US2513335A - Demodulator system - Google Patents

Description

July 4, 1950. E. LABIN ETAL DEMoDuLAToR SYSTEM 2 Sheets-Sheet 2 Filed sept.' 1, 1945 A TTU/WYE Y Patented `uly '4, 19.50

DEMODULATQR SYSTEM Emile Labin, New York, and Donald D. Grieg, v Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application September 1, 1945, Serial No. 614,078

4 Claims.

This invention relates to multi-channel communicationv systems andmore vparticularly to multi-channel systems employing a plurality of series of pulses wherein each series represents a signalling channel and the pulses of the different series are interleaved into'a single train of pulses ducing structure and means to cause the beam y to sweep through a given movement for coaction With a' plurality of channel electrodes to separate and demodulate the signal energy of a plurality of series' of time modulated pulses. Each channel electrode may comprise either a collector electrode or a combination barrier and secondary emission electrode arrangement across which the beam is caused to sweep. The time modulated pulses of the different channels are applied in any one of-a plurality of ways to control coaction between the beam and each channel output electrode. In the forms described in detail hereinafter, the pulses are applied to key the beam on and off according to the leadingl and trailing edges of the pulses. The beam is synchronized to the channel period to sweep the channel electrodes once each such period so that the keying on and off of the beam coacts with the channel output electrodes Ato produce output energy corresponding in amplitude to the time modulation of the input pulses of each channel.

According to the multi-channel beam demodulators of our aforementioned application, a large number of channels may be separated and demodulated by eachv demodulator by providing a long sweep path for the electron beam with channel output electrodes located along the sweep path. The channel electrodes, however, must not be located so close to each other as to permit carry-over of signal energy by way of the beam from one channel electrode to the next; to present objectionable capacity between adjacent electrodes or to collect secondary` electron emission from adjacent channel electrode arrangements. Further, for a given size tube, the number of channel output leads is limited, and the size and therefore the life of the electron collecting electrodes are also limited.

beam demodulator devices without' the necessity of building tubes of great size. 5 K

Another object of this invention istoprovide a multi-channel demodulator system utilizing a plurality oi demodulator tubes each having a much smaller number'of channel electrodes than the ultimate number of channels desired.

One of the features of the invention is to 'provide a plurality of beam demodulator tubes with a limited number of channel electrodes? per tube; the channel electrodes being spaced apart a distance sufficient `to avoid cross talk interference or carry-over of signal energy from one channel to the next, to reduce capacity and inter-collection of secondary electron emission between adjacent channel electrodes and toymake thechannel electrodes large and sturdy. v

A further feature of the invention is toprovide means for synchronizing the operation of .the demodulator tubes, the beams of the tubes being phased in their sweep movements so that .the channel separating and demodulating functions of the different tubes occur at different timing in' order for the .beam to be in proper channel electrode impinging relation upon the occurrence of the pulses of the corresponding' channel; The pulses occurring between those of the channels selected may be rendered impotent in a given tube or otherwise blocked as hereinafter described. l 'I The above and other objects and features of the invention will become better understood upon consideration of the followingdetailed description and the accompanying drawings in which:

Fig.v 1 is yadiagrammatical illustration l of a multi-channel pulse demodulator system according to the principles of this invention;

Fig. 2 is a graphical representation of the signal pulse separation according to the system shown in Fig. 1; and

Fig. 3 is a graphical representation of the time demodulating operation ofl one of the channels.

Referring to Figs. 1 and 2 of the drawings, a multi-channel pulse time vdemodulating system is shown for twelve signal receiving channelsfl to I2, wherein the pulses of channel I are distinguished in width for synchronizing purposes.

It is one object of this invention to overcome 56 the above mentioned difficulties in multi-channel The pulses shown in Fig. 2 are numbered according to the signal receiving channels of Fig.v 1'. As shown in Fig. 1, three multi-channel demodu-i lators I3, I4 and I5 of the type shown in our aforesaid application are included, although it will be understood that a lesser or greater number may be employed dependingupon the num,- ber of signal receiving 'channels to'be provided and also the number of signal receiving channels each demodulator may have.

way of example, four receiving channels are provided for each demodulator although a greater i as. phones 3I'.

` ampleY comprises a cut-oli biasing value.

As indicated by number may be employed in actual practice.

By applyingv the train of received pulses from input I 6 toa synchronizing pulseselector I'I which may comprise any suitable known form of pulse width discriminator, energy only of the synchroy nizing pulses I will be :obtained which, in turn, may be applied to a base Wave producer I8` for the generation of wave energy for controlling the sweep movement of the beam of the electron tube I3. For a circular sweep movement, the wave iS;

period of the multi-channel train.

vIt will b e understood, of coursefthat the circular movement is illustrated herein for purposes. of

providing; the proper sweepA potentials for the deiiecting elements-22 to 25. For example, the sweep patterni mayff'ollow the. zig-zag tracing commonly usedirrtelevision.

.The electron tube I3 is provided with a pluralie ty of'channel output electrodes or collectors 26, 2'I,

28 and 29, which correspond in number, in spacing and timeposition relative the beam movement,

will be clear to those versed in the art. For eX- ample the output pulses of each channel may be used to provide blocking pulses for the associated distributor tube.

The input pulses are preferably shaped by pulse Shaper 31 to insure a givenl amplitude and duration for the pulses prior to application to grid 33. The shaper 3'I, which may be a known form of multivibrator, is particularly useful in improvtions in duration or time position caused by inillustration only, and that anyother type ofl cyclic sweep.: movement may be substituted by merely to channels I, 4, 'I and I3. Channels 4, 'I and I are each connected to a receiving channel circuit which may include a low pass kfllter'such as in dicated at 30- forl channel 4, the output of which is applied to any desired utilization circuit such The collector 26 corresponds in position to the synchronizing pulses I4 in the timing of the channel pulses and vmay be used` for providing synchronizing pulse energy for any synchronizingpurpose, that may beV required, for eX- ample, it may be used for-.synchronizing an as-v 33 and suitably shaped by the usual focusing means 34. The grid 33 is provided with a source of biasingpotential at 3.5 which, in the present4 ex- The multi-channelpulses are applied from input I5 over connection 36 and Shaper 31,;line 38, cen'- denser 39 andlline 43 to control grid 33 to key the beam on and .off according to the leading and trailing edges of the pulses. The bias at 35 permits all of the pulses applied .to the grid 33y to control-energization of the beam. While such operation may be practiced, if desired, the pulses of channels other than channels I, 4, 'I and I0 occurring YWhile the beam is between output electrodes`,'i`t is preferred that the pulses of channel 2, 3, 5, 6, 8, 9, II and I2 are lblocked at the grid.

This blocking may be accomplished in different i ways.Y VAs shown in Fig. 1, a control wave produced at 4I is applied through condenser-'42 to terference.

While the channelelectrodes- 25through 2,9 may comprise `vany one of several-vdiierent,.electrode arrangements, they may be referred. to for the present as electron collectors adaptedftocollect theelectrons of the beam as the beam traverses the areas thereof. For'other forms of collectors or electron responsive devices, reeienoemay be had toour aforesaid application. y

In the operation. of the receiver system of Fig, l, a trainA of multi-channel pulses according to those of graph Al,'ig..2, are received over input connection I6. The pulses, of the synchronizing channel I being of. a width greater than thevpulses of the other channels, are separated therefrom by the selector I'I. The outputof: the selector I'I controls producer`A I8 to produce base wave41, graph B. The base wave output of producer I8 is fed both to phase splitter Iii)v for. production. of sweep control potentials, and to phase shifter 43. AfterV proper phasing the wave energy is multiplied in frequency at 4'4, such as indicated by wave 48, graph B. vBy' full-wave rectification at 45, a cusped wave 4$I 'graph'C, is produced. By clippingV and amplifying the cusps between amplitude levels 50 andV 5I in Shaper 45, a control wave 52 is produced. The gridl 3 3 being biased to out off at a leve153, is controlled by coincidence of the undulations of' control wave 52 with signal pulses as indicated in graph E. This coincidence between the undulations of . wave 5,2 and a channel pulse determines the energizationy of the beam, the energization of `Athe beam of tube I3,A being Vin accordance with the occurrence of the pulses of channels l. 4, 1 land IB, as `irwlicated in graph F. The pulses of channels 2. 5, 6.3 and 9 arethus blocked and are notpermittedto act upon the beam. i

It will be apparent. that, `the grid 3,3 of tube I3, is supplied with pulse energy corresponding tothe pulses. ofchannels I ,.4 'I and it, 'I he pulses. of these channels, or at least channels 4:, l and lil. beine modulated. in timepositionfkey the/beam on for .the duration of each pulse there@ by causing electron collector action at the vcorresponding `channel ,output electrodes V(,215` to 2 9) for the time interval of coincidence. between the pulse enereizedbeam and the .collector electrodes.-

By reference toA Fie. 3, the .demodulation actin of .tube I3 isl illustrated for one channel. Graph G represents .the pulses of yone channel only, three pulses' being shown. `These pulses lare not the ordinary consecutive pulses, but are ,selected to represent certain pulse positions, pulse 5,511.61)- resenting the extremev displacementpostion 00rrespondingY to the maximum. neeatvemtental of the modulating wave. The dotted line 56 rep# resents the trailing edge of pulse 55 when it is displaced to the opposite extreme or positive potential of the modulating signal. Pulse 51 represents zero modulation of the pulse, that is to say, it is half way between the two extreme positions indicated. Pulse 58 represents the opposite eX- treme displacement position, such as resulting from the maximum positive potential of the modulating energy.

Graph H represents the sweep potenti-al for -controlling the beam. For a circular sweep, another wave potential would be required 90 displaced from the one shown. However, for indicating the cycle of operation of the beam in its sweep, the one wave will be suincient.

In graph I, three electron collector positions are shown, the three positions representing one electron collector in its recurring relation with the sweep voltage of graph II. Referring first to pulse 5l which corresponds to zero modulating energy, this pulse keys the beam on and oir for the duration thereof, thereby causing the beam to occur for the duration of the pulse similarly as shown at 57a, graph I, the duration of the beam coinciding for only half of the duration of the pulse. This produces an output current, the energy of which is represented by the pulse 51o, graph J. Pulse 55, corresponding to the maximum negative modulating potential, keys the beam on and off as in-dicated at 55a just prior to the coincidence of the beam with the collector 59. Therefore, no current flows in the output circuit for this pulse position. The pulse 58, however, keys the beam on when it is in full coincidence with the collector 59 as indicated at 58a., thereby producing the maximum ow of current in the output circuit of the collector. This is represented by the pulse 58h. Thus, it will be clear that the tube operation not only commutates, that is separates the pulses of the different channels, but also demodulates the time displacement thereof into corresponding amplitude modulated energy.

From the foregoing description, it will be clear that the staggering of the channel pulses between f the different receiving or demodulating tubes, greatly lessens the occurrence of interference or cross-talk in the terminal equipment. In pulse time modulation transmission over various communicating links, whether they include repeaters r or not, the time displacements of the pulses are kept within predetermined limits and therefore do not overlap or otherwise produce cross-talk between channels. The present invention carries further this freedom from interference into the receiving terminal. The staggering of the channels between the different tubes removes the adjacent channels one from the other and, in the construction of the tubes, reduces to a minimum the capacity between adjacent output electrodes, avoids inter-collection of secondary electron emission between the adjacent electrodes, and at the same time enables the construction of sturdier, longer lasting demodulator tubes of a convenient size.

While we have disclosed the present invention in connection with a specinc circuit arrangement, it will be clear that many variations may be made without departing from the invention. It should therefore be clear that the present disclosure is given by way of illustration only and not as a limitation on the scope of the invention as set forth in the appended claims.

We claim:

1. In a receiving system for receiving a multichannel train of signal pulses, a plurality of channel selectors, each including means to produce an electron beam and a plurality of output electrodes corresponding to certain of said channels only, means to apply the train of signal pulses to control the energization of the beams of Said selectors, and means to cause the beam of each selector to sweep over the output electrodes thereof to cause ow of current in the output circuits in response to the pulses of selected channels only.

2. In a receiving system according to claim 1, further including means to produce control waves according to the channels to be selected by said selectors, and means to apply said control waves to the corresponding selectors to control the operation thereof.

3. In a receiving system for receiving a multichannel train of signal pulses wherein said train includes synchronizing pulses distinguished in sume characteristic from the channel pulses, a plurality of channel selectors, means to apply the train of signal pulses to each selector, means to produce control waves in response to said synchronizing pulses, and means to apply said control waves to cause each selector to select from said train predetermined pulses of a plurality of non-adjacent channels only, each selector including means to produce an electron beam, a plurality of output electrodes, means to cause said beam to sweep said electrodes in accordance with said control waves, the pulses of the train being applied to the beam producing means to control operation thereof in accordance with the occurrence of signal pulses,

4. In a receiving system for receiving a multichannel train of signal pulses wherein said train includes synchronizing pulses distinguished in some characteristic from the channel pulses, a plurality of channel selectors, means to apply the train of signal pulses to each selector, means to produce control waves in response to said synchronizing pulses, and means to apply said control waves to cause each selector to select from said train predetermined pulses of a plurality of non-adjacent channels only, each selector including means to produce an electron beam, a plurality of output electrodes, means to cause said beam to sweep said electrodes in accordance with said control waves, the pulses of the train being applied to the beam producing means to control operation thereof in accordance with the occurrence of signal pulses, means controlled by said synchronizing pulses for producing a blocking wave for each selector and means to apply a blocking wave to the beam producing means of each selector.

EMILE LABIN. DONALD D. GRIEG.

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

UNITED STATES PA'I'ENTS Number Name Date 1,918,252 Dunham July 18, 1933 1,928,093 Coyle Sept. 26, 1933 2,036,350 Montani Apr. 7, 1936 2,048,081 Riggs July 21, 1936 2,094,132 Miller Sept. 28, 1937 2,172,354 Blumlein Sept. 12, 1939 2,403,210 Butement et al July 2, 1946 FOREIGN PATENTS Number Country Date 475,239 Great Britain Nov. 16, 1937

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