US2101703A - Phase modulation receiver - Google Patents

Description

M. GQCROSBY 2,101,703 PHASE MODULATIO N RECEIVER Dec. 7, 1937.

Original Filed Jan. 23, 1932 3 Sheets-Sheet l CARR/ER SOURCE LEAMPUF/Ek AND LIMIT-ER 0 1407041147 IC' V01 l/ME (047ROL CARR/ER I Hi. TER

CARR/ER AMPUFIER AND l/M/TER 0? AUTOMATIC VOZUMF 60/V7'k0l INVENTOR MURRAY CROSBY ATTORNEY Dec. 7, 1937. G CROSBY 2,101,703

PHASE MODULATION RECEIVER 3 Sheets-Sheet 2 I Original Filed Jan. 25, 1932 INVENTOR MURR CROSBY BY *5? ATTORNEY Dec. 7, 1937. M. e. CROSBY 2,101,703

PHASE MODULATION RECEIVER Original Filed -Jan. 23, 1932 3 Sheets-Sheet 3 11 4 36 36 40 '32 if 34 msoamcr v POWER MUlT/PUER AMPl/F/ER I l j 4 P/MSFMflDUMIOk CARR/ERUM/TER 0/-' FIGURE! 0R AUTOMATIC V01 l/Mf C0/V7k0l B c 0 v E IIHERWYNE CARR/ER j PHASE RECEIVER FILTER ADJUSTER {I E AMPl/F/ER AND CAM/5k LIM/TE/Z lIM/7Ek0R/ll/TOM477C 0/94070444776 VON/ME cameo:

VOLUME CONT/UL AMPL IFIEK V INVENTOR MURRAY G. CROSBY I BY ATTORNEY Patented Dec. 7, i937 7 t is 2,101,703 7 UNITED STATES PATENT OFFICE" PHASE MODULATION RECEIVER MurrayG. Crosby, Riverhead N. Y., assignor to Radio Corporation of America,- a corporation of Delaware 7 Original application January 23, 1932, Serial No.

588,309, now Patent No'.2,081;577,"dated May 7 25, 1937. Diyided'and this application Octoher 1, 1936, Serial 'No.'103, 505 V 6 Claims. (01. est-20) This invention relates to the signalling art and multiplied by the order of the harmonic, or order pertains especially to the transmission of intelof frequency multiplication. ligencefrom one geographicallyseparated point. Another general object of my present invento another by the useof phase'modulated waves 'tion is to provide improved reception methods or carrier energy and is a division of'Crosby. and means for phase modulated waves. United States application #588,309 filed January A further object of my invention is to provide 23, 1932, Patent No. 2,081,577,May 25, 1937. i a receiving system wherein the collectedphase' An object of my present invention is to promodulated energy is' combined in predetermined vide a new and useful system for producinga phase relationship with energy of substantially phasemodulated wave of substantially constant constant frequency and phase and wherein the 10 frequency and, briefly, to do so I provide an arcombined. energies are then detected and trans rangement and a method wherein two voltages 'lated. It is desirable, of course, to have the of substantially like frequency are combined less energy combined with the received energy in than 180 degrees-or any multiple of 180 degrees exact synchronism with the received carrier out of phase to produce a resultant voltage. energy; To provide for such energy, I separate According to my invention, further, the relative the carrier energy f the received e e y n phase of the resultant voltage is varied by varying combine it in proper phase as will be explained the relative values of the voltages combined with o ful y hereinafter With all Of e received the predetermined number of degrees, out of energy whereby the combined energy is in aform 20 phase. r which may be detected to give the transmitted 20" 1 As' such procedure may introduce a certain si c r amount of amplitude modulation in the resultant It is a further obje Of y invention to utilize phase modulated wave, which of course is unheterodyning at y receiver for phase medulated desirable, it is a further object of my present in waves, using preferably a local heterodyne oscilvention to eliminate the amplitude modulation l r f a le fr q e y, a f rx mp 25- component. To do so the resultant phase moduusing a cry eentrelled'eseilletor With p lated energy is limited by, for example, electron able crystals o difierent fundamental q discharge devices operated at their saturation cies'. a point, to substantially constant value. 'By heterodyning to the intermediate frequency More specifically, according to my present init is possible to'have all of the intermediate frevention, I carry out the foregoing objects by q y a p n and the final detector i applying to a pair of electron discharge devices Qu s tu ed o e fi eq y 80 that O ly e voltages of like frequency a predetermined numtuning 'of the circuits ahead of the first detector ber of degrees out of phase such that the phase and the frequency of the first beating oscillator difference is not 0, 180 or any whole multiple requires adjustment f u i e ss of 189 although phase differences varying slightgr t y facilitates the tuning Operations a d 1y from 0, 180 etc., are suitable. The outputs makes it possible to apply complicated filter or of the devices are so combined that there is a, crystal circuits in the final stages of the receiver resultant voltage of like frequency, To vary'the Which o d be e p if it W necessary 40 phase of this resultant voltage, or, in other words, to ke t e eq y V b i the phase of the resultant carrier energy, I vary Th s f h hctcrodync pr pl ls make oppositely the internal 'impedances of the elecit p ss toobtein energy from the final d tron discharge devices. Preferably, I apply m dt'ectorcircuits which :varies when the transmitter ulating voltages to screen grids of the devices frequ c or receiver oscillator varies, which v and carriervoltages out of phase to other energy C be 11ti1iZet0e0htr01 the frequency electrodes of the devices as will be explained more of t fi t beating oscillator in aimanncr to p fullyvhereinafter. the receiver automatically tuned in to the de- As described, a' maximum shift of less than s d Sighelr r ispossible with the foregoing'arrangement. Moreover, for Short Wave reception the o To augment still further the phase shift produced q y band f h h q n y s ages is much by the modulating energy is a further object greater than the band of frequencies occupied by of my present invention. To do so, according thesignal with its sidebands. This excessively to my invention, the phase shifted energy is wide frequency band allows noise to enterthe frequency multiplied asa result of which the receiver; By heating or heterodynlng down to Q5. frequencymultiplied output has a phase shift an intermediate frequency and there applying additional frequency selectivity it is possible to limit the frequency band of the receiver to the band occupied by the signal. This results in minimum noise and interference.

Further, in connection with heterodyning it may be noted that the first heterodyne detector in a superheterodyne receiver serves the function of subtracting from all of the incoming frequencies, a frequency equal to that of the first beating oscillator. If an incoming signal of, say 10,000,000 cycles is modulated at the rate of 1,000 cycles with either phase or amplitude modulation, there will be produced sidebands 1,000 cycles above and 1,000 cycles below the carrier. In this case these sidebands have a spacing from the carrier of only 0.01% which is much too small to permit ordinary circuits to discriminate between carrier and sidebands in the manner required for detection of phase modulation. If the signal with the 10,000,000 cycle carrier is beat with a first oscillator having a frequency of, say, 9,900,000 cycles, I obtain an intermediate frequency of 100,000 cycles, which contains the sidebands still spaced 1,000 cycles from the carrier or an amount now equal to 1%. This separation is sufiiciently great so that two band pass filters may be utilized to separate the sidebands from one another in the manner described in the copending application of C. W. Hansel], Serial #611,050 filed May 13, 1932, Patent No. 1,999,902 granted April 30, 1935, and my copending application, Serial #565,005 filed September 25, 1931 and it is also suificient to allow the carrier to be taken out through, for example, a crystal filter, separately amplified and reintroduced with adjusted phase as described more fully hereinafter.

It may seem that, since at the transmitter, increasing the frequency increases the phase shift, at the receiver decreasing the frequency by heterodyning should decrease the shift. However, this is not so since there are two different processes involved. At the transmitter the frequency is raised by frequency multiplying and at the receiver it is lowered by heterodyning. When a Wave is frequency multiplied it is passed into a harmonic generator and a harmonic is chosen for the multiplied output. Thus, only integral values of multiplication may be obtained corresponding to the 2nd, 3rd, 4th, etc., harmonics.

When this sort of multiplying is applied to a wave the phase or frequency shift of phase or frequency modulation is multiplied by the order of multiplication; that is, 2, 3, 4, etc. Thus, a 10,000 cycle wave frequency modulated by a 1,000 cycle shift has a 3,000 cycle shift when it is multiplied to 30,000 cycles. The same amount of multiplication is obtained in phase modulation.

As required by law, my present invention is defined with particularity in the appended claims. However, it may best be explained both as to its structural organization and. mode of operation by referring to the accompanying drawings wherein:

Figure 1 is a. wiring diagram of a phase modulation transmitting system, according to my present invention.

Figures 2 and 3 are vector diagrams given in order to explain the operation of the system shown in Figure 1.

Figure 4 is a block diagram of a phase modulating system wherein the phase of a transmitted carrier may be shifted to an angle greater than degrees.

Figure 5 illustrates one form of receiver, built in accordance with the principles of my present invention, for receiving and translating a phase modulated wave.

Figures 6 and 7 and 7a are vector diagrams explanatory of the operation of the receiving arrangement shown in Figure 5.

Figure 8 is a modified form of phase modulation receiver according to my present invention.

Figures 9 and 10 are vector diagrams explanatory of the operation of the receiver of Figure 8.

Turning to Figure 1, illustrating a transmitter for transmitting phase modulated energy, carrier energy or potentials from an oscillation generator 2 are fed to an artificial transmission line 4, terminated by a resistance that is equal in value to the surge impedance or resistance of the line 4. The generator 2 may be a crystal controlled oscillator, or any other form of substantially constant frequency oscillation generator. By virtue of the termination of the loaded line 4, at the desired carrier frequency, only travelling Waves appear in the inductive portion 8 of line 4.

The control electrodes or grids I0, I2 of electron discharge devices I4, I6 are tapped through blocking condensers I8, 20 to points 22, 24 at inductance coil 8 which are less than apart, for example, 90. Accordingly, voltages of the same or like carrier frequency from source 2 are fed to tubes I4, I6, 90 apart.

The vectorial relationship of the voltages so fed is illustrated in Figure 2 for the particular case of 90 degrees separation where Ea illustrates the voltage applied to tube I4 and Eb indicates the alternating voltage applied to tube I 6. Consequently in the output circuit I8 of tubes I4, I 6 there appears voltage Er as shown in Figure 2. This is a resultant voltage which is of like frequency to the voltage applied from source 2.

Carrier source 2, of course, for the purpose of obtaining voltages a desired number of degrees apart to be applied to the two electron discharge devices I4, I 5 may take the form of two alternators mechanically tied together so that they can generate voltages 90, or any other desired number of degrees apart in which case the output of each alternator would be fed across the grid and cathode of one of the tubes. Or, the transmission line for obtaining voltages of predetermined phase displacement may be replaced by a network of resistances, inductances and capacities to which energy of constant frequency is fed, each tube being coupled to portions of the network which have voltages generated thereacross the desired number of degrees out of phase.

By oppositely varying the output of each of the two electron discharge devices I4, IS the resultant may be made to receive any phase as shown in Figure 3 from vector Er to E: as indicated. This shift in phase is accomplished by relatively decreasing the amplified voltage Ea, appearing in the output circuit due to the amplifier action of tube I4 and relatively increasing amplified voltage Eb from tube I6 appearing in the output circuit and vice versa.

In order to cause this opposite variation in voltages in tubes I 4, I0, modulation energy from a suitable source 24 and amplified by push-pull amplifier 25 is fed as indicated in opposite phase to the screen grids 28, 30 of tubes I4, I6. sequently, the internal impedance of the two tubes is varied oppositely and, as a result, their outputs are varied inversely to their internal impedances, thereby causing a phase shift of the Con-' phase modulated energy so I appearing in the output circuit iii of electron ception of power amplifier .The output of the phase modulator may be fed discharge devices 5-, I6 may then be amplified by a suitable amplifier 32 and radiated or propagated through space in the form of electromag-' 'netic wave energy by means of a suitable antenna M.

As will be evident from an inspection of Figure 3, thegreatest amount of phase shift pos-. far described is a value sible with the scheme so less thanlSO degrees, or with 90 degrees phase displaced voltages, 90 degrees; and it is also evident that this arrangement introduces a small modulation. To eliminate the amplitude modulation the power amplifier amount of amplitude 32 should be operated at all times to its saturation point. ative amount of phase modulation, the apparatus 32 should include also some form of frequency multiplier; V 7

Such an arrangement is shown diagrammatically in Figure 4 wherein rectanglefifi indicates all of the apparatus of Figure 1 with the ex- 32 and antenna 34.

to a harmonic generator or frequency increaser dt which, by multiplication in frequency of the output of apparatus 3 will cause an increased phase shift in the multiplied frequency energy corresponding to the order of its harmonic, or order of frequency multiplication. 7

To eliminate amplitude modulation introduced by either the phase modulation or the frequency multiplication, the frequency multiplier is followed by a limiter ill-whose output, in turn, is fed to power amplifier 32. If desired, the lim- 7 iters may be placed ahead of the frequency multiplier, or, limiters may be used both ahead of and behind the frequency multiplier.

Figure 5 illustrates a system for receiving, tecting and translating electromagnetic waves propagated by 'a transmitter such as described in Figures 1 and 4. Propagated energy is col- 42 and beat to a suitable band of intermediate frequencies by the action of heterodyning apparatus 44 of known construction including a variable frequency heterodying oscillator variable so that signals over a wide range of frequencies may be received. The intermediate frequency energy so derived is amplified to a constant value by the action of intermediate frequency amplifier and limiter 46. A portion of the energy of the intermediate frequency band is fed to filter 48 which filters out energy only of the carrier frequency and is fed to a carrier amplifier and limiter 5B.

The remaining portion of the intermediate frequency energy is fed to electron discharge devices 52 through the action of transformer 54. The limited carrier frequency energy, however, is fed through a phase adjusting device .56 and transformer 58 to the input side of the electron discharge device 60 whose anode is connected as shown in parallel with electron discharge device 52. The phase adjusting device 56 is so adjusted that the potentials fed to tube 60 are substantially 90 degrees out of phase to the potentials fed to tube 52 as indicated in Figure 6 wherein Es illustrates vectorially a potential fed to tube 52 and E0 indicates the potential fed to tube 60.

Now, with the reception of a non-modulated wave, the output of detector 62 will be substantially constant as a result of which no sound will secondary of transformer To increase or augment the rel-'- grids of the detectors 8!], 82, 180

been modulated 'in accordance with signals reducing the frequency of said amplitude limited 64. However, asa phase modulated wave is'rewill be present in 66. Consequently, detector 62 will, throughthe intermediary of low frequency amplifier produce sound in the during the reception of phase modulatedsignals for the arrangement shown in Figure 5 is given in Figures '7 and 7a., the-resultant 'electromotive force E'r fed to the control electrode of detector E2, varying, of course, with the phase shift of the phase modulated'wave E. Of course, the same result may be obtained by feeding energy from a synchronously run local oscillator to the 54 or the primary 'of 58 rather than use the carrier apparatus, 50, 56, 58, Bil. However, the arrangement'shown is. preferable in view of the known difficulties of synchronously operating a local oscillator.

Moreover, it is to be clear that heterodyning lation receiver, is not essential.

end, amplifiers M, 46 take than passing the mean frequency of an intermediate band 'of frequencies'pas'ses the mean frequency of the received radio frequency: band.

Another desirable form of receiving apparatus is shown'in Figure 8. l frequency energy is fed to the control electrodes of detector tubes 80. 82 cophasally as shownby the vectors E5 in Figures 9 and 10, while filtered carrier, energy is fed to the control electrodes or out of phase, as shown by the vectors E0 of Figures 9 and. 10. Amplitude variations characteristic of the phase variations and of the signal modulations will be produced in the anode circuit energy.

I claim:

1. In a phase modulation signalling system the method of demodulating carrier wave energy the phase of which has been modulated in accordance with signals which includes the steps of, collectsaid wave energy to a lower frequency to increase the percentage of frequency spread be-' tween the carrier and sideband energy of said lower frequency, limiting the amplitude of said wave energy of lower frequency, producing unmodulated energy characteristic of said carrier of said lower frequency limiting the amplitude of said produced unmodulated energy and combining said limited unmodulated energy with amplitude limited sideband energy of said lower frequency in substantially phase quadrature relation to produce resultant energy characteristic of the phase modulations on said collected energy.

2. The method of demodulating high frequency oscillatory energy the phase of which has which includes the steps of, limiting the amplitude of said phase modulated oscillatory energy,

oscillatory energy and simultaneously increasing the degree of phase modulation thereon to thereby produce characteristic energy of lower frequency, producing oscillatory energy characteristic of the carrier wave of said energy of reduced frequency limiting the amplitude of said produced oscillatory energy, separating said produced amplitude limited oscillatory energy into be heard in the transmitting device or phones transmitting device or ear. phones E i. An instantaneous vectorial diagram:

As indicated, intermediate two portions of opposed phase, combining amplitude limiter connecting said input electrodes to tude limited sideband energy of said reduced said filter a. circuit connecting said intermediate frequency wuth both of said portions in substan frequency amplifier to said input electrodes, and tially phase quadrature, and differentially coma phase adjuster in one of said last two circuits. 5 bining the resultants produced by said first com- 5. Means for demodulating wave energy modu- 5 bining steps to produce a resultant which varies lated in phase at signal frequency comprising a in amplitude in accordance with the phase modupair of electron dischar e d vi es e ch hav n an lations on said oscillatory energy. anode, a cathode and a control grid, an output 3. The method of demodulating oscillatory encircuit connecting the anodes of said tubes in ergy modulated in phase at signal frequency push-pull relation, an input circuit connecting 10 which includes the steps of, reducing said oscilthe control grids of said tubes in parallel, an latory energy to a lower frequency and simulinput circuit connecting the control grids of said taneously increasing the degree of phase tubes in push-pull relation, wave amplitude limmodulation of said oscillatory energy of reduced iting means for impressing said wave energy on frequency, limiting the amplitude of said energy one of said input circuits, and wave amplitude 15 of reduced frequency, separating a portion of limiting and phase adjusting means for impressthe energy of said reduced frequency and reing oscillatory energy characteristic of the carmoving therefrom all phase deviations, and imrier frequency only of said wave energy on the pressing said energy from which the phase deviaother of said input circuits. tions have been removed on energy of said re- 6. In a. system for demodulating oscillatory enduced frequency in substantially phase quadraergy modulated in phase, a pair of electron ture to produce a resultant characteristic of discharge devices each having a control grid, phase modulations on said energy. an anode and a cathode, an output circuit cou- 4. In a system for demodulating phase modupling said anodes together, separate input cirintermediate frequency amplifier and amplitude odes of said devices, Wave amplitude limiting limiter, a filter coupled to said intermediate fremeans for impressing phase modulated Wave enquency amplifier and amplitude limiter, said filter ergy on one of said input circuits, and wave ambeing tuned to the frequency of the carrier passed plitude limiting and phase adjusting means for by said intermediate frequency amplifier and amimpressing energy characteristic of the carrier plitude limiter, a pair of electron discharge deonly of said phase modulated wave energy on the vices having input electrodes and output elecother of said input circuits.

trodes, an indicating circuit connected with said output electrodes a circuit including an ampli- MURRAY G. CROSBY.

' lated energy, a heterodyne receiver including an cuits connected with the control grids and cath- 25,

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