US2568336A - Cathode-ray tube commutator system - Google Patents

Description

W. D. HOUGHTON CATHODE RAY TUBE COMMUTATOR SYSTEM Sent. 18. 1951 3 Sheets-Sheet 5 Filed April 9, 1947 TIME - 5mm I wax 010mm FIRST REVOLUT/Op TIME- INVENTOR. WILLIAM D. HOUGHTON ATTORNEY Patented Sept. 18, 1951 asses CATHODE-RAY TUBE COMMUTATOR SYSTEM William D. Houghton, Port Jefferson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application April 9, 1947, Serial No. 740,375

14 Claims. 1

This invention relates to a multi-channel si nalling system, and more particularly to a multichannel printer telegraph system employing a telegraph code of the multi-unit type in which the units in each letter or symbol of the code are of equal length. Examples of such telegraph printer codes are the conventional 5-unit and 'l-unit codes.

The invention is particularly applicable to a system employing pulses which are short compared to the time intervals between pulses. In such a system, there is transmitted for each frame or cycle of operations a train of pulses preceded or followed by a synchronizing pulse. The pulses in each train are assigned to different channels. The interval between two consecutive synchronizing pulses is divided into equal time periods, and the different time periods are respectively assigned to different channels.

A better understanding of the broad general principles of transmission of the multi-channel system of the invention may be had b referring to Fig. 1 which shows a train of short pulses transmitted for each frame or cycle of operations, as measured from the start or beginning of one synchronizing pulse to the start or beginning of the succeeding synchronizing pulse. The synchronizing period or time interval for each cycle of operations includes a synchronizing pulse P and a series of sequentially appearing channel pulses l to '7 inclusive, assuming the case of only seven channels. The different pulses l to '7 represent transmission from different channels. Each channel has assigned to it a time interval which occurs at a difierent time from those assigned to the other channels but the different time intervals assigned to the different channels are equal. The solid line pulses indicate the position within the assigned channel intervals that the channel pulses would take when sending a mark signal, and the dotted line pulses indicate their respective positions within these same assigned channel intervals when sending a space signal. It will thus be seen that the channel pulse (which can be called the intelligence carrying pulse) may occupy one of two positions within the assigned channel interval, depending upon whether the pulse is to represent a mark or space signal. Preceding and succeeding frames or cycles of operation will include similar trains of pulses, each train including a synchronizing pulse followed by the seven channel pulses, in the assumption that seven channels are employed. The synchronizing period is identical for all trains of pulses.

In the printer multi-channel system of the invention, the speed of operation of all pick-ups or auto heads are synchronized, as will appear in more detail hereinafter, and the repetition rate for the channel pulses is determined by the main sweep frequency which also controls the speed of the tape in the printer pick-ups or auto heads.

Briefly stated, the present invention involves a novel type of cathode ray tube which electronically scans a plurality of sets or pairs of targets for producing the channel pulses. The pairs of targets are spaced apart and arranged in a circle at a location corresponding to that of the fluorescent screen in the conventional cathode ray tube. The electron beam is caused to traverse a circular path and to sequentially pass over the different sets or pairs of targets. The different pairs of targets are allotted to different channels. Each time the electron beam moves across a set or pair of targets, there is generated a pulse. The pulse may occupy one of two positions and is generated when the electron beam leaves one of the targets of a pair, but the position of the associated pick-up relay for that particular channel determines whether the pulse is generated when the electron beam leaves the first or the second target of that pair. The targets of each set or pair are so arranged that the beam crosses first one target and then the other. The position of the pick-up relay is a function of whether the pick-up is scanning a mark or space signal element. The auto heads or pick-ups for the different channels are driven by their respective motors at a speed which is synchronized with the repetition rate of the scanning sweep of the tube. Stated in other words, the driving voltage for the pick-ups or auto head motors is made synchronous with the main sweep or scanning frequency, and each pick-up or auto head is retarded in phase slightly, by electrical or mechanical means well known in the art, so that at the time of scanning the pick-up or auto head will be in the middle of its mark or space signal element.

A more detailed description of the invention follows, in conjunction with a drawing, wherein:

Fig. 1 illustrates a series of pulses representative of the train of pulses occurring for the output of the transmitter of the invention, for each frame or cycle of operations;

Fig. 2 is a diagrammatic view, partly in section, of a cathode ray tube and circuit therefor in accordance with one form of the invention;

Fig. 3 is a view of the target end of the beam tube of the invention as seen from the cathode or gun end;

Fig. 4 is a diagrammatic view, partly in section,

focussing anode.

3 of the target end of the beam tube and the circuit for producing pulses;

Fig. a is a detailed view showing a single pair or set of targets in relation to the path of travel of the electron beam and to the electron collector electrode;

Fig. 5b graphically illustrates the voltage wave form developed across the load resistor I3 of Fig. 4;

Fig. 5c graphically ilustrates the pulses produced by differentiation of the waveform of Fig. 5b;

Fig. 6 graphically illustrates a modified voltage waveform which may be applied to the deflection plates of the cathode ray tube of the invention;

Fig. 7 illustrates the sweep circuit which may be used to apply the waveform of Fig. 6 to the deflection plates of the beam tube, and

Fig. 8 illustrates a modified form of target construction for the beam tube when using the defleeting voltage of Fig. 6.

Fig. 2 shows a cross section of the cathode ray tube of the invention in association with part of the circuit employed 'in the transmitter arrangement. This cathode ray tube comprises a glass envelope I which encloses an electron gun I shown within the dashed line box. This gun I is well known in the art and comprises the usual cathode, a multiplicity of grids and an electron Two pairs of deflecting plates 28 and 28' are used to cause the electron beam to traverse a circular path over a group of spaced sets or pairs of targets 9, '9. One pair of deflecting plates 28 is fed by a sine wave oscillator 2 through leads 4 and 5, while the other pair of deflecting plates 28' are fed from the sameoscillator 2 at a 90 degree phase relation through a phase shifter 3 over leads 4 and B. The targets 9 and 9' of each channel are arranged as shown in more detail in Figs. 3, 4 and 5a. The target 9 of each pair or set is located between the target 9 of the same set and the electron gun I and slightly overlaps the target 9', as shown. One set of targets 9 and 9' is allotted to each telegraph channel in the system. A common electron collector disk I9 is placed in back of all of the targets 9 and 9' to collect those electrons which do not strike the channel targets.

A frequency divider II is connected between the sine wave oscillator 2 and the lead I22 eX- tending to the pick-up motors of the system of Fig. 4. Such an arrangement enables the pickup motors to be synchronized with respect to the scanning sweep frequency of the electron beam.

Fig. 4 shows the method of connecting the channel targets in a system employing N number of channels.

The transmitter arrangement of Fig. 4 shows a plurality of sets or pairs of targets 9, 9, and associated with each channel a pick-up relay I2, an auto head or pick-up 40 for controlling the operation of the relay I2, and a motor I 2| for driving the pick-up or auto head 49. The various motors I2I for the different channels are connected through individual phase shifters 22 to the lead I22 which extends to the frequency converter II of Fig. 2. By suitable adjustment of the phase shifter 22 associated with each channel, the pick-up for that channel will be in the middle of its mark or'signal element at the time the beam of electrons strikes or scans the set of targets for that particular channel.

All targets 9 of the difierent channels-are connected in parallel to lead I6 by means of connection 30. The other targets 9 of the diiferent channels are connected to the armatures I9 of their respective pick-up relays I2. A common load resistor I3 is connected between the lead I6 and ground, and in circuit with this load resistor is a differentiator circuit comprising a resistor I5 and a condenser I4. The output from the system is taken off from lead M which may extend to a suitable amplifier, in turn, connected to a suitable radio frequency oscillator, not shown. The output from lead M is in the form of D. C. pulses which may be used to modulate a radio frequency transmitter, such as a magnetron. This 100% modulation may be amplitude, frequency or phase modulation.

In explaining the operation of the system of Fig. 4, let it be assumed that the electron beam is striking channel target 9 at point X (note Figs. 3 and 5a), and the beam is being rotated in a clockwise direction along path A. Electrons will then flow to target 9 and. through resistor I3 (Fig. 4) via lead I6. This will cause a negative voltage to be developed across resistor I3 with respect to ground, assuming that negative potential is applied to the electron gun I in a manner employed in many conventional cathode ray circuits.

The negative voltage developed across resistor I3 will remain until the electron beam crosses point Y in Figs. 3 and 5a. That is, the beam leaves target 9 at point Y and electrons flow to target 9. If the pick-up relay I2 is actuated at this time, this armature I9 will engage makecontact I8, and the electrons which strike target 9 will flow to ground through contacts I8 and I9, and the voltage developed across resistor I3 will cease. However, if printer relay I2 is not actuated, this armature I9 will engage contact 20, and electrons which strike target 9' will flow via lead I! and through closed contacts I9 and 20 to resistor I3 via lead I 6. This will cause the negative voltage which was developed across resistor I3 when the electron beam struck target 9 to remain negative when the electron beam crosses point Y. The negative voltage in this case will remain until the electron beam crosses point Z (note Figs. 3 and 5a) at which time the beam leaves target 9 and the electrons flow to collector plate I9 and to ground. When the electron beam leaves target 9', the negative voltage developed across resistor I 3 will cease.

Fig. 5a shows a detail front view of one set or pair of channel targets 9, 9' and the electron collector plate I0 as viewed from the electron gun. The electron beam is indicated by the circle at X and the path of the beam is indicated by the dashed line A. The arrow shows the direction of travel or sweep of the electron beam.

Fig. 5b represents the voltage developed across resistor I3 as the electron beam follows path A. The dashed line curve in Fig. 5b represents the voltage wave which will result when relay I2 is unactuated and contacts I9 and 2!) closed While the electron beam is traversing target 9'. As Will be seen from Fig, 5b, when the electron beam crosses point X at time R, a negative voltage is developed across resistor I3. This negative voltage continues until the beam reaches point Y at time S, assuming that relay I2 (Fig. 4) is energized and operated, in which case contacts I 8 and I9 will be closed. If pick-up relay i2 is unactuated, contacts I9 and 20 will be closed and the negative voltage will remain until the electron beam reaches point Z at time T, at which time the voltage developed across resistor I3 decreases to zero. The duration of the negative pulse across resistor I3 will be equal to the time required for the electron beam to travel from point X to point Y, or from point X to point Z depending upon the condition of relay l2.

The negative voltage developed across resistor I3 is differentiated by condenser l4 and resistor 15 as a result of which sharply peaked voltage impulses occur as shown in the curve of Fig. 50. When relay [2 is actuated, a pulse will appear in the mark position at time S, shown by the solid line curve Fig. 50. When relay [2 is unactuated, the pulse shown in Fig. 5c in the mark position at time S will not appear but a pulse will appear in the space position at time T, shown by the dashed line curve of Fig. 5c. The solid line negative pulse at time R in Fig. 50 appears in the same position regardless of the condition of relay I2, but this pulse is not used in the utilization circuits connected to lead M in Fig. 4.

It will thus be seen that a pulse is formed each time the electron beam sweeps across a pair or set of targets 9 and 9, and the position of the pulse will depend upon the condition of the relay I2 associated with that particular set 01' pair of targets.

The synchronizing pulse may be generated in numerous ways. As an example, it may be generated in circuits external of the cathode ray tube and combined with the channel pulses in the amplifier portion of the system. I prefer to use two closely spaced pulses for synchroniaztion rather than a single pulse which is wider than the channel pulses as shown in Fig. 1, although either kind of synchronization pulses may be used in the transmission system. If two synchronizing pulses are used for each frame or cycle of operations, these should be more closely spaced than the channel pulses. One way of producing these two is to provide two closely spaced targets 8, 8 in the manner shown in Figs. 3 and 4. The spacing between targets 8, 8 is closer than the spacing between any point Z on one set of channel targets and the point Y on a following set of channel targets.

A modification of the invention is shown in Figs. 7 and 8 in which the circular path of the electron beam on path A is made to jump to an inside ring and follow path B. (Note Fig. 8.) This is done by suddenly reducing the amplitude of the sine wave voltage applied to the deflecting plates of the cathode ray tube in such manner that the voltage wave applied to the deflecting plates follows the curve shown in Fig. 6. One way of doing this is shown in Fig.7.

Referring to Fig. 7, the output of the sine wave oscillator 2 is applied to an amplifier 6 and also to a flip-flop gate generator 4. This gate generator produces in lead 5 a square wave voltage of 50% mark and 50% space as shown by waveform 58. The gate 4 may be a self-restoring trigger circuit. The mark time of the square wave 5!! is made equal to the time of one complete cycle of oscillator 2, and the space time of the square wave 50 is also made to be equal to one complete cycle of the oscillator 2. This square wave 5 is applied to lead 5 in order to change the gain of the amplifier B which is located between the oscillator 2 and the phase shifter 3. Thus, for one complete cycle of oscillator 2, the circular beam trace will have one diameter while for the succeeding and preceding complete cycles the circular beam trace will have another diameter.

Obviously, other types of sweep arrangements could be used with the system of the invention to obtain various types of combinations of output pulses.

In using a sweep arrangement as shown in Fig. '7, in which the form of the sweep voltage wave applied to the deflecting plates is like that shown in Fig. 6, the sets of targets for the different channels may have an arrangement like that shown in Fig. 8. The arrangement of Fig. 8 enables the use of more sets of targets than can be provided on a. single diameter path of travel of the electron beam.

Although relatively few channels have been shown in the drawings, it should be understood that as many channels may be used as desired. As an example, it is possible in a large cathode ray tube to provide a hundred or more sets or pairs of targets 9 and 9 within a single envelope and thus connect the targets of a number of such cathode ray tubes in parallel using interlaced sweeping arrangements, as a result of which there may be employed many hundreds and perhaps thousands of channels. In the systems which use the invention, the motor drive for the pick-up or auto heads must be controlled with the sweep frequency so that each printer is in the middle of a baud when scanned by the tube of this invention.

An advantage of the system of the invention lies in the fact that the construction requires relatively few mechanical parts and provides a simple method of multiplexing a large number of telegraph channels.

If desired, more than two concentric rings of target plates could be used in practicing the invention, in which case the gain of amplifier 6, Fig. '7, would be changed to various levels sequentially in order to make the beams scan past one ring and then the other. The number of changes in gain of amplifier 6 would be equal to the number of concentric rings of target plates.

The changes in gain of amplifier 5 could be accomplished by making apparatus 4 of Fig. 7 produce a step wave output voltage. The length of each step would be made equal to the period of time required to scan each ring or in other words equal to the period of 2.

What is claimed is:

1. A commutator cathode ray tube for use in a multiplex system comprising an electron gun, a plurality of physically spaced sets of targets arranged in a circle, each set of targets comprising a pair of plates spaced one behind the other and whose adjacent ends overlap, whereby first one target and then the other target of each set is adapted to be bombarded by the electron beam emanating from said gun as said beam traverses a circular path, and means for causing the electron beam to traverse a circular path whose diameter is the diameter of the circle on which lie said sets of targets, whereby the sets of targets are sequentially bombarded by the electron beam.

2. A cathode ray tube comprising a cathode for producing a stream of electrons, means focussing said stream into a beam, electron deflecting elements, a plurality of physically spaced sets of targets arranged in a circle, each set of targets comprising a pair of overlapping plates spaced one behind the other, and means coupled to said deflecting elements for causing said beam to traverse a circular path whose diameter is the diameter of the circle on which lie said sets of targets.

3. A cathode ray tube comprising a cathode for producing a stream of electrons, means focussing said stream into a beam, electron deflecting elements, a plurality of, physically spaced sets of targets arranged on two concentric circles at one end of said tube, each set of targets comprising a pair of overlapping plates spaced one behind the other, and means coupled to said deflecting elements for causing said beam to alternately traverse circular paths of difierent diameters corresponding to the diameters of said two concentric circles.

'4. A cathode ray tube comprising a cathode for producing a stream of electrons, means for focussing said stream into a beam, a plurality of physicall spaced sets of targets arranged end to end, each set of targets comprising a pair of overlapping plates spaced one behind the other, and means coupled to said deflecting elements for causing said beam to bombard said sets of targets sequentially, whereby first one target and then the other target of each set is bombarded by the beam.

5. In a signalling system, a cathode ray tube having a cathode for producing a stream of electrons, a pair of overlapping targets spaced from and positioned one behind the other, deflecting elements for causing said stream of electrons to impinge on said targets in succession, a relay under control of the intelligence to be sent out over said system, said relay having an armature, a break contact and a make contact in association with said armature, a connection from one target of said tube to said break contact, a connection from the other target of said tube to said armature, a load connected to one of said last connections, and a connection from said make contact to ground.

6. In a signalling system, a cathode ray tube having a cathode for producing a stream of electrons, a pair of overlapping targets, deflecting elements for causing said stream of electrons to impinge on said targets in succession, a relay under control of the intelligence to be sent out over said system, said relay having an armature, a break contact and a make contact in association with said armature, a connection from one target of said tube to said break contact, a connection from the other target of said tube to said armature, a resistor connected to said first connection, a differentiator circuit connected to said resistor for difierentiating the voltage wave developed across said resistor, a connection from said make contact to ground, and means coupled to said diilerentiator circuit for utilizing the output from said system.

7. In a signalling system, a cathode ra tube having a cathode for producing a stream of eletrons, a pair of overlapping targets, deflecting elements for causing said stream of electrons to impinge on said targets in succession, a relay under control of a telegraph circuit, said relay having an armature, a break contact and. a make contact in association with said armature, a connection from said break contact to that target which is first impinged upon by said stream of electrons, means coupled to said connection for utilizing the output from said system, a connection from said armature to said other target, and a connection from said make contact to ground.

8. In a signalling system, a cathode ray tube having a cathode for producing a stream of electrons, a pair of overlapping targets, deflecting elements for causing said stream of electrons to impinge on said targets in succession, a relay under control'of a telegraph circuit, said relay having an armature, a break contact, and a make contact in association with said armature, a connection from said break contact to that target which is first impinged upon by said stream of electrons, a resistor coupled between said connection and ground, a connection from said armature to said other target, a connection from said make contact to ground, a differentiator circuit coupled to said resistor for producing short pulses from the voltage wave developed across said resistor, and means coupled to said differentiator circuit for utilizing the output from said system.

9. In a multi-channel signalling system, a commutator cathode ray tube for use in a multiplex system comprising an electron gun, a plurality of physically spaced sets of targets, one set for each channel, arranged in a circle, each set of targets comprising a pair of spaced plates whose adjacent ends overlap, whereby first one target and then the other target of each set is adapted to be bombarded by the electron beam emanating from said gun, and means for causing the electron beam to traverse a circular path whose diameter is the diameter of the circle on which lie said sets of targets, whereby the sets of targets are sequentially bombarded by the electron beam, a relay in each channel under control of keying mechanism for that channel, said relay having an armature, a break contact and a make contact, means for connecting together all of the break contacts of all said relays and only those targets of said sets which are first bombarded by said beam, a connection between the other target of each of said sets and the armature of the particular relay for that channel, a connection from the make contact of each relay to ground, and a common load impedance connected to said break contacts.

10. In a multi-channel signalling system, a commutator cathode ray tube for use in a multiplex system comprising an electron gun, a plurality of physically spaced sets of targets arranged end to end, each set of targets comprising a pair of spaced plates whose adjacent ends overlap, whereby first one target and then the other target of each set is adapted to be bombarded by the electron beam emanating from said gun, and means for causing the electron beam to bombard said targets sequentially, said sets of targets being assigned to diiTerent channels of said system, a relay in each channel under control of keying mechanism for that channel, said relay having an armature, a break contact and a make contact, means for connecting together all of the break contacts of all said relays and only those targets of said sets which are first bombarded by said beam, a connection between the other target of each of said sets and the armature of the particular relay for that channel, a connection from the make contact of each relay to ground, and a common load impedance connected to said break contacts.

11. In a multi-channel signalling system, a commutator cathode ray tube for use in a multiplex system comprising an electron gun, a plurality of physically spaced sets of targets arranged in a circle, each set of targets comprising a pair of spaced plates whose adjacent ends overlap, whereby first one target and then the other target of each set is adapted to be bombarded by the electron beam emanating from said gun, and means for causing the electron beam to traverse a circular path whose diameter is the diameter of the circle on which lie said sets of targets, whereby the sets of targets are sequentially bombarded by the electron beam, said sets of targets being assigned to different channels of said system, a relay in each channel under control of keying mechanism for that channel, said relay having an armature, a break contact and a make contact, means for connecting together all of the break contacts of all said relays and only those targets of said sets which are first bombarded by said beam, a connection between the other target of each of said sets and the armature of the particular rela for that channel, a connection from the make contact of each relay to ground, circuits for synchronizing the operation of the keying mechanisms in the different channels with the sweep of the electron gun in said cathode ray tube, and a common load impedance connected to said first bombarded targets of said sets.

12. In a multi-channel signalling system, a commutator cathode ray tube for use in a multiplex system comprising an electron gun, a plurality of physically spaced sets of targets arranged in a circle, each set of targets comprising a pair of spaced plates whose adjacent ends overlap, whereby first one target and then the other target of each set is adapted to be bombarded by the electron beam emanatin from said gun, and means for causing the electron beam to traverse a circular path whose diameter is the diameter of the circle on which lie said sets of targets, whereby the sets of targets are sequentially bombarded by the electron beam, said sets of targets being assigned to different channels of said system, a relay in each channel under control of keying mechanism for that channel, said relay having an armature, a break contact and a make contact, means for connecting together all of the break contacts of all said relays and only those targets of said sets which are first bombarded by said beam, a connection between the other target of each of said sets and the armature of the particular relay for that channel, a connection from the make contact of each relay to ground, circuits for synchronizing the operation of the keying mechanisms in the 10 different channels with the sweep of the electron gun in said cathode ray tube, a common resistor connected to said first bombarded targets of said sets, a difierentiator circuit connected across said resistor, and means coupled to said difierentiator circuit for utilizing the output from said system.

13. A cathode ray tube comprising a cathode for producing a stream of electrons, means f0- cussing said stream into a beam, electron deflecting elements, a plurality of physically spaced sets of targets arranged on a plurality of concentric circles near one end of the tube, each set of targets comprising a pair of overlapping plates spaced one behind the other, and means coupled to said deflecting elements for causing said beam to sequentially traverse circular paths of different diameters corresponding to the diameters of said concentric circles.

14. A cathode ray tube comprising a cathode for producing a stream of electrons, means focussing said stream into a beam, electron deflectin; elements, a plurality of pairs of physically spaced targets arranged on two concentric circles, the targets of each pair being positioned behind one another and overlapping in their lengths. and means coupled to said deflecting elements for causing said beam to alternately traverse circular paths of difierent diameters corresponding to the diameters of said two concentric circles.

WILLIAM D. I-IOUGH'ION.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,585,591 Lowy May 18, 1926 2,024,979 Metcalf Dec. 17, 1935 2,057,773 Finch Oct. 20, 1936 2,110,548 Finch Mar. 8, 1938 2,124,973 Fearing July 26, 1938 2,185,693 Mertz Jan. 2, 1940 2,250,528 Gray July 29, 1941 2,265,848 Lewis Dec. 9, 1941

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