US2474244A - Amplitude modulated time modulated pulse system - Google Patents

Description

AMPLITUDE MODULATED TIME MQDULATED PULSE SYSTEMv Filed May 19, 1944 D. D. GRIEG June 28, 1949.

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Patented June 28,` 1949 AMPLITUDE MODULATED'TIME MODULATED PULSE SYSTEM DonaldD. Grieg, Forest Hills, N. Y., .-assignorto Federal Telephone and Radio Corporation,"New York, N. Y., a corporation of Delaware Application May 19, 1944, Serial No. 536,301

12 Claims.

This invention relates to pulse communication systems, especially multi-channel systems, incorporating relay and in and out branching stations.

In communication by means of pulses -many methods of modulating the pulses to convey intelligence have been proposed, for example, various types of pulse time modulation (hereinafter abbreviated as P. T. M.) have been proposed. Pulse amplitude modulation (hereinafter abbreviatedas P. A. M.) has also been proposed.

In the co-pending application of Emile Labin and myself for Multi-channel communicating systems, led April '7, 1944, bearing Serial Number 529,933, now Patent No..2,428,118, granted September 30, 1947, it has been suggested that the same pulses may be time modulated to convey intelligence and amplitude modulated to convey additional intelligence.

In order to satisfactorily communicate by P. A. M., it is essential that substantial deterioration of signal to noise ratio and distortion ofthe pulses be avoided. This requirement limits the use o-f P. A. M. to comparatively shortdistances or entails the use of relatively expensive linear relay stations. On the other hand, P. T. M. pulses may be substantially distorted and attenuated as regards amplitude and yet serve kto adequately convey the intelligence represented by that type of modulation. Therefore P. T. M. may be used over much longer distances than` P. A. M. without adverse effects. Moreover if 4the distances are so great as to require amplification of the P. T. M. pulses, then relatively inexpensive non-linear relay equipment may be employed.

It will, therefore, be seen that while P. T. M. is suitable for long distance transmission, P. A. M. is not, unless expensive linear relay stations are employed. This statement applies whether the communication is carried on by co-mmon line transmission, carrier wave line transmission, through a radio link, .or otherwise. In using the term short distance, I am using it in a special sense to refer to a distance which will not produce substantial distortion and attenuation of P. A. M. pulses, while a long distance will produce suchdistortionand attenuation. The actual physical distance-implied by these terms depends upon the communication medium and other factors such as `the frequency, power, and equipment employed.

An object of the present invention is the provision of ak communication vsystem which makes eicient Ause of the combination of P. A. M. and P. T. M. In one yform this is accomplished by using P.- TLM.I for lon-gA distance transmission and superimposing P--A.,M. :on the P; T. M. pulses to provide additional channels for `communication over lesser intermediate distances, which .lesser distances maybe short distances .in the special sense. hereinabove .defined,for may be greater than said-short distances .where theamount of .traic warrants the use of linear repeaters.

.Anotherobject of thepresent Ainvention is the provision .of...a communication system including two. stations' between -which communication is held by.. P..'T.M.,.said..system including a relay station fonsaid. P. .T. M.communication, which relay station is adapted to have additional communication lwith eithery another similar relay stationor with one of said P. T. stationsbymeans of P. A. M. carried on the P.,T. M. pulses.

Another object of the present Vinvention is the provision of -a-.mult'i-ohannel pulse communication system in whichcommunication is carried onbetween two mainstations byv AP. T. M. pulses, and additionalcommunication is carried on between one ormoreintermediate relay and in and out branching .stations..and .any -other station by means of P. A. .M..carried.by, the P. T. M. pulses.

Otherand. furtherobjectsof .the present inventionv willfbecome apparent and the foregoingvwill .be best understood fromy the .fo1lowing.de-

scription of. embodiments thereof, reference being had tothe drawings, iny which:

Fig.. lis a schematicdiagram of=a communication system embodying my invention;

`Fig..2. fis. a schematicand blockdiagram of a relay Vunit for ,use with .a .single `channel of pulses in 4accordance `with .my invention;

. Fig..3is a schematicandblock diagram ofa relay unit .for-ruse 'with multi-channel pulses;l and Fig. 4 is 4a .setofcurvestowhich reference is made in the following..description It is to be understood thatthese curves and others shown .in -thedrawingsare-not drawn toscale and only .have signicance to :the extent :pointed out herein.

2 are a relatively long distance apart, in accordance with my invention communication between said stations is carried on by means of P. T. M. pulses such as those designated by the numeral 5.

Any suitable known type of P. T. M. modulator may be used, it being considered suicient to point out that pulses may be displaced in time within the limits indicated by the dotted lines 6.

The P. T. M. pulses transmitted from west station I which are modulated with intelligence at said station may be transmitted over long distances and if the distances are suiciently long, non-linear repeaters I may be inserted in the sections 8 of the line covering said long distances. The fact that repeaters 'I are non-linear will not materially affect the communication by P. T. M. pulses. The pulses arrive at a station 9 which, for purposes of conciseness, shall be termed a relay station. At relay station 9, the P. T. M. pulses 5 are amplied and transinitted over a short distance line section IB to another relay station I I It may be desired to carry on local communication between relay stations 9 and II and for this purpose the P. T. M. pulses which are relayed as station 9 may be pulse amplitude modulated 4by means such as described hereinafter to carry additional intelligence to station I I as illustrated by pulses I2. At station II the pulses I2 are treated so as to remove the P. A. M. and derive the information represented` thereby. The P. T. M. pulses are sent on towards east station 2.

It may be desired to carry on additional local communication between station Il and station 2 and for this purpose the P. T. M. pulses transmitted from station II to station 2 may again be amplitude modulated with additional intelligence as represented by pulses I3.

If section I4 of the lines between station Il and station 2 is greater than a short distance, repeaters may be necessary. Since sections I4 are to carry P. A. M. as well as P. T. M., it will be necessary to use linear repeaters I5 for this purpose. At east station 2 the intelligence carried by the P. A. M. and the separate intelligence carried by the P. T. M. of pulses I3 may be derived from said pulses by any known forms of P. T. M. and P. A. M. demodulators.

In the pulses travelling from east station 2 to the West station I by line d, local P. A. M. communication may be carried on in a similar manner between station 2 and station II as well as between station II and station 9. However, P. A. M. is not carried on between station 9 and west station I because of the length of the lines involved and the non-linear repeaters 'I.

From the foregoing description it will be seen that communication is carried on by P. T. M. between the east station and west station while local communication is carried on between relay station II and either the east station or relay station 9 by P. A. M. carried by the P. T. M. pulses.

While I have described the foregoing communication system with reference to a single channel of P. T. M., it may also be used as a multichannel system and the relay stations 9 and II may also serve as in and out branching stations not only for P. A. M. but also for P. T. M. Furthermore, although I have shown a given number of stations, it will be apparent that many more relay stations may be incorporated in the system in accordance with theforegoing description.

Referring now to Fig. 2, I have there illustrated a relay and in and out branching unit I6 for a single channel which unit may be employed in any one lof the stations. This unit is designed to receive pulses I'I having both P. A. M. and P. T. M. Pulses II are fed through a decoupling amplier I8 and a low-pass lter I9 to an indicating device such as a receiver 20. In the lowpass lter I9, the pulses are integrated so as to yield a resultant wave 2I representing the intelligence with which pulses I'I were amplitude modulated. Pulses I'I are also sent through a limit clipper amplier 22 where they are clipped yalong the level 23 and amplified and inverted to produce pulses 24. Pulses 24 still carry the intelligence represented by their time modulation but they have no amplitude modulation.

II" unit is also used as a P. T. M. out branching station then switch 25 is closed and pulses 2d are sent through a pulse time demodulator 26 of any known type, such for eX- ample as disclosed in U. S. patent to Reeves No.

2,266,461, and a low-pass lter 21 to a reproducing device 28. The domodulator 2 serves to translate the time displacement of pulses into amplitude displacements. The low-pass lter 2'! serves to eliminate any high frequency components.

If unit E6 is also used as a P. T. M. in branching station, then switch 29 is also closed and pulses 39, produced by a P. T. M. modulator` 3i such for example as disclosed in the aforementioned Patent No. 2,266,401, and time-modulated by a signal from a source 32, are fed through the circuit including switch 29 to an amplitudemodulating circuit 33. The wave generator 3ft for producing a control wave for modulator 32 may be synchronized by means of pulses 24 so that the pulses will have the same timing as the pulses I 'I in the absence of time modulation.

If unit I6 is not to be used as a P. T. M. in branching and out branching station then switch 35 is closed While switches 25 to 29 remain open. In this case pulses 24 are relayed. When switch 29 is closed and switch 35 open, then pulses 39 are transmitted.

Either pulses 24 or the pulses S are fed through an amplitude modulating circuit 33 having a tube 36 where the pulses are amplitude modulated with a signal 31 from a source 38 which may be a microphone or the like to thereby produce pulses 39 which carry both P. T M. and P. A. M. The pulses 24 or 30 are fed to grid 40 of tube 36 while signal 37 is fed to screen grid 4I of tube 36. The pulses 24 and signal 31 combine to produce pulses 39 in the anode circuit 3B.

The unit of Fig. 2 thus, not only amplies and relays the P. T. M. pulses, but also removes P. A. M. from received pulses and adds by amplitude modulation further intelligence to the output pulses. The unit may also be used to demodulate the P. T. M. of the pulses, if desired, and to introduce a new series of P. T. M. pulses. Since the unit is intended to handle only one way traic, two of such units may be employed in relay station II to handle two way traffic.

If the system illustrated in Fig. l is to be used for multi-channel P. T. M. communication, multichannel units such as unit 43 illustrated in Fig. 3 and described in connection with the curves of Fig. 4 may be employed. One such unit sufces where one Way traffic is handled and two of such units are used for two way traino. Relay station I I of Fig. 1, for example, if used for multichannel communication, would include two such anim; M;

t Inmunilcation nels to form a sinslegtainoipulses.. 'In curve.

nl three channels si; 5,5. 'andn st are-li11ustrated. The pulses of r onefoi the fchalnelsfpreieihly.is modulated with an id,ent'ifyi'ngy characteristic dis.- tinct from the pulsejcharacterijstics Yof other'lchannels for synchronizing the nreceive'rs tothe trans# mission sequence ofA the 4channels'. Channel '5d of Fig. 4 is the selected channel which has4 been modulated with a distinct id ntifyg characteristicas indicated byfits 'great pulse width.' This distinct width characterisf jisfusedfto provide synchronizatin 1for' theseparationof the various channels.

The `pulses of curve lllluarekfedlthrough a limit clipper 5l y v'vherel 'they are clipped fat av level .Y 51a (see curve lill) so thatallwthepulses 'are of constant Yamplitude when deliverd'- byy the limit clipper to the'neXt stage, which consists of the channel selector 58. Thefchannel selectory 581s adapted tosele'ct pulsesfaccerding'rto 4their width and is tuned to select puls'esoffthe channel having the distinct widltl'"'cl1a cterisitic'fused for.

synchronization; 'to vvit,"cha nn/tell 5,4;I "The channel selector 58 which Aselects pulses according to their width may be'ovf any'flnown type,4 and may be of the form disclosed'finthe,co-pending application of E. Labinl and applicant. Serial No. 487,072, led May 15,1943,A issued 4U. S. Patent crimination between two given' pulsefwidthsmay be accomplished by any oneoffsevr'al well known pulse width discriminators.v

The output o'fithe lchannelselector V58 may be represented by the train of pulses illustrated in curve 45. which is produced i bythe' pulses of channel 54. The pulses` ofa'zurvev l5 are shown delayed for' a slightfinterval in relation tothe pulses ofchannel 54 .toallow for anyydelay that mightoccur during the`selction' process. Itwill` be understood, of course, that the selector'may be of the type capable offs'election Without dei" laying the selectedipulseenergy. Any'delay, however, is ofno particular significance since delay devices are required, asvvill be' described hereinafter which are used to selected pulse energy..

The pulses of curve .fidare .used to separate the various channels but in order to dso; itis preferablethat these pulsesbeshaped .to 'greaterwidth properly tinithe and greater amplitude.. Fonthislp'urpose, the pulses of curve1l5`are sent throughashape'r 59- which may be a multivibrator or any other known type of shape?A Which will produce the desired effects. Thev output oi `Shaper, 59 represented by curve 136,-, and thepulses there represented willl be hereinafter calledV separating pulses.

The'Y separatmg.. pulses; (curve 46).'. are fed through a series of delay devces, 6l, and 62,. each of said devices v,Serving to delay the separating pulses a ljlurtlfier. amount., The ,devices are p lr'eierably adjustable, yit being understood .'that..

escilaed in relaties. te..

depuesto the,

6. there, be.. meer m r are in. andout branch encens. sotnat the;

justableffeaturez allowsjchoice of channel.; A'They outputfoffeach oisaiddeviceslilD- 6l, and..{iL-is7 fed-toA minerslili,y 6.4i; andflid'` respectively. `MiX`er gl'serves. tos'eparate channel` 55.as.,il,.

lustr'ated in curve fil.' Delay device. lldelays the separating vpulses of curve 46.y so that the separat-Q ingpul'ses lare coincident with A.the pulsesv of1 channel'j 55. The s'e`1'caratingl pulses are of greater. width" than" the ,pulses .of any .ci the .other channels andthe delay device isadjusted so that not only. are` theA separating pllls'esand the pulses .of

channeled, coiruidel'ntA but'the separating pulses. arev'videenough to allow for. anyshift in [time due toftimem'dulation of the pulses'of ychannel sa? if the puissof channel 54, 'from whichY the separating pulses arelderivd. are` time mdulated, the separating pulses', will have to-beiurf-v ther, widened' to` allow` for this. Usually itvr is.v preferredthat. the pulses. of, channel 54 shouldV not, be time modulated.A

The mixerI 63 includesa tubey 65 onwhose grid fltlieincoming train of pulses shown incurve le'is'impress'ed. The tube 66`also has a'seeond, grid 68 on which the separating pulsesfromdelay device Sil yare likewise impressed. Thus the pulses of channel haare given agreater, ampli; tude than the pulses ofother channels. Tube 65.: is biased .tocut-'ofi below the'level 6.9 of curve Llll,

so that only pulses appearing above said level will produce an eiect in the plate'circuit 'lllol tube 65. Thus only the p uls'esrof channel 55.* will apfpear inthe output of mixer E3, asJshownin, curve d8.

Mixers l6d and toperate in asimilarmanner.

to separate channelsl vandfirespe':ti vely so as to deliver at their outputspulsesdepicted inA curves 4Q and 5l] respectively.

They channels fand 56 whichhave beenseparated inthe mixers Strand Silmconsist oa 'pluraltyoftpulses AWinch carry both P. A. M. and

P. T. Theselchannels as'well'aschannel Bil; mayltnen vbetreated,ina lrelayunit of the typey described in Fig. 2." For this purpose relay units.v

ll. l2 and '13 are` connenc'ted to,A they output of miners 63,- S-fland 65;. Thus each.orselectedones` of the channels maybe treatedfso vasto remove, the amplitude modulation and derive the'intelliguencelrepresen'tedwthereby. amplify the P. T. M. pulses, andadd thereto further intelligence`A as P.- A.. In addition, the?. T.l M. ofA selected channels may be removed and new channels'of P. T. M. substitutedY inV synchronism in their plages.` Where new P. T.-

channels are' to' 'be substitutedifoi Fig. 2, it is important substitute channel pulses before time'modulation is thesame as tlieunmolulated timing of the.

replaced channel pulses. Thisw is accomplished by synchronizing the wave generatorA 3Iklz'ontlriefA average timing of the pulses 24.-

Theoutput of unitsll, 12,and '13 are delivered to a miner 'ille-which serves to interleave the pulses of the various channels to produce a single train of interleaved pulses. themixer 'lll is thenvdeliver'ed to the transmissiony means which may consist-of .a common lline4 l5,-l

orla linear R.f translator 'IS v4connected. to a transmitting Aantenna Tl.. v

While. I havejdescribed .all the essential'elements .fori a complete. relay. and in and-out branching station which^ provideslfor. amplitude modulation.communicationas wellas time modulation, it is tobe understoodthat itis'not yneces-- sary.. to. .use ...alli of. ithesel .elements.inlany given.

e. channels than. there other channels n as indicated: in` that the timing of the The output ofI station. For example, in relay station 9 for traffic moving from the west station towards the east station, it is unnecessary to have the decoupling amplifier lll, low-pass lter I9 and indicating device 2l) shown in Fig. 2 since the pulses transmitted by west station l carry no P. A. M. Again in relay station 9 for the unit which is used for traic going in a westerly direction, it it unnecessary to have the amplitude modulating unit 33 of Fig. 2 since the pulses which are sent from relay station 9 to west station I are only to carry P. T. M. and no P. A. M.

It will therefore be seen that many changes can be made in the number of elements of each unit selected for each station. Numerous other changes such as in the particular type of element employed may be made without departing from the teaching of this invention. Accordingly while I have described the principles of my invention in connection with speciic embodiments, it is to be clearly understood that this description is made only byv way of example and not as a limitation on the scope of my invention as set forth in the objects and the accompanying claims.

I claim:

l. In a communication system including a plurality o stations, means for communicating intelligence between two of said stations by the use of discrete time modulated pulses, said means including a relay station for amplifying and relaying said time modulated pulses, and means at said relay station for communicating additional intelligence between said relay station and one of said stations by superimposed amplitude modu- A lation of said time modulated pulses comprising a source of intelligence signals and means for amplitude modulating said pulses with said signais.

2. In a communication system including a pair of communicating stations, means including two relay stations spaced from said communicating stations for relaying intelligence between said communicating stations by the use of time modulated pulses, and means for communicating additional intelligence between said relay stations by superimposed amplitude modulation of said time modulated pulses.

3. In a communication system including a plurality of stations, means for communicating intelligence between two of said stations by the use of time modulated pulses, said means including a relay station for relaying said time modulated pulses, one of said two stations including means for amplitude modulating said time modulated pulses superimposed in accordance with additional intelligence, said relay station including means for removing and demodulating the amplitude modulation of said time modulated pulses to derive the additional intelligence represented thereby.

4. In a communication system a relay station adapted to receive pulses time modulated in accordance with intelligence and amplitude modulated in accordance with additional superimposed intelligence, means for removing the amplitude modulation of said pulses and deriving the additional intelligence represented in said amplitude modulation, means for amplitude modulating the time modulated pulses in accordance with other intelligence, and means for relaying the resulting doubly modulated pulses.

5. In a multi-channel pulse communication system, a relay station adapted to receive a plurality of pulses representing more than one channel, the pulses of at least one channel being time modulated with intelligence, means for separating the pulses of said one channel from the pulses of other channels, means for amplitude modulat ing the pulses of said one channel with additional superimposed intelligence, means for reinserting the pulses of said one channel among the pulses of the other channels, and means for relaying the pulses of the various channels.

6. In a multi-channel pulse communication system, a relay station adapted to receive a plurality of pulses representing more than one channel, the pulses of at least one channel being time modulated with intelligence and amplitude modulated With additional superimposed intelligence, means for separating the pulses of said one channel from the pulses of other channels, means for removing the amplitude modulation of the separated pulses, and means for reinserting the pulses representing said one channel among the other channels and relaying the pulses of the various channels.

7. In a multi-channel pulse communication system, a relay station as set forth in claim 6, including in addition means for amplitude modulatine' with other intelligence the separated pulses of said one channel before reinsertion of said pulses among the pulses of the other channels.

8. In a multi-channel pulse communication system, a relay station adapted to receive a plurality of pulses representing more than one channel, the pulses of at least one channel being time modulated with intelligence, means for separating said one channel for out branching purposes, means time controlled by the pulses of said out branching channel for generating pulses and time modulating said generated pulses in accordance with other intelligence, means to amplitude modulate said last-mentioned pulses in accordance with additional superimposed intelligence, means to reinsert said last-mentioned pulses amongst the pulses of other channels in place of the separated pulses, and means for relaying pulses of various channels.

9. In a multi-channel pulse communication system, a relay station adapted to receive a plurality of pulses representing more than one channel, the pulses of at least one channel being time modulated with intelligence and amplitude modulated with additional superimposed intelligence, means for separating the pulses Of said one channel for out branching purposes, means time controlled by the pulses of said out branching channel for generating pulses and time modulating said pulses in accordance with intelligence, means for inserting said last-mentioned pulses among the pulses of other channels in place of the separated pulses, and means for relaying the pulses of various channels.

10. In a multi-channel pulse communication system, a relay station according to claim 9, including in addition means for also amplitude modulating the generated pulses in accordance with other intelligence superimposed before insertion of said pulses among the pulses of other channels.

11. In a multi-channel pulse communication system including a plurality of stations, means for communicating intelligence between two of said stations by multi-channel time modulated pulses, said means including two relay stations for relaying said multi-channel time modulated pulses, means for communicating additional intelligence between said relay stations, said lastmentioned means including means for separating the pulses of one of said channels from the pulses of other of said channels, and means for superimposedly amplitude-modulating the pulses of the separated channel.

12. In a multi-channel communication system including a plurality of stations, means for communicating intelligence between two of said stations by the use of multi-channel time modulated pulses, said means including a relay station for relaying said time modulated pulses, and means for communicating additional intelligence between said relay station and another of the stations of the communication system, said lastmentioned means including means for separting the pulses of one of said channels from the pulses of other of said channels, and means for superimposedly amplitude-modulating the separated pulses.

DONALD D. GRIEG.

REFERENCES CITED The following referenlces are of record in the I'lle of this patent:

UNITED STATES PATENTS

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