US2183232A - Electrical wave receiving system - Google Patents

Description

' J/gauf 1939- I 1 D. A. WILBUR 2,183,232

ELECTRICAL WAVE RECEIVING SYSTEM Filed Aug. 18, 1938 2 Sheets-Sheet 1 CO "ed r os il l for //v l/EN TOR Dona/0 A. Wflbur' A 7- TOR/V5 Y ELECTRICAL WAVE RECEIVING SYSTEM Filed Aug. 18, 1938 2 Sheets-Sheet 2 Patented Dec. 12, 1939 UNITED STATES ELECTRICAL WAVE RECEIVING SYSTEM Donald A. Wilbur, Troy, N. Y., assignor to American Industrial Research, Inc., Albany, N. Y., a corporation of New York Application August 1 8,

.14 Claims.

My invention relates to an electrical wave receiving system and more particularlyto means and methods of creating an electrical" carrier wave through the agency of the so-called side band or carrier and side band waves of modulated carrier energy and for combining the created carrier wave with the received electrical Wave in any desired relation.

Distortion of detected, modulated signals results from various causes, as will hereinafter appear, and the principal objects of my invention reside in the provision of a method and means for substantially eliminating such distortion. More particularly, my invention contemplates the provision of an electrical wave receiving system in which the received signal and a carrier component, created in a local generator,'may be synchronized, or, correspondingly, the transformed frequencies of the received signal as derived, for example, from an oscillator may be synchronized with the local generator, with the result that in both cases energy, from thelocal generator, at the carrier frequency, may be added to the signal in an amount sufilcient that, upon detection, the difference frequency components resulting from reactions between components of the signal, other than those due to reactionsbetween any component and the carrier, are effectively reduced or eliminated.

The principal objects of my invention, broadly, may be attained by dividing a signal, as received, or as obtained in a different part of the frequency spectrum by a reaction between the signal and the output from a local oscillator, into two separate signals, creating thru the agency of one ofthese signals a component of a frequency equal to a multiple of the carrier frequency, separating this component, creating from this separated component a component of a frequency equal'to' the carrier frequency, adding "energy from this last mentioned component to the second "of the above separated signals in an amount and relation such that upon detectionthe difference frequency components resulting from reactions between components of the resultant signal, other than those due to reactions between anyicomponent and the carrier, are elfectively reduced or eliminated. v i

correspondingly, a similar result is obtained. by creating thru the agency of one of the above mentioned separated signals a component of a frequency equal to a multiple of the carrier frequency, separating this component,.modulating this component by a signal of a frequency equal to the same multiple of the frequency of a local os- 1938, Serial No. 225,533

cillator, separating one of the side components produced by this modulation, creating, thru the agency of this separated side component, a com ponent of a frequency equal to aJ-suitabl'e sub-- multiple of the separated side component, modu 5 lating the second of the above separated signals by this last created component, separating'the resulting modulation components which correspond in form to the original signal but have as their carrier frequency :one corresponding to the frequency of the local oscillator, adding energy from the local oscillator to these components in an amount and relation such that upon demo'dulation the difference frequency components resulting between components of the resultant signal, other than those due to reactions between any component and the carrier, are effectively reduced or eliminated. With the foregoing and other objects in view, my invention includes the novel elements and the 20 combinations and arrangements thereof described below and illustrated in the accompany-' ing drawings in which- Fig. 1 is a wiringdiagram of a fragmentary portion of an electrical wave receiving circuit embodying one form of my invention;

Fig. 2 is a Wiring diagram illustrating another embodiment of the invention; and j Fig.3 is a Wiring diagram of still another form of my invention. In order clearly to describe my method of'pr'o cedure and the operation of my circuit, consideration will be given first to the general requirements which should be fulfilled and to their cause, and'cthen to the methods and'means of fulfilling these requirements; a

An electrical signal or wave such as referred to above may be produced "by modulating a sinusoidal energy wave, hereinafter called .the'carrier wave or carrier component, with a'simple or ec=the instantaneous value of the voltage Ec=amplitude v v w=21rfc=angular frequency fe=frequency =time terms of voltage" be Let the intelligence wave be represented by:

( n m Sin (pm 'l Where-- m=1,2,3,...n em=the instantaneous value of the voltage Em=amplitude of the m component pm=21rfm=angular frequency of the 121. component fm=frequency of the m component dm=initial phase of the m component t=time The resultant modulated signal will then be represented by:

Where-- Ec sin wt=carrier component 12 cEE, cos pr) r] 1 =side-band components The reception of a modulated signal such as that symbolized in Equation 3 involves the application of such signal or one of similar form to a demodulator or detector. In this process the angular frequencies of all the components may remain the same or may be changed by the same amount as for example in the superheterodyne type of receiver. Thus we may represent the signal applied to the demodulator by Equation 3 where to then represents the angular frequency of the carrier component of the signal as applied to the demodulator.

r,s,=1,2,3, n

Thus it is evident that the additive result of the first two summations is identical in wave form to the modulating signal as given in Equation 2. These demodulation components shall hereinafter be designated as the desired demodulation components and are described as being due to 2.

reaction between the carrier component and the side band components of the received signal.

It is also evident that the last two summations represent demodulation components having no counterparts in the modulating signal as given in Equation 2. These demodulation components shall hereinafter be designated as undesired or distortion components and are described as being due to reactions between the components comprising the side band components of the received signal.

In considering the production of the desired demodulation components by a reaction between the carrier and side band components it is also Well to note that should the phase of the carrier component be varied from its original phase with reference to the side band components, the additive result of the first two summations in Equation 4 will be varied, or, as the phase of the carrier component is varied from 0 to 180 from its original phase the amplitudes of the desired components decrease becoming zero at a variation and then increase to their original magnitude but in an opposite sense at a variation. An identical variation in these amplitudes takes place as the phase of the carrier is varied in the opposite sense. Also, should the amplitude of the carrier component be changed relative to the amplitudes of the side band components a corresponding change is produced in the amplitudes of the desired components relative to the amplitudes of the undesired components. Thus, if for any reason the amplitude of the carrier component be reduced to zero, the amplitudes of the desired components will also be reduced to zero. Such a variation of the amplitude of the carrier component, however, will produce no change in the amplitudes or phases of the distortion components.

Therefore, it follows that:

(a) A suitable carrier component is necessary for the production of the desired demodulation components.

(17) The amplitudes of the distortion components may be reduced relative to the amplitudes of the desired components by increasing the amplitude of the carrier component relative to the amplitudes of the side band components.

A signal in which the amplitude of the carrier is reduced relative to the amplitudes of the side band components, or in which the amplitude of the carrier becomes zero, or in which the phase of the carrier varies from its original phase with reference to the side band components, may be produced, among other ways, by:

(a) Selective fading.

(b) Interference between ground and sky waves.

(0) Partial or total suppression of carrier at the transmitter.

Therefore, the aforementioned creation of a carrier or a wave of the character of that of a transmitted carrier through the agency of the side band components, or the carrier component of a signal or both, may be used to great advantage in the following situations.

Selective carrier fading, general signal fading and. interference resulting from natural phenomena may be corrected, even in the extreme case where no carrier component is present in the received signal, by the creation of an appropriate carrier in the receiver.

Interference between transmitting stations duc'edmay then be'isolated by means of a selec-' maybe considerably reduced either by" reducing the transmitted carrier wave energy with respect v to the; transmitted side band energy or by completely eliminating the carrier wave energy in the transmitted wave and then creating an appropriate carrier wave in the receiver. e

- A considerable reduction in the power necessary to transmit a'signal may be effected either disposed with respect to that of the carrier com- This component may then be isolated by means by reducing the transmitted carrier wave energy relative to the transmitted side band energy or by completely eliminating the carrier wave enerbe represented in terms of current by 1'' cr Sin 1 2 c r Sin The component representedloyv Ec cos 210i is produced by the action of the carrier component. I

The component represented by 2E 1' s cos pr+.pa) r+ s]; f 1:3

which reduces to is produced by reactions between those side band components whose frequencies are symmetrically ponent.

Thus a component having a frequency twice that of the carrier will be produced either by a reaction between side band components or by a reaction of the carrier component alone, or by both. Thus this component will be produced even though the amplitude of the carrier be materially reduced or made equal to zero.

Let this component be represented by of a selective filter, as for example, one employing a quartz crystal. After isolation the component e20 may be used to producea component having an angular frequency w.

This maybe accomplished as follows. this component may be used to control a synchronized oscillator or multivibrator whose output energy will contain a component having an angular frequency The, component so prolated signal.

ment and a selective filter.

First,

tive filter. Secondly, this component may be used to control a device whose output energy will contain a component of frequency one-half that of the controlling component. The component so produced may then be isolated by means of a selective filter.

It is also to be noted that the component e20 regardless of whether it is produced by the carrier or side band components, depends for its phase upon the phase of the original carrier en-' ergy which was modulated to produce the received signal. It should also be noticed that the controlling action of the component 620 on the devices described 'above'may extend to the phase of the componentof output energy whose angular frequency is w. Thus the phase of this component depends upon the initial phase of the original carrier which was modulated to produce the received signal. This component shall hereinafter be calledthe created carrier component. Therefore, since this created carrier component depends for its phase upon the phase of the aforementioned original carrier, this phase may be made to maintain any desired relation to the phase of the original carrier by a suitable adjust received signal and isolated regardless of whether or not the carrier component is present in the received signal and this created carrier component may be combined with the signal to serve as the carrier or to augment the carrier thereof as the case may be.

A corresponding method for obtaining the objects above pointed out consists of creating a component by means of a local generator and then translating the frequencyand phase of the received signal so that thelocally generated component fulfills the requirements for a suitable carrier component for the received and trans- An example of this method is as follows.

Let the received signal be diverted through two paths, one of the paths including, as in the method described above, a non-linear circuit ele- From this is obtained, as shown above, a component 62c.

A locally generated component produced by an oscillator or other device is represented by The component cm is applied to a non-linear circuit element, such as for example aso-called "frequency doubler. duced, among others, having twice the angular frequency of the applied component and may be isolated by means of a selective filter. Let this component be represented by It should be noted that the phase of this component will be dependent upon that of the component em.

Now let the components 620 and 6210 be applied together to a non-linear circuit element, such as, for example, a vacuum tube commonly known to the art as a mixer tube. This will produce, among other components, a component whose angular frequency is equal to the sum of the angular frequencies of the applied components and a component whose angular frequency is equal to the difference of the angular frequencies of theapplied components, Either of these com- A component is thus proponents may be isolated by means of a selective filter. Let these components, be represented by (9) CZdc -EZdc cos (Zia-2a) t (19) 62sc=E2sc COS (2w+2a) it Let the component 6250 be isolated and applied either to control a synchronized oscillator or multivibrator whose output energy will contain a component having an angular frequency (w-i-a) or to control a device whose output energy will contain a component of an angular frequency one-half that of the controlling component. The component so produced may then be isolated by means of a selective filter, and may be represented by (11) esc Esc cos (w+a) t It is also well to note that since such control may extend to phase, the phase of the component produced will be dependent both upon the phase of the original carrier energy which was modulated to produce the received signal and upon the phase of the locally generated component.

The received signal in the second of the aforementioned two paths is then applied simultaneously with the component @so to a non-linear circuit element such as has been previously described.

This will produce among other components a band of components which may be represented by and which may be isolated by means of a selective filter. Therefore, it is evident that these components represent a frequency translation of the received components to such angular frequencies as permit the locally generated component elc to fulfill the requirements of a created carrier component; also that the phases of the translated components depend upon the phase of the locally generated component and upon the phase of the original carrier energy which was modulated to produce the received signal and that, therefore, by a proper adjustment of circuit constants the phase of the locally generated component may be made to have and maintain any desired value with respect to those of the frequency translated, received components.

It is to be noted that the component e2dc may be used in an analogous manner to produce the same result and that in both cases the action takes place regardless of whether or not the carrier component is present in the received signal. Furthermore, various combinations of the above methods may be used and it will be understood that the foregoing steps are illustrative.

For a further illustration and a complete understanding of the method and means employed in carrying out the same, including the operation of the circuits, of my invention, reference may be made to the following description taken in connection with the drawings.

Referring to the drawings and first to Fig. 1, illustrating a circuit embodying one form of my invention, a signal, as received either with or without a carrier component and as amplified or translated in frequency, such as a signal of the character denoted by Equation 3, is impressed upon the grid of vacuum tube I. This vacuum tube is suitably energized and functions as an amplifier. Thus the applied components appear as current components in tuned circuit 4, resonant to these components. These current components are then transmitted to tuned circuit I, also resonant to these current components, by means of coils 5 and 6 and the circuit including these coils and thus impressed upon the grid of vacuum tube 2. Vacuum tube 2 is suitably energized and is non-linear in its plate current-grid voltage characteristic, and thus the square term of the series representing this characteristic will cause to be produced in coil 8 current components corresponding to those given by Equation 5. These latter current components are induced in the circuit to selective filter 9 by coil 8 and its associated coil in the filter circuit. Selective filter 9, for example a quartz crystal type of filter, passes to tuned circuit I0 substantially only the component corresponding to 62 given in Equation 6. Tuned circuit i0 is resonant to this component and impresses it upon multivibrator or controlled oscillator II. Multivibrator or controlled oscillator II is harmonically synchronized by means of the applied component to oscillate in such a manner that its output energy includes a current component whose angular frequency is w, or one-half that of the applied component. This current component is induced in tuned circuit I3 by means of the coil therein and its associated coil I2 which is connected to the multivibrator H.

The signal current components present in tuned circuit 4 are also induced in tuned circuit I3 by means of coils I5 and I6. Tuned circuit I3 is resonant to these components and thus also to the above mentioned component of the output energy of multivibrator or controlled oscillator Thus a created carrier component is induced in tuned circuit I3 by means of coil I2 regardless of whether or not a carrier component is present in the received signal, and as previously shown, may be made to maintain, by proper adjustment of circuit constants, any phase relations with respect to the signal components induced in tuned circuit I3 by means of coil I6. In particular, these phase relations may be the same as those existing between the carrier and side band components as given in Equation 3.

The components present in tuned circuit I3 are impressed upon the grid of vacuum tube 3. This vacuum tube is suitably energized and func-- tions as the usual detector or demodulator. Thus there will be produced in transformer I4 demodulation components corresponding to those given in Equation 4 and it should also be evident that these will be produced regardless of whether or not a carrier component is present in the received signal. Also referring to Equation 4, it may be seen that the amplitudes of the desired demodulation components depend upon the amplitude of the carrier component Ec while the amplitudes of the undesired demodulation components are independent of the amplitude of the carrier. Thus the amplitudes of the desired components may be increased to any desired degree relative to those of the undesired components by making Ec sufilciently large.

In Fig. 2, I have illustrated a circuit embodying a modified form of my invention wherein the respective vacuum tubes are indicated generally by the reference characters ZI to 26, inclusive. A signal, as received either with or without a carrier component and as amplified or translated in frequency, such as given in Equation 3, is impressed upon the grid of vacuum tube 2|. This vacuum tube is suitably energized and functions as an amplifier. Thus the applied components appear as current components in tuned circuit 21, resonant to these components. These current components are then induced in tuned circuit 36, also resonant to these components, by coils 28 and 29 and thus impressed upon the grid of vacuum tube 22. Vacuum tube 22 is suitably energized and is non-linear in its plate currentgrid voltage characteristic, and thus the square term of the series representing this characteristic will cause to be produced in coil 3| current components corresponding to those given by Equation 5. These components are induced by means of coil 3| and its associated coil in the circuit of a selective filter 32. Selective filter 32, for example a quartz crystal type of filter, passes to tuned. circuit 34 by means of coil 33 substantially only the component corresponding to age given in Equation 6. Tuned circuit 34 is resonant tothis component and impresses it in phase opposition upon the grids of vacuum tubes23 and 24. Vacuum tubes 23 and 24 are suitably energized and are non-linear in their plate currentgrid voltage characteristics.

Tuned circuit 35, resonant to a component of angular frequency w, is connected to the plates of vacuum tubes 23 and 24 in a so-called pushpull configuration. Now, therefore, when due -to shot-efiect, thermal agitation, or any cause,

a current component having an angular frequency w is produced in tuned circuit 35, this current component will be transmitted by means of coils 36 and 31 and the circuit including these coils to tuned'circuit 38, resonant. to this component, and thus applied to the grids of tubes 23 and 24 in phase agreement.

Let the above current component be represented by (13) icc=Icc cos wt and the component induced in tuned .circuit 38by 6cc=Ecc 005 wt Thus ecc+e2c will be applied to the grid of one of said vacuum tubes 23 and 24 Whi1e-6cc2c will be applied to the grid of the other. Thus the square term of the series representing the plate current-grid voltage characteristics will cause to be produced in the plate circuit of the first of these tubes, among other components, the

current component given in the following equation, (15), and in the plate circuit of the second of these tubes, among other components, the current component given in the following equation, (16).

(15) 21:11 cos wt As is evident, the resultant current component in tuned circuit will be the diiferencebetween components i1 and i2. Y

Let this be represented by I It should be noted that this current component is in phase agreement with the original component as expressed in Equation 13, and that therefore the above action may be made self-sustaining. Moreover, it may be seen from a c'onsideraceived signal, and thus by properly adjusting the circuit constants,,may be made to maintain any desired relation to the components of the received signal.

This current component is transmitted by means of coils 39 and 40 and the circuit including these coils to tuned circuit 41, resonant to the angular frequency of this component, and thus the component is impressed in phase agreement on corresponding grids 25a and 26a, respectively, of vacuum tubes 25 and 26. The signal current components present in tuned circuit 21 are transmitted by means of coils 42 and 43 and the 'circuit including these coils to tuned circuit 44, resonant to these components. Thus, as shown, these components are applied in phase opposition to the corresponding grids 25b and 2612, respectively, of vacuum tubes 25 and 26. Vacuum tubes 25 and 26 are suitably energized and operated in such a manner that there are produced incremental plate current components proportional to the product of the incremental potentials applied to grids 25a, 26a, 25b and 26b.

The constants of the circuits are so adjusted that the phase of the component applied to grids 25a and 26a relative to that of the components applied to grids 25b and 26b is such that the demodulation components produced in the plate circuit of one of the vacuum tubes correspond in form to those given in Equation 2. Hence, those demodulation components produced in the plate circuit of the other vacuum tube likewise correspond in form to those given in Equation 2, but are opposite in phase. nents of transformer 45 are obtained by taking the difierence between the output components of these two vacuum tubes 25 and .26, the output components obtained from transformer 45 are equal 'to the additive result of the above mentioned output components of vacuum tubes 25 and 26 taken in like phase.

Moreover, it should be noted that demodulation components produced by reactions between components impressed on grids 25b and 26b will be identical in form and phase, and thus produce no components of output energy in transformer 45.

Therefore, it is to be seen that, Whether or not carrier is present in the received signal,'.de modulation output components are obtained identical in form to those used to modulate the original carrier energy.

In Fig. 3, I have shown a circuit embodying" another form of my invention and the vacuum tubes therein are respectively indicated generally by the reference characters 5| to 59, inclusive. A signal as received either with or without a carrier component and as amplified or translated in Since the output compo-1 frequency, such as given in Equation 3,is im-i.

upon the grid of vacuum tube 52. Vacuum tube 52 is suitably energized and is non-linear in its plate current-grid voltage characteristic, and thus the square term of the series representing this characteristic will cause to be produced. in coil 64 current components corresponding to those given by Equation 5.- These-latter current-2o .3

components are induced in the circuit of selective filter 65 by coil 64 and its associated coil in the filter circuit. Selective filter 65, for example a quartz crystal type of filter, passes to tuned circuit 66 substantially only the component corresponding to en given in Equation 6. Tuned circuit 66 is resonant to this component and impresses it upon grid 53a of vacuum tube 53. Vacuum tube 53 is suitably energized and is operated in such a manner that there are produced, among other components incremental plate current components which are proportional to the product of incremental potentials applied to grids 53a and 53b.

The vacuum tube 59 together with its associate circuit elements including tuned circuit 61 is suitably energized and operated as an oscillator. An output energy component 61c, as given in Equation 7, of this oscillator is applied to the grid of vacuum tube 58 by resistors 68 and 69. Vacuum tube 58 is suitably energized and is nonlinear in its plate current-grid voltage characteristic, and thus the square term of the series representing this characteristic will cause to be pro duced in tuned circuit 19 a current component 6210 as given in Equation 8. Tuned circuit 10 is resonant to this component. This current component is passed to tuned circuit 7!, also resonant to this component, and thus applied to grid 53b of vacuum tube 53. It should be noted that the phase of this applied component depends upon that of the component e10. Due to the mode of operation of vacuum tube 53, there will thus be produced in tuned circuit 12, among other components, the components can and ease as given in Equations 9 and 10 respectively. Tuned circuit l2, resonant to the current component @250, isolates this component and it is induced in tuned circuit 13, also resonant to this component. Thus this component is applied to grid 54bof vacuum tube 54.

Each of vacuum tubes 54 and 55 is suitably energized and operated in such a manner that there are produced among other incremental plate current components, components proportional to the product of the incremental potentials applied to grids 54a, 55a and 54b, 55b.

Tuned circuit 14, resonant to a component of angular frequency (w+a) is connected in the plate circuit of vacuum tubes 54 and 55. when, due to shot effect, thermal agitation, or any cause, a current component having an angular frequency (w +a) is produced in tuned circuit 14, this current component, is transmitted to tuned circuit 75, resonant to this component, and thus applied to grid 55a of vacuum tube 55. Coil 16, situated in the common cathode circuit of vacuum tubes 54 and 55, presents a high value of impedance to this component. Coil 16 thus prevents such a current component from appearing in the common cathode circuit, and therefore results in effect in the application in phase opposition of the component in tuned circuit 15 to the corresponding grids 54a and 55a of vacuum tubes 54 and 55.

Let the above mentioned current component produced in tuned circuit Hi correspond to isc given in Equation 18, following.

(18) sc=Isc cos (w-|-a)t Let the effective component applied to grid 54a of vacuum tube 5 correspond to est as given in Equation 11 and that applied to grid 55a of tube 55 correspond to es. Thus due to the mode of operation of vacuum tube 54, there will be produced in tuned circuit 14 among other current components, a component corresponding to 3 as given in Equation 19.

(19) 63:13 cos (w-l-a') t It should be noted that this component is in phase agreement with the original component isc as expressed in Equation 18, and that therefore the above action may be made self-sustaining. Moreover, it may be seen from a consideration of the above-mentioned components that this is the only self-sustaining action which may occur. It should also be noticed that the phase of the component expressed in Equation 19 depends upon the phase of the original carrier energy which was modulated to produce the received signal and upon the phase of the output energy of the local oscillator.

The component in tuned circuit corresponding to sc is applied to grid 56a of vacuum tube 56. Vacuum tube 56 is suitably energized and operated in a manner similar to that of vacuum tube 53. The signal current components present in tuned circuit 68 are transmitted to tuned circuit F9, resonant to these components, by means of coils Ti and 18 and the circuit including these coils and thus applied to grid 55b of vacuum tube 56.

Due to the above indicated mode of operation of vacuum tube 56, there will be then produced in tuned circuit 38, among other components, a group of current components corresponding to etc as given in Equation 12. Tuned circuit 86 is resonant to and isolates these current components. These isolated current components are then passed to tuned circuit 8!, resonant to these components, and thus applied to grid 51a of vacuum tube 5?. Vacuum tube 51 is suitably energized and operated in a manner similar to that of vacuum tube 53. It should be noted that, as previously shown, these above-mentioned components depend in phase upon the phase of the original carrier energy which was modulated to produce the received signal and upon the phase of the output energy of the local oscillator and thus may be made to maintain any desired relation to that of the output energy of the local oscillator by proper adjustment of circuit constants.

A component of output energy of the local oscillator, corresponding to em as given by Equation '7, is transmitted from the local oscillator by coils 82 and 8S and the circuit including these coils to tuned circuit 84 and thus impressed upon grid are of vacuum tube 5'1. The constants of the circuits are so adjusted that the phase of the components applied to grid 51a. relative to that of the component applied to grid 51b is such that, among other demodulation components, components will be produced in the plate circuit of vacuum tube 51 and hence in the output circuit of transformer 85, which correspond in form to those given in Equation 2.

Therefore, it is seen that, whether or not carrier is present in the received signal, demodulation output components are obtained of the same form as those used to modulate the original carrier energy. Moreover, it should be noted that since the desired demodulation components are produced by reactions between the carrier component and the side components, while the un desired components are produced by reactions between side components, the amplitudes of the desired components may be made to have any desired relation to those of the undesired componresulting from a change in the envelope of the ents by adjusting the amplitude of the carrier component corresponding to em to the appropriate value. I

By my method of reception, distortion, due to lowering of the level of the carrier, including to zero level, and to change in its phase relations with respect to the side components, and a consequent relative increase in the amplitude of the difference frequency terms due to reactions between side band components, as compared with the reactions between carrier and side band components, cannot occur due to the fact that the carrier component may be maintained at any desired level and relation by means of its introduction from a local generator. Also, distortion signal produced by a decrease in the amplitude of the carrier component or from its elimination, or from a change in phase, regardless of the cause cannot occur since the desired shape of the envelope may be recreated by the addition of a suitable carrier component from the local generator. Distortion of the type described above is ordinarily noticeable when interference occurs between the ground and sky waves in the case of radio signals or when interference occurs between synchronized stations. Such distortion may also occur due to suppression of the carrier component at the transmitting station or through selective fading. Itshould be noted that distortion due to the above causes occurs regardless of the type of detector used and, hence, by employing the method herein described, such distortion will be eliminated or, in any event, considerably reduced regardless of the type of detector used.

Another desirable feature of my invention lies in the fact that synchronization between the signal applied to the final detector and the component derived from the local oscillator is automatic and that in the case where the last mentioned component is derived from a local oscillator such synchronization is independent of any reaction of the incoming signal upon the-local oscillator.

Still another desirable feature of my invention resides in the fact that extremely sharp tuning may be obtained since either a balanced detector may be used or a circuit of the character last described wherein no modulated signal is applied to the final detector, and, therefore, in either case there is no output from the detector except" when the signal is tuned in a fixed relation to the frequency of the filter. -Hence my invention will provide automatic interstation noise suppression with no loss in sensitivity.

It is also well to note that the resonant and selective circuits may be fixed in their tuning since in the superheterodyne type of receiver the p incoming signal may be shifted to any desired frequency and hence may betuned in any desired relation to the selective filter mentioned in the above description.

While the condensers illustrated in the draw-;

ings are shown as fixed condensers, it is to be understood that, in the first instance, in order to secure proper tuning, these condensers may be adjustable. But once the circuits are properly tuned the condensers may be permanently set and it will not be necessary thereafter to adjust them.

While I have described my invention in its preferred embodiment, it is to be understood that the words which I have used are words of description rather than'of limitation. .He'nce,

* comprising side components of the character of those of the received signal but in which its carrier of the frequency of said created, first carrier wavemay be absent and means for combining said resultant signal and said first carrier wave.

2. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for producing from the received signal first and second separate signals having components corresponding to those of the received.

signal, of means. for producing through the agency of the first of said separated signals a signal comprisinga first component of a frequency substantially equal to the frequency of thecarrier of the received signal multiplied by an integer, means for separating out said first component, means for creating a carrier wave, means for producing through the agency of said created signal a second component of a frequency substantially equal to the product of said integer and the frequency of the created carrier wave, means for modulating said'separated, first component by said second component, means for sep-' I arating out a side bandcomponent produced by said modulatiornmeans for creating through the agency of said separated side component a third I component of a frequency substantially equal to the frequency of said separated side band component divided by'the said integer, means for modulating the second of said two signals by said third component, and means for separating from said modulated second signal components thereof corresponding in form to the received signal but having as their carrier frequency a frequencysubstantially equal to that of said created carrier wave. v

3. In a device for receiving modulated signal energy which at least initially comprises'carrier and side components, the combination with means for producing from the received signal first andsecond separatesignals'having components corresponding to those of the received signal, of means for producing through the agency of the first of said separated signals a signal comprising a first'component of a frequency substantially equal to the frequency of the carrier of the received signal times an integer, means for separatingout said first component, means for creating a carrier wave, means for producing through the agency of said created carrier Wave a second component of a frequency substantially equal to the product of said integer ponent by said second component, means for separating out a side band component produced by said modulation, means for creating through the agency of said separated side band. component a third component of a frequency sub-v stantially equal tol,the...frequency. of said .sepa-.,

rated side band component divided by said integer, means for modulating the second of said two signals by said third component, means for separating from said modulated second signal components thereof corresponding in form to the received signal but having as their carrier frequency a frequency substantially equal to that of said created carrier wave, and means for combining said components so separated from said modulated second signal and a component of said created signal of known character.

4. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for producing from the received signal first and second separate signals having components corresponding to those of the received signal, of means for producing through the agency of the first of said separated signals a signal comprising a first component of a frequency substantially equal to the frequency of the character of the received signal multiplied by an integer, means for separating said first component, means for creating a carrier wave, means for producing through the agency of said created carrier wave a second component of a frequency substantially equal to said integer times the frequency of said created carrier wave, means for modulating said first, separated component I by said second component, means for separating out a side band component produced by said modulation and of a frequency substantially equal to the sum of the frequencies of said first, last mentioned separated component and of the said second component, means for creating through the agency of said last mentioned separated side band component a third component ofa frequency substantially equal to the frequency of said last mentioned separated side band compo nent divided by said integer, means for modulating the second of said two signals by said third component, means for separating from said modulated second signal components thereof corresponding in form to the received signal but hav ing as their carrier frequency a frequency substantially equal to that of said created carrier wave, means for adding to said components so separated from said modulated second signal a component of said created carrier wave, and means for demodulating the resultant signal.

5. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for producing from the received signal first and second separate signals having components corresponding to those of the received signal, of means for producing through the agency of the first of said separated signals a signal comprising a first component of a frequency substantially equal to the frequency of the character of the received signal multiplied by an integer, means for separating said first component, means for creating a carrier wave, means for producing through the agency of said created carrier wave a second component of a frequency substantially equal to said integer times the frequency of said created carrier wave, means for modulating said first, separated com ponent by said second component, means for separating out a side band component, produced by said modulation and of a frequency substantially equal to the difference of the frequencies of said first, separated component and of said second component, means for creating through the agency of said last mentioned separated side band component a third component of a frequency substantially equal to the frequency of said last mentioned separated side band component divided by said integer, means for modu" lating the secqnd of said two signals by said third component, means for separating from said modulated second signal components thereof corresponding in form to the received signal but having as their carrier frequency a frequency substantially equal to that of said created carrier wave, means for adding to said components so separated from said modulated second signal a component of said created carrier wave, and means for demodulating the resultant signal.

6, In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for creating by employing side band components derived from the received signal a signal comprising a carrier wave of means for thereafter combining said created signal and the received signal whereby a resultant signal is produced comprising side components substantially of the character of those of the received signal and of said carrier frequency, said resultant signal being characterized by the fact that its carrier component may be absent, and means for combining with said resultant signal carrier component from said created signal.

7. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with an oscillator of means for creating by employing side band components derived from the received signal a signal having side band components substantially corresponding in form to those of the received signal and of a frequency equal to the frequency of the oscillator frequency, means for adding energy from said oscillator to said created signal, and means for demodulating the resulting signal.

8. The method of improving the reception of modulated signal energy, which at least initially comprises carrier and side components, which comprises separating the received signal into a first and second signal, generating a carrier signal, producing by employing said first and second signal and said generated carrier signal a signal comprising side components substantially of the form of those of the received signal and substantially of the frequency of said generated carrier signal, adding energy from said generated carrier signal to said last mentioned signal and demodulating the resultant signal.

9. The method of improving the reception of modulated signal energy, which at least initially comprises carrier and side components, which comprises separating the received signal into a first and second signal, generating a carrier signal, producing by employing said first signal and said carrier signal a third signal, combining said third signal with said second signal so separated from the received signal whereby to produce a signal comprising side components substantially of the form of those of the received signal and substantially of the frequency of said generated carrier signal, adding carrier energy from said generated carrier signal to said last mentioned signal and thereafter demodulating the resultant signal.

10. In a device for creating from a given signal wave a signal comprising a component of predetermined character relative to said given signal, the combination with cooperable means for producing from a first signal a second signal having a frequency equal to a predetermined fraction of the frequency of said first signal, of means for reintroducing said second signal in said cooperable means whereby production of said second signal will be maintained.

11. In a device for creating from a given signal wave a signal comprising a component of predetermined character relative to said given signal, the combination with cooperable means for creating from a first signal a second signal having a frequency equal to a predetermined fraction of the frequency of said first signal, of means for re-introducing said second signal to said cooperable means and means for effecting a substantially balanced operation of said cooperable means wherebythose output components of said cooperable means produced by said created second signal component alone are efiectively balanced and may be eliminated.

12. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for creating from the received signal a first component of a frequency substantially equal to a multiple of the carrier frequency, of means for producing from said first component a second component of a frequency substantially equal to a sub-multiple of the frequency of said first component; said last mentioned means being operable to produce a signal component only when signal energy is supplied thereto.

13. In a device for receiving modulated signal energy which at least initially comprises carrier and side components, the combination with means for creating from the received signal a signal comprising a first component of a frequency substantially equal to a multiple of the carrier frequency, of means for separating out said first component, means for producing from said separated, first component a second component of a frequency substantially equal to a sub-multipleof the frequency of said first component, said sub-multiple being the inverse of said multiple, and said last mentioned means being operable to produce a signal component only when signal energy is supplied thereto, and means for combining said second component with the received signal.

14. The method of improving the reception of modulated signal energy, which at least initially comprises carrier and side components, which comprises generating a carrier wave, creating by employing a side component of the received signal a signal comprising side components substantially of the form of those of the received signal and of the frequency of said generated carrier wave but in which the carrier may be absent, adding carrier energy from said generated carrier wave to the signal so created and thereafter demodulating the resultant signal.

DONALD A. WILBUR.

Images