[1]Patented Dec. 26, 1950 2 @ 5 3 5 9 0 6 1 U,L@IITED STATES PATENT OFFICE 2,535,061 ELECTRICAL PULSE WIDTH SHAFER AND SELECTOR Donald D. Grieg, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware AP-ulication August 19,1944, Serial No. 550,183 13 Claims. (Cl. 250-27) 2 This invention relates to electrical systems and porticularly to signaling and control systems such as those adapted to utilize pulses. An obj'ect oil the present invention is the provision of a single means, -common to a trans- 5 mitter and a receiver, for shaping the pulses to be transriitted to a desired width, and for selecti-Lig from received pulses those having said desired width. A further object of the present invention is @0 the provision of a pulse-width selector which wi'bhout requiring any tuning will receive pulses of any v@,idth, but which when pulses of more than one wid'uh are being received operates to select only those pulses nearest the desired width. 15 It thus becomes possible to merely turn on the receiver in order to ascertain if any pulses are being transmitted. If pulses of more than one width within predetermined limits are being trans.mitted, the receiver will select those of the 20 wi@-th nearest the width for which the receiver is ti-ined and re4ect the others. Any of the other puise wi.dths r@iay be selectively received by tuning the receiver to the width of the desired pu@lses. 25 Another object of this invention is the provi,l@ioii of ai iiriproved shaper circuit for reshaping pulses of a. given width into pulses of a. selec@@-ed width less than said given width. Another object of the present invention is the @,0: provision oi an improved combination of a trans@nitter for shaping pulses to a given width and mGO.ulating said pulses with intelligence, and a re.,eiver for select4ng pulses of a desired width and dei-r@odulating said pulses to derive the in- 35 @el',ig,-nce represented by said modulation. 1, @ . Another object of the present invention is the provis-lon of a cord-bination as stated hereinabove in,@vhich the -owses are time modulated with int@lligence, 40 Another object of the present invention is the provision of a. combination, as stated hereinabove, in wh4ch the pulses are frequency modulated w,'@th intelligence. Ar@other ob-ect of tlie present invention is the 45 j pi ovision of a con@ bination, as stated hereinabove, iii which the pulses are amplitude modu@- le.ted with ntelligence. Other and further objects of the present inventio7i will become apparent and the foregoing 50 will be best uiiderstood from the following des crit)tion of enibodiments thereof, reference being had to the drawings, in which: @, Fig. I is a schematic diagram of a time modulated pulse coin-@nunication system embodying 55 tl@s iiivention; Fig. 2 is a schematic and block diagram of a, modification of the system illustrated in Fig. 1; Figs. 3, 4 and 5, are sets of curves to which, i-eference is rrade,in describing the operation'of, the systeirs illustrated in F-igs. 1 and 2; Fig. 6 is a schematic and block diagram of @afrequeiicy modulated pulse communication sys-, tem embodying this invention; Fig. 7 is a sebematic and block diagram of an amplitude modulated pulse communication -system eir@bodying this invention; Fi,,,. 8 is a set of curves to which ref erence is @.nade in describing the operation of the system i',Iustrated in Fig. 7; Fig. 9 is a schematic diagram of a portion of.' a rnodified form of the pulse-width shaper and selector circuit; Figs. 10 and 11 are sets of curves to which reference is made in describing the operation of the circuit illustrated in Fig. 9. It is to be understood that the curves shownin the drawings are not intended to have an exact quantitative significance, and are only in-, tended to have meaning to the extent brought out by the description. According to this invention a single means, or. pircuib, is provided serving the dual function of, shaping the pulses to be transmitted to a desired@ width and simultaneously selecting receive4 pulses of or nearest said desired width. Said means or circuit may be employed with various @ypes of pulse rnodulation. The modulation, foreya.-nple, may be one of several forms of P. T. M., (pulse time modulation), or it may be P. F. M. (pulse frequency modulation), or P. A. M. (pulse@. ar@iplitudeiiodulation) or any combination of: the different types of modulation so long as one does no interfere wi another. . By diff-erent for.-Liis of P. T. M. modulation, ref-erence is inade to "single" pulse time modulation with respect to a given tirae position or some pulse or pulses fixed in time position, and various forms of "double" pulse tirne modulation such as where the successive pulses of a given channel are time displaced from normal time positions in push-pull" manner toward and away from, each other. In Fig. I there is illustrated a "double" pulse time modulated syster.1 embodying this invention, whereiii pulses are generated, time modu-', lated w-ith intelligence, and passed through the% i@lidth shaper and selector circuit of my inven-. tion to shape the pulses to a desired width. These pulses are then d6livered to a receiver by any suitable - means, such as for example by means@ of a radio link or by line transniission,
[2]3 In the receiver, the received pulses are detected so as to remove the carrier frequency if a radio link is employed, and are then applied to the width shaper and selector circuit which selects the desired pulses and transmits them to a demodulator. The demodulator translates the time modulation of these pulses into amplitude variations and these amplitude variations are impressed upon a suitable utilization device such as for example a speaker system. Pulses may be generated and time molulated in any suitable manner. One preferred type of pulse generator and modulator is described in the copending application of Emile Labin and myself, Serial No. 455,897, filed Aligust 24, 1942, for "Push Pull Modulation System. " since issued as U. S. Patent No. 2,416,329. O@e form of pulse generator and modulator there dp-scribed aiid designated herein in Fig. 1 by the numeral 15, includes an oscillator 16 for producing preferably sinusoidal oscillations 22 as illustrated in curve a, Fig. 3. The sine wave 22 may have a frequency equal to one half the repetition frequency of the pulses to be generated. The sine wave 22 is then fed through a cusper circuit 17 which serves tO translate it into pulses and at the same time provides for time modulation of the pulses. The cusper 17 includes a transformer 18 having a primary 19 connected to the output of oscillator 16. The transformer 18 has two secondary coils 20 and 21 coupled to the control grids of two vacuum tubes 24 and 25 respectively in push-pull arrangement similar to a full wave rectifier. The cusper amplifies and, in effect, full wave rectifies the sine wave 22 of curve a, Fig. 3, to obtain a cusper wave 29, curve b, Fig. 3. The modulation of the cusper wave is produced by applying the signal intelli-ence derived from a source 34 to primary coils 3i'on transformer I B. While rectification of these waves iiiay be symmetrical relative to zero axis 26, it is shown for purposes of illustration as being offset by diff erent biasing potentials 32 and 33. This gives the effect of an offset axis 28 about which modulation takes place. The signal intelligence operates, in effect, to vary the sirie wavd 22 of curve a teiative to its offset axis 28 as regards the full wave rectification. This relative variation between the wave and the zOr6 akis thereof is illustrated in curve a 6f Fig' 3 by the upper and lower modulation limits 26 and 30. When the input signal varies the relative relation between the offset axis 28 and the sine wave as indicated by limit 30, the cusper wave, fbr example, is displaced as shown by the broken line 3 1, and when varied to the opposite limit 26, it is displaced as shown by line 27, curve b, Fig. 3. It will be observed that the signal wave thus varies the time positions of the cusps in push-pull manner toward and away from each other thereby decreasing or increasing the time interval between successive cusps. : The output of tubes 24 and 25 is fed to a gate clipper and amplifier 37. The clipper of device 37 may be of any well-known form, such as a double diode clipper, that clips the cusps between levels 38 and 39, curve b, Fig. 3, to thereby ]Orodilee base pulses which when amplified appear as shown in curve c. Of course, it is to be understood that by adjusting the gate clipper, the limit levels may be varied so as to obtain a base pulse of a lesser or greater width. It is preferred that the width ol the base pulse thus produced be greater than any pulse width which is to be transmitted. 4 The output of tlle device 37 may then be fed through a multiple-type switch 40, to a width shaper and selector circuit 41. To translate the base pulses shov,7n in curve c of Fig. 3, into pulses of the desired width, the base pulses are impressed unon a resonant circuit 42, said resonant circuit comprising a capacitance 43 and an inductance 44. Either the capacitance 43 or the inductance 44, or both, may be (-i made variable to enable tuning of said circuit to a desired frequency. Said resonant circuit is tuned to a frequency having a period equal to twice the period of the desired pulse width. It is desirable that an impedance be placed in series viith the resonailt circuit 42 which is relatively high in compariso,-q with the impedance offered by said circuit so that the potential of the pulses impressed across the resonant circuit wiH not be great enough in relation to the poten2fj tials developed by the free oscillations of said circuit to nullify the latter. The impedance may consist in part of an electron tube 45, preferably one of the high impedance type such as for example, a tetrode. 2 The resonant circuit 42 is arranged in the anode circuit of tube 45 with one end 46 of said resonant circuit connected to the anode 47 and the other end 48 of said resonant circuit connected in series vvith an impedance 49 to a point 30 50 which is connected to a source of anode potential. Tube 45 and its associated circuit is a known limiting circuit which serves to assure that all pulses impressed upon the resonant circuit 42 35 will not exceed a c.@-rtain amplitude, indicated by I)roken line 5 1, curve c, Fig. 3. The incoming base pulses shown in curve c, Fig. 3, are impressed, through tube 45 inverted as shown by curve d on the resonant circuit 42, the leading 40 and trailing edges of said pulses t--nding to produce damped oscillations in ,3aid circuit. Means such as are next described may be prgvlded for damping out or substantially critically damping certain selected undulations of said damped oscil45 lations. . An electron tube 65 is arranged in shunt across said -resone@nt circuit 42 with its anode 66 connected,to end 46 of said circuit and its cathode 67 connected to the other end 48. The control 50 grid 68 of said tube is connected throu.-h grid resistor 69 to point 50, grid resistor 69 being shunted by the usual grid condenser 70. Grid 68 is also connected to ground through a resistor 'i I shunted by a condenser 72. 55 Referring now to Fig. 3, it will ba seen that when positive pu'ses such as shovrn in curve c are impressed upon the gri-d 54 of tube 45, pulses of opposite polarity, shovvn in curve d, will be applied to end ciO of resonant circuit 42. The 00 P(tenti-al on grid GS, with respect to cathode 67 sh6wri in curve e will be positive for the ertire duration of each of the pulses of curve c. The leading edge of each of the r@ulses appearing at cnd 46 will shock-excite said resonant circuit into 05 Oscillation thereby producing undulations. At the first undulation 7@l, curve f, the anode 66 of tube 65 will be -negative so that despite the positive voltage on grid 68, tube 65 ivill not conduct and anegativepulsewillbed eliveredasoutput. After 70 the undulation 73 has I)een produced in resonant circuit 42, the potential across said circuit reverses Prid tends to form undulations 70,, etc., shown in dotted lines in culve j'. However, the grid 68 of tube 05 is positive and when the potential across 75 the resonal'it circuit reverses, anode, 0 6 of the tube
[3]66 likewise becomes positive and tube 65 conducts. Thecgnditction of tube 65 serves to dampout undulation 74 so that instead of undulation 74, a slight ripple 75 (curve b) may be prc>duced. It is preferred that the pulses impressed on grid 54 of tube 45 be of greater width than the width of any Gf the ,3ulses to be p@roduced by the width shaper circuit. Therefore when the trailing edge of the pulses impressed on grid 54 arrives, undulation 73 h,,is already been produced, and the energy teTadip-.- to form undulatic.- @i 74 is being d,,imped out thi-ough tube 65. The effects of said trailing edge which would also tend to impress a positive voltage on anode 66 of tube 65 are also damped out through the conduction of tube 65. -Since the width of the pulse 73 depends iipon the tuning of the resonant circuit 42 it will be @pparent that by tuiing said circuit pulses of various wi-dths may be produced, for example, a narrower pulse 76, curve j, Fig. 3, may be obtained by tuning said resonant circuit to a fre.:Iuency greater than the frec,,uency to which it was tuned to produce pulse 73. LLI,,ewise, piilse 77 -will be produced if said resonant circuit is tuned to a frequency less than tl-le j'requency at which ptilse 73 was obtained. The width shaper and selector circuit 41 also includes a limit clipper 78 ar@d a peakfollower threshold clipper 79, Fig. 1. The iimit clipper 78 may be of any known variety and preferably has means for varying the ievel at which the clipping is produced. The grid 83 of tube 84 '@S biased close to cut-ofl' so that the t-iibe will r@ol. -oass the tips 88 of the pu-ses extending beyond lev,l 89 as shown in curve f, Fig. 3. By varying the bias applied to grid S-3, the level 09 may be varied. FGr exaniple, a tapped potentionieter 85 w@.th its resistance connected to a source of biasing potential mgy be used for this purpose. The pulses 9 I delivered by limiter circuit 78 will thiis appear as illustrated -in curve g, Fig. 3. The pulses 91 are substantially rectangular and have the desired pulqe w-ldth. It will be noticed, however, that the ri7)pl-- 75 is not eliminated. In the peak-follovier tiireshold clipper 79, this ripple disappears and a rectqngular pulse form remains. In the peak--foliower threshold clipper 79, pulses 91 are fed tlirough a switch 93 and a condenser 94 tG the grid 95 of aii electron-discharge tube 96. The grid circuit includes a resistor 97 and a biasing resistor 98, the latter being shunted by the usual by-pass condenser 09. The anode 101 of tube 96 is connected through the usual load resistor 102 to the positive eiid. 103 of q source of potential having its negative end connected to ground and through ground back to the cathode 100 through resistor 98. Potentials developed across resistbr 102 are delivered as output to the next stage. The operatior, of such peak-follower threshold clippers is understood in the Prlu. Therefore, oWy a brief descr,Dtion will be given. When a positive potential, slich as a Dulse 9 I is applied to side 104 of condenscr 94, grid cui-rent wil@, flow charging side 104 positi-Vely on@u side 105 negatively. Thus a ne-otive pol,cntial will be applied to the grid 95, this @@oti@ntial be@'ng prcp_Dortional to @Lhe val-ae of the pulse applied. The time constant of condenser 94 and its associated resistors is such that the condexiser will lose its charge relatively slowly. Thus assult-i-ng that the first pulse of curve g is the L-irst pulse applied to condenser 94, the charge on conderaser 94 w4ill rise to @ level such as that i,idicated by the brokc!n line ICF,. The charge 6 of the charge will be dissipated during the intervals between pulses, and this will be replenished by each succeeding pulse. The effect c@.L' the charge on condenser 94 is to maintain a cut-off. bias on tube 96 at the level designated by broken line 106, curve g, Fig. 3. Therefore, only the portions 107 of pulses 91 which appear above said level will be passed by said tube 96 and delivered as output. It will be 10 therefore seen that the function of the peak-follower threshold clipper 79 is to clip o-ff a fixed amount from the top of each of the incoming puises regardless of the amplitude of such pulses. If pulses of lesser amplitude than the level 1 r, desi-nated by numeral 106 in curve g occur betwe(;@ pulses 9 1, said lesser pulses would not appear in the output because of the clipping level. It will, therefore, be seen that the peak-follower clipper serves to separate pulses of different am2o plitudes and to select only those pulses having greater amplitud,-s. As will be explained hereinafter, the position of level 106 var-ies with the amplitude of the pulses received so that if all the pulses received are of smaller amplitude than tlle pulses shown in curve g, the level IC 6 will be proportionately, lower. But since the level will be lower, the tips of t'hese latter pulses, despite their lesser amrlitude, will be pa-gsed to the outpult-. It will thus be seen that the clipding level tends to be prodortioned to the level of the pulses of maximum amplitude present, regardless of whether sgid maxiri'lum amplitude is in absolute terms large or small. If common line transmission is to be employed, 3,I) the output of the peak and follower clipper 79 riay be directly delivered to the line, or applied through amplifers thereto. If, however, thetransmission is to be acco@- nplished throu.@h a radio link, said output is delivered through the 40 swi_tch 40 to a radio frequency translator I 10 where it is impressed with a carrier .@reauency, curve i, Fig. 3, and from tlience through switch 40 to an antenna system I I 1, While I have shown the pulses as being both 4 generated and r.,iodulated in pulse generator and modulator 15, it is to be understood, of course, that such modulation may be accomplishied, after the pulses have been shaped in width shader aild selector circuit 4 1, by a modulator iricorporated in the R. F. translator II@. The source of the electrical signal 34, may be connected by means of jack 192 to the radio frequency translator and produce time modulations of the pulses in said translator. Circuit 41 not only functions as a ividth shaper as has been explained hereinbefore, but also serves to select pv-lses of the desired width. IfPoili@-pon line transmis ion is used, the i-neomin.a pulses may be directly applied to said circuit or (iO applied thereto through an amplifier. In the case of a radio link, an antenna system which may be the same antenna systerd I I I used for 'transmiqsion may also be employed for reception. Such double use of the antenna system (35 is likely to be especially desirable with portable transmitting and receiving systems. The circuit illustrated in Fig. I is particularly adapted for such portable tise. Assuming that pulses of varioas widtlis are re70 ceived as illustrated in curve j, Fig. 4, these pulses are preferably passed through a carrier frequency a-mplifier and detector 113 leaving only the envelope of the pulses as shown in c-arve k. The output of amplifier and detector II 3 is prefwill remain at this level as only a small quantity 'I-45 erably in the form of pulses negative with respect.
[4]7 io giround, as shb@,vn by the curve k, this outi)ut being dehvered to the width sharer and selector circuit 41 throu.@h switch 40. It will be noted that while the pulses to be shaped were of positive pelarity with respect to ground (curve c, Fig. 3), the pulses to be selected are of negative polarity (curve k, Fig. 4). It is preferred that the gain of the amplifier and detecto): If 3 be such that t,@ie pulses which are to be selected (curve k, Fig. 4) should be of less amplitude than the pulses which are to be shaped (curT.7e c, Fig. 3). The pulses which are delivered to the input of the width shaper and selector circuit 41 are impressed through tube 45 on resonant circuit @2. it is preferred that the impressed pulses be of constant amphtude. For this purpose suitable rie-ins rnay be provided iii the araplifier and detector II 3, or this riay be accomplished by means of the limiting action of tube 45 and its associated circuit. For this purpose it i-@iay b-, -qecessary to vary the level at which said tube limits v@hen -hifting fro,-n tral-ismission to reception. Vlhere for example, occasional pulves of unusually large ainplitude like pulse I 1 4, curve k, F-i g. 4, are dell:vered to tube 4 5, it may be desirable @@o adjust the circuit associated -@,iith said tul)e to prov.'Lde limiting action at the level I @ 5, curve k, to assure obtaining pulses of ec;nstant alnplitride. The received pulses, the envelopes of vihich are shovin in curve t, r.-ia37 i-nelude, for exa-,nple, pulses I i 4, 116, 117, 118, and II 9 whi-Ch are of the desired width, as vfell as pulse 120 which is three times the desired width, pulse 121 vvhich is iwice the desired width ai-id pulse 122 which is half the desired puilse width. These pulses bein.negq-tive, as showli by curve k of F-ig. ! will appear as positive pulses at p-nint 46, as shown in curve L o-@ F-ig. 4, and v,,ill produce ne.@ative voltages in pulse for,,-r@ on gi-id 68 -.,@,ith respect to cathode 07 (curve 7i-.) corresponding in wid'ul-@ to the received pulses. It @,jill be re-,aiembered that in order to shape tl-le pulses to be transinitted to a desired width, resonant circuit 42 vias tuned to a frequency having a per-lod equal to twice said desired width. Thus the leading edpe of the pulses to be transmitted produced by srockexcitation oscillations of the reso-.---nt circuit in -,7ihich each half cycle had a period or viidth equal to the desired v,,idth. )Tihen i@u i-s desired that tlie receiver 1,,e tuned to select pulses of the same v,7idth as is transmitted, no adjustri'lent of the resonant circuit 42 is necessaiy and the circuit is kept tuned to the same frequancy, that is, a f@,equency havini.@ a period eclual to twi@-e the period of the desired width. The leadin.- eclges o.-' the pulses 114, and 116 th,rough 121 will all@ shock-et"cite resonant circiiit 42 into oscillation. More srecifically, the leading edge of pulse q I 6 will produce a positive undula,tion 126 (curve n) ",vhip-h is the first half cycle of the dan-ii)ed oscillatioiis of circuit 42. The next undulation x,@ou"Ld +.end to be a negative undulation 127 of lesser amplitude because of the inherent damping of the eireiii-t. Tlae beginning of undulation 12-o wbuld occur at the time of the arrival of the trailing e'uge of pulse 1 1'3. This trailing ed.,e tends to produce an undulation 123. The effects which teids to produce undulatioiis 127 P-nd 128 combined to produce an undulation 129 of rela+@ively large @,mplitude. . The negative undula'uion 129 tends to be followed by a positive undulation 130 of lesser amplitude. But it viill be noted that after the traila,5351061 ing edg6 of -pulse 11 6 has passed, the gtid 54 of tube 45 becomes less negative, tube 45 conducts, and there is a current flow across resistor 49. Therefore a positive potential is applied to grid 63 of tube 65, and said tube will conduc'c, at any tin'le after the trailing edge of pulse ,IO has pass-ad, provided a posi.tive voltage is applied to its anode 66. At the end of undulation 129, such pos@@tive voltage is applied to anode 66, and tube 10 C5 therefore conducts and substantially damps out any further oscillations in eircliit 42. PLilses 114, 1;7, 118 and 119 which are of the desired width, will all produce the same effects. Undulations 126 and 129 then pass through the 1.5 limit clipper 78. It is preferred that the level 89 at which said clipper operates should be greater than the peak of undulation 129, so that no limit: clipping occurs. However, if the negative undulations produced by the received pulses are of, 20 greater amplitude than the level 89, it may be desirable when changing over from transmission to reception to shift said level in order to prevent clipping of these undulations. This shift may be accomplished by an adjustment of potentiometer 25 85 in the limit clipper 78. The polarity of the pulses is reversed iii the limit clipper 78 so that at the output of clipper 78 the pulses appear as shown in curve o, Fig. 4. Ti-lese pulses are then passed through the peak 30 _follower threshold clipper 79 and are clipped at level iUG, which is the same level designatcd by like number in curve 9, Fig. 3, to thereby deliver at the output of clipper 79 pulses such as shown in curve p. 35 Pi:@lse 122, curve 7,@' Fig. 4, is of less than the desired pulse width. The leading edge of pulse 122 will shock-excite circuit 42 a.,id tend to prc)duce undulation 133 shown in dogted lines in curve n. The trailing edge of pulse 122 v.@ill tend 40 to produce undulation 134 also shown in dotted lines in curve n. The resultant oscillation produced will consist of a positive undulation 135 and a negative undulation i 3 G. The negative undulation 136 will be of very siiiall ampli.tude in comroduced 4:5 parison wit h negative undulation !29 p by a pulse of the selected width. The smau amI?Iitude of undulation 133 is due to the out of phase relations of uildulations 133 and 134, and may aiso be partially due to loss of energy through 5 0 conduction of shunl@ tube 65 which tends to rapidly damp undulation i33. Since it is the negative iuidulations of curve n which are clipped in the peak-follower threshold clipper 79 and since negative undulation 136 is of insufdcient ampli55 tude to be clipped, said undulation will have no effect on the output. Tb-i).s it will be seen that a pulse which is of less than the selected width will be eliminated. Pulses of greater than the selected width vvill, 60 likewise be eliminated since their negative undulations will be of lesser ampli,@ude than undulation 129. For example, 121, curve k, Fig. 9, is twi,@e t'lle selected width. The leading ed.-e of pulse 121 produces a positive undulation 140 fol65 lowed by a negative undulation 4 Li I which tends to be followed by a-nother positive undula'6ion 142 shown in dotted lines, curve ?z. But at the end of undulation 14!, the trailing edge of pulse 421 intervenes tending to produce a negative undula70 tion 143. The resultant is a slight negative uiadulation i44. It will be noted that nega'tlive undulation 141 is of considerably less amplitude than negative undulation 129 produced by pulse I @ 6 of the selected width. Therefore, undulation 141 75 will be eliminated in the peak-follower clipper '@g.
[5]9 Pulses having a width which is b@ii odd multiple of the selected vjidth will produce negative undulations greater than those produced by even multiples but of less amplitude than the iiiidulations produced by pulses of the selected width. For example, pulse 120, curve k, Fig. 4, has a width ea-Ual to three times the selected wid@uh. The leading edge of said pulse produces positiare undulation 148, negative undulation 149, and positive undulation 150. Positive undulation I-Li@, tends to be followed by a negative undulation 15'@ shown in dotted lines, curve n. It Vii-11 be notc@d that negative undulation 151 is of considerably less amplitude than negative undulation 149 diie to the damping of the circuit ' The trailing ecge of pulse 120 tends to produce an undulation 152. @Undulations 151, 152 add to produce.iindulation 153. But since undulation I 5 I is of lesser ampli-tude than undulation 111,9, or the correspondin,@ undulation 12 7 produced by pulse I IS, undulation 153 will be of lesser amplitude than undulation 129. Consequentl@y undulat-ion 153 will be of insufficient amplitude to be clipped by the peakfollower clipper 79. It will therefore be seen that while pulses of a width equal to an odd multiple of the selected @vidth will produce undulations having greater amplitude than those produced by even multill@es of said selr,-cted width, the aforesaid undulations will still be of lesser amplitude than those prod-Liced by piilses of the selected width. From the foregoing it will be seen that, i3uls-,.s of the selected width wil@l be translated into negative undulations of maximum amplitude and@ that pulses of other widths will produce iiegative uiidulations of lesser amplitude. This-variation in amplitude of the negative undulations produeed tends to vary sinusoidally with varying deviations from the selected pulse width. This is illustrated in Fi.@. 5 where the ar(iplitude of the negative undulations produced Is plotted along the Y axis against the width of the pulses along the X axis. Point pi represents the selected width, point P2 twice the selected width, point P3 three times t'ile selected width, etc. it will be seen that the maximum amplitude occlirs at pi. It will b,-@ noted J"hat on both sides of pi, the amplitude declines sinusoidally. At point V2 .the amplitude of the negative undulations is at a minimum. It then i-nereases from P2 tG P3 until at P3, which is the first odd multiple of pi, there occurs another peak. The peak at P3 is less than the peak at pi because of the damping occurring in resonant circuit 6 1. The same variation is again repeated with the liew peak at p5 which is lesser in amplitlide than peak p3. Whi-,n pulses of the selected width, such as pulses I 1 4 and I I 6 through I 1 9 are being received, the undulations 129 produced by such pulses will have the amplitude indicated in curve n and will be clipped at the level indicated by broken line 106, curve o. If such pulses are not being received, then the level at which the peak-follower threshold clipper operates will vary and will be of a value generally determined by the maximum amplitude of the undulations present. This is .illustrated in c-arve q, 4, whi-,Ph represe.lts the. input to the peak-follower threshold clipper 79@ -when no pulses of the selected viidth are present. Numeral 155 designates the clipping level. It will be seen that this leve! rises from zero vaiii.e to a given valve at undulation 149 and to-a greater value au undulation 153. T.hi@s the peaks of undulations 149 and 153 @vill be clipped and delivered as oijtput as will aisg be -the peal@, o@i' utidulation 14 1. 21535,061 10 Proixi7@the -foregoing it 'will be seen that- wheii pulses of the selected width are being receiv6d, pulses of other widths will be eliminated in the width shaper and selector circuit 4 1. In the absence of pulses of the selected width, other pulses will be received and transmitted t,irough said circuit 41. Furthermore the resonant circuit 42 may be tuned to shtpe and select pulses of any desired width within the limits iw-posed by the io paramet6rs of the system. A fixed level threshdld clipper 156 may beuq-ed in place of the peak-follower threshold clipper: 79. With such a clipper, the clipping level iO6 would be fixed so 'Lhat only the positive undulations i5 shown in curve o whicli have a greater amplitiidia than level 106 )#ould be accepted ' Since@such uhdtilations are only produded by pulses of substantially the @elected width, it will be obvious that by using a fixed clippet 156 only pulses of 20 the selected width'wollid be received and in the absence of'such ptilses of the selebted width, no other pulses would be received. With this arrangement, it beebmes possible by a single adjustment of resonant circuit 42 to select the width :.),5 of the pulses to be transixiitted and by the same operation limit the receiver to receiving only pulses of said sele&ted width. This @Lrrangement, therefore, provides for @ingle channel transmission aiid reception at any one time and diffefs @o from the arrangement using the peak-foliower clip@e@ in that when the latter is emplo@ed, the receptioh ma'y be multi-channel. - 'The otitput'of the width shaper and select6r circuit 41, which ineltid6s the clippers 78 and 79, 35 and altetnatively clip@er 1'56, is delivered to' a demodulat6r circiiit 157 (Fig. 1). This output Is a 'p]@lied'to the c6ritr6i grid of the dernodulator tube 161 and causes tuned circuit 173 connectod to the screen grid of the tube, to'oscilfato - o@t 'a 40 desired frequenck producin@ in the output circuit of tube I GI a combined wave in -the form of'@a combination of the *ave g6nerated in the circuit 173 and the ihconling @Lilse@. The circuit 173 Is preferably tuned to some harmonic of the cadence i li frequency df the pulses when they @Lre unniodulated so that as the pulses are time-disploeed due io modula'Li6ii sign@tls, the output Ptilse8'6f tube 161 will be raised to different leveis deperiding upon their time displacement. Accordingly, @,) o in the outpiit of tube 161 there v@,ill appear a modulation envelope of pulses carrying: signal modulations according to the amplitudemeasurements thereof. For a further understanding of the @rinciples of this type of modlilator, reference 55, may be had to the copending application of D.- D. Grieg, Serial Number 459,959, filed September @8, 1942, now PE@tent No. 2,416,306, issued February 25, 1947.- Alowi@6,ssfilter'176isprovidedtoby-passthe 60 'hi@h frequericy pulse components and pass (>n the modula-tion frequ6ndies that defirie the signal ehvelope. Proni the-for6g6ing description it will be seen -that I hftve provided a OWse time modulation 05 system iiicluding a single, common width shap,6r and selector circuit 41 which serves not only to shape the pulses to be transmitted to a desired widt.-h but also serves to select receiv0d pulges of said desired width. TO In the embodiment shown in Fig. 1, a multiple type switch P@O is employed to connect the transmitter or the receiver to the width shaper and .selector circuit 41 and is likewise used to connect either the transmitter or receiver to the antenna 75 system I I 1. Instead of a switch, however other
[6].idevices may be used which will permanently con.nect both the transmitter and receiver to the :grid shaper and selector circuit 41 without the necessity of manipulation. In common line transi--ission, and in rtlier 7Lis,,-s where the rerietition frequency of the pulses is not very higb, hybrid coils may be used for this purpose. How.ever, in other cases, where the frequencies are -too high for conveniently using hybrid coils, an electronic mixer circuit and an electronic distrib@utor circuit may be used to connect both the transmitter and receiver tG circuit 4 1. . A. preferred embodirient utilizing electronic -mixer and distributor circuits is illustrated in Fig. 2. The output of pulse generator and modu.lator 15 is delivered to the grid of tube ZO I of a - mixer stage 200. The mixer stage also includes another tube 2'Lk2 whose grid is in turn connected with the output of the rarrier frequency amplifier and detector If 3. It will thus be seen that -the pulses to be shaped are impressed upon tube .201 and the received ptilses from which selection is to b-, made accordin.- to pulse width is im..pressed upon tube 202. The anodes of tubes 201 :and 202 are connected together and to the width shaper and selector circuit 41. Because of +.he arrangement of the mixer 200 there will be no -reaction between the Pulse generator and modu@lator 15, and the carrier frequency amplifier and detector If 3. To insure against such reaction ,through the interelectrode capacities of tiibes 2 Of and 2 0 2, such tubes are pref erably of the type -having high int,-rnal impedance such as tetrodes. . 'nie outpvt of the wi-dth shaper and selector :circuit 41 is deli-Vered to the electronic distributor 2 t 0. The distributor 2 1 0 is of the cathode f ollower tvpe having negative feed-back produced by Etn unby-pass,,cq resistor in the cathode Jeads of tubes 21 1 and 212. The iiegative f eed-back serves ,to produce a more linear and stable operation. ;The output of the width shaper and selector circuit 41 is applied to the grids of tubes 21 1 and 212. The potential developed across the cathode resistor 2.13 is delivered to the radio-freciuency ..translator fig while the potentials developed across the cathode resistor 214 are delivered to the demodulator f 57. It wiU therefore be seen that because of the arrangement of the distributor 210, no inter-reaction will ocetir betiveen tho, R. F. translator II 0 and the demodulator 157. I The output of the R. F. translator I IO is fed through ,i coupler 220 to the antenna system I i 1. ,-The pt3.lses re--ei-Ved by the antenna system II I rlre fed b,,ick tnrough said coupler to the input of the carrier frequency amplifler and detector .tf3. . A blocki-ng voltpge generator 225, synchronized with pililses produced in the pulse generator aiid rpodulator 15, supplies blocking voltages to a mixer sta-e in the carrier frequency amplifier and detee 113 so that whenever pulses are being impressed upon the grid of tube 201 by the P-ulst- generator and modulat6r 15. the car.rier frequency amplifier and deter-tor 113 is blocked so t-hat no pulses are impressed upon the grid of tube 202. It will therefore be seen that no interference will occur in the width @hat)er and sele-ctor circuit 41 and the distributor 2[0 between pulses that are to be transmitted bnd Pulses that are received. With the arrangement shown in Fig. 2 the width shaper and selector cireiiit 41 is connected both to tne transmitter and:to the receiver and no manipulation is necessary to switch from one to the other. If. however, the carrier fre2ta3b 061 12 quency amplifier and detector bas too liigli a gain so tiiat the re-.eived. pulses are of the same amplitude as the pulses to be transriaitted, it may ba advisable to change the bias and level of operation of the limit clipper 78 which fo,-ms part of the vvidth shaper ard selector circuit 41 (s,,e Fig. 1) - For thispiirpo.,-e, the potentiometer 8 5 may be Fdjusted from one tap to anotli,-r. Ordili@ narily, however, if t',Ie gain of the carrier frcquency qmpl-'fier and detector 113 is propr.,rly adjusted, si-ich change be unnecessary. As stated hereinbefore my invention is also applicable @o frequency-modulated pulse sys'Len-Ls and olie such system embodying my invention is i;,, illustrated in Fig. 6. Any suitable mea.,2s may be employed for generatinp, and frequency-med-,"Iatin.- the pulses. One suitable form is shovin by way of exarqple as including a blockin.- oscillator 229. The time constant of cond,-nser 234 and its associated resistances is chosen so that a charge builds up on said condenser which neriodically blocks conduction of the tube 230. Vnien this charge leaks off, tl-ie tube wiH a.-,.Lin start to oscillate. By applying a modulating voltage in series with the giid 235 of tutbe 230 the time at which tube 2@.0 will again begin to conduct after haviiig been blocked by the .ootential oncondensr@r 234 may be varied. Thlis the outr-,ut of the blocking oscillator will consist of pulses which -,,re frequency modulated in accordance with the signal energy. This outout may then be fed throligh a multi@,)Ie sr,7itch 145 to a viidth shap,,r and sr@lector 41 to shape the pulses to the selected width, and through the R. P. translator I I 0 to the antenna system III. The PLIses receiv@,d ljy the antenna system I I I are fed to the carrier frecILiency amplifier and detector 113, thence through width shader and 40 selector circuit 41 to an integrating circuit 251,1 of any kn.own type whirh 7;ill translate the frequency--irodiilated puls(,s into a mi)lit-..,,de-medulated enerp,,y. The oiitpijt of the integratin, (-ii,ciiit 250 may then be fed through an ainT31ifier -1 -) 251 to the utilization device, which @n,,iy b@-@ for example, a ,;peaker 177 or any othei- ii-idicatin@@ device. This invention is also applicable to amplitilde modulated pulse systems. One form of amplitude riodiilated pulse system embodying my invention is illustrated in '-Pig. 7 and its operation is describ-d ii.-i connection with the curves of Fig. 8. Peferring to F-ig. 7, pulses may be generatp-d by any siiitable means such as, for e.7amiole, a multivibrator 252. The pulses are then fed throtigh the width shaper and selector eireiiit 41 where they are shaped to the desired width. They are next fed throi-igh switch @.9 to a pulse ariplitude -rnodulator 253 which may be of any kno@,in t),Pe. The pulses are then amplitude-mcdulated in aeeordance with the signal and delivered to a radio fteqilency translator 254 whose oiitput is iii turn fed to t)-ie antenna system I I 1. Amplitude modulated pulses which are received 65 in antenna s@stem III are fed through switch @0 to the carrier frequency implifier and detector x 13. The output of said amplifier detector 113 is separated into two different channels. It is preferred that the output of carrier frequency airpli-rier -Ind detector 113 consist of negative puises with respect to ground. one portion of said output is fed to the width shaper and selector circuit 4 1. Assuming that the received pulses consists of 75 pulses of various widths and amplitudes such as
[7]i3 shown in curve aa of Fig. 8, these pulses wM be limit-@elipped along the li--qe 255 by tube 45 of the width shciper and selector circuit 4 i. Thus 'a series of nositi-Ve liulses, such as shown in ei-irve bb of Fig. 8, of equal amplitude but of different widths, will be applied to the resonant circuit 42 of the width shaper and selector circuit 41. Assuming that pu,,Ises 256, 257 and 258 of curve bb are of the selected v@idth, undulations such as those shown in curve cc of Fig. 8 will be produced by resonant eircuil@- 42. These are clipped along the level 265 in the peak-follower threshold clipper 79 thas delivering as the output of the width shaper and selector ei-reiiit 41 negative pulses 259, 2@ng and 26@, curve dd, Fig. 8, each of which begins qt the trailing edge of its corres-oonding pulse 256, 257 and 258 of curve bb. It will thus be seen that th,@se pi,,Ises are de!-.yed for a time Ti equal to the width of any of the pulses 256, 257 or 258. Pulses 2r)2 and 2fj,'@, of curve bb which are pulses of other th,@),--q th-:,, s,@lected width, will be suppressed within the width shaper and selector circuit 41. The output of the width shal3er ard selector circuit ,II is fed to a mixer stage 264 which ircliides a threshold clipper. The positive ptilses shown in curi7e aa which ,are the olitput of the Parrier freauency amplifier and detector 9 13 ore fed not only to the width shaper and selector eire-Liit 41 biit also to a width shrper ond sele-.tor circuit 266. Cireiiit ?.96. is similar to that of circuit 41 biit does .iot include the clii3per stages 78 and 70. Moreover the constg,nts of thp eirctiit including tube 45 are si-tch that Tio limiting action is produced. Thus when the piil,,5es shov-7n in curve au ar(- imprc-ssed on the eire-uit 266, the resonaiit circuit of said width shf,p.,@r qnd selector v7ill oscillate nroducing u--qdu.lations si-7ch qs shown in curve ee. It is to be remembered that the in-oiit of circuit 266 consists of pulses varying in width as well as in ainolitude, Pulses having the dpsired width will tend to prodiiee greater T-ieg@ative undulations than pulses hf@?vir.g other widths. The voltages shown in ei3rve ee are fed into the mixer sta--e in clipper 2r),'@ vhere they arfadded to th- voltages shown in ci-,rve dd. Tbe@7 ore theti threshold-clipped @,,Ior,g level 267 to th@-,,reby d-rive piilses 118, 269 and 271 which vary in amplitude in accordance ivith thc-ir amoliti3de varia,tio,.ns. By Pdding the o,,Itpi-@t of the widtt-i shaper and selector cir,-,.-iit P 1 which consistg solelv of pulses of ttie desired width to the oiltdut of,@iiidtti shaper Rnd selector -ircuit 2fiq which incliidf-s pulses both of the des-Ared width and other widths, but ,,@ihich latter circuit tends to discriniiT).a,'tle in amplit,,.ide in favor of pulses of the desired width, the pulses of the desired width are given a suf,qcj.ent additional a-mdlj.tude so that they may be disti--qg,3ished or sepa,rot-d by th,@ threshold clipper frorn plilses having other widths. Circ7oit 2CG iiot only serves, as stated hereinbefore. to discriminate i-n fovor of pulses of the desired width but also seri7es to produce a time dela-Y equal to Ti for the nbgative undulations as showninel-@rvee-,,thesq,rnef.).sineircuit4l. Thtis ptilse 25C, a.-Dd its corresponding negative undulatio-D. of clizve ee occ,,ir at the same time, and therefore can be added i-n the mixer stage. Pulses 2o-S. 2rg and 270 are then fed through an integrating deiiiee 271 to the utilization device @177 as explai-aed in con-@iection with Mg. 1. From the J'orego;.'Dg i't, will be seen that I have provided a pulse amplittide modulation system 2,5351061 14 which Is-common to both the. transmitter and receiver and which when tuned to shape a trans@ mitter pulse to a certain width will also serve to select a received pulse of said certain width. 5 A modified form of the width shaper and se@ lector circuit i-S illustrated in Fig. 9. This circuit is simil5-,r to that described in the copendin4 application of Emile Labin and myself, filed May 15, 1943, Serial Number 437,072, now Patent No. lo 2,440,278, issued on April 27, 1948, for "Pulse Selecting and Eliminating System." The circuit illustrated in Fig. 9 differs from that illustrated in Fig. I in the following respects. The c6nnection of anode 47 and the connection 15 of the source of positive potential to the circuit consisting of resonant cireliit a2 and resistor 49 are reversed. That is, anode 47 is connected to poiit 50, and the source of positive potential is connected to end 0,6 of the resonant circuit 42. 20 The output is taken off the cathode 07 of shunt tube 65 instead of off its anode. With this arrangeme.,it, no bias is required on grid 60 of the shunt ttibe. The oppration of this circuit is similar to that of width shaper and selector circuit 26 41, and will be described with reference to Figs. j.0 and 11. -@7'lhen the c;rcuit oi Fig. 9 is to be used as a shaper the puises su-oplied thereto are preferably negative pulses, curve j@, Fig. 10. These produce 30 positive potent--'.als, eiirve kk, on anode 47 whi-ch are in turn applied throv..gh resistor 49 to end 48 ol' resonant circuit 42. Thereuron resonai@t circuit 42 oscill@ates, -croducing pos;@tive, undulatlons, curve LL i@,,hich are clipped at the levels 35 89 and 106 respectively by limit clipper 78 and peak-follov,,er tl-i"-shold clipper 79, to thereby Produce Pulses of ttie sele,ct,-d width. I\To negative undulations are rroduced in curve LL because shunt tube 6@5 will conduct v,7hen its cath40 ode becomes neaative. For width gelectioii -ourposes, nositive piilses are supplied to t-,Iie inpu@u of the e'reuit of Fig. 9, curve ?-.,zm, Fl:g. 11. The potentials impressed on end A3 of resonant eirci-iit C,2 by these pulses are 45 negative, clirve ni?,. The leadin@,, ay-id traili-ng edp;es of t'@I)e pulses shock-excite resonant circuit 42 to produce u@idulations, curve oo. These are then clipped between the levels 89 and 196 to thereby select pul@ses of 'I@he de@,i-r.,-d v7idt'-ri, '-t beiiig 60 understood th,,).t the nositive undtilations, prQduced by ptil-ses having widths other than the desired vridth, will be o-P iesse:,- a,-P,,31itude than those produced by pulses ol@ th,-- desired width. Shu,.it tube 65 becorqes ready to conduct e@t any 55 time after the traiiing ed@,,;e of a pulse has pasqed and will condiict wher- a negative potent'al is applied tc> cathode 67. Th4s negative potential appears after the positive undulatiops of curve oo and bhe consequ-@nt condiietioii of tube 65 60 critically da.--ps the ei@ergy -in r-,sonant circuit 42. it will therefore be seen that the circuit 6f Flg. 9 n, ay be used is a pulse width shaper and selector eir-cuit in place of 'ul-ie circuit of Fig 1, in a-iiy of t:@ie sist-- rqs disclosed. Bu'Ll, in zueh case, 65 the polarities of t-e -13,,ilses arpli6.d to the inpi@t are reverqed. While I have des@-ribed my invention in detail and several bpplic-qtions thereof, it will b-- readily apparent that my invention is of brooder scope 70 th,,In tlae sp.-@ci-"L@c types illustrated. Additiona-I applicat,ons o-'L my inventld-ii will be apparent to those versed in th6 art. Foi@ e%ar@iple, T have shown my invention iii cor-,il,--ctio-n w'lt-- only Q@'@ne type of time-n-od,,Ilated pulse system. Obviously, embodying a width shaper and selector eireuit 73 it. may be used with variolis other types of time
