USRE20821E - Synchronizing system x - Google Patents

Description

Aug. 9, 1938. H. J. J. M. DE R. DE BELLESCIZE 20,821

SYNCHRO-NIZING SYSTEM Original Filed Sept. 29, 1932 ,4 Sheets-Sheet 1 ZiBaZZeScujz e;

Aug. 9, 1938. H. .1. J. M.DEY R. DE BELLESYCIZE 20,821

SYNQHRONI Z ING SYSTEM Original Filed Sept. 29, 1952 4 Sheets-Sheet 2 BeZZesaz'ze Aug. 9, 1938. J. J. M. DE R. DE BELLESCIZE Re. 20,821

' SYNCHRONIZING SYSTEM Original Filed Sept. 29, 1932 4 Sheets-Sheet 3 flzvevfar I I defi a2 BeZZescz'ze {fo my I Aug.'9, 1938. H. J. J. M. DE R. DE BELLESCIZE 20,321 smcnnomzme SYSTEM Original Filed Sept. 29, 1952 4 Sheets-Sheet 4 or the time constant as large as possible.

PATENT OFFICE srncrmomzmo srs'rm Henri lciae,

Jean Joseph Marie de ltegnauld dc Neuilly-sur-Seine, France Belle- Original No.1,990,4 dated February s, 1935,

Serial No. 635,451, September 29, 1832.

Application for reissue February 2, 1937, Serial No. 123,717. In-France October 6, 1931 18Claima.

My invention relates broadly oscillation systems and more particularly to a method and circuit arrangement for synchronizing local oscillations with respect to impressed oscillations.

The present invention is directed to improvements in methods whereby a first sinusoidal oscillation S sin (21rF|.t+|) is utilized for obtaininga second sinusoidal oscillation H sin (ztrhswn,

which is characterized in that its amplitude H and its phase difference from the first oscillation, namely (2a'Fn.t+h) (2I'Fl-t+l) are both substantially constant. In the case for instance, of a message transmitted by wire or electromagnetic Hertzian waves, one of the oscillations is the carrier or pilot wave of the signal and it is required to obtain in the receiver a local oscillation which is in step with the carrier wave.

In all the arrangements enabling such a synchronousoscillation to be obtained, the receiving apparatus is provided with a circuit specially designed for the purpose, and the wave-band of which should be rendered as narrow as possible, Up to the present it has never been possible to make the band-width less than the sum is of the changes liable to affect one or the other of the frequencies Fa, F.. In many instances this sum 1'- is, itself, the resultant of two kinds of superimposed changes: the one kind developing at an extremely slow rate but'capable of attaininga very considerable amplitude (f5) 1, in the long run-namely, the change progressively affecting the frequency of the transmitting station in relation to the oscillation generators of the receiver, by reasons of slow changes in the temperature of potential of the sources of supply. The other changes, (tm, are of much smaller amplitude than the foregoing, but develop or disappear far more rapidly, and arise for example, from modifications in the course of'the Hertzian waves, or the slight mechanical tremors which inevitably affect the circuits of the transmitting and receiving stations. Hitherto, the receiving circuits specially allocated to the production of the local synchronous oscillation had to have a band with a width at least equal to ll (,0) 1+ (fl) 2,

more oscillation generators in the receiver, so as to adapt said regulation to the slow variations (I01 whichthe frequency F. of the carrier or pilot oscillationv undergoes. This forms the object of the present invention, which consequently dg.

scribes a new method and a manner of carrying it into efiect.

According to the present invention the method broadly consists in so controlling the frequency of one of the said oscillations that gradual frequency changes are counteracted.

The method of my invention further comprises combining the said oscillations as to produce a Physical agency slowly varying in accordance with the said gradual frequency changes, selecting said slow variations of the physical agency and controlling thereby the frequency of one of said oscillations.

More particularly the method consists in combining in the receiver two devices, the first of which is an arrangement controlling the fresuency of the local generator by impressing on the frequency of one of the two oscillations H or S, a correction which from instant to instant compensates the frequency difference which the very slow variations (is) 1 would tend to introduce between two frequencies Fh, F5; while thesecond device, which, when combined with the first one, has only to take account of the variation of greater rapidity but of very small magnitude, maintains the two oscillations in step with one another.

The procedure, in accordance with this method, consists in generating the local synchronous oscillation by utilizing for that purpose an oscillator connected 'with circuits which have a wave band having a width equal, or slightly superior, to the amplitude (fa): of the relatively rapid but slight frequency changes. Under these conditions, these" are the best possible circuits, but, after being in operation for a certain time they no longer sufiice to correct the very slow variations, the magnitude (I!) 1 of which becomes excessive after the lapse of a predetermined time interval. In proportion as the said magnitude increases, the local synchronous oscillation would become progressively out of phase in relation to the control oscillation; the phase difference angle I' would vary and be subject to an error. A? the value of which would finally become excessive. By the employment of suitable means, this error A? is utilized for modifying the intensity of a current, or a difference of potential, and, by the agency of said current, or difference of potential, the regulation of an oscillation generatorin the receiver is automatically controlled. This control, the effect of which is to limit the error Ai is exercised through the agency of circuits which are distinct from the foregoing and have extremely large time constants, so as to respond solely to the very gradual variations (m1. I

The nature of my invention will be more fully set forth in the following specification by reference to the accompanying drawings, in which: Figure l is a characteristic curve representing the variations (1.): and (Ina-as a function of the time t--sustained by the carrier frequency F. while functioning in the interval between the instants T1 and T2; Fig. 2 is a circuit diagram by able amplitude which aifect the carrier frequency; Fig. 5 diagrammatically shows a modified circuit arrangement embodying my invention:

Fig. 6 is a vector diagram of the circuit illustrated in Fig. 5; Fig.1 diagrammatically shows a circuit comprising a combination of the circuit arrangements shown in Figs. 2, 4 and 5. having means for the attainment of synchronism and the correction necessitated by the very gradual variations affecting the frequency of the carrier oscillation; and Fig. 8 illustrates a further'circuit arrangement showing a modified form of the synchronizing system of my invention.

Referring to the drawings in detail, Fig. 1 shows a curve which has been plotted with time as the abscissa and frequency as ordinates. From the characteristic curve it will be seen that the mean value of the carrier frequency 1''. varies slowly by (II): periods, during the time interval TiTz, and that the momentary value of said frequency undergoes-with regard to its mean value-fluctuations which are more or less rapid, but of small magnitude, not exceeding (1.): periods.

The synchronizing arrangement of Fig. 2 is the one forming the subject of my'copending application Serial Number 574,858, filed November 13,

193l,entitled Synchronization system. The principle of this method will first be reviewed as a knowledge of the same is n for an understanding of the present invention. The signal, received at 2 synchronizes the local electron tube generator 3 which supplies the receiver with the synchronous oscillations necessary for its op-.

eration. In order to obtain this synchronism, both the signal and the electron tube generator 3 excite, either directly or through interposed circuits of any kind, an electron tube detector I, the plate circuit of which comprises a resistance I shunted by a condenser l, which may be replaced by a low pass filter. The time constant of the unit 4-! t so'determined asto pass, with- 1 out appreciable weakening or change of phase,

the currents varying at a frequency equal to or less than the variations (f-)1 represented in Fig. 1 and to suppress the currents varying at higher frequencies. Under these conditions the current in the resistance lis exclusively furnished by the mutual modulation of the local oscillation and the carrier oscillation, .in the detector tube I. This current has the form:

In this expression Jo is a meancurren 1c is a numerical coefllcient depending on the sensitiveness of the detector tube I and on the constant amplitude H of the local oscillation, .S is the amplitude of the carrier or pilot oscillation, and '1' is the previously defined angle. 80 long as the frequencies Fe and F. differ appreciably, regulation not having been eflected, the term k8 cos 9 represents an alternating current to which the D. C. milliammeter ll does not respond, said milliammeter then indicating the mean current Jib-which is thus easily known. On synchroniphase different inf- 1.

sation (Fn=F-), the term k.S. cos 4/ represents, on the contrary, a continuous current, the intensity k.S. cos (en-e.) of which depends on the This current is utilized for controlling the frequency Fa of the generator I. For example,theplate circuit of said generator is fed by the conductor II from the connection I, thepoteritialof which is determined by the value of the current J in the resistance 6. This potential across resistance 6 changes the effec tive plate potential of oscillator 3, thereby changing its internal plate conductance and therefore its frequency of oscillation. The frequency F11 of the generator 3 depends therefore, not only on the tuning of the main condenser 8 and its ver- ,nier adjustment condenser 8, but also on the current J and the angle p. Consequently, this frequency varies between a certain upper limit Fn+h when the angle #1 is zero and the current Jo+kS, and a certain lower limit Fit-4n, when the angle t is equal to 1 and the current is 111-705. It is assured for instance by suitably selecting the grid-bias connection 5, that the maximum correction :L-fn thereby applied to the frequency Fa of the. generator 3, when the current J varies value (for 11: 0). It has been demonstrated that this device is synchronized automatically by merely regulating the condensers 8, 9, and that this synchronism is'most stable when the vector H is in the position He, in quadrature with the vector 8. This' regulation is obtained by carefully adjusting the condenser I so as to bring the current reading in the milliammeter ill to the mean value (for =180) to the Jo, whereupon This regulation having been eifected, the gradual variations (Ii); represented in Fig. 1 tend.

progressively to nullify it. The gradual variation of the current J will be indicated by the milliammeter II. In short, the maintenance of synchronism demands that every variation. A F sustained 'by the carrier frequency should be counterbal- The representative vector H has come into the position H. forming with the. normal position Ho an angle A t. At the end of a longer or shorter period, the variation sustained by the carrier frequency attains a value (M1 for which the error in the angle 4/ exceeds the permissible limit. With the circuit as shown in Fig. 2 it then becomes necessary to readjust the setting of the regulating condenser 9 by hand, in order to restore to the current J and angle their normal values, Jo and "Fig. 4 represents one form of circuit arrangement of my invention which performs these essential adjustments automatically. In addition to the elements already described and to the control, which through the agency of the conductor ll compels the local generator 5 to follow the relatively rapid but low magnitude variations (11):, a second control is provided by the variations in the resistance of the plate circuit of an auxiliary valve l9, coupled to the generator by a coil It, as shown. The internal resistance of the valve l9 depends on the biasof its grid, or in other words (the switch 32 being set in its normal position 34) on the potential of the condenser 20. This potential is governed by a relay 2|, the armature 25 of which closes the circuit of said condenser, through a very high resistance 28, alternately through two connections 29 and 30 to different potentials on a suitable potential source, both connections 29 and 30 being negative in relation to thatoi the filament. The time constant of the unit comprising condenser and resistance 28 may be equal to several seconds. The potentials of the connections 29, 50 are such .that, if they were successively transmitted to the grid of the valve IS, as would occur if the armature rested successively on each of the contacts 26, 21 for any considerable time, the generator 2 would produce, successively, two frequencies differing by several hundred periods. This difference is selected to exceed the variation (1;)1, eventually produced by the instability of the generators during a long period of service. Given these conditions, it can easily be verified that the frequency Fh of the generator 3 varies in a very gradual manner, for example by-some tenths of a period per second, so long as the armature 25 rests on one of the two contacts 28, 21 and that the direction 0 this frequency variation is reversed when the armature passes from one of the contacts on to the other. The main winding 22 of the relay is traversed by the current J, and an auxiliary winding 23 is traversed by an additional current, adjustable by a rheostat 24. The receiver is regulated in the following manner: at the commencement of the operation, when the frequencies F, and Fh still difl'er considerably, the current in the milliammeter III has the value Jo. The switch 32 is set, provisionally, on the contact segment 33, which gives the grid of the valve I! the polarization 3|, that is, the mean between the connections 29 and 20. The rheostat 2| is adjusted so that the armature 25 is in a state of equilibrium between, the contacts 25 and 21, without touching either of them. The armature will subsequently pass through this position of equilibrium every time the current J resumes the value Jo. As was explained in my application, supra, describing the circuit according to Fig. 2, the condensers 5, 9 of the generator are tuned so as to obtain synchronism and to bring the vector H (Fig. 3) into the position H0, in quadrature with the vector 5.

The current J then resumes the value Jo represented by the length 1a, 14. Finally the switch 22 is returned to the normal position 34, as shown in Fig. 4.

The arrangement operates in the following manner: When this regulation has been effected ,the slow variation due to the instability'of the generators tends to nullify it, and the current J varies, therefore progressively, from the mean value Jo. When it attains a certain value JoiAJ, that for example, represented by the length the armature 25 comes to rest against the contact 25 or 21 and completes the circuit of, the corresponding connection 29 or 30. This results in a gradual variationin the charge of the condenser 20, the polarization of the grid of the valve It, and the frequency Fa of the generator I. The representative vector, which is then in the position H, begins to rotate in the suitable direction, which is ascertained by trial by reversing the connections 29 and 30 as required; the said vector returns towards the optimum position Ho. The current J acquires a value more closely approximating to Jo, the armature 25 moves away from the contact on which it has been bearing and the condenser 20, the circuit of which is again open, retains the acquired potential, until the gradual and uninterrupted variation of the carrier frequency F; again requires the intervention of the relay. When, at the end of a very long time interval, for instance several hours, the milliammeter indicates that the potential of the condenser 20 nearly attains one of the limits, 29 or 30, beyond which the automatic control would cease to function, the condenser 5 must again be regulated by hand, by temporarily replacing the switch 22 in the position 32. The conductors 25 and 31 (Fig. 4) represent the feeders for the branch circuits for which the signal and the'local oscillation are placed in phase before becoming rectified in the second detector valve which permits the reception of the signal.

Another important observation must be made as regards the device illustrated in Fig. 4: It has been stated that the rheostat 24 is adjusted so that the armature 25 is in a state of equilibrium between the contacts 26 and 21, every time the current J resumes the particular value Jo." Now, according to the relation J=Jo+KS cos I said particular value Jo is-resumed by J, both happens for instance during a deep fading). So, a temporary suppression of controlduring 'fading does not affect in any way the local oscillation's frequency F'ii. As long as the intensity of S remains very small, the circuit of condenser 20 is open, owing to relay 2i; said condenser keeps up the potential which it had at the very moment fading began; and the local generator 3 l operations, it is desired to synchronize a local oswhen 0:90 (normal value), or when 8:0 (as cillation H sin (ZrFnt-l-Qn) with a controlling oscillation 8 sin (21F.t+ To obtain such a in some way either on the phase difl'erence I for perfect synchronism as illustrated and described -in my copending application Serial No. 574,858, or on the difference of frequency Fnl"'|. The following explanations relate to both methods of control, but for p poses of illustration, I shall consider only the method which utilizes the phase difference I l' and by the conductor vll is given by:

Fh=Fo+function (\r) where F0 designates the proper. frequency, which would be taken by generator I, if the controlling oscillation received by I should be non-existing.

is the condition obtained when there is an extended fading interval and S then equals 0. In other words, F0 is the frequency of the generator when the current recorded on 'milliammeter II has the value J0, independent of the controlling oscillation. This is a clear and concise definition of F0. Function I') is the correction imposed by current J on the local frequency when said current passes from J0 to any other particular value Jo-I-KS cos I'; i. e. when the variation of the current J is KS cos I'. In practice, these frequency corrections are small, and the proportional relation:

is obtained, in which in designates the correction imposed on the local frequency Fa by a unit variation of current J. [0 is readily measured and modified, for instance, by changing resist-.

ance 6 or by choosing an adequate electron tube 3; but this being done and theapparatus once constructed, in is a constant. From the above it is clear that when the two oscillations are in synchronism, the equation of this synchronism is:

be greater than 1. In that case the interfering current KS cos 1 whose frequency was previcomp:-

- ously 0 suddenly becomes oscillatory. when this fre uency becomes too high, the current is stopped by the condenser I or by the low-pass filter and no longer passes through resistance.

6. The two oscillations then become independent of each other and resume their natural frequencies F. and-Fa respectively.

With this brief summary in mind, Fig. 2 showing a single control and Fig. 4 showing a double control of the present application will now be considered. In Fig. 2, at the initial time T; (Fig. 1),

the operator has adjusted condensers I, 9, so as to bring the two oscillations into quadrature, i. e.,

result, the frequency Fa must necessarily depend In Fig. 2 the control exerted upon the localfrequency F11 by the current J equals J0+KS cos Ii'JoKS equals 1000, cos =0.1 and =84.

working of the device appears to be good. But if to obtain a current J, as indicated in milliammeter Ill, having the particular value J0. According to Equation 3, if I equals cos 1 equals 0 and the proper frequency F0 of the local generator 3 is equal to the control frequency Fl.

As illustrated in Fig. '1, F. now begins to vary with respect to F0. Phase diiference p automatically deviates from theinitial value 90 and approaches 0 or 180. From Equation 3, it will be evident that in order to keep the change in phase difference t as small as possible for fluctuating values of Ft; it is necessary to give f0.KS a large value. For example, should the device be working four hours without any supervision and should slow variation (is) 1 of control frequency F. reach 200 cycles. i. e. [(fs)1=200] at theiend of said lapse of time, a correction of 1,000 cycles (f0.KS= 1,000) would be necessary to prevent the variation of angle 11/ from exceeding 12", for instance:

On the other hand, so large a correction as 10KB equals 1000 cycles, results in a sacrifice in accuracy. .If KS=1 milliampere (current recorded in lOvarying 1 milliampere when t passes from the normal value of 90 to the limit 180), the equation f0.KS=1000'implies that a 0.1 milliampere variation of the detected current imposes a 109 cycles correction to thelocal frequency Fa. Such a high value of f0 results-in the synchronism no longer being well protected against electromagnetic perturbations arriving through conductor tubes. i

In spite of the excellent selection insured by condenser l (in homodyne reception 4,6 acting as a resonator) or by the low pass fllter,.suchperturbations produce-small variations M of the current .1 in resistance 6 and according to the definition of [0, these accidental variations of M impose variations fnAj on the local frequency. From this point of view, the highvalue of I0 is undesirable.

Let us now suppose that, at a given time T: (Fig. 1) the difference F| Fo equals cycles. The

there is a long fading interval not compensated by automatic volume control, 8 becomes very weak and synchronism expressed by Equation (3) no longer exists since cos it cannot exceed 1. The two oscillations become independent of each other and the interfering current frequency passes from 0 to 100 cycles. Such frequency is usually audible in spite of-the weakening of S and furthermore, itv exceeds the band widthof 4,6 (or of the lowpass filter), and prevents the synchronizing current from reaching resistance 6. When fadlng is over, synchronism is not restored automatically and the operator must readjust condensers I therefrom. Accordingly, the double control described in my present application is. very desirable.

Considering now Fig.4, it willbe noted that current J=J0+KS cos t recorded-in 10 takes on the same value J0 either when the ,working is perfect (ip=90) or when a fading temporarily suppresses the controlling oscillationv (8:0) In both cases the control provided for compensating the slow variation (for of F., is temporarily suppressed,- I

from 25 and 28, and the circuit of condenser 2| being open. Said condenser .then actsasabiasterference: indeed, the slow control.

The part played by the slow uniting connection 1 22, Ii, 25, 28, 20, I9, l8,'can therefore be described as follows: this part-is intermittent: as long as up is very close to 90 (for instance, 85.5" ip 94i5) the connection is cut off; but as soon as w somewhat differs from 90, KS cos-l1 from zero and J from Jo, theuniting connection resumes its part, modifies F and brings back J within the chosen limits. This leads exactly to the same result as when an operator frequently adjusts the condensers 8, 9 and thus compels the generators proper frequency F0 to follow the control frequencys low variations (m1.

The fundamental difference between Fig. 2 and Fig. 4 resides in the fact that in Fig. 2 the proper frequency F0 is a constant whereas in Fig. 4 this frequency is a broken line practically indistinguishable from the average'value of F!- The part played by the other control II is now merely to maintain the synchronism of two oscillations whose proper frequencies F. and F0 only difl'er from each 'otherby the small rapid variations (in) 2 of F8. .According to Equation (3), the maximum correction of fn.KS which connection II has to insure, is but very small, for example 6(1.) 2. and the drawbacks of Fig. 2 are avoided.

Synchronlsm is protected in the best possible manner against any kind of electromagnetic' inl is non-responsive to such interference owing to the slowness of relay 2i and to the high time constant 28, 20. The other control is not much more sensitive to this interference, as the band width of selecting circuit 4, l and the maximum correction {c.KS are exclusively imposed by the small varia- "tions (fl): and therefore are small themselves.

When a fading renders the signal inaudible, it does not matter very much whether or not the oscillations temporarily fall out of synchronism: no hissing due to interference can be heard since the differential frequency F.Ft is only of about 1 cycle. As soon as fading is over, the two oscillations automatically come again into synchronism. The whole of the above description can be applied without any modification to the othercase, where the synchronizing current is a function, not of the phase diiference 1/, but of the difference of frequency F|Ft. I

In most receivers, the frequency of the signal is modified by a heterodyne. In such case, if F1 be employed to designate the frequency of the carrier or pilot oscillation, as received by the antenna, and F: to represent the frequency of'the heterodyne, the new frequency F. acquired bythe carrier oscillation on arriving at the detector valve I will be F| =Fi-Fz, and depends therefore on the frequency of the heterodyne. It is evident that the synchronism obtained in Fig. 2 by controlling the frequency Fa of the localgenerator I by means of the conductor ll, may equally be obtained by controlling the frequency 1'': of ,the

This modification is represented in Fig. 5, in

which the frequency F1 ot'the signal received at I is modified by the heterodyne ll. The signal, of which the carrier oscillation, S sin (2rF|t+|) acquired the new frequency F. as delivered by the output of the detector at, is transmitted by suitable circuits, lil to the detector i, in which it interferes with the synchronous local oscillation H sin (2a-Fat+n) furnished by the generator 3. The current in the resistance Ii has the same value J=Jo+k.S.cos p, as befiare. Through the conductor II, the connection I controls the frequency F: of the heterodyne 38 and therefore the diiIereniai frequency F5 of the carrier oscillation. The explanations furnished respecting Fig. 3 in my patent application describing the arrangement of Fig. 2 may also apply to Fig. 6 in which the .vector H. representing the local oscillation, is now stationary, whereas the vector S representing the heterodyned carrier oscillation of the signal becomes mobile. In practice, in order to obtain synchronism and then place the representive vector S in quadrature in the optimum position St, in which the current J read off in the milliammeter iil regains the mean value Jo, represented by the length l3, ll, either the condensers 8, I of the synchronous generator 3 or the condenser ll of the heterodyne, may be regulated at will.

Consequently the arrangement represented in Fig. 4 may be modified as shown in Fig. '7, in which the control established by the conductor ll acts, as before on the synchronous generator '2, while the control established by the coil i8 and valve I! acts on the heterodyne 38. The conductor H compels the frequency of the generator 3 to follow the variations relatively rapid, but of small magnitude, (It) a sustained by the carrier frequency FI- tions are not transmitted to the valve ii, on account of the very high time constant of the assembly formed by the resistance 28 and condenser 2|, but this assembly 2!, 20 transmits to the valve I! the variations of potential applied, at the connection I, by the progressive variations of the current J resulting from the extremely gradual variations (1.)1 due to the possible instability of the transmitting station. Hence the double control functions in the manner already described.

Fig. 8 shows how the invention is applied when the synchronous local oscillationisobtained by the method described in the United States Patents Nos. 1,491,372 and 1,722,789, and application Serial Number 185,813, and others. In this method the signal received at 2 interferes, in the detector tube I9, with the heterodyne 3!, and in.

the circuit ll, its carrier frequency assumes the diil'erenial frequency Ft. The circuit 4|! supplies two branches. The branch 2 excites the detector valves 43 and '52, which receive the complete signal comprising the heterodyned carrier'osciilation and the signal oscillations distributed in the adjacent bands. By means of a valve 45, the other branch ll excites a resonator or band pass filter ,tuned to the frequency FI-and constructed so as to allow the frequencies comprised be- {tween Fr- (It): and F i-(Ii) where (is): represents thevariations of Fig. 1, to pass without any notable change of phase. The width 20.): of the band being extremely small, the circuit 46 arrests the signal oscillations contained in the adjacent bands. and transmits to the valve 41, only the continuous oscillation due to the action of the carrier oscillation. This continuous oscillation is therefore a synchronous local oscil- '75 On the other hand, these varialation. A phase corrector, for example an artifiparatus 50.

cial line 48- along which the contact ll is moved, enables this local oscillation to be brought into phase, inthe detector, with the carrier cscillation of the signal arriving through the conductor l2. Synchronous reception is thus assured, in the usual manner in the indicator ap Hitherto, the working of this arrangementwas rendered impossible by the variation (1-)1 due to the instability of the transmitting station. Under the influence of these variations, the frequency of the carrier oscillation soon ceases to lie within the limits of the band of the filter 4t and the continuous oscillation sustained a phase frequency deviates from the value F. for which to be positive in its operation and extremely ac the filter 48 is designed. In fact, the phase of the oscillation transmitted by said filter then varies by a certain amount 1A1, and the current J assumes the new value:

The current variations actuate the relay fl, and through its agency, the frequency of the heteroe 3|, until the differential carrier frequency ain exactly acquires the value F. at which the current J returns to the mean value J. This control is operated similar to the arrangement shown in Pig. 4.

The system of my invention has been found curate in the maintenance of predetermined phase relation between the impressed oscillations and the locally generated oscillations. I have described my invention in certain of its preferred embodiments but it will be understood that modifications may be made and that no limitations upon my inventionareintended other than are imposed by the scope of the appended claims. I

What I claim as new and desire ,tosecure by Letters Patent of the United States is as follows: 1. A method for maintaining an IDPI'OXF, mately constant phase difference between two oscillations, the frequencies of either or both of which may undergo very gradual but relatively large changes superimposed on changes of greater rapidity but of lesser magnitude, which comprises so combining in an electron tube circuit the two oscillations as to produce an interference current whose intensity, depending upon the said phase difierence. admits simultaneously of very progressive variations produced by said gradual frequency changes, and of more rapid variations produced by said more rapid frequency changes, utilizing through suitable means said more rapid intensity variations to exert on the frequency of one of said oscillations a first control compelling this oscillation to follow the small but rapid frequency changes of the other oscillation. whereby the two oscillations are synchronized; and furthermore utilizing through separate means, said very progressive intensity variations of the said interference current to .exert a second frequency control whereby the normal value of the phase difi'erence is maintained.

2. In a system for maintaining an approximately constant phase difi'erence between two oscillations, the frequencies of either or both of which may undergo very gradual but relatively large changes superimposed on changes of greater rapidity but of lesser magnitude, means for efiecting locked synchronism between the oscillations comprising a circuit having a band width corresponding with the magnitude of the said more rapid frequency changes, said circuit operating to control the frequency of one of said oscillations to counteract said rapid frequency changes, and means operated by the very slow phase displacements produced between the two so synchronized oscillations by the said gradual frequency changes for controlling the frequency of said one of said oscillations so as separately to counteract the said gradual changes, both of said controlling forces being simultaneously operable.

3. In a system for maintaining an approximately constant phase dlflerence between two oscillations, the frequencies of either or both of which may undergo very gradual but relativeLv large changes superimposed on changes of greater rapidity but of lesser magnitude, a circuit atrangement including a detector in which said two oscillations are mutually modulated, means for producing a synchronizing current by the mutual modulation having an amplitude depending upon the said phase difference and which admits simultaneously of very gradual variations produced by the gradual frequency changes and more rapid variations produced by the more rapid frequency changes, a selecting circuit for selecting said synchronizing current, the band width of said circuitextending from zero to a limit corresponding with the small magnitude of the more rapid frequency changes, and means connected with said selecting circuit providing two separate controls whereby the normal phase difference is maintained, one of said controls being exerted through a device having a very large time constant so as to be exclusively responsive to the verygradual variations in theamplitude of the synchronizing current.

4. 'In a system for maintaining a normal phase difference between two oscillations, the

frequencies of either or both of which may undergo very gradual but relatively large changes superimposed on changes of greater rapidity but 'offlesser magnitude. circuits comprising a de-' tector in which the two oscillations are mutually modulated, means for-deriving from said mutual modulation a synchronizing current of amplitude varying approximately as the projection of the vector representing one of said oscillations upon the vector representing the other oscillation, a circuit in the output of the detector constituting a selecting path for continuous and low frequency currents. so as to accurately transmit the most-rapid variations in .the amplitude 'of the synchronizing current, and means connected withv said circuit providing two separate controls whereby the normal phase difierence is maintained,-- one of said controls being exerted very gradual but relatively large changes super-imposed on changes of greater rapidity but of lesser magnitude, a circuit comprising a local heterodyne generator operating to modify the frequency of the received oscillation, a selecting circuit actuated by said modified received oscillation, the band width of said selecting circuit being approximately equal to the magnitude of the balance'the variations which affect the relative frequency of two oscillations separately generated, said variations due to very gradual but large changes superimposed on changes of much greater rapidity but of small amplitude usually undergone by the natural frequencies of either or both of these oscillations. which consists in maintaining the normal relative frequency of the oscillations by way of two separate frequency controls. a first one of small magnitude but of sufllcient rapidity to counterbalance the said small but rapid frequency changes, and a second one very progressive but of large magnitude to separately counterbalance the said gradual but large frequency changes, v

7. The method for maintaining a constant frequency relation between two oscillations, the natural frequencies of either or both of which may admit very gradual but relatively large changes superimposed on changes of greater rapidity but of lesser magnitude, which comprises providing a first control for exclusively compelling one of these oscillations to follow the small but rapid frequency changes undergone by the other one, combining the oscillations so as to'produce a variable resultant current varying under the joint control of the coacting oscillations, and utilizing the resultant current for actuating a second control whereby the gradual but large frequency changes are separately neutralized.

8. A method of synchronizing two oscillations, the frequencies of either or both of which may undergo very gradual but relatively large changes superimposed on changes of greater rapidity but of lesser magnitude, which comprises, insuring by one frequency control means the synchronism of the oscillations exclusively against the said rapid but small frequency changes, and furthermore producing by the combination of the so synchronized oscillations a variable current whose variations, when exceeding two predetermined limits, exert on the frequency of one of these oscillations through separate frequency control means a. very slow operative control, whereby the said current is restored within the said limits.

9. A method of frequency control for maintaining a normal frequency relation between a received oscillation and a local oscillation, the frequencies of either or both of which may undergo very gradual but relatively large changes superimposed on changes of greater rapidity but of lesser magnitude, which comprises, insuring by one frequency control means the synchronism rapid but small frequency changes, and furthermore producing in a suitable circuit by the joint action of the so synchronized oscillations a variable current whose intensity resumes a particu lar value when the amplitude of the received oscillation is zero, and when the frequency relation is normal, said variable current, when exceeding two predetermined limits situated on either side of the said particular value, being utilized to exert on the frequency of one of the synchronized oscillations through separate frequency control means a very slow and discontinuous control whereby the said'current is restored within the said limits.

10. In a synchronizing system, a source of oscillations of varying frequency, a second source of variable frequency; means under the joint control of said sources for producing a current fluctuating in amplitude over a predetermined range in accordance withthe relative frequency fluctuations of said sources, means whereby said cur rent controls the frequency of said variable source, there being a predetermined relationship between each value of said current and the re suiting frequency of said controlled source, and

means for varying said predetermined relationship f said current and said frequency whereby a same value of current produces a different frequency of said controlled source.

11. A system for maintaining a normal frequency relation between a local oscillation and a received oscillation issued from a Hertzian wave whose frequency may fluctuate rapidly with reference to a slowly variable mean value, which comprises means for producing a synchronizing current from the interference of the said oscillations, means for selectively transmitting the most rapid intensity fluctuations of this current, a plurality of means constituting frequency controls, one'of said control means being disposed in the output of said selecting means and responsive to the rapid fluctuations of the synchronizing current, another of said control means being slowly operative when the mean value of this current departs from zero.

12. A system for maintaining a local oscillation in-quadrature with a second oscillation issued from a received wave, which comprises: means for producing by interference of these oscillations a synchronizing current whose intensity is zero when the said oscillations are in quadrature; a relay having an armature, a contact on each side thereof, and a main winding;

a circuit forming a path for said synchronizing current and including said winding, said armature being movable between said contacts, two

' of means constituting frequency controls, one of said controlmeans being responsive to the action of the synchronizing current through electrical circuits, another of said control means being operative to increase or lessen the controlled trically independent frequency correcting controis operative in cooperation for controlling the generation of the waves so as to substantially neutralize this unbalance, and proportioning two at least of these controls to'be operative over different ranges of frequency corrections.

- 14. In a device where two separately generated waves are coacting, the method of maintaining these waves at a predetermined phase relation which comprises detecting unbalance in this phase relation, causing the detected unbalance to act on the generation of the waves through a plurality of electrically independent paths so as to substantially neutralize the unbalance by controlling the frequencies of the waves, and supplying two at least of the independent paths .with different time constants.

15. In a system utilizing two separately generated waves, the method of maintaining a predetermined frequency relation between these waves characterized by controlling the frequency relation therebetween relatively slowly over a frequency range and simultaneously controlling the same more rapidly over a. narrower frequency range. M

16. In a receiver in which a resultant electric wave is derived from the interference of the received wave with a generated heterodyning wave, the method of frequency control which comprises locally generating an electric oscillation, combining the locally generated electric oscillation with the resrltant wave to derive a frequency correcting current, deriving from this current two substantially independent frequency correcting controls for individually controlling the generation of the heterodyning wave and the generation of the local oscillation, and proportioning the control on the heterodyning wave so as to be operative over a larger range of frequency corrections and at a slower rate of action as compared to the control on the local oscillaum 17. In a receiver where a received wave coacts with a locally generated/heterodyne wave, the method of controlling the frequency relation of these waves which comprises beating the received wave and the heterodyne wave for producing a resultant oscillation, locally generating an auxiliary oscillation tuned to this resultant oscillation, beating the resultant and auxiliary oscillations for producing a frequency'controlling current, individually applying to the generation of the auxiliary oscillation and to the generation of the heterodyne wave two substantially independent frequency correcting controlsboth established by the frequency controlling current, controlling the auxiliary oscillation by the frequency controlling current so'as to maintain this oscillation in locked synchronism with the resultant oscillation, further controlling the heterodyne wave by the frequency controlling current so as to substantially annul the mean intensity of the frequency controlling current, and proportioning the control of the heterodyne wave so as to be operative over a larger range of frequency corrections and at a slower rate of action as compared to the control of the auxiliary osciliation.

18. The method 01" frequency control which comprises generating an electric wave, determining changes in the frequency of this wave, simultaneously applying to the generation of the wave two substantially independent frequency correcting controls both established by the determined changes, proportioning one of these controls to be operative over a smaller range of frequency corrections and at a relatively faster rate of action as compared to the other control, and arranging the slower acting con'trol so as to cause thefaster acting control to operate substantially at the mean frequency of its frequency range of operation. I

HENRI JEAN JOSEPH MARIE or REGNAULD n: BELLESCIZE.

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