US2134033A - Receiver - Google Patents

Description

M. G. CROSBY Oct. 25, 1938.

original Filed June', 1935 2 sheets-sheet 06f. 25, 1938.. vM G CRQSBY 2,134,033

RECEIVER Original Filed June 5, 1955 2 Sheets-Sheet 2 Q: im INVENTOR s MURRs/j. CROSBY /J ATTORNEY yPatented Oct. 25, 1938 UNITED STATES RECEIVER Murray G. Crosby, Riverhead,` N. Y., assignor to vRadio Corporation of America, a corporation of Delaware Application June 5, 1935, Serial No. 25,026 Renewed December 21, 1937 13 claims. (c1. 25o- 20) This disclosure relates to'a frequency or phase modulation receiver wherein the received energy is frequency multiplied and thence converted to amplitude modulation by means of a frequency modulation conversion circuit. The resulting amplitude modulation in the output of the conversion circuit is detected in the usual Way if frequency modulation is being received. If phase modulation is being received, equalization may be applied to correct for the inherent frequency'distortion.

An object of this invention is to provide a simple receiver for the purpose of detecting and tracing extraneous or unwanted' frequency or phase modulation on a modulated transmitter. By applying frequency multiplication plus heterodyning to the received energy the depth offrequency or phase modulation is multiplied by the order of the frequency multiplicationy so that the receiver may be made vultra-sensitive and more suitable for working with 10W degrees of modulation. This feature is especially valuable in the case of low modulation frequency or phase modulation where the effective degree of frequency modulation.y is low and the frequency modulation converting circuit is insensitive to these modulations.

The present receivers available for detecting phase modulation are usually considerably complicated Whereas frequency modulation receivers are fairly simple. Phase modulation. may be receved on a frequency modulation receiver, but

the inherent difference between frequency and phase modulation makes the output of a frequency modulation receiver, receiving phase modulation, directly proportional to frequency. Consequently, the receiver would be insensitive to the low modulation frequencies of phase modulation. Equalizing circuits may be applied to the detected energy of this type of a receiver to correct for the frequency distortion. However, in cases where unwanted modulations are being traced, equalization is unnecessary. The receiver of this invention then proves valuable.

An advantage of the principles disclosed in this invention is that by using this frequency multiplication plus heterodyning system, the requirements of the frequency modulation converting circuits do not have to be so exacting and receiver design is facilitated. Thus a frequency multiplication of two might be employed `in order to reduce the lengthof the artificial line or retard circuit in the articial line type converting circuit, to one half. k

A further novel feature of this invention is one of its means for producing frequency multiplication. By utilizing the higher order effects of a power law detector, a harmonic of the signal is caused to heterodyne with a harmonic of the local oscillator so that the resulting output is the same as though the intermediate frequency energy were passed through a harmonic generator or frequency multiplier. monic generator is dispensed with and the change from one order of frequency multiplication to another isv effected by merely tuning the local oscillator. vWhere' a separate frequency multiplier is used, thechange of order of multiplication requires the tuning ofl several stages.

The novel featuresof my invention yhave been pointed out with particularity in the claimsv appended hereto, as required by law.r The natureof my invention and the manner in which the same operates will be understood from the following'detailed description thereof Y and therefrom when readk in connection with the attached drawings through which likereference characters indicate like parts insofar as possible, and in which:

Figs. l and 2 each illustrate different modifications of wave receiving meansarranged in ac-r cordance with the principles of my invention.

In Fig. '1, the intermediate frequency energy resulting from the heterodyne detectory is frequency multiplied to increase the depth of modulation and the modulations are converted in a novel circuit into modulationsA of a different charf acter for demodulation. ,Y

In Fig. 2, the depth of modulation is increased by harmonic action of the heterodyne demodulatory and the resulting energy is converted and demodulated. c

Figs. 3. and 4 are characteristic curves, illustrating the operation of the demodulatorp and harmonic generating tube in the circuit of Fig. 2;l while Figs. 5, 6 and '7 are graphs illustratingthe op-l eration of the demodulating means in the circuit.

In this manner the separate harfrequency amplifier 5 ampliles and-filters the intermediate frequency energy. The intermediate frequency energy is then passed through the frequency multiplier 6 Where it is multiplied the desired number of times.. By means of detector 'l and intermediate frequency oscillator 8, the multiplied energy is heterodyned to a lower frequency which is more suitable for filtering in the frequency modulation demodulator coupled tol Hl. This demodulator may be any type of frequency modulation converting circuit-that is, a circuit capable of translating frequency modulated energy to its signal energy. vFor example, the output of the intermediate frequency amplifier may be fed tothe primary Winding of transformer Ill, the secondary winding of which is coupled to control electrodes in tubes l2 and I4', as shown. The

output of tube I2 is filtered by lter sections I5 and I6 and the filtered energy is then` fed to the control grid of a detector tubefll and also to the control grid of a combining tube I3. The

output of tube I4 is combined with the output` of tube I3, through the impedance coupling 22. 'f A potentiometer 23 controls the volume of .thej energy supplied from the -filters I5, .I6 Vto theY tube I3. Potentiometer 2I`regulates the voltage supplied from the impedance coupling 22 to theV control grid of detector tube I8, so that this energy is equal to the energy that-'isv fed from I5, I6 to the control grid of detector tube I1. Transformer I9 combines the audio outputs of the detectors II, I8. The combined signal appears 'iin an 'indicating or recording' device 20 .either directly from thesecondary winding of quires that one *detector be fed by thesignal passed through a filterof positive slope, as shown in Fig.f5, andthe other detector by a filter of negative slope, asshownin Fig. 6. Ordinarily, two filters having these slopes are built separately. However, by combining a filter of one slope lwith a filter of -flat topcharacteristic as shown by Fig. 7 a filter-'of opposite slope may be obtained.

For instance, the output of the filterk of Fig. 6 y

may be subtracted fromthe output of the'filter of Fig. 7 andrthe'resultant wouldfbera negative slope filter, as'shown by Fig. 5. Inthis manner, the output of the filter I5, I6 in Fig. 1 may be given by Fig. 6, for ,fc as the carrier frequency and fo fZ,/the band limits. The output of tube I4 is an aperiodic amplification of the signal giving a fiat top characteristic, like that of Fig. 7, although not necessarily a bandpass action, as Fig. 7iportrays. (In Figs. v5, Gland 7, the characteristics are assumed to be ideal, so that the filterscut 'off at the outer limits lof the received wave bandi iii-the actual Ycase this would only be approximated.) The combination of the outputs of ytubes I3 and I4 is in reality a subtractionof the characteristics of Fig; 6` from that of Fig; 7, so that Fig. is obtained, thus', the slope of the filter has been reversed. Thus, feeding the output of the filter I5, I 6 directly to one detector tube, say I'I, and reversing the slope for the other detector, say I8, gives the equivalents of two filters and a back-to-back action. Tubes I3 and I4 then merely function to apply the output of the one filter with its slope reversedto thedetector I8. The inputs to the two detectors are balanced by means of the potentiometer 2 l For the reception of phase or frequency modulation, the use of opposite slope demodulating lter effects applied from I5, IItoV I'I and from 22 to I 8 causes the resulting two amplitudeamodulations fed V from the outputs of detectors I1 and IB to be 180 out of phase. To make the detected outputs add, they are combined in the transformer I9 with the series of push-pull connectionsv to produce an 180 reversal of phase of one output. In the case of amplitude modulation, however, the phaseofthe .modulation is unaffected bythe demodulating filters and the Vparallel connection of transformer 9 is used. A

similar converting and demodulating system has been described in detail and claimed in my U. S. application Ser. No. 703,770, filed Dec. 23, 1933, Patent No. 2,061,611, November 10, 1936.

Thus, it is seen that the signal is received on a superheterodyne receiver, units I, 2, 3, 4 and 5 and is frequency multiplied to a higher frequency so thatV the depth of its phase or frequency modulation is multiplied. This'higher depth modulation is then 'heterodyned down to a lower frequency which is more suitable for receiving on a filter-type'frequency modulation receiver. The first intermediate frequency voltage is given by:

E sin (wt-4: cos pt) (1) where w=2arr intermediate frequency, f.=phase deviation in the case ofV phasel modulation or =fd/fm, where fd=frequency deviation and fm'=modulaiton frequency, in the case of frequencymodulation p=21rm- Hence the equation covers both phase and frequency modulation,

Ydependingupon whether indicates phase deviation or modulation index, fri/fm.` In this respect, Vthe following analysis is general-that is, it covers both the frequency modulation and phase mod-` ulation. cases.

-Y It is known to the art that after passing the intermediate frequency voltage through the frequency multiplier, the result is:

t e=E sin N(wtncos pt) (2) e=E sin (21rNfte-Nqb cos pt) (3) where N is Vthe order of frequency multiplication.

VIt is seen from (2) and (3), that f as Well as are multiplied by N; consequently, the frequency as Well as the depth ofV modulation are both multiplied.

This multiplied energy is then heterodyned fromV its frequency vN to a third intermediate frequency which is suitable for filtering; the result is: l

ve=E sin (21rf1t-N cos pt) (4) Equation (4)V Vshows that the energy has been converted from a frequency of (l) with a depth of modulation of to a frequency f1 with a .depthof modulation of Nc. Consequently, the depth of modulation of all the modulating frequencies has been increased. As a result, the

f(radirans/sec)=d dt (5) Consequently, if (7) is linear and faithful to the signal of modulation on a frequency modulation receiver, ,a wave with an instantaneous frequency given by (6) would produce an output proportional to fm, the modulation frequency. For this reason, the principle of frequency multiplication at the receiver becomes'valuable for the lower vmodulation rfrequencies of phase modulation.

The circuit of Fig. 2 is an adaptation ofthe higher order effect type of detector and frequency multiplier, and a long line type of frequency modulation converting circuit. The 'radio' frequency amplifier 2 fed by antenna I feeds the control grid Gl of the pentode detector 3. The suppressor grid G2 of tube 3 is fed by energy from the high frequency oscillator 4'. The oscillator 4 may be tuned so that fundamental energy therefrom beats'with the harmonic of the signal carrying wave energy or may be tunedso that a harmonic of the fundamental wave of the oscillator beatsv with a harmonic of the fundamental signal carrying Wave energy. The frequency multiplied and heterodyned output of detector 3 is fed tothe intermediate frequency amplifier 5 where it is amplified and filtered. The output of 5 is fed to the grids of detectors 28 and 29 via transformer 21 which has an astatic shield 35. It is also fed via line'l 2B to the detector grids through the midtap of 21. The output of detectors 28 and 29 is resistance coupled to audio amplifiers 30 and 3| and translated by pho-nes 23. Thel frequency modulation conversion `circuit from 5 on is essentially'the same as Fig. 3 of my U. S. Appln; Ser. No. 618,154, filed June 20, 1932.

In the Fig. l2 circuit, the signal energy is fed to the control grid of the pentode detector, and the high frequency oscillator energy to the suppressor grid. By adjusting these two gridsl so that they operate on the non-linear portion of their dynamic characteristics, a harmonic of the signal may be heterodyned by a harmonic of the local oscillator to produce anV intermediate frequency. The resultant effect is then the same as though the signal had been frequency multiplied by means of a separate-frequency multiplier, and heterodynedfto the intermediate frequency by means of an 'intermediate frequency oscillator. The manner in which the pentode detector acts to produce this type of frequency multiplying is'most easily explained by the following mathematical-analysis:

The curves of Figs. 3 and 4 show the platev current-control grid Vvoltage (Ip=E'g1) and plate current suppressor grid voltage (Ip=Eg2) characteristics fo-r a pentode detector'. `It is well known that the varying current in the output Y of the detector, due to a single grid, may be expressed asl a function of the'sinusoidal voltage impressed upon the input by the power series:

v J=a1e+b1e2+c1e3| (8) The output due to two grids will be given by:

Multiplying (9) out and eliminating all but the terms causing beats or a heterodyneoutputz- From (10) it can be seen thatterm 1) will produce beats between the fundamental of the signal applied on one grid, say GI, and the fundamental of the local oscillator applied to the other grid, say G2. When the detector isA adjusted for normal detection, Without frequency multiplicationen-efficients a1 and ai are made large compared to b1 b2, c1 cz, etc.,'by adjusting the grid biases so that the signal and oscillator swing over the linear portion of the tube characteristics as the point a in Figs. lSand 4. l

Terms (5) ,A (9) etc., are Vthe higher order terms which produce the frequency multiplication. Term (5) isthe product of the squares of the signal and local oscillator which produces 'the beat between the second harmonic of the signal and the second harmonic of the ocillator. In the same manner term (8) produces the beats between the third harmonics.' The remaining terms (2), (3), (4) (8), etc., all contribute fundamental and harmonic beats but to a lesser degree than (l), (5), (9), etc. Thus, it can be seen that, to operate the detectoras ar frequency multiplying detector, coefficients b1, b2, c1 c2, etc., must be made as large as possible. This is done by operating with the grid biases at the curved portion of the characteristics as at "b of Figs. 3 and 4. Also the output is an exponential function of the two input voltages so that the input'voltages must be made highY comparedl to their normal detection values; that is, the'detector should be overloaded.

In Vorder to show how term (5) f produces a beat between the second harmonic of the signal and the second harmonic of the oscillator, the signal of equation 1) will be Vapplied as e1 of one grid anda local oscillator Y f 62:11"or sin' ,wir 11) on the other grid. Term. 5) of 101s; Y j=b1b2e12eg2 i I, (172) j: [J1/52E? sin2 (Wt- 3 Vcos PEUZ sinz wlt (13) Y Y (lcos 2Wt) (14) Multiplying and separating out the heterodyne term:

cos((2wt- 2W1t)2 cos pt) (16) Equation (16) gives the beats between the second harmonic of the signal, and the oscillator, The depth of phase or frequency modulation is 2(1). Consequently, the intermediate frequency signal is weI. 1?.:KE2E02 cos (unt-241 cospft) (17) quency modulated waves of increased modulation depth inthe output of 5 are democlulated,l it must be kept in mind that conversion of the frequency modulations depends upon the fact that the electrical length of aglter or transmission line, such as 26, which consists of a series of sections composed of inductive, capacitive and/or resistive elements in a series'and/or .parallel arrangements or any one of a combination of saidelements in said arrangement, varies with the impressed'frequency.' In the following ex.-

planation, a transmission line, such 'as 26,"will be utilized, although it Will be understood that a file ter, such as a high passlow pass, bandpass, band elimination, etc., may be used.' `If the line is a given number of wave lengths long-forI a predetermined frequency, at a higher.. frequency4 the electrical length will be greater and-at a lower frequency the velectricalv length of the line will b e less. The fact that Vthis electricalA lengthdoes change with frequency makes the phase at the output of the line changeY with respect to that at the input ofthe line,` if the frequency of the signal transmitted by the line is varied. Consequently, if the signal impressed on the input of the line iscombined with the signalat the output of the lineanadjustment of the line may be made, sothatthephase difference atA the voltage of the signal impressed on the input of the line and the voltage of the signal appearing on the output of the lineV increases Vas the degree; of Vfrequency modulation is increased. Thisphase difference will cause a variation in the amplitude of the resultant of the combined voltages, so that an amplitude` modulation is formed which is truly characteristic of the frequency modulation of the original signal. n y

In the specific application,'the control grids of the differential detectors 28 and 29 are energized in phase opposition from unretarded energy derivedfrom the output of rtheintermediate frequency amplifier 5. The control grids of tubes 28 and 29 are simultaneously energized cophasally by energy derived from a selected point on the retard circuit26.` By properly selecting the tap onY 26 the resulting amplitude modulations due to the combination of the energy from the two paths which is fed to the' control grids ofA detectors 28V and 29 may be made 180 out of phase. The resultants of the phase displaced energies from the two paths on the control grids of 28 and`29 produce variationsv in the amplitude ofthe energy in the output of tubes 28 and 29 which are characteristic of the frequency modulations on the signal wave. The energy from the outputs of tubes 28 and 29 is supplied by way of couplings 40 and 4I to coupling tubes 30 and 3| and from the output of the coupling tubes and 3| to indicator 20. If frequency modulated waves are to be received, the outputs of tubes 30 and 3l are connected in push-pull relation. If amplitude modulated waves are to bev received, the outputs of tubes 30 'and 3| are connected in parallel.

Another method of utilizing the higherorder effect detector for this type of frequency multiplication and detection would be to tune the local oscillator to approximately the harmonic of the signal so that a heterodyne, between the fundamental of the local oscillator and a ;harmonic of the signal, is obtained.V This Vtype of operation utilizes terms (2), (4), (3), (6), etc. of Equation r(10)'. YWith e1 as the signal and ez 'as the local oscillator, terms (2), (3) etc., would be utilized. With e1 as the oscillator and e2 as the signal, terms (4), (7), etc., would be utilized. As an example with e1 as the'signaland e2 as the local oscillator tuned to approximately twice the frequency ofthe signal, the development similar to that of Equations (11) tov (17) `gives the following heterodyne output:

]=a2b1e12e; (term (2) of Erq. (10)) monic of the signal.

Instead of performing the multiplying and heterodyningat the first detector as shown in Fig. 2, the second detector ofl a triple detection superheterodyne receiver might be used. That is, the radiofrequency amplifier 2 of Fig. 2 could be the intermediate frequency amplifier of a superheterodyne receiver. Thus, the multiplying and heterodyning could be done at any frequency.

The principle of multiplying the received energy can be appliedto the use of any type of frequency or phase modulation conversion circuit for use on either phase or frequency modulation.

A triode detector maybe used in place of the -pentode detector to produce the multiplying and heterodyningaction. The higher order effects producer the same sort of harmonic beats in any type of detector. i

It is understoody that limiting or automatic volume control may be incorporated at any point in these receivers in order that signal variations may be minimized. Similarly, automatic frequency or tuning control may be applied to mainf tain the receiver in tune with the signal.

- What is claimed is:

1. In asignal modulated wave energy demodulating means, 'a thermionic tube having a plurality of grid-likeelectrodes and a cathode, a source of oscillatory energy coupled to one of said grid-like electrodes, a circuit coupling another of said grid-like electrodes to a source of signal modulated wave' energy, and means for biasing the grid-like` electrodes in said tube negative relative to the potential of the cathode of said tube an amount such-that the said tube operates to beat a harmonic of the. wave energy with energy from said source of oscillatory energy.

2. Signal modulated wave energy demodulating means as recited in claim 1 including means for tuning said source of oscillatory energyto a frequency of -the order of the harmonic frequency of the modulated wave energy.

3.V In a frequency deviation multiplier. a ther'- mionic tube having a plurality of gridflike electrodes a cathode and an anode, a source of oscillatory energy coupled to one of said grid-like electrodes, a circuit coupling another of said grid-like electrodes to a source of signal modulated wave energy, and means for biasing the grid-like electrodes in said tube to negative potentials relative to the cathode potential such that the said tube operates to beat a harmonic of the signal modulated wave energy with a harmonic of the fundamental oscillatory energy from said source.

4. Phase or frequency modulated wave energy signalling means comprising, means for increasing the frequency of said wave energy for increasing the depth of phase or frequency modulation on said wave energy, modulated wave energy demodulating means, a circuit having a sloping characteristic coupling said first named means to said modulated wave energy demodulating means, and a secondcircuit having a characteristic which slopes in a sense opposite to the sloping characteristic of said first circuit coupling said first named means to said demodulating means.

5. PhaseV :or frequency modulated Vvvaye `.energy signalling means comprising, means for 'increasing .the frequency of said 'vv-ave nenergy, thereby increasing the depth of modulation .on said Wave energy, modulated -vvave energy demodulating means, .a circuitincluding a filter having a sloping `cha-rac-teristic coupling s a-id, demodiilrating means to 4said first nar-ned means, a circuit including a filter having .a flat topped charac-teristic coupled to said named means, ,al circpit includingv said :filter having a sloping characteristic coupled to said first named means, combining means coupled with the output of said last two circuits, and a coupling between said combining means and said demodulating means.

6. Phase or frequency modulated wave energy signalling means comprising, means for increasing the frequency of said wave energy for in creasing the depth of phase or frequency modulation on said Wave energy, modulated Wave energy demodulating means, a circuit having a sloping characteristic coupling said first named means to said demodulating means, a second circuit having a characteristic which slopes in a sense opposite to the sloping characteristic of said first circuit coupling said first means to said demodulating means, and means connected with said demodulating means for combining the outputs of said circuits in phase or in phase opposition.

7. Signal modulated Wave energy signalling means comprising, modulated wave absorbing and amplifying means, a demodulator and a source of local oscillations coupled to said amplifying means, said demodulator having an output, a frequency multiplier coupled to the output of said demodulator, a source of local oscillations and a demodulator coupled to said frequency multiplier, said demodulator having an output, an intermediate frequency amplifier coupled to the output of said last named demodulator, said intermediate frequency amplifier having an output, a pair of thermionic tubes each having a control grid and having their control grids connected in parallel and coupled to the output of said intermediate frequency amplifier, each of said tubes also having an output electrode, an additional thermionic tube having a control grid coupled to the output of one of said last named tubes, said additional tube also having an output electrode, an indicator, and means for coupling the output electrodes of said three tubes to said indicator.

8. In a frequency or phase modulated wave energy signalling system, Wave absorbing and amplifying means, a demodulator and a source of local oscillations coupled to said amplifying means, said demodulator having an output, a frequency multiplier coupled to the output of said demodulator, a source of local oscillations and a demodulator coupled to said frequency multiplier, said demodulator havingan output,an intermediate frequency amplifier coupled to the output of said last named demodulator, said intermediate frequency amplifier' having an output, a pair of thermionic tubes each having a control grid connected to the output of said intermediate frequency amplifier, each of said tubes alsov having an output electrode, an additional thermionic tube having a control grid coupled by way of filters of sloping characteristic to the output electrode of one of said pair of tubes, said additional tube having an output electrode, a filter having a square topped characteristic coupled With the output electrode of the other of said pair of tubes and with the output electrode of said additional tubaand 4an 4-indicator V`coupled `with both of said filters.

9. Ina frequency ,or phase modulated Wave energy'demodulatingpsystem, wav-e absorbingmeans, an ampliereupled there@ ther-mimic. will@ having a plurality of grid-like electrodesa .catliode, and v an anode, .a sourceof local voscillations coupled to .one of said grid-like,electrodeslacircuit coupling another of ,sa-id grid-like auxiliary electrodes to Ithe koutput ,of said amplifier,means for biasingwthe grid-like .electrodes in said tube relative to the cathode to such potentials'that said tube operates as a harmonic generator, an intermediate frequency amplifier having an input coupled to the anode of said tube, said intermediate frequency amplifier having an output, a circuit of considerable electrical reactance coupled to the output of said intermediate frequency amplifier, a pair of detector tubes each having a control grid, a circuit coupling the control grids'of said detector tubes in phase opposition to the output of said intermediate frequency amplifier, and a circuit connecting the control grids of said detector tubes cophasally to said circuit of considerable electrical reactance. 10. In a frequency or phase modulated Wave energy demodulating system, Wave energy absorbing means, an amplifier coupled thereto, a thermionic tube having a plurality of grid-like electrodes, a cathode, and an'anode, a source of local oscillations coupled to one of said grid-like electrodes, a circuit coupling another of said gridlike electrodes to the output of said amplifier, means for biasing the grid-like electrodes in said tube relative to the cathode to such potentials that said tube operates as a harmonic generator,

an intermediate frequency amplifier having an input coupled to the anode of said tube, said intermediate frequency amplifier having an output, a transmission line coupled to the output of said intermediate frequency amplifier, a pair of detector tubes each having a control grid and an output electrode, a circuit coupling the control grids in said detector tubes in phase opposition to the output of said intermediate frequency amplifier, a circuit connecting the control grids of said detector tubes to a point on said transmission line, and an indicator coupled with the output electrodes of said detector tubes.

l1. In a system for demodulating Wave energy the frequency of which has been modulated in accordance with signals, means for multiplying the frequency of said wave energy to thereby multiply the degree or amount of frequency modulation of said wave energy, means comprising a plurality of paths for said wave energy, said paths being capable of passing all the frequencies of the Wave energy to be demodulated, means connected with said first named means for impressing Wave energy representative of said Wave energy of multiplied frequency and multiplied degree or amount of frequency modulation on said paths, reactive elements in one of said paths, means for combining the waves passed by one of said paths With that passed by the other of said paths, and means for producing indications of the combined Waves.

12. The method of receiving a frequency modulated Wave which consists in multiplying the frequency of said frequency modulated Wave to thereby increase its frequency and the degree of frequency modulation of the wave of increased frequency, deriving fromsaid Wave of increased frequency and increased degree of modulation a plurality of currents each varying in frequency in accordance with variationsof the Wave of mulent characteristics of transmission for said currents and combining the output currents of these two paths in a detector to re-create the transmitted signals.

13. The method of receiving a frequency modulated wave which includes the steps of multiplying the frequency of said frequency modulated Wave to thereby'increase the degree of frequency modulation of the resultant energy,v deriving from said wave energy of multiplied frequency a. plu- 'rality of currents,v each varying in frequency in accordance with variations in said energy of multiplied frequency, passing each of the derived currents through a path, causing one of said paths to change the phase of the current passing therethrough with respect to that of the current passed transmitted signal.

tector to re-create the MURRAY G. CROSBY.

Images