US2086918A - Method of frequency or phase modulation - Google Patents

Description

July 13, 1937. D. G. c. LUCK METHOD OF FREQUENCY OR PHASE MODULAIION Filed Aug. 22, 1935 l 5 Sheets-Sheet 1 @Mill fafa-p July 13, 1937. D. G. c. LUCK 2,086,918

METHOD OF FREQUENCY OR PHASE MODULATION Filed Aug. 22, 1955 5 Sheets-Sheet 2 XXX lfgd,...

0 @evo VOL 77965 raz/11127* m55/e6" gaz/,25d C/ccff July 13, 1937. D. G. c. LUCK METHOD OF FREQUENCY OR PHASE MODULATION Filed Aug. 22, 1935 5 Sheets-Sheet 3 July 13, 1937. D. G. c. LUCK 2,086,918

METHOD 0F FREQUENCY OR PHASE MODULATION Filed Aug. 22, 1935 5 Sheets-Sheet 4 CURRE/vr L/M/TER July 13, 1937. D. G. c. LUCK 2,086,918

METHOD OF FREQUENCY OR PHASE MODULATION Filed Aug. 22, 1955 5 Sheets-Sheet 5 l r s QS Q N was@ Sw Z l f W70/M m77@ Patented July 13, -1937 UNITED STATES' yPATENT oFFINc ME'rnon 0F FREQUENCY on PHASE MonULA'rroN David G. C. Luck, Woodbury,

Radio Corporation of Delaware N. J., assigner to of America, a corporation l Application August 22, i935, serial No. 37,270

20 Claims.

My invention relates to the transmission and" reception of energy at radio frequency. In particular, my invention relates to a method of frequenrcy or phase modulating a transmitted wave, and means for receiving and demodulating the wave.

means for receiving and'demodulating a phase or frequency modulated wave.

Other objects willappear from the accompanyn ing drawings, specification, and claims.

In the accompanying drawings,

Figure I represents :in schematic outline form one embodiment of my invention applied to a transmission System.

Figure II illustratesin outline form the na- '4 ture of a lreceiving system employing one form of my invention,`

Figure III is a graph illustrating a saw-tooth wave without modulation,

Figure IV is a graph illustrating a saw-tooth wave with modulation,`

Figure V is a graph illustrating a series of lmpulses derived from a saw-tooth wave,

Figure VI is a characteristic curve of a current limiter which may be used in the derivation of impulses from a ysaw-tooth wave,

FigureVII is adiagram ofva constant frequency oscillator,

Figure VIII is a circuit diagram of` a current d limiter,

` electron relay,

Figure VIII(a) represents the 'characteristic curve of the current limiter shown in Figure VIII, Figure IX represents the` combination of a current limiter and a saw tooth generator,`

" Figure X is a diagram of a modulator circuit, Figure XI is a diagram of an impulse operated invention.

If the amplitude of an oscillatory current is varied in accordance with a desired signal, the oscillation is said to' be amplitudemodulated.

fLikewise, if the frequency of an oscillatory curi ent is varied in accordance with the signal to be transmitted,` the oscillation is said to be frequency modulated. The rate of change of the phase of an oscillatory current is termed the frequency of that current. Therefore, it may be seen that a frequency modulated current may be 5 termed a phase modulated current. 'I'he difference between thetwo depends upon the particular relation between the Variations of the original signal and the variation of phase or `frequency produced by it. The system I am A about to describe may be adapted to either phase or frequency modulation. V Y V With the existing systems it has been diiilcult to obtain phase modulation exceeding thirty degrees without serious distortion, if the mean freg quency of the transmission is to remain stable.

It is diilicult to apply phase modulation to a crystal controlled oscillator system. In the application of my invention I can obtain phase modl ulations of the order of one hundred and eighty degrees and employ al constant source for the mean frequency of transmission. 'I'he explanation of the operation of my system may best be understood by referring to Figure I.

Any constant frequency source of radio energy I supplies the radio frequency oscillations 3. These oscillations are impressed on a duplex sawtooth generator 5 which converts the wave form `to the sawtooth wave represented by the graphs 1 and 9 by a process oi' limitation, differentia- 30 tion, rectification, and integration. Each of these `wave forms corresponds with the frequency of the loscillatory source I but the phase of one of the sawtoth oscillations 9 is one half period behind that of the other sawtooth oscillation l.

The sawtooth oscillations 'I and 9 are impressed respectively on the modulators II and I3. Although I have described the oscillations as saw toothlin wave form, any triangular wave form may be employed. 40

`Th`e modulators II and I3 convert the wave form by limitation, differentiation, and rectification to a series of equally spaced positive impulses of equal amplitude and in opposing phase relationship. These impulses are indicated by the graphs I5 and Il. The impulses I5 and Il act on the impulse operated electron relay I9 which controls a local source of energy. The lower impulses I1 start the currents in the electron relay I9 and the upper impulses I5 stop the currents 50 in the relay I9. The currents from the output circuit of the relay I9 may be represented as a square fiat top wave 2|. The currents represented by the square Wave form 2l may now be shaped by appropriate filter circuits 23, Whose resultant output is represented by the graph 25. These currents are then impressed on the transmitting antenna 21. It should be understood that amplifiers or frequency multipliers may be interposed between the wave shaping circuit 23 and the antenna. The frequency multipliers increase the frequency modulation. as well as the carrier frequency. Independent control of the final carrier frequency may be effected by any of the known methods which permit the addition or substraction of other frequencies.

Thus far my description has been limited to the transmission of radio frequency currents without impressing on these currents the modulation of the desired signal representing currents. If a source of signal representing energy is impressed on the microphone 23 or the like, and passed through an amplifier 3|, modulating currents are generated as represented by the curve 33. These modulating currents may be linked to the modulators II and I3. The modulators |I and I3 have the effect of varying the relative timing of the two series of positive impulses I5 and I1 which may then be represented as variably spaced impulses 35 and 31. If these vimpulses 35 and 31 are impressed on the electron relay I9 the resultant output will be a square wave 39 which is accurately phase modulated in accordance with the modulation current 33. After the square wave 39 is applied to the wave shaping circuit 23, the resulting wave is a phase modulated sinusoidal wave 4|. An inspection o this wave form 4| shows that its phase varies and its amplitude is constant; in other words, it is phase modulated.

Before describing the details of the circuits employed for transmitting and receiving phase or frequency modulations in accordance with my invention, I shall briefly set forth the theory underlying my invention. If a saw tooth wave is generated by suitable means, the wave form may be illustrated by Figure III. The frequency of the saw tooth wave should be high compared with the frequency of the desired modulating signals. If a modulating signal of lower amplitude than that of the saw tooth is added to the saw tooth wave, the result may be illustrated by Figure IV. If the saw tooth wave shown in Figure III is applied to a current limiting circuit having the limiting characteristic shown in Figure VI, the result will be in effect the switching on of current by the passage of the signal upwards through a particular value (zero for example), and the switching off of current by the downward passage of the signal thro-ugh the same voltage. This effect may be further described as a set of dots of current separated by spaces when no current flows. The rate of repetition of the dotspace cycle being constant, while the relation of dot length to space length is varied in accordance with the modulating signal. These dots may be converted, by differentiation with respect to time, into a set of short pulses, marking the starting and stopping of each dot, as shown in Figure V.

The value of the dot signal of amplitude a, at any time t, during the nth dot, the original dot repetition period being T, is

The value of the modulating signal of amplitude b (b is less than a) is A.: b-f(t) (2) where the function Nt) describes the time variation of the modulating signal. The condition for a dot to end, such that the total signal of Figure IV is zero, is

t b f A phase modulated wave, of unmodulated frequency Tv may be dened as where B is the maximum phase shift in degrees produced by the modulating signal, which varies with time in accordance with the function ;(t). The phase modulated wave passes through the zero value in one particular direction whenever the angle p (which is the phase of the wave) has a value of any integral multiple of 2r radians. Therefore the times when the phase modulated wave is zero are given by where n is any integer.

Comparison of equations (3) and (5) shows clearly that the instants at which a set of modulated dots stop are the same as those at which the phase modulated sine wave passes through zero. A phase modulated wave, corresponding to a set of dots of repetition period T (or frequency N) and amplitude a, modulated by a signal of amplitude b, has an unmodulated period 1=T (frequency N), and is modulated degrees. The passages of this dot-frequency wave through zero in the other direction are at the instants of stopping of dots formed by modulating with the same signal a second saw tooth wave identical with the first but being displaced in time by a half period.

The foregoing theory, taken in conjunction with the explanation of Figure I, makes it clear how the respective impulses of a pair of modulated dot trains with a half dot period relative time displacement can be used to switch on and olf a current which produces a series of square top waves which will be accurately phase modulated in accordance with the original modulating signal. The negative voltage impulses, indicated dotted in Figure V, having no useful effect, have been removed by rectifying means. The resulting square wave may be accurately phase modulated by any amount less thah 180 degrees by the modulating signal. The square wave may be sent through a wave shaping filter to give an approximate sine wave, which as has already been described, will be phase modulated up to almost 180 degrees.

I shall now describe the detailed circuits represented in block forms I, 5, II, I3, I8, and 23 of Figure I.

The constant frequency oscillator I of Figure I may be any of the well known oscillators. One such oscillator is the piezo-electric control shown in Figure VII. The piezo-electric crystal |5I is connected to the grid and cathode of thermionic tube |53. In the anode circuit of the tube |53 is connected resonant circuit |55 and a suitable anode current source |51. The output terminals of the oscillator are represented as ISS-IGI.

iter illustrated in Figure VIH; the other, a saw tooth generator proper represented as Figure IX. The current limiter, Figure VIII, is composed of two thermionic tubes |1| and |13. lI'he input to the limiter is represented as a pair of' terminals |15|11 and its output as two terminals |19|8|. The two tubes |1|'and |13vare resistance coupled. The input bias voltage of the first tube |1| is adjusted to normally prevent anode current from flowing in the anode circuit of the first tube |1|. The secondtube |13 is adjusted to permit full anode current to flow. As the input voltage across the input terminals 11S-|11 is increased a potential will be reached at which anode current will flow in the first tube |1|. The current in `the anode resistance of the first tube |1| places a negative bias on the second tube |13 whichV tends to block currentsv in the anode circuit of this tube |13. The limiting action may be illustrated by the curve ofFlgure VIlI(a).

The eect of the current limiter is illustrated by its reshaping of the Wave form of the constant frequency oscillation |83 of Figure IX, and may be shown as a'flat top wave form 4|85 after passing through the current limiter |91. The circuit and apparatus represented by the block form |81 corresponds with the current limiter just devscribed in connection with Figure The limiter may also amplify. 'I'he voltages represented by the fiat top wave form |85 are applied to the diferentiator circuit |89|9| which comprises a capacity |89 having a large reactance and a resistance |9| of relatively small value. The impulses produced by this differentiator are impressed on the input of a thermionic tube |93. The output circuit of this tube |93 includes an integrator circuit composed of a resistance |95 of large value and a capacity |91 of relatively small reactance. The output terminals of this part of the circuit are represented as |99-20I. The impulses are reversed in phase lby the phase reversing tube 203 whose output circuit is connected to the input of a therxnionic tube 205. The tubes |93 and 205, which include the integrator circuits, are similar with respect to their functions and output circuits. Both tubes have input biases which are normally adjusted to cutoff. 'I'he bias makes these tubes |93 and 205 rectify-or respond to only positive impulses. The output terminals of the second integrator and rectifying tube 205 are shown as 20L-209. It should be understood that these tubes |93 and 205 may be triodes, tetrodes or any suitable thermionic tubes.

The modulators and |3 of Figure I are represented diagrammatically as Figure X. The one of the duplex saw tooth oscillations is impressed on the input terminals of the modulator 2|| 2|3. These terminals connected to the input circuit of a `,thermionic tube 2|5. The signal representing voltages, which may be amplified, are impressed on the input terminals 2|12|9 of a second tube. The input of this tube 22| is connected to the input terminals 2|1 and 2|9 through a potentiometer 223 which permits adjustments of the degree of modulation produced. Since the anode circuits of the first two tubes of the modulator 2|5-22l are made common, the signal and saw tooth currents are added in the common anode resistor 222. 'I'he voltage across the common resistor is impressed on the input 'terminals of the current limiter 225. The current limiter, represented as 225, may be of the type previouslyi described in connection with Figure VIII.

The output of the current limiter is connected to a diiferentiator circuit composed of a low value of resistance 221 and a capacity 229 of relatively high reactance. The potentials across 221 are impressed on the input terminals of a rectifier 23|. This rectier is biased to cut-oil so that it is only responsive to positive impulses. 'I'he output terminals of the rectifier are represented as 233-235. A similar modulator circuit to the one just described is employed to modulate the other saw tooth oscillation. That is, a pair of circuits similar to Figure X areemployed to perform the functions of modulating represented by and I3 of Figure I.

The impulse operated electron relay illustrated by block |9 is shown in schematic form in Figure XI. The impulse relay employs a pair o f thermionic tubes 231 and 239 which are connected as a multi-vibrator. The multi-vibrator has a free frequency of the order of the desired carrier frequency. The "on impulses are impressed on the input 24S-241 of one of the pair of tubes and the off impulses are impressed on the input circuit 24H- 243 of the other tube 239 of the pair. The output circuit of the pair of tubes 231 and 239 is represented by Iterminals 24S-25|.

The nal step in the transmissionv system is the wave shaping. The complicated sideband pattern of the phase modulated rectangular Wave 39 is such that, if the carrier frequency is of the vorder of twelve times higher than the highest frequency present in the modulation, (or the ratio may be somewhat lower than twelve times if the higher modulation frequencies are of relatively low amplitude) a` band pass lter circuit may be used. A single section band pass filter circuit is shown in Figure XII. The input circuit of the filter is composed of a resonant circuit 253. The output circuit is composed of a second resonant circuit 255. The two resonant circuits are coupled by any suitable type of mutual coupling,

such as M. 'I'he degree of coupling is one of thel factors which determines the relative width of the frequency band which the filter will pass. The effect of the lter is to re-shape a square Wave form 39 of Figure I to a sinusoidal wave 4| of the same gure. The output of the wave shaping circuit, which may comprise several such filter sections, may be amplified and is coupled to a work circuit which may be a transmission line, antenna or the like.

The same circuits may be used to frequency modulate by the simpleexpedient of connecting an integrator circuit, comprising a large resistance and a capacity of relatively low reactance, between the microphone 29 and the amplifier 3|. 'I'he integrator circuit is similar to Figure XIII with the carrier frequency trap circuit omitted.

Frequency and phase modulated signals cannot be demodulated, without deleterious distortion, by impressing the transmitted wave on one or more tuned circuits resonant to the mean transmitted wave frequency and detecting by any of the conventional` detector circuits.- 'This conclusion follows from the fact that conventional detectors are operated by amplitude variations of the signal representing voltages, rather than variations in the frequency of the received currents. A frequency modulated wave mayl be translated by employing a series of tuned circuits adjusted so that oscillatory currents of the mean frequency of the transmitted wave drive the circuits at a frequency other than their resonant period. The circuits themselves will then translate the frequency modulated wave into an amplitude modulated wave which may be detected by any of the well known detecting circuits. Such a method is relatively inefficient. The phase modulated wave may be received by supplying a local carrier and conventional detector, but this method produces bad distortion for phase modulation exceeding twenty or thirty degrees. This is a well known method, but I prefer the arrangement of Figure II for the reception and translation of a phase modulated wavetransmitted by means of the arrangement of Figure I.

In Figure II a source of phase modulated energy is connected to the input terminals of a radio amplifier IOI. The amplifier may consist of the conventional thermionic tubes and tunable circuits responsive to a band of frequencies centered on the mean transmission frequency. A local oscillator |03 is synchronized by any of the known means, with the oscillator I of the transmitter shown in Figure I. The-currents I05 and VI01, representing the received wave and the local oscillations, are fed into impulse generators |09 and III. The impulse generators by limitation, differentiation and rectification, produce a series of sharply defined positive impulses represented by the graphs I I3 and I I5. 'Ihe positive impulses H3 act as the off impulses and correspond to the impulses` I5 generated by the modulator II at the transmitter Figure I, if the wave is unmodulated, and to the modulated impulses 35 if the transmitter is modulated. The on impulses" are uniformly spaced as represented by the positive impulses of the graph II5 and correspond to the impulses I1, or to the negative impulses of the transmitted wave when the wave is un-` modulated. The positive impulses II3 and II5 are applied to the impulse operated electron relay II`I which corresponds to the relay I9 at the transmitter. The output of the electron relay II1 will be a unidirectional pulsating current of square Wave form, such as IIS, and comprised of a series of dot impulses of a constant rate of repetition but having a ratio of time on to time off which varies in accordance with the modulation of the received signal. These impulses are capable of operating a loud speaker directly but, as a large percentage of radio frequency energy is present, I prefer to reshape the modulated dot frequencywave IIS. 'Ihe square wave may be shaped by a lter I2I which corresponds broadlyto the wave shaping circuit 23 of the transmitter. I also integrate, and reject the carrier wave frequency. The output from the filter I2I will be a Wave corresponding to the original of the signal frequency modulating wave 33 impressed on the transmitter of Figure I.

The circuits represented by the block diagrams |09, III, II1 and I2I will now be described in detail by schematic circuit diagrams.

Radio amplifiers, IUI of Figure II, are so Well known to those skilled in the lart that a detailed showing is unnecessary. 'I'he amplier, per se, is not part of my invention. 'I'he same is true of the local oscillator |03 which may be of any conventional type. 'I'he oscillator may be locked in step with the carrier frequency by coupling between the radio amplifier and the oscillator. In any event the local oscillator should have a constant frequency output and remain in step with the carrier, as is necessary for any phase modulation translating system.

The impulse generators IOI and III may be a pair of circuits similar in arrangement to Figure X with the tubes preceding the current limiter and their circuits omitted. One of the pair of impulse generators has its input terminals, which correspond to those of the previously described current limiter 225, coupled to the radio amplifier IOI of Figure II, and the other input terminals are connected to local oscillator I03 of the same figure. The outputs of this pair of circuits are connected to the impulse relay .corresponding to I I1 of Figure II. The detailed schematic diagram of the impulse relay circuits is shown in Figure XI.

'Ihe output of the impulse operated relay is connected to the input of the wave shaping circuit. The essentials of this circuit, represented as I2I of Figure II, will be found in Figure XIII. The input terminals 251, 25S of the wave shaping circuit are connected to integrator elements. These elements include a resistance 26| which is of large value, and a capacity 263 whose reactance is relatively small. It is desirable to remove the carrier frequency. This may be done by shunting a series resonant circuit, comprising inductance 265 and capacity 261, across the output of the wave shaping circuit. The series circuit is resonant to the carrier frequency and preferably of relatively low resistance at resonance. 'Ihe output of the wave shaping circuit is represented as a pair of terminals 26S-21|. A loudspeaker or other signal responsive device is connected to the output of the wave shaping circuit.

In connection with Figure I, I have described how a constant frequency oscillation may be converted into two series of positive impulses, how these impulsesmay be phase or frequency modulated and impressed on an impulse controlled relay. The modulated currents of square wave forml set up by the relay are shaped and become phase or frequency modulated sinusoidal oscillations. These oscillations may be transmitted and demodulated in accordance with the system described in connection with Figure II. My conception of this system is broader than the exact process as illustrated. It is by no means essential that the method of employing my invention follow the exact sequences or all of the steps I have described. For example, in certain cases the wave shaping may be omitted in transmission or reception.

As an example of another modification within the scope of my invention, the receiving system of Figure II may be used, with slight modifications, as a transmitter of modulated impulses, or dot transmission. For simplicity and brevity I have illustrated these modifications in the block diagram of Figure XIV. A detailed description is hardly necessary. 'I'he dotted lines, through the impulse relay block, indicate direct impulse keying of the transmitter. The only new element is the phase modulator which may be any of the phase modulating devices well known to those skilled in the art. The remaining functions may be performed by the several circuits already shown and described in connection with the foregoing description and figures.

These modifications are merely suggested by way of example. Other obvious modifications Within the scope of my invention will occur to those skilled in the art. I do not limit my invention to the foregoing description, but desire that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

Iclaim:

1. The method oi' communication which comprises generating two saw tooth oscillations substantially in synchronism and in opposing phase, converting said saw tooth oscillations into a series of positive impulses, applying said impulses to start and stop a ilow of local energy, transmitting waves generated by said local energy, converting said transmitted .waves into a series of positive impulses, generating a second series of positive impulses, alternately applying the impulses of both mentioned series to start and stop the iiow ot current in a local source thereby generating currenta'and impressing the last mentioned currents on a signal translatingdevice.

2. 'Ihe method of communication which comprises generating two oscillatory currents of saw tooth wave form substantially in synchronism and opposing phase relation, converting said oscillatory currents into two series of positive impulses, applying a modulating signal-representing current to said series of impulses, applying the mod--` ulated series of impulses to start and stop currentsfrom a local source of energy, ulated waves generated by converting said transmitted modulated waves into a series of positive impulses, generating a second series of positive impulses, alternately applying the` impulses of both mentioned series to stai-tand stop the ilow of current in a local source thereby generating modulated currents in accordance with the transmitted modulations, and.` impressing the last'mentioned modulated currents on a signal translating device. 3. The method of communication which comprises generating a substantially constant fre- `quency oscillatory current,rconverting said current into two currents substantially in contra-` phase relation and of saw tooth wave form, converting said saw tooth wave form currents into two series of` positive impulses, applying a modulating signal current to said series of impulses, alternately applying said modulated positive impulses to generate and stop the generation of currents, transmitting said generated currents, converting said transmitted generated currents into a series of positive impulses, initiating a,

local oscillation in synchronism with the rst mentioned oscillatory current, converting said local oscillation into a series of positive impulses, alternately impressing positive impulses from the two series of impulses to start and stop the ow of current in a local source, and impressing the last mentioned current on a translating device.

4. The method of communication described by claim 3 and characterized by the further step of wave shaping the currents generated from said local source.

5. The method of communication described by claim 3 and'characterized by the further steps of wave shaping before transmitting and Wave shaping before impressing the currents on a translating device.

6. The method of transmitting an oscillatory current which comprises generating a saw tooth oscillation, generating a second saw tooth oscillation synchronous and in substantially contraphasal relation with the ilrst saw tooth oscillation, converting said saw tooth oscillations into transmitting mod-` said local energy.'

tooth wave form, retarding impulses, applying modulating a series of positive impulses, applying said impulses to start and stop a iiow of a local source of energy, and transmitting waves generated by said local energy.

7. The method of transmitting an oscillatory current which comprises generating a saw tooth oscillation. generating a second saw tooth oscillation synchronous and in substantially opposing phase relation with said rst saw tooth oscillation, converting saidvsaw tooth oscillations into a series of positive impulses, applying said impulses to start and stop a local source of energy, reshaping `the wave representing said local energy and transmitting waves of said reshaped energy.

8. Themethod of transmitting a modulated oscillatory current which comprises generating an oscillation of saw tooth Wave form, generating a. second oscillation of saw tooth wave form synchronous and substantially in contraphasal relation with the iirst mentioned saw tooth oscillation, converting said saw tooth oscillations into a series oi?` positive impulses, applying modulating signal representing currents to said series of impulses to vary their relativetiming, applying the modulated positive impulses to start and stop a wave whose energy is derived vfrom a local source, and transmitting waves of 'said modulated wave energy.

9. The method of transmitting an oscillatory current which comprises generating an oscillatory current of substantially constant frequency, converting said current into two currents of saw to an opposing phase relation with respect to the other current, converting said two currents into a series of positive impulses, applying said currents to eiect the operation of a relay controlling a local source. whereby a series of square topped waves are transmitted from said local source.

10. 'I'he method of transmitting an oscilla-l tory current which comprises generating an oscillatory current of substantially constant frequency, converting said current into two currents of saw tooth Wave form, adjusting the timing of one of said currents to the other so that a substantially contraphase relation exists, converting said two currents into a series of positive signal currents to said series oi impulses to vary their relative timing, applying the modulated impulses to start and stop a wave whose energy is derived from a local source, and transmitting waves created from said local source.

1l. The method of transmitting an oscillatory current which comprises generating a substantially constant frequency oscillatory current, converting said current into two currents of saw tooth wave form bearing an opposing phase relationship, converting said two currents into two series of positive impulses, applying the positive impulses to start and stop a wave whose energy is derived from a local source. reshaping the wave from said local source, and transmitting the reshaped wave.

l2. The method of transmitting an oscillatory current which comprises generating a substantially constant frequency oscillatory current, converting said current into two currents bearing a substantially opposing phase relation and having a saw tooth wave form, converting said two currents into a series of positive impulses, applying modulating signal currents to said series of impulses to vary their relative timing, applying the modulated impulses to start and stop a wave whose energy is derived from a local source, re-

one of said currents shaping the modulated wave from said local source, and transmitting said reshaped modulated wave.

13. The method of transmitting phase modulated radio frequency energy which comprises generating a substantially constant radio frequency current, converting said current into a pair of oscillations having an opposing phase relation and a saw tooth wave form, converting said pair of oscillations of saw tooth wave form into two series of positive impulses, modulating said series of positive impulses with a desired signal current whereby the relative timing of the impulses is accurately varied in accordance with the modulating signal, alterriatel1, impressing the positive impulses to start and stop the flow of current in a local source whereby oscillatory currents of square wave form are generated, reshaping said square wave form, and radiating the reshaped phase modulated oscillatory currents.

14. 'I'he method of translating phase modulated oscillatory currents which comprises converting said currents into a series of positive impulses, generating a series of positive impulses in substantially opposing phase relation and in synchronism with the positive impulses o! unmodulated received oscillatory currents, applying both series of said positive impulses to start and stop the flow of current in a local source thereby generating currents of a square wave form,'and impressing the last mentioned currents on a signal translating device.

15. The method of translating phase modulated oscillatory currents which comprises converting said currents into a series of positive impulses, generating a series of positive impulses in substantial contraphase relation and synchronism with positive impulses of unmodulated received oscillatory currents, applying both series of said positive impulses to start and stop the ow of current in a local source thereby generating currents of a square wave form, reshaping the currents of said square wave form in accordance with the original signal modulations, and translating said currents into indications corresponding to the original signal energy.

16. The method of receiving and translating phase modulated oscillatory currents which comprises selectively amplifying said currents, generating a local oscillation substantially in synimpulses, an electron relay, a source of energy in the output circuit of said relay, means for impressing the positive impulses on said relay whereby the output circuit is alternately energized and deenergized, means for altering the wave form of the output currents of said electron relay and means for transmitting said altered output currents.

18. In a system o! the character described in claim 17, means for modulating said positive impulses.

19. In a system of the character described, means responsive to phase modulated currents, a local oscillator of constant frequency, means for converting said phase modulated currents and said local oscillations into two series of positive impulses, an electron relay, a source of energy in the output circuit of said relay, means for impressing said series of positive impulses on said relay whereby its output circuit is energized and deenergized by said local source of energy, and means for translating currents. in the output circuit of said relay into intelligible signals corresponding to said phase modulation.

20. In a system of the character described by claim 19, a rejector circuit connected to the output of said electron relay to eliminate radio frequency oscillations contained in the output currents of said relay.

DAVID G. C. LUCK.

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