US2392546A - Pulse modulation receiver - Google Patents

Description

Jan. 8, 1946. H. o. PETERSON PULSE MODULATION RECEIVER Filed Feb. 20, 1942 5 Sheets-Sheet l lNVENTOR Y [i 0 PeZ/u/olc B .M ATTORNEYl Jan. 8, 1946. l H. o. PETERSON 2,392,546

PULSE MODULATION RECEI VER ATTORNEY Jan. 8, 1946. i H. o. PETERSON 2,392;546

PULSE MODULATION RECEI VER Filed Feb. 20, 194,2 5 Sheets-Sheet 3 P Pl le P /a/l J; rl ri f/Ofoaff/Qzzaf @i P Pl P Pl l rLl H1 riv 0mm P P P P/ h Cl VLI lll lll /VOMILZOWIZ Y Paap m4. 5 me e #Sgm ATTORNEY Jan'.A 8, 1946.

H. o. PETERSQN 2,392,546

PULSE MODULATION RECEIVER Filed Feb. 20, 1942 5 Sheets-Sheet 4 @i lsf aen PaZJ'e Generar 46 49 A oww l 47* 5,

nZ-nna U N lNvENToR arow eZrJ/on 7 /w'fff/l/ ATTORNEY Jan. 8, 1946. H. o. PETERSON 2,392,546

PULSE. MODULATION RECEIVER F'led Feb. 20, 1942 5 Sheets-Sheet 5 I ligne.

sezZZ'r 4 w N 5 0.9 d I 8O Qgl fcogolze .90 el 0m-225,. emoczialr INVENTOR lygfo. enx/on ATTORNEY Patented Jan. 8,1946

PULSE MODULATION RECEIVER Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America., a corporation of Delaware 4Application February Z0, 1942, Serial No. 431,617

5 Claims. ('Cl.v Z50- 20) This invention relates to a pulse communication system in which the phase or frequency of the generated pulses is a function of an intelligence signal.

It has been customary to modulate transmiters by modulating the amplitude. phase, or frequency of the radiated carrier. In the vsystem of the present invention the radiated carrier is broken up'into pulses of short duration and the frequency or phase relationship of the pulses varied in accordance with the signal to be transmitted.

There are certain advantages to be had from pulse transmission at the ultra high frequencies. One of these advantages lies in the fact that it is possible to use certain types of ultra high frequency generators which require such a high voltage that it would not be possible to leave the advantage in pulse transmission systems is that the frequency stability of the radiated carrier does not need to be maintained to the same close limits necessary in a continuous wave system.

A more detailed description of the invention follows, in which:

Figs. l, 3 and 6 each illustrate graphically three conditions of the transmitted pulses which are respectively obtained by the three different pulse type transmitter embodiments of Figs. 2, 4 and 7 of the invention;

Figs. 2B, 5 and 8 illustrate three different receivers of the invention, for use respectively with the transmitters of Figs. 2, 4v and 7;

Fig. 2A illustrates in detail, by'way of example only, circuit arrangements which thepulse generator 'l and the vultra high frequencygenerator 8 of the transmitter of Fig. 2 may take;

Figs. 2C, 2D, 2E, 2F and 2G graphically illustrate the operation of the system of Figy 2A.

Figs. 9 and 10 respectively illustrate a transmitter and a receiver for use in a multiplex pulse modulation system, in accordance with the invention.

Figs. 1, 2 and 2B illustrate one form of a pulse communication system. In this system the phase of the transmitted pulse is modulated in accordance with the signal to be transmitted. This is shown in Fig. 1. With no modulation, the pulses are transmitted at a uniform rate (as shown in line A of Fig. 1). Whenmodulation is applied, the phase of the radiated pulse 'is varied back and forth, as illustrated in lines B and C of`55 plier 6 is passed through limitercircuits tos con- Fig. 1. This type of modulation may be generated in a system such as that shown in Fig. 2 and these signals may be received with a system such as that shown in Fig. 2B;

Referring to Fig. 2, Ithere is shown a system for the transmission of a telephone signal in which I, 2 and 3 represent a microphone, a battery, and a transformer, respectively. A sinusoidal Wave producing oscillator 5 generates a frequency which controls the frequency of the pulses and which may, for example, be a frequency of 300 kilocycles. A phase modulator 4 to which is passed the voice modulation from transformer 3 varies the phase of Ithe 300 kilocycle carrier generated by sinusoidal generator 5. Such a phase modulator is well known in the art, and, if desired, may beof the type shown in Crosby United State: Patent 2,081,577, granted May 25, 1937, 0r in Fig. 5 of Luck Patent 2,113,214, granted April 5, 1938. The phase modulated output of 4 is conducted to a frequency multiplier 6; which in turn is connected to a pulse generating circuit l, the latter in turn feeding direct current pulses into the ultra high frequency generating system 8, Whose output is carried through transmission line 9 to an antenna I0 which radiates the pulses. Ultra high frequencygenerator 8 may be a magnetron, Barkhausen oscillator or any other suitable device which is made to be operative solely at such times that Ithe direct current pulses are supplied thereto by pulse generator l. The connection from pulsel generator l may extend to the anode of the generator 8, for example. The amount of phase modulation applied by modulator 4 is multiplied by the frequency multiplier 6. Thus, if the `order of frequency multiplication in `B is great, the degree of phase mod ulation will be greatly increased and by the application of suitable correction circuits in the audio system feeding phase modulator 4, in a manner well known to the art, the modulation may be made equivalent to a frequency modulation of the pulse rate. l

Fig. 2 A illustrates, by way of example only, the component parts of the pulse generator 'land the ultra high frequency oscillator 8 of the transmitter of Fig. 2. Inasmuch as there are numerous devices which will create the desiredv effects of the pulse generator and ultra high frequency oscillator, it should be'understood that these .are set forth by way of example rather than limitation. The. apparatus of Fig. 2A corresponding to `units 'l and 8 of Fig. 2 have been similarly labeled in the dotted boxes. The output lof,"thefmultivert it from a sinusoidal wave form (such as shown at Fig. 2C) to a square wave form (such as shown at Fig. 2D) Squarewave form current (as shown at Fig. 2D) is passed through the primary of transformer |00, which is of such design that low frequency components are substantially absent in the wave form of the secondary voltage.

'The wave form'of the secondary voltage of transy former is substantially that shown at Fig. 2E.

It will be noted that the secondary voltage represented by Fig. 2E consists of alternate positive and negative pulses of relatively short duration. Plate current ows in tube IOI, except when its grid is biased negative past cut-olf. This current through resistor |01 keeps the grids of tubes |02. |03 biased negative past cut-olf. Consequently,

radiates a series of'pulses timed in accordance with the relationship shown In Fig. 3, line A. In the system as shown, there is one series of pulses indicated as P, the frequency and 'phase 'of which remains constant. There is a second series of pulses indicated as P', the phase of which is modthe high frequency carrier from |04 will be transy mitted to the' antenna only during the time when no plate current ows in resistor |01. This conf dition occurs only for the duration of the negative 'mediate frequency. Selective circuit I3 may be an amplifier or band pass filter which is selective to the transmitted carrier frequency and wide enough to pass the pulse frequency sidebands. This intermediate frequency is amplified by selective amplifier I6 and then rectified in rectifier I1. The outputof rectifier I1 is a series of direct current pulses -which is, in turn, transmitted to an amplitude limiter system I8 in which disturbances above and below predetermined levels may be excluded. Thus, the output of limiter I 8 will be in the form of direct current pulses having substantially constant amplitude and from which there will be eliminated any respouse to noise disturbances below a predetermined value. The output of limiter |8 feeds a selective circuit |9 which is responsive only to the frequency of the transmitted pulses, :plus and minus such frequencies as will be necessary for the transmission'of modulation. Thus, if the transmitted pulses occur at the rate of 300,000 per second, selective circuit I9 may be a band. pass filter on the order of 6 kilocycles wide lwith a mid band frequency of 300 kilocycles and which will transform the direct current pulses substantially to a sinusoidal carrier. The output of selective circuit I9 is transmitted through an amplitude limiter 20 and a discriminator and detector 2|. The limiter 20 and the discriminator and detector 2| may be of the same type as those commonly Vused in receivers built for phase modulation and/or frequency modulation purposes. 'Detector 2| may be of the type known as a discriminator circuit which can employ a pair of off-tuned circnitsor a circuit of the kind described in Seeley United States Patent 2,121,103, dated June 21, 1938, or it may be of the type shown in Figs. 5 and 8 of Crosby United States Patent 2,081,577. The output rof this detector system will be the original voice modulation.

Figs. v3, 4 and 54 represents a, slightly different Aform of communication by pulse modulation.

`When there is no modulation, the transmitter ulated.- The normal phase and frequency of pulses P and P remain constant for the condition of no modulation, which is illustrated in line A of Fig. 3. Modulation causes the relative phase between pulses P and P to vary, as indicated in lines B and C of Fig. 3. In the example shown, only the phase of pulse P' is varied by the `m0d' ulation. VIt would obviously be possible to simultaneously modulate the phase of pulses P and P' in opposite directions.

Fig. 4 illustrates a means for producing 'sig-` nals with this type of modulation. A microphone is shown at 22, abattery at 23, and a transformer at 24. A sinusoidal oscillator 26 generates a ferequency Iwhich controls the frequency of the pulses. The output of 26 is a constant frequency carrier which is caused to control two pulse generators 21 and 28. The control for pulse generator 28 is transmitted through a phase modulating circuit 25 so that the phase of the pulses coming out from generator 28 is modulated with' respect to the phase of the pulses coming out from generator 21. It should be understood that phase modulator 25 includes a phase delay circuit such that the pulses from generator 28 are normally about 90 behind the pulses from "generator 21 when no modulation is applied. The

outputs of pulse generator circuits 21 and 2B are in the form of direct current pulses which operate to cause pulses of ultra high frequency carrier to be generated in 29, the output of which is con,-

ducted through transmission line 30 and radiated kby antenna 3|. Referring back to Fig. 3, pulses P are generated by` apparatus 21 and pulses P are generated by apparatus 28 (Fig. 4).

Fig. 5 shows a receiver for receiving the output of the transmitter of Fig. 4. The pulses of ultra high frequency carrier are received on antenna 32 connecting through transmission line 33 to selective circuit 34, the output of which is conducted to converter 35 Where it is combined with the frequency from oscillator 31 to produce an intermediate frequency which is amplified by frequency selective amplifier 36 feeding rectifier 38. A voltage derived from rectif-ler 38 is conducted vback to amplifier 36 through an automatic gain control circuit marked AGC which normally includes time constant circuits, usually of the resistance-condenser kind. The output of rectifier 38 is in the form of direct current pulses which are passed through an amplitude limiter 39 which operates in such a manner that noise below a certain level is discarded and pulses of any value above a predetermind level produce output pulses of a constant level. Thus the direct current pulses in the output of limiter 39 are of substantially constant amplitude. These pulses are passed through a pulse frequency'band pass selective circuit 40 which is responsive only to the pulse frequency, plus and minus such fre* quencies as are essential to the transmission of the modulation. Thus, if the frequency generated by oscillator y26 of Fig, 4 is 300 kilocycles, circuit 40 may be a band-pass filter with a band width of about 6 kilocycles and amid band frequncy of 300 kilocycles, and which will transform the direct current pulses to substantially a sinusoidal carrier. The output of selective cirassaults cui-t 40 is amplitude modulated and feeds a rectifiery 4I. in the output of which appears the origina1 telephone modulation.

Another vform of the/pulse modulation system is shown in Figs. 6,/7 and 8. In this system the basic form of modulation is illustrated in Fig. 6. This is essentially the same form of modulation as shown in Fig. 3, withA the exception that a greater degree of time phase variation is used.

Fig. 6. line A, illustrates the time relationhip of the pulses for the condition of no modulation. The time phase of pulse 2 is varied over a range of plus and minus almost 180 with respect to the time phase of pulse I. l

One way in which this may be accomplished is illustrated in Fig. 7. A microphone is shown at 4 2, a battery at 43, and a transformer at 44. The

output of oscillator 46 is conducted to phase modulator 45 and frequency multiplier 41. Phase modulator 45 also includes such time delay circuits as will give the correct relationship between the phase of pulses i and 2 for the condition lof no modulation.` Normally, circuit 45 willbe capable of producing a degree of phase modulation up to about plus and minus 45 in the carrier frequency output. of oscillator 46. This degree of modulation is increased to the desired valu'e of'approximately a maximum of plus and minus 180r by frequency multiplier 48. There is the same degree of frequency multiplication in frequency multiplier 41 so that lequal carrier frequencies comeout of the frequency multipliers 41 and 48 during the condition of no modulation.

The outputs of 41 and 48 control pulse generator circuits 49 and 50 which produce short direct current pulses at the phase and frequency'determined by the outputs of 41 and 48. These short direct current pulses control the radiation of ultra high frequency pulses through the ultra high frequency generator 5I, transmission line 52 and antenna 53. In effect, apparatus 41 produces the pulses I of Fig. 6, while apparatus 48 produces the pulses 2 of Fig. 6.

'I'he output of the transmitter (Fig. 7) may be received on receiving system (Fig. 8). The transmitted short pulses of ultra high frequency carrier are received on antenna 54 and conducted -below a predetermined level and passes direct current pulses of constant amplitude to a detector circuit through condenser/'62. The detector in this case is a gas triode'oscillator circuit of the type known as a counter circuit. It is so arranged that the number of cycles appearing in the output is one-half of the number of cycles impressed at the input. This type of counter circuit is quite extensively used in connection with Geiger counters for the study of cosmic ray phenomena and its operation is well known to the art. With such a circuit it will be found that the audio modulation can be taken off. as shown, in transformer 1B. The transformer 16 will not pass the pulse frequency but only the audio frequencies. j

Figs. 9`and 10 illustrate how the pulse modulation systemy above described may be used in a multiplex system. Fig. 9 represents a multiplex transmitter in which two different pulse frequencies are used. These pulse frequencies are` carrier are received on antenna 92 which is connected to receiving system 99, which may be of any of the types above describes up to the point where the pulse frequency appears. The rectified pulse frequency 'energy is impressed on Vtwo branches in which the desired channels are selected by selective circuits 94 and 91, respectively, followed by amplitude limiters 95 and 99 which, in turn, are followed respectively by demodulating and detecting circuits 96 and 99.

While only two channels are shown, it should be understood that the system may be `extended to transmit a larger number of channels. It should lalso be understood that one or more of the channels may in turn be multiplexed by either frequency, phase or amplitude modulation. For example, channel one instead of being a telephone channel may consist of a number of tone channels each of which is either amplitude modulated, phase'modulated, or frequency modulated.

What is claimed is: Y l

1. In a pulse modulation radio communication system wherein the radiated carrier is broken up into equal length pulses of short duration and the relationship of the pulses varied in accordance with the signal to be transmitted, a receiver for said radiated pulses comprising an antenna, a selective circuit coupled to said antenna and selective to the transmitted carrier (frequency, said selective circuit having a` pass band sufficiently wide to pass the pulse frequency sidebands, a heterodyne converter coupled to the output of said selective circuit, a beating oscillator coupled to the input of said converter,

whereby an intermediate frequency is produced by said converter, a selective amplifier for amplifying the intermediate frequency output of said converter, a rectifier coupled to said amplier, an amplitude limiter coupled to the output of said rectier for excluding disturbances outside a desired level and for producing substantially constant amplitude pulses, a selective wave shaping circuit coupled to the output of said limiter and responsive only to the frequencypf the transmitted pulses plus and minus such frequencies as are necessary for the transmission of theA modulation, said selective wave shaping circuit being constructed and arranged to`transform the pulses passed thereto to substantially a sinusoidal carrier, and means for transforming the output of said last selective circuit to reproduce the original modulation at the transmitter.

2. In a pulse modulation radio communication system wherein the radiated carrier is broken up into equal length pulses of short duration and the relationship of the pulses varied in accordance -with the signal. to be transmitted, a receiver for said radiated pulses comprising an antenna, a selective circuit coupled to said .antenna and selective to the transmitted carrier frequency, said selective circuit having a pass band sulciently wide to pass the pulse frequency sidebands, a heterodyne converter coupled to the output of said selective circuit, a. beating oscillator coupled to the input of said converter,v whereby an intermediate frequency is produced by said converter, a selective amplifier for amplifying the intermediate frequency output of said converter, a rectifier coupled to said ampli-v fier, an amplitude limiter coupled to the output -of said rectifier for excluding disturbances outsinusoidal carrier, an amplitude` limiter coupled to the output of said selective circuit, and a discriminator circuit coupled to the output of said last limiter for producing in its output a reproduction of the original modulation at the trans- 3. In a pulse modulation radio communication system wherein the radiated carrier is broken up into equal length` pulses of short duration and the relationship of the pulses varied in accordance with the signal to be transmitted, a receiver for said radiated pulses comprising an antenna,

-a selective circuit coupled to said antenna and selective to the transmitted carrier frequency, said selective circuit having a pass band sufiiciently wide to pass the pulse frequency sidebands, a heterodyne converter coupled to the output of said selective circuit,y a beating oscillator coupled to the input of said converter, whereby an intermediate frequency is produced by said converter, a selective amplifier for amplifying the intermediate frequency output 'of said converter, a rectiiiertcoupled to said amplifier for producing a series of direct current pulses, an automatic gain control circuit including suitable time-constant circuits for deriving a, voltage from said rectifier and for feeding back said voltage to said selective intermediate frequency amplifier, an amplitude limiter coupled to the output of said rectifier for excluding disturbances outside a desired level and for producing substantially constant amplitude direct current pulses, a selective wave shaping circuit coupled to' the output of said limiter and responsive only to the frequency of the transmitted pulses plus and minus such frequencies as are necessary for the transmission of the modulation, said selective wave shaping circuit being constructed and arranged to transform the direct current pulses passed thereto to substantially a sinusoidalV carrier, and means for transforming the output of said last selective circuit to reproduce th'e original modulation at the transmitter.

4. In a pulse modulation radio communication ascaue system wherein the radiated carrier is broken up into equal length pulses of short duration and the relationship of the pulses varied in accord'- ance with the signal to be transmitteda receiver for said radiated pulses comprising an antenna, a selective circuit coupled to said antenna and selective to the transmitted carrier frequency, said selective circuit having a pass band suiciently wide to pass the pulse frequency sidebands, a heterodyne converter coupled to the output of said selective circuit, a beating oscillator coupled to the input of said converter, whereby an intermediate frequency is produced by said-converter, a selective ampler for amplifying the intermediate frequency output of said converter, a rectifier .immediately following and coupled to the output of said amplifier for producing a series of direct current pulses, an amplitude limiter coupled to the output of said rectifier for excluding disturbances outside a desired level and for producing substantially constant amplitude direct currentI pulses, a pulse frequency selective circuit coupled to'the output of said limiter, and means coupled to the output of said pulse frequency selective circuit for reproducing the audio modulation of the transmitted signal.

5. In a pulse modulation radio communication system wherein the radiated carrier is broken up into two series of time spaced equal length pulses, one series of which is of constant frequency and phase, and the other series of which is of constant average frequency but Whose phase varies in accordance with the signal modulation, a receiver therefor comprising an antenna, .a selective circuit coupled to saidantenna and selective to the transmitted carrier frequency, said selective circuit having a pass band sufficiently wide to pass the pulse frequency sidebands, a heterodyne converter coupled to the output of said selective circuit, a beating oscillator coupled to the input of said converter, whereby an intermediate frequency is produced by said converter, a selective amplifier for amplifying the intermediate frequency output of said converter, a rectiiier coupled to said amplifier, an amplitude limiter coupled to the output of said rectifier ford excluding disturbances outside a desired level and for producing substantially constant ampltude pulses, a selective Wave shaping circuit coupled to the output of said limiter and responsive only to the frequency of the transmitted pulses plus and minus such frequencies as are necessary for the transmission of the modulation, said selective wave shaping circuit. being constructed and arranged to transform the pulses passed thereto to substantially a sinusoidal carrier, and means for transforming the output of said last selective circuit to reproduce the original modulation at the transmitter.

HAROLD O. PETERSON.

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