US2521229A - Electronic time division channel scanning system - Google Patents

Description

. Sept. 5, 1950 l H, J, KOCH 2,521,229

ELECTRONIC TIME DIVISION CHANNEL SCANNING SYSTEM lFiled June 8, 1949 2 Sheets-Sheet 1 4FIG. 2.

ATTO NEY Sept. 5, 1950 H. J. KOCH 2,521,229

ELECTRONIC TIME DIVISION CHANNEL SCANNING SYSTEM Filed June 8, 1949 2 Sheets-Sheet 2 SIX PHASE POTE/VT/AL SUI/RCE FIG. 4

51X A)DH/45E POTENTIAL 50i/RCE FIG. 3

INVENTOR. r3 HENRY KOCH ATTORNEY Patented Sept. 5, 1950 UNITED STATES PATENT OFFICE ELECTRONIC TIIVIE DIVISION CHANNEL SCANNING SYSTEM Application June s, 1949, serial No. 97,792

9 Claims. (Cl. 179-15) This invention relates to communication systems of the multiplex kind, and more especially to multiplex systems of the pulsed channel type.

A principal object of the invention is to provide a simplified and eflcient channel scanning arrangement for timed division multiplex transmission.

Another object is to provide an improved pulsed multiplex transmitter employing as the pulsed channel source an electron tube of the focussed rotary beam type. 4

Another object relates to a novel combination of rotary beam tube and a signal-controlled multi-section output tube, which tubes are interconnected to provide timed division multiplex signals having a relatively low noise level. l

A feature of the invention relates to the combination of a rotary beam tube which acts as a multiplex channel pulse generator, a plural-section inverter tube, and a plural-section signalcontrolled tube, which tubes are interconnected to provide an improved timed division multiplexing transmitter having a relatively low noise level.

A further feature relates to the novel organization, arrangement and relative location of parts which cooperate to provide an improved and efficient timed division multiplex transmitter.

In the drawing, which shows, by way of example, one preferred embodiment:

Fig. 1 is a schematic structural and wiring potential.

of a metal sleeve having its external surface coated with electron-emissive material. 4Concentrically surrounding the cathode 3, are six metallic screens 5-I0 which are spaced apartV to form respective Windows |I-I6, all the windows being of the same dimensions and being equally spaced around the cathode 3. Each of the screen plates 5-Ill also has a central window |122 of substantially the same dimensions as the windows II-IG. There are thus provided twelve windows of the same size, equally spaced around the cathode 3. Surrounding the screen plates, and in radial alignment with each of the respective windows, is a corresponding anode 23-34. While the drawing shows twelve of these windows and anodes, it will be understood that a greater or less number may be employed, depending upon the number of multiplex channels to be desired. Each of the screen plates 5-l0 is provided with a separate lead-in 357-40, which lead-ins `are cohnected to any Well-known six-phase source of The cathode 3 is returned to ground through a suitable bias resistor 2l. 'I'he anode plates are likewise connected through respective lead-ins 4I, 42, 43, etc. and through respective load resistors 44, 45, 46, etc., and thence in parallel to the positive terminal 41 of a suitable source of plate potential represented schematically by the battery 48. As explained in said application,

diagram of a multiplex pulsed transmitter according to the invention.

Fig. 2 is a series of pulse graphs explanatory of the operation of Fig. 1.

Fig. 3 is a schematic structural and wiring diagram of a multiplex receiver according to the in-i' vention.

Fig. 4 is a modification of Fig. 1.

Referring to Fig. 1, the numeral I represents schematically a tube of the focussed rotary beam type. For a detailed description of such a tube, reference may be had to Proceedings of the I. R. E., vol. 36, No. 11, November 1948, pages 1354-1357. The tube comprises a suitable evacu- .ated enclosing envelope 2 containing a central electron-emitting cathode 3, provided with the usual internal and electrically-insulated heater lament or element 4. The cathode 3 maybe of the type well-known in so-called indirectlyheated cathode tubes, for example in the form by choosing the proper bias for the cathode 3 and for the various plates, the electron beam from the cathode is focussed into a substantially planar beam 49 whose transverse width is equal to'or less than the transverse distance between the centers of the windows |I-22. said publication, the beam 49 is rotated synchronously at a predetermined rate controlledby the six-phase potential source connected to the screen plates 5-10. Therefore this beam successively completes a circuit through each of the twelve respective resistors 44, 45, 46, etc. Consequently as the beam rotates, it develops across the respective resistors, negative pulses 50, 5l, 52, i Thus the pulses are spaced apart .o

etc. (Fig. 2). in time by a regular interval "t, and the recurrence time T is equal to Nt, where N is the total number of anodes.

The pulses developed across the resistors 44, 45, 46, etc., are applied through respective coupling condensers 53, 54, 55, etc., to the respec- As explained in with each -one of said windows.

current characteristic curve.

tive control grids 56, 51, 58, etc. of another tube 59. This tube can be structurally substantially the same as that of tube I, except that all the screen plates are electrically connected together and to the same positive potential 60. In other words, the electrons from the cathode 6| are not focussed into a planar beam, so that they are emitted simultaneously in all radial directions through the respective twelve windows 62, 63, 64, etc. of the screen plates. The central cathode 6| can `.beiconnecteddirectly -.to ,ground and is surroundedlby a 1; positively chargedgrid 65 7which acts as a space charge grid for the tube by being connected to a suitable positive direct current biassing source 66. In alignment with each of the grids 58, 51, 58, etc., :are the respective output anodes 61, 68, 69, etc., which nare Vcon- CTI nected to the positive directcurrentsupply terminal 41 through respective load-resistors 31.0, 12|, 12, etc. The potential of the negative pulses 50,

5|, 52, etc. are such that when .they .are im pressed upon the respective gr'ds'56, 51, '58. etc., they out off plate current flow from the'fcathode 6| to the respective ariodes 61, 68, 69, etc. Thus .the negative pulses are .converted -into Apositive r pulses-across therespective .resistors .10, 1| ,`.12, ctc. These positive `.pulses .are .applied through .respective .coupling condensers 13, .14, 15, etc., to .respectiveiswitching controlgrids L16, 11, .10, etc., -.to .another tube 1.9. This tube may comprise lan.evacuated .envelope 80 containing a ,central .electron-emitting .cathode 8| which is surrounded ,bya ,positively-charged.-spacefcharge ,-grid l82 sup- ;pliediby'a suitable Ypositive direct currentibias- .-'singpotentialiromthe source l83. .Concentrically :surrounding the .grid .82 are the .screen plates ssimilar to the lplates \.5|.0 of -tube vI, -but .with :all .the '.plates electrically-connected togetherfand @to these-me positiverdirect current potential84. Thus there aretwelve windows 85,185, I181etc., #equally spaced-around thecathode 8|, the grids 16, 1.11, ,18, etc., being in .alignment .respectively Also concen- `.trically :surrounding Ythe 'cathode in alignment withthe saidwindows andlocatedfbetween ,these windows 'and -the switching grids, is asimilar fseriesof signal input controlgrids 88,-89, 90, etc.

asingleoutput anode y9| concentrically surrounds fall the i-electrodes, .and is connected y=to vthe posi- `tive terminal -41 of the .directrcurrentfpower., supnply through a single -.plate loadfresistor f9.2, and thence to a common output terminal .93 -which may leadto asuitabletransmisson line or channel. All the switchinggrids 16, :11,118, etc., are kconnected through respective grid-leak .resistors .94, 95,l *96,fetc., to thefnegative .terminal .91..of a `suitable-direct :current-biassing source 98, so .as normally tobias the switching grids 19, 11, .18, -etc to plate'current'cutoff. =Each;of thesignal --input grids 8.8, 89, .9.0, etc., is connected through a ysuitable coupling condenser 99, |00, IDI, etc., `torespective signal input-channels |03, |04, |05, etc. These signal inputgrids are'biassed through respective grid-leak resistors I 06, |01, |08, etc., yto asuitablenegative potential 109 to maintain theyarious sectionsof thetube operating=on the zstraight .line portion-of their control grid-plate From the -foregoingidescription .it vwill be seen y.that the ytube I ,generates regularly recurrent ,and -spaced negative pulses which when .applied to the tube 59, .produceat the grids 16, .1.1, 18, '.etc., correspond- ,ing,positive lpulses. .However the amplitude of .these positive pulses-can befchosen with respect to the negative bias on the grids'88, 89, 90, etc.,

so that plate current does not ilow from the cathode 8| to the anode 9| except upon the timed coincidence of a positive pulse applied to a switching grid, and a positive signal pulse applied to the corresponding signal input grid from the respective signalling channel. On the other hand, the magnitude of the positive pulses applied to the switching grids can be proportioned with respect to the negative bias on the signal grids, so that the signal potentials applied from `the respective .channels L03, |04, .|05, etc., cause a 'modulation or the :platecurnent fflowing from the cathode 8| to the anode 9| respectively rthrough the successively switched-in sections of the tube.

VFIthas-'b'eeniound that by this particular combination of tubes, and the particular manner of Agenerating the .switching or timing pulses by .means-,of .airotary beam tube which is separate .LEO :from the channel output tube 19, a considerable .reduction in signal-to-noise ratio is obtained in 'the output signals at terminal 93. It will be understood, of course, that at the receiver any wellknown channel distributor can be provided for .connecting .the various receiving channels .into

circuit, with Vterminal 93 in Ytimed .coincidence with .theimpingement of the 'electron .beam .'49 on thesuccessiveanodes23434. Preferably this distributor may comprise a rotary beam tube IIO (seeFig. 3), similar to tube I, havingits 'focussed electron beam rotating in timed synchronism with .the beam 4.9. Thus this tube may comprise a central electron-emitting cathode I'I which is surrounded bythe six screen Yplates I I2, |`|'3, '|4, etc., to provide a series of twelve equally-'spaced windows `I I5, II6, I|1, etc., similar to the twelve windows in the screenplate of tube 'I. vThesesix screen plates are then connectedto 'a suitable .sixfphase .alternating .current source which jis synchronized with the six-,phase alternating 'current source at the transmitter. Concentrically surrounding the twelve windows is a unipoten- .tialgrid I 8 which is connected to the transmission channel 9-3. Concentrically surrounding the cathode, and in alignment with the 'twelve windows in the screen plates, are twelve output anodes I9, .|20, 112|, etc., which are connected through respective load Aresistors |22, |23, 124, etc., and thence through respective coupling con- .densers |25, |26, |21, etc., to the respectivereceiving channels |28, |29, |30, etc. The output anodes ||9, |20, 2|, etc., are connected through their respective load resistors |22, |23, "|24, etc., tothe positive terminal ylill of the direct current plate power supply |32. The grid |I8 can be vbiassed negatively by a suitable direct current supply |33, so that a pulse ofplate current does not ow to the respective output anodes V'except upon the receipt of a positivepulsereceivedirom the .transmission channel'93, andyif desired, the magnitude of this pulse of plate current can "be in proportion to themodulation or amplitude of the received positive pulse.

Eig. '4 shows a modification o'f the .system of Fig. '1, whereby the tube A59 :can be eliminated,

55 The slat electrodes` |1`22 vare connected to a suitablesix-phase source, and the cathode 3 is biassed -with respect to the remaining electrodes, to cause the focussed planar beam 49`to rotate at the requiredrate. Located between the slat electrodes Y ,and .the anodes, is a cylindrical mesh grid |34 which is connected to a positivel terminal |35 of .ethe direct current plate power supply source |36.

The anodes 23, 24, 25, are connected through their respective load resistors 44, 45, 46, etc., to another tap |31 on the supply |36. Thus the anodes are at a lower positive potential than the electron collector grid |34. Consequently as the beam 49 rotates, it impinges successively upon the anodes and produces positive pulses at these anodes, and these positive pulses can be coupled through the condensers 53, 54, 55, etc., to control the tube 19 in the manner above de scribed.

While certain particular embodiments have been disclosed herein, various changes and modications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A multiplex communication system, comprising, an electron tube having a central electron-emitting cathode, a plurality of separate anodes concentrically surrounding the cathode, means to develop the electrons from the cathode into a beam originating at the cathode and terminating successively at said anodes, means to develop a beam-rotating iield to cause said beam to sweep said anodes to develop regularly recurrent pulses at said anodes successively, means to derive from said regularly recurrent pulses another set of switching control pulses synchronized therewith another electron tube having a central electron-emitting cathode and a surrounding anode, a rst set of separate grids surrounding the cathode of said other tube, a second set of separate grids in said other` tube and surrounding the first Iset of grids and in radial alignment therewith, a plurality of signal input channels connected respectively to the grids of the first set, a single output channel connected to said anode of said second tube and means to apply said derived pulses respectively and recurrently to said second sets of grids to control successively the conductivity between each grid of the first set and said single anode.

2. A multiplex communication system according to claim 1, in which the electrons from the cathode of the first-mentioned tube are electrostatically focussed to produce a beam which extends radially in one direction only from the cathode to each of said anodes in succession.

3. A multiplex communication system according to claim 1, in which the means to develop the said beam of electrons and the means to rotate said beam, comprises, a plurality of slat electrodes located between the cathode and the anodes with the slat spaces aligned each with a respective anode, and a source of multi-phase potential connected to said slat electrodes to develop a rotating electric eld.

4. A multiplex communication system according to claim 1, in which a third electron tube is provided having a central electron-emitting cathode with a plurality of spaced surrounding grids and a plurality of spaced surrounding anodes, means connecting each of the grids of said third tube respectively to the anodes of the first-mentioned tube, and means connecting the anodes of said third tube respectively to the secondmentioned grids of said other tube.

...6 5. A multiplexcommunication system of the pulse transmission type, comprising', an electron tube of the rotary beamtype having a plurality of output anodes fordeveloping'regularly recurrent spaced pulses in response to the sweeping of said anodes byN said beam, a pulsel 'inverter tube having a plurality of control grids and a corresponding plurality of output anodes for inverting the polarity of said pulses, and a switching and signal control tube having av plurality of signal input grids connected respectively to a series of signal input channels, a corresponding series of switching grids connected respectively to the anodes of said inverter tube, and a signal output channel connected to the anode of said switching and signal control tube.

6. A multiplex communication system according to claim 1, in which the first-mentioned tube has its anodes provided with a coating of secondary electron-emissive material facing the cathode, and means are provided for causing positive pulses to be produced at said anodes in response to the rotation of said beam past each anode.

7. Multiplex communication apparatus, comprising, a rst electron tube of the type having a central electron-emitting cathode and a plurality of surrounding spaced anodes, means to focus the beam from said cathode into a substantially flat beam with one edge extending along the cathode and the opposite edge terminating at one of said anodes, means to subject said beam to an electric field to cause it to rotate at a predetermined rate and thereby to generate recurrent pulses successively at said anodes, a second electron tube having a central electronemitting cathode, a plurality of spaced signal control grids surrounding the cathode, a plurality of switching grids surrounding the control grids and in radial alignment therewith, a single anode surrounding the switching grids, means connecting a plurality of signalling channels respectively to said signal control grids, means to energize said switching grids respectively by said recurrent pulses from the anodes of the iirst tube, a third electron tube having a central electron-emitting cathode, a plurality of separate anodes concentrically spaced around the cathode of said third tube, a control grid surrounding the cathode of said third tube, means to focus the electrons from the cathode of said third tube into a substantially dat beam having one edge extending along the cathode and the opposite edge extending along the anode of said third tube, means to subject th-e beam of said third tube to an electric field to cause it to rotate in synchronism with the beam of the first-mentioned tube, a signal transmission channel connecting the anode oi' said second tube to the control grid of said `third tube, and a plurality of signal receiving channels connected respectively to the anodes of said third tube.

8. Multiplex communication apparatus according to claim 7, in which the first-mentioned tube develops said recurrent pulses as negative pulses at its anodes, and a pulse inverter tube is connected between the rst and second tubes to convert said negative pulses into positive pulses.

9. Multiplex communication apparatus according to claim 8, in which the inverter tube comprises a central electron-emitting cathode, a plurality of circumferentially-spaced control grids concentrically surrounding the cathode of said inverter tube, a plurality of circumferentiallyspaced anodes surrounding the cathode of said

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