves in a manner well known particularly in television.

When the condenser MI or I45 becomes charged, depending upon which contacts are closed, the saw tooth voltage wave in the plate circuit of tube I 39 is impressed on the grid Hit of the multi-unit amplifier tube IBI through an adjustable contact I52 on the voltage dividing resistance I53, and by this adjustment controlling the amplitude of the saw tooth wave. The outputs of the amplifier tube I5i supplied to the load resistances 555 and I55 will gradually increase the potential on the grids H36, H31, and I58 of tubes I53, Hit and Iii! respectively. Tubes I59, sec, and It I' are biased so that maximum current through their load resistances will be at different intervals for a gradual increase of potential on their grids. That is, tube I59 is biased so that approximately maximum current will flow through the load resistance I62 after a short interval of time with no-appreciable change of current in the tubes ltd and lfil'during this interval. In tube I; having a greater negative bias, current will become approximately maximum value through its load resistance I83 after a greater or second interval of time and in tube ISI having the largest negative bias, the current through its load resistance it will become approximately maximum value a short interval of time after the peak current flow through the preceding tube it. These tubes or the grid bias on the tubes may be arranged. to give the desired voltage drops in their plate circuits at predetermined intervals of time corresponding to the intervals for intermittent messages being transmitted. Other tubes may be added at its to give a greater number of communications that may be received over a single carrier, or a greater number of intervals for the duration of one saw tooth voltage wave.

The large current through the load resistance Hi2 causes a voltage drop to be applied to the control electrode I65 oi the oii and on relay tube Iiil. This change lowers the potential on the electrode I66 below the potential on the anode I68 which causes first, an increase of potential on control electrode I69 through the resistance I and adjustable contact I'll. The increase of potential on electrode I69 to approximately the same potential as that of anode I12 will permit electrons to flow from the'cathode to the anode I12, causing adrop in potential in the load resistance I13 which is applied to the grid I14 of tube I26 thus blocking the electrical signals from the second detector I25 during the time current is flowing through the resistance I13; second, the potential change on the control electrode I66 causes the deflection of the electrons from the anode I68 thus raising the potential at the load resistance I15 which is applied to the grid I19 of the amplifier tube I21 rendering this tube operative to the signals from the second detector.

A short interval after the current in tube I59 has reached its peak value the amplifying tube I68 will function to increase the current flow in load resistance I 63 thereby lowering the potential on the control electrode I11 of tube I18. This change lowers the potential on the electrode I11 below the potential on the anode [19 which causes an increase of potential on the control electrode I88 to approximately the same potential as that of anode I'8I which will permit electrons to flow from the cathode to the anode I8I'causing a drop in potential in the load resistance I 82 which is applied to the grid I83 of the power amplifier tube I21, thus rendering this tube inoperative to the signals from the second detector during the time that peak current is flowing through the resistance I82. The potential change on the control electrode I11 causes the deflection of the electrons fromthe anode I19 thereby raising the potential at the load resistance I84 which is applied to the grid I85 of the amplifier tube I28 rendering this tube responsive to the signals from the second detector.

The signals from the second detector will continue to be amplified in tube I28 until the current in tube IBI reaches approximately its peak value, whereupon the voltage drop developed across the load resistance I64 and applied to the control 10 'arate message. The tube I32 is for controlling the duration of the saw tooth wave and it may be biased so that the sound signals will not produce plate current but it will respond to the synchronizing pulses transmitted at the end of each saw tooth wave. The synchronizing signals applied to the grid I95 may be amplified in the anode circuits and supplied through the coupling condenser I96 to the grid I94 of the trigger tube I49.

The period of the saw tooth wave or the interval of time between synchronizing pulses is arranged to be slightly shorter than the time required for the off and on relay tube I81 to control the discharge of the condenser MI; and in-this manner the receiving stations are synchronized with the transmitter. To explain more specifically; the receiving stations are synchronized by utilizing the high amplitude impulses transmitted over the carrier at regular intervals to control the duration of each saw tooth voltage wave. That is; the impulses are employed to regularly restore the condenser charging apparatusand associated circuits to their start charging condition.

electrode I86 of tube I81 will prevent electrons from flowing to the anode I88 thereby increasing the potential'on the control electrode I89 which will produce a voltage drop at the load resistance I98. The voltage drop at resistance I99 may be applied to the grid I9I ofthe power amplifier I28 to hold the tube momentarily non-responsive to sound signals while restoring the saw tooth wave generating circuits to their starting condition. The increased potential developed at the load resistance I92 may be applied through the coupling condenser I93 to the grid I94 of the trigger tube I49. This voltage impulse causes, the tube I49 to become conductive thereby discharging the condenser I4! and restoring the saw tooth generating apparatus and associated circuits to their starting condition. However; upon the reception of synchronizing signals the tube I81 will not control the discharge of the condenser I4I. This tube will only function during the absence of synchronizing signals resulting from fading or when tuning between stations or the receiver may be tuned to a certain carrier waiting for signals.

Sound and synchronizing signals are detected at tube I25. The sound signals may be applied to the control grids of the power amplifier tubes I26, I21, and I28 in parallel. Thusit is shown that each one of the speakers will be intermittently actuated by electrical signals from a sep- From the above description it is shown that the message distributor in the receiving station sepe arates and, collects the parts or fragments of a plurality of different messages received intermittently over a single channel into several separate and distinct messages.

With reference to Figure 11 I have shown mechanism for expanding the interval or decreasing the frequency of electrical signals produced by two separate and distinct messages by recording them on a moving fluorescent coated film, through the action of a scanning screen or device moving in the opposite direction.

The mechanism shown in Figure 11 is very similar to that explained in connection with Figure 6. The film may be of translucent material provided with a coating of fluorescent material activated by light from a conventional glow lamp, or a light valve similar to' that shown in my above mentioned application may be used.

The expanding mechanism comprises a container or light proof box I98, shown with one side removed for clearness, having an endless fluorese cent coated film I91 arranged to be rotated downward past the reproducer or photo cell I39. The glow lamp I36 is for recording a message on the film I91 through the action of the scanning screen I99 rotated in a direction reverse to that of the film I91 but at approximately the same speed.

Another glow lamp I31 is directly back of the lamp I36 and as illustrated in Figure 13 is for recording a second message on the film I91.

The film and scanning screen may be divided into sections or frames as shown by the hori zontal lines 209 in Figures 12 and 13. The glow lamp I36 through the action of the rotating mirrors 28! projects light to the film forming one sound track 292 in all frames as illustrated in Figure 12; and the glow lamp I31 through the action of the rotating mirrors 293 projects light to the film forming a second sound track 284 in all frames. v

The revolving scanning screen I99, back of the film I91, is provided with small reflecting mirrors 29I and 293 rotated one at a time, past the film to reflect light from the glow lamps to the film. As the film is moving downward and the mirrors on the scanning device are moving upward at the same time variable intensities of light from the glow lamps will be recorded on the film in two separate and continuous sound tracks. That-is;

each mirror will spread the light variations over a spaceof two frames on the film.

The lamp 2&5 in a separate compartment, located below the recording mechanism, is for projecting light to the sound track 262 to increase .or intensify the variable glow of the fluorescent material so that the increased glow from the sound track may actuate the photo cell its to reproduce one of the messages. Another lamp directly back of the lamp 2&5 is for projecting light to the second sound track to increase the glow in this track to actuate the photo cell ME for reproducing a second message.

Themotor 2% drives the sprocket wheel Zil'l' to rotate the film in a clockwise direction. lhe sprocket wheel 28? drives the sprocket wheel 26% in a counterclockwise direction. One complete revolution of the sprocket wheels moves the film a distance of four frames. In order to synchro nize the movement of the film with the frequency of the saw tooth wave and also with similar operations at the transmitter I provide a relay are located in the box 98 and operative each time that the synchronizing impulses restore the distributor mechanism F33 to its starting condition.

In Figure the tubes I52, lii'l, and 526 will be inoperative by opening the switches 2.5% 2'! i, and H2 when using the mechanism of Figure ii.

The film is rotated inside the light proof box I98 for ageing or for restoring it to its normal condition. The fluorescent material coating may have a short decay time and the film may be run over idle pulleys to give greater time before being again exposed.

The operation is as follows. The synchronizing pulses after suitable amplification in tube I32 are also applied to the grid of tube 2 i through the switch 2 M. The switch is opened when more than two conversations are being received or when mechanism I33 is idle. This impulse supplied to the grid of tube 213 permits suificient current to flow through relay 299 for operating its armature to move the pin 2M out of engagement with the pin 2 i5 in the sprocket wheel .293. The scanning device E99 is driven a distance of two frames in slightly less time than the interval between synchronizing pulses. Therefore, the pins 2H5 and M6 would engage the armature pin 2M alternately to hold or slow the movement of the screen i539 momentarily through the friction clutch indicated by the circle 25?. The operation of relay 2%39 at the end of each two frames :disengages the pins and permits the scanning device to continue its movement. Thus the movement of the scanning device will be automatically synchronized with the scanning device at the transmitter.

In the various circuits shown and described I have simplified the drawings by indicating the source of potential by a positive or negative sign. Also I have omitted the heater element from the various tubes. 7

The embodiments of the invention which have been given herein are illustrations of how the various .features may be accomplished and of the principles involved. It is to be understood that the invention contained herein is capable of em bodiments in many other forms and adaptations, without departing from the spirit of the invention and the scope of the appended claims.

Having thus described my invention, I claim:

'1. In .a multiplex communication system, a transmitter, means at said transmitter to produce a carrier wave, means at said transmitter to produce a first series of successive saw tooth waves, including control signals to terminate the waves, means to select different recurrent periods of time in said saw tooth waves for controlling the transmission of different signals in the recurrent periods, said last means comprising apparatus and suitable circuits to select amplitude measurements in the said saw tooth waves for both initiating and'terminating each of the said periods, means to transmit signals representative of difierent messages and said control signals modulated on said carrier wave during a number of the said recurrent periods, a receiver, means to receive said signals, means at said receiver to produce a second series of successive saw tooth waves under the control of said control signals, means to select recurrent periods in the said second series of saw tooth waves corresponding to said recurrent periods at the transmitter for con trolling the reception of difierent signals in the said recurrent periods, said last means comprising a message signal amplifier for each of the said recurrent periods, and a plurality of relay tubes under control of said second series of saw tooth waves to interrupt substantially current through the several relay tubes in successive rotation for controlling said amplifiers to reamplify said signals representative of difierent messages in successive rotation.

22. In a multiplex communication system, a radio transmitter, means to produce a carrier wave, apparatus and suitable circuits associated with the said transmitter to produce a series of recurrent saw tooth Waves, a source of current, a plurality of relay tubes each having at least an anode and a cathode connected to said source of current and an electron deflecting electrode controlled by amplitude measurements in each wave of the said saw tooth waves to substantially interrupt the anode cathode current in the several relay tubes in successive rotation, thereby, selecting a number of recurrent periods in .said saw tooth waves, means to modulate said carrier wave with fragmentary portions of signals representative of a difierent message in each of the said recurrent periods, said last means comprising a modulation amplifier, and a number of message signal amplifiers, one for each recurrent period, connected in parallel to said modulation amplifier under control of said relay tubes, and mechanical switching means for adjusting said apparatus to vary the number of saw tooth waves in a given time, thereby varying the number of fragmentary portions of the signals in each of the said messages transmitted in a given time.

3. In a multiplex communication system, a radio transmitter, means to .produce a carrier wave, apparatus and suitable circuits associated with the said transmitter to produce a series of successive saw tooth waves, a source of current, a plurality of relay tubes each having at least an anode and a cathode connected to said source of current and an electron deflecting electrode controlled by amplitude measurement in each wave of the said saw tooth Waves to deflect the electrons away from the anode to interrupt substantially the anode cathode current in the several relay tubes in successive rotation, thereby, selecting a number of recurrent periods in said sawtooth waves, and means to modulate said carrier wave with fragm ntary portions of signals representative of a different message in each of the said recurrent periods.

i. In a multiplex communication system, a radio transmitter, means at said transmitter to produce a carrier wave, apparatus and suitable 13 circuits associated with said transmitter to produce a first series of successive saw tooth waves including synchronizing signals, a source of current, a plurality of relay tubes each having at least an anode and a cathode connected to a source of current and an electron deflecting electrode under control of said sawtooth waves for deflecting the'electron away from the anode to substantially interrupt the anode cathode current in the several relay tubes in sequence, thereby, selecting a number of recurrent periods in the sawtooth waves, means to modulate said carrier wave with signals representative of a difierent message in each of the said recurrent periods and with synchronizing signals in another recurrent period, means to transmit said modulated carrier waves, a receiver, means to receive said modulated carrier wave, apparatus and suitable circuits associated with said receiver to produce a second series of successive saw tooth waves under the control of said synchronizing signals, a second source of current, other relay tubes each having at least an anode and a cathode connected to said second source of current and an electron deflectingelectrode under control of said second series of sawtooth waves for deflecting the electrons away from the anode to interrupt substantially the anode cathode current in the said other relay tubes in sequence, thereby, selecting a number of recurrent periodsin said second. series of sawtooth waves corresponding to. the selected periods at said transmitter, and means to demodulate the received carrierwave to produce message signals in each recurrent period in said second series of saw-tooth waves representative of a different one of said messages.

5. In a multiplex communication system, a radio station for transmitting a number of mes sages in successive rotation over a common path, means at said station to produce a series of successive saw tooth waves, including control signals for terminating the waves, message recording and reproducing means under the control of said control signals comprising a movable film coated with material sensitive to light and glow lamps for directing light rays toward the film for recording signals representative of a number of messages in narrow strips forming sound tracks thereon, with a source of light and light ray control members movable in a direction opposite from that of said film to direct other light rays from said source of light toward the said sound tracks, devices responsive to the recordings in said sound tracks to reproduce signals for each of the said messages in spaced periods of time, and a message distributor under the control of amplitude measurements in each of the said saw tooth wave to select recurrent periods of time for transmitting the said reproduced signals for a difierent one of said messages in each recurrent period.

6. In a communication system, a'transmitter station, means at said station to produce a series of successive saw tooth waves including synchronizing signals to terminate the waves, message recording and reproducing mechanism to record message signals representative of a number of messages and to reproduce the signals at a greater speed relative to the speed of recording for intermittently grouping the signals for each of the several messages, a message distributor under the control of said saw tooth waves to control the periods of time for transmitting the grouped signals in each of the said messages, a receiver station, means at said receiver station to produce another series of saw tooth waves under the control of said synhronizing signals, a m'essagedistributor at said receiver station under the control of said another'series of saw tooth wave to control the periods of time for the reception of the grouped signals for each of the said messages, and another message recording and-reproducing mechanism for recording said grouped signals and to reproduce the signals at a slower speed relative to the speed of recording for uninterrupted reception of the said messages.

7. In a communication system, a radio transmitter provided with apparatus and associated circuits to produce a series of successive saw tooth waves, a rotatable fluorescence coated film associated with said transmitter, a number of glow lamps to direct light rays of variable intensity corresponding to signals representative of a number of messages toward said film for producing several variable glow sound tracks thereon, a source of light, light ray control members movable in an opposite direction relative to said film to direct light rays from said source of light toward said sound tracks to intensify the variable glow, a photo electric device for each sound track sensitiveto the intensified glow for reproducing said signals intermittently, means to produce a carrier wave, and a plurality of electron deflectmg relay tubescontrolled by said saw tooth waves to select a number of recurrent periods for modulating said carrier wave with said reproduced signals representative of a difierent one of said messages in each recurrent period.

8. In a communication system, a radio station, means at said station to produce a carrier wave, means at said station to produce a series of successive sawtooth waves, a plurality of relay tubes under control of said sawtooth waves to select a number of recurrent periods, means to modulate said carrier wave with fragmentary portions of message signals representative of a different message in each recurrent period, said last means comprising a modulation amplifier, and a number of message signal amplifiers, one for each recurrent period, connected in parallel to said modulation amplifier under control of said relay tubes.

9. In a communication system, a radio station,

means at said station to produce a series of successive saw tooth waves, a plurality of relay tubes under control of said saw-tooth waves to select a number of recurrent periods, means to receive a modulated carrier wave, means to demodulate said carrier wave and to select in each recurrent period fragmentary portions of message signals representative of a different message, said last means comprising a demodulator, and a number of message signal amplifiers, one for each recurrent period, connected in the output circuit of said demodulator under control of said relay tubes.

10. In a communication system, a radio receiver, apparatus and suitable circuits associated with said receiver to produce a series of successive saw tooth waves under the control of received synchronizing signals, a source of current, a plurality of electron off and on relay tubes each having at least an anode and a cathode connected to said source of current and an electron deflecting electrode controlled by amplitude measurements in each wave of the said saw tooth waves to substantially interrupt the anode cathode current in the several relay tubes in successive rotation,

thereby, selecting a number of recurrent periods in said sawtooth waves, means to receive a modulated carrier wave, means to demodulate said carrier wave and to select in each recurrent period 15 fragmentary portions of message signals representative of a different message, said last means comprising a demodulator, and a number of message signal amplifiers, one for each recurrent period, connected in the output circuit of said demodulator under control of said relay tubes.

11. In a communication system, a transmitter to produce a carrier wave, means associated with said transmitter to produce a series of successive saw tooth waves including control signals for terminating the waves, and a message distributor comprising a number of relay tubes each having at least an anode and a cathode connected to a source of current, and an electron deflecting electrode under the control of said saw tooth waves for deflecting the electrons away from the anode to interrupt current flow in the several relay tubes in sequence, thereby, selecting a number of recurrent periods in the said saw tooth waves for modulating said carrier wave with signals representative of a different message in each recurrent period.

12. In a communication system, means to produce a series of successive saw tooth waves under the control of received synchronizing signals, a message distributor comprising a number of electron deflecting tubes each having at least an anode and a cathode connected to a source of current, and an electron deflecting electrode to deflect electrons away from the anode for interrupting current flow in the several deflecting tubes in sequence, said tubes adapted to allot different periods-of time in successive rotation to portions of received signals representative of a number of messages and said control signals.

JOHN H. HOMRIGHOUS.

rini nnnnons orrni) The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Gibboney Nov. 17, 1891 Hammond Mar. 24, 1925 Mathes Feb. 23, 1926 Hartley Apr. 12, 1927 Parker Nov. 8, 1927 Bryant Feb. 26, 1929 Schapira June 9, 1931 Hough Nov. 1, 1932 Coyle Sept. 26, 1933 Baird Feb. 6, 1934 Nicolson Nov. 19, 1935 Riggs July 21, 1936 Zworykin Feb. 14, 1939 Samuel June 20, 1939 Henroteau Feb. 27, 1940 Roberts Apr. 23, 1940 Goldmark June 4, 1940 Goldmark June 4, 1940 Branson Sept. 30, 1941 Skillman Nov. 18, 1941 Wolf Dec. 9, 1941 Von Felgel-Farnholz Dec. 30, 1941 Wilson Mar. 24, 1942 Goldsmith May 5, 1942 Bruce Nov. 10, 1942 Hammond July 30, 1946

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