US1521380A - Receiving system - Google Patents

Description

LSZLSQ Dec, 30, 1

D. G. M CAA RECEIVING SYSTEM Filed Nov. 17, 1922 4 Snvwntoz W Q9 M Patented Dec. 3(1 1924.

ire sTA'rEs PAE OFFIGE.

DAVID G. MGCAA, 0E LANCASTER, PENNSYLVANIA, ASSIGNOR TO THE ELECTRIC AP- PARATUS 00., OF PARKESBURG, PENNSYLVANIA, A CORPORATION OF PENNSYL- VANIA.

RECEIVING SYSTEM.

Application filed November 17, 1922. Serial No. 601,455.

To all whom it may concern:

Be it known that I, DAVID G. MGCAA, a citizen of'the United States, residing in Lancaster, county of Lancaster, State of Pennsylvania, have invented new and useful Improvements in Receiving Systems, of which the following is a specification.

My invention relates to a method of and apparatus for'eliminating or reducing the effects of electrical disturbances in the reception of signals, telegraphic, telephonic or otherwise, represented by alternating current, and particularly alternating current o r\ oscillations of radio frequency.

In accordance with my invention, the effects of static, atmospherics, strays and other natural or artificial disturbances including other radio signals, are reduced or eliminated in a radio or other receiving system, whereby the desired signals are readily distinguishable or become intelligible notwithstanding the simultaneous existence of strong disturbing effects.

In accordance with my invention, the received energies representing both the desired signal and the disturbing effect are divided into paths including reactive devices, one of which is employed for effecting the translation of the desired signals, and with another of which is associated a local source of alternating current or'oscillations in such wise as to cause the effect of said other reactance to fluctuate within wide limits and thereby causing the signal-representing energy in the first reactance to fluctuate in amplitude and at certain instants to be reinforced by energy from the local source, to the substantial exclusion or great reduction of the effects of the simultaneously existing disturbing energy. v

In accordance with my invention, the aforesaid current locally produced has a frequency which preferably is different from the frequency of the energy representing the desired signal, though it may be of the same frequency as hereinafter described, and in either or both cases it is preferred that the locally produced energy in its reaction with the oscillations representing the desired signal and the disturbing effects shall be substantially equal to the amplitude of the oscillations of the desired signal, whereby the ratio of the effect upon the signal translating instrument of the energy representing the desired signal to the eflect upon that in- 5 strument of the energy representing the simultaneously existing disturbing energy is increased, as compared to what would be the normal effects of the signal-representing energy and the disturbing energy were my invention not employed.

.My invention resides in the method and apparatus hereinafter described and claimed.

For an understanding of my method and for an illustration of some of the many 55 forms my apparatus may take, reference is to be had to the accompanying drawing, in which:

Fig. '1 is a diagrammatic view of circuit arrangements embodying my invention.

Fig. 2 is a fragmentary diagrammatic view illustrating a modification.

Fig. 3 is a diagrammatic view of a modification where the corrective circuit or device is applied in a secondary circuit.

Fig. 4 is a diagrammatic view of a modilied system wherein my corrective device 1s in effect in series with the receiver coil.

Fig. 5 is a diagrammatic view of a system involving my corrective device in a modified arrangement.

Referring to Fig. 1, A represents the autenna or other absorption structure of a radio or any other receiving system, connected through the variable inductance L and the primary I of an oscillation transformer to earth or other counter-capacity E, the variable condenser C serving to tune the antenna path and the circuit including the primary I to the frequency of the oscillations pro- 99 duced in the antenna system by the energy absorbed from the natural or other medium. Inductively related to the primary P is the secondary S of an oscillation transformer whose circuit, particularly for long wave reception, may include the adjustable inductance L For tuning the secondary circuit, there is provided the usual tuning condenser C whose terminals are connected to the grid circuit of the audion or other vacuum tube detector-amplifier V comprising the filament or cathode f, grid 9, and anode or plate a.

In the grid path may be connected the condenser C shunted by the leak resistance 7'. In the anode circuit of the tube V is the source of current or battery 18 and a winding T, which may be the winding of a telephone receiver, or may be the primary of a transformer delivering the plate circuit current or a component thereof to one or more stages of radio or audio frequency amplifying devices, as well understoodin the art, the condenser C and theresistance 1' being omitted when the amplification is to occur at radio frequency. In shunt to the winding T may be connected the condenser C when the winding T is that of a telephone or the primary of an audio frequency transformer, the condenser G being omitted in the case where the winding T is the primary of a radio frequency transformer, all as well understood in the art.

As thus far described, the receiving apparatus is a usual one and per se is not my invention.

However, in accordance with my invention, there is connected in parallel with the primary P, or in any other divided or snuably related path or position therewith as regards the antenna circuit or other path traversed by the oscillations of the desired signal and the simultaneously existing dlsturbing effect, a reactance, either capacitative or inductive, but preferably, as shown,

, an inductive reactance L whose amount may be adjustable as indicated. It is preferred that the resistance of the inductance L shall be small as compared with its inductance. The magnitude of the inductance L is preferably so chosen that its reactive effect is great compared with that of the primary P for oscillations of the frequency corresponding with that of the desired signal.

whereby, if the reactances L and P only were present, the oscillations representing the desired signal attain a far. greater magnitude in the primary P than in the inductance L However, the reactance or inductance L i by itself is insufficient for my purposes, and

there is connected in series therewith a variable condenser G which may be connected as indicated, and preferably. to the terminals of additional inductance in series with the inductance L this additional series in-- ductance being indicated at L and may be in effect a continuation of the inductanc:

L and forming therewith in effect an autotransformer. For a given frequency of the oscillations representing the desired signal, the capacity of the condenser C. may be adjusted to a value 'with respect to the magnitude .of L -L which causes the reactance of the" path L C, L in shunt to inductance L for that; fre-' quency to Vanish or become zero or sub stantially zero, whereby, under suelrcondition and for such time, the effect is the same as if the reactance of inductance L? were reduced to zero because primary P is substantially completely robbed of signal-representin'g ener y. That is to say, this effect is.

the same as if inductance L were short circuited or as if the leads to the two terminals of the inductance L were brought into low resistance conductive contact with each other. The magnitude of the capacity of the condenser G for this condition is not that which would be given to the condenser Ctto tune the control circuit L L C by itself or when isolated, to the frequency of the oscillations representing the desired signal, but has been found to be considerably greater, and for long wave lengths, as of the order of 13,000 meters, is substantially three or four times as great. In operation of the system, this large desired value of the capacity of the condenser C is found by trial by manually adjusting the condenser,

to produce optimum effect.

If the control circuit L L O with such large value of capacity of the condenser C is opened, the reactance or impedance across the terminals of the inductance L resumes 'its initial or normal value, with the result that in the primary P the amplitude of signal-representing oscillations would again be large. 'Therefore, .by periodically interrupting the circuit L L C the amplitude of signal-representing oscillations in the primary P will be alternately large and substantially zero.

What has been said of the oscillations representing thedesired signalis also true of those oscillations simultaneously present in the antenna system and due to the absorption thereby of the energy representing the "disturbing efli'ects of static, atmospherics,

L C is closed, the amplitudes of the two sets of oscillations in the primary P are sub stantially niI. v

I With the apparatus thus far described, the effects-of static, etc., have not been reduced or eliminated, as distinguishedvfrom the .signal -representing energy; both are absent from the receiving-"apparatus represented-by the prlmary P when the control circuit.

L L C is closed, though both are present in said-control circuit and the remainder of the antenna path, and both are present in the receiving apparatus when said circuit L L 0 is open. i

However, to greatly reduce the effects of static or other disturbances, there is placed in inductive relation to the control circuit 1 or to any suitable part thereof, a one of the inductances L, a coil D,- pref and the disturbing effects of static, etc., and

so much different therefrom that the beat is of audible frequency for telegraphy and is of super-audible or inaudible frequency for telephony.

lVhen the frequency of the oscillations traversing the source D is equalto the frequency of the oscillations representing the desired signal and the interfering staticeffects, the apparatus is uti]izable\ for telephony. t f

Byway of example, merely, the local source of oscillations is an oscillating audion V it being understood, however, that any,

other suitable source may be employed.

Assuming the oscillations representing the desired signal to be weak or to have small amplitude, and the interfering effects, as static, strays, etc., to be of great amplitude or relatively strong, the oscillations representing the desired signal have an amplitude which is small compared with the amplitude of the oscillations set up in the receiving antenna or other circuit by the atmospherics, strays, static, etc.

In order that the strong oscillations representing the disturbances shall not maintain their relative strength in their effect upon the telephone or other instrument T, the coil D is rotated or moved to such position with respect to the coil ll that the amplitude of the oscillations .induced in L by the coil D shall be substantially equal to the amplitude of the oscillations representing the desired signal, though simultaneously there exist in the circuit L L C oscillations representing the static or other disturbances of an amplitude which is relatively great with respect to the amplitude of the oscillations of the desired signal.

There accordingly occurs in the circuit L L C reaction by the weak oscillations induced in that circuit by the coil D upon the.

oscillations representingthe desired signal, and also upon the oscillations of relatively far greater amplitude representing the disturbing efiects of static, etc. There are accordingly produced two sets of beats. The first set is the beats produced by reaction with the oscillations of small amplitude representing-the desired signal, and these beats are full or perfect in the sense that the signal waves are non-decadent, and, secondly,

in that the beat amplitude varies between substantially zero and twice the amplitude of the oscillations representing the desired signal. The other set of beats is that produced with the oscillations of relatively far greater amplitude and representing static, etc., and these beats are imperfect, first-in the sense that the oscillations representing static'are generally decadent, and secondly, because the amplitude of the oscillations representing static is great compared with the amplitude of the reacting oscillations induced by the coil D, with the result that the beats whose components are the weak oscillations from D and the strong oscillations representing static, etc., a maximum amplitude which is only relatively slightly greater than the amplitude of the oscillations representing static, etc., while in the case of the beats eifected by means of the oscillations of lesser amplitude representing the desired signal the maximum beat amplitude is about tions from the local source D upon the amplitude of the beats caused by oscillations representing st'atic. etc. is proportionately smaller than the efiect upon the amplitude of the beats due to the oscillations representing the desired signal.

Accordingly, during the presence of oscillations of small amplitude representing the desired signal in the circuit L L, 0*, there is a time when the resultant of the reaction thereof with the oscillations of equal amplitude induced by the coil D is substantially zero, and the reactance across the terminals of the inductance L is the normal one corresponding to the conditions of opening the circuit L L C; at another period the oscillations representing the signal and induced-by the coil D are cumulative, andthere is flowing in the circuit L If, C a signal-representing current of substantially double amplitude; and under these circumstances, the condenser C having the aforesaid capacity, the reactance between the terthe oscillations representing thedesired signal. When the oscillations induced by the coil- D are in opposition to the oscillations representing the weak signal, there is a cumulative effect in'the primary P of the locally produced oscillations and those representing the desired signal; and vice versa, when the local and signal oscillations are cumulative or assist each other in the circuit of the condenser they oppose each other in the primary P. That is to say, in addition to the aforesaid fluctuations inmagnitude of effects upon the receiving instrument, as the signal-translating instrument T, the oscillations traversing the coil Dproduce an effect upon the primary P, and therefore upon the signal-translatmg mstrument T, cumulative with the aforesaid sigternating current of certain magnitude is flowing therein, the impedance across the terminals of L is small or zero, or when there is zero or substantially zero current in the circuit L L C the impedance or reactance across the terminals-of the inductance L is its normal one, as if said circuit were' open. In other words, the arrang ment and mode of operation are such tha the inductance L may be said to exhibit normal or substantially zero-reactance, according as the current in the circuit including the condenser C is zero or of finite value.

Assuming now that there exists simultaneously with the oscillations representing the desired signal oscillations of far greater amplitude representing static or the like, there is in the circuit of the condenser C, due to the oscillations representing static or the like, a beat current which does not fall to Zero,but fluctuates between narrow limits 1 at relatively high. amplitude. Accordingly,

as regards the beat current due to static orother effect, the impedance or reactance across the terminals of the inductance L is small or zero, and, no more static effect reaches the primary P and signal-translating instrument T than corresponds with the amplitude of the oscillation induced in the circuit of the condenser C by the coil D.

Accordingly, by choosing the amplitude of the oscillation induced in the circuit of the condenser C by the coil D of a magnitudesubstantially equal to that of the oscillations representing the desired signal, the impedance or reactance across the terminals of the inductance L is low or zero for all of that part of theenergy representing static except that part which is comparable to the amplitude of the oscillation induced by the coil D, with the result that the eflect upon the primary P, and therefore upon the signal-translating instrument T, of static is no greater than that of the desired signal effects. y

In other words, by the employment of the condenser C of the desired magnitude and its circuit, the greater portion of the rela- .tively greater effect due to static is withheld from the primary 1? and signal-translating instrument T because of the then correspondingly low or zero reactance across the terminals of the inductance L Viewing the matter in another way, there exist simultaneously in the circuit of the condenser C oscillations .of great magnitude representing static and oscillations of relatively small magnitude representing the desired signal; these oscillations produce reaction with the Weak oscillations induced,

by the coil D resulting in heat eflects in the circuit .of the condenser Cflwhich, as regards variation of amplitude of the beat effects, are substantially equal for both the static and signal effects, and the remaining weak signal oscillations are in oppositephase and neutralizing each other, and a signal is therefore manifested at T, because the reactance across the terminals of the inductance L is great under such condition; while as regards the strong static effects, the weak oscillations induced by the coil D do not completely annul the static oscillations in beat format-iomand therefore, as regards the static effects, there is always substantial current flowing in the circuit of the condenser C, and for such static effects, therefore, the reactance across the terminals of the inductance L is small or zero, and such strong static effects are therefore withheld from the primary P and the signaltranslating instrument T.

When the frequency of the oscillations induced by the coil D is equal to the frequency of the oscillations representing the Weak signal and also the strong static, beat effects are produced, or beats of zero frequency are produced, the characteristic action being the same in that the predominant effects of static cause the reactance across the terminals of the inductance L to be zero or small, and therefore produce no effect upon the signal-translating instrument T, and only that portion of the energy representing static produces an effect upon the instrument T which corresponds in amplitude with the amplitude of the oscillations representing the desired signal.

In connection with the receiving circuit proper, as the circuit of the secondary S and its adjuncts, it will be found that when the condenser C is adjusted to that magnitude which will attune the circuit S, L C to the frequency of the oscillations representing the desired signal, and with the circuit L,

' signals through static as above described,

with the circuit L L C present with the local source of oscillations in operation. But the condenser G must be adjusted to a value of capacity greater or less than its aforcsaidvalueto tune to the radiocomponent of the partial beats due to static, ac-

cording as the coilD is inducing in the cir-- cuit of the condenser C oscillations of frequency less than or greater than the frequency of the oscillations representing the desired signal. And the greater the difference between the frequencies of the locally produced oscillations'and those representing the signal, the greater is the difference in the settings of the condenser G as between tuning to the frequency of the signalrepresenting oscillations and the radio com-' ponent of the static effects. In other words, by varying theadjustment of the condenser C as aforesaid, the receiving circuit may be attuned with respect to the signalrepresenting oscillations, and for the same setting the circuit will be de-tuned with re spect to the radio component of the static effects in the same circuit.

While in the arrangement of 1 the condenser C is in a circuit or path conductively related to the antenna circuit'or path or directly coupled to L it may be placed in a path coupled to or inductively related to the antenna path, as indicated in Fig. 2,

'- wherein the aforesaid inductance ill 5 serves as the primary ofan oscillation transformer whose secondary is an mductance L, H]. circuit with which isthe aforesaid condenser as before, in the case of Fig. 1, when the cir- (3*, and in inductive relation to the circuit L, C is disposed the aforesaid coil D tra.v

ersed by the locally produced oscillations. in this case the magnitudes of inductance l. and capacity C are such as to tune to the frequency of the oscillations representing the desired signal when coupled to L but,

. cuit L C is isolated, a smaller value of capacity C will serve to tune to the frequency of the oscillations representing the desired signal.

As indicated in Fig 3, the primary P and the inductanceiL correlated in the manner indicated in Fig. 1 or 2, are disposed not directly in the antenna path, but in a secondary circuit comprising the secondary S inductively related to the primary P in the antenna path, the S being tuned by the variable condenser C and, if suitable or desirable, by the inductance L. r

Referring to FigzA, there is shown an arrangement wherein, in effect, the corrective or control circuit is serially related to the receiver coil or primary P. In this instance the inductance L of-the control cirtance L and primary circuit of the-secondary cuit or corrective device is in series with the receiver .prnnary P, whether directly in the antenna circuit, asindicated, or in a seconprimary P.

In action, the closecoupling between the coils L and L causes large transfer of energy to the circuit L C during thoseltimes that it is effectively closed by the efiect of the locally produced oscillations traversing the coil D. On the other hand, the loose coupling between P and S permits suitable amount of signal energy to be transferred. from P 'to the secondary circuit S at those times when the circuit L 0 is in effect open. When the circuit L O is in effect open, that is, when the impedance L has its normal or'maxi'mum eflect, L and P, to-

locally produced oscillations of getherwith the condenser C, attune the antenna circuit or other path to the frequency of the received energy. While herein the condenser C is shown as in series with the which is suitable particularly antenna path,

it will be understood that for short waves,

it may be connected in parallel to the induc- P for long wave reception.

Referring to Fig. 5, the secondary receiving circuit is, as before, associated with the primary P, with which-is associated in turn a circuit L L C as in Fig.1. In circuit with theprimary P is a further primary P of an oscillation transformer whose secon dary S is in the grid circuit of a thermionic or audion amplifier V in whose anode or plate circuit is the coil D in inductive relation with the circuit containing the 0011- denser G which is adjusted to the capacity magnitude discussed in connection with Figsl.

' lhe primary P when traversed by feeble signalsrepresenting oscillations, inductively affects the grid circuit of the amplifier V which in turn causes an amplified signalrepresenting"oscillation traversing the coil D which inductively affects the circuit containing the condenser 0 with the result that when signal-representing oscillations traverse the primaries P, P*, thereactance of the inductance 1L attains its normal or high value, forcing more signal-representing current through the primaries P, P*, and the action is again built up through the coil D cillations possible.

in its efi'ect upon the circuit of the condenser C until finally the signal effects in P are increased to a maximum, due to the fact that the reactance of the inductance L has attained a maximum." In this case, the coil D is traversed by oscillations of signal frequency, and not of a frequencyv diflering from that of the signal frequency or a frequency representing the static or other disturbance, and the circuit arrangement is utilizable for telephony. Tn shunt to the secondary 8* may be connected the tuning condenser C for tuning the grid circuit for enhancing the efiects described.

, By the arrangement of Fig. 5, signal-rep resenting oscillations passing through the primary P are utilized in amplified form for influencing the circuit containing the condenser C to eflect such current strength therein as to in effect open that circuit, as by the increase of reactance of the inductanee L accordingly forcing moreof the received signal energy through the primary P, Here again the reaction of the signal frequency oscillations with the strong osrepresenting the relatively stronger static or other disturbing effect produces the result hereinbefore described in connection with Fig. 1, in that there is an increase in the ratio of the magnitude of the effect in the telephone or other translating instrument T of the'oscillati'ons representing the desired signal to the magnitude of the effect produced upon the instrument T by the static or other disturbing effect.

While in the foregoing description currents of radio frequency have been assumed and considered, it will be understood that my invention is not limited thereto, but in its broader aspect comprises a method of and apparatus for differentiating between currents, whether of audio or radio frequency, which may be of the same frequency 'but of different amplitudes; or comprises a method of and apparatus for reducing the dlfi'erence between effects of'such .audio or radio frequency currents, whereby the weaker may produce a desired effect of:

greater relative magnitude than otherwise What I claim is: \i 1. The method of distinguishing between I fluctuating currents of, diflerent amplitudes,

which comprises impressing the currents upon a current-translating circuit and upon a control path upon the magnitude of whose reactance depends the magnitude of effect in said translating circuit, and rendering said'reactance of small magnitude for withholding from said translating circuit effects of said current of greater am litude.

2. The method of distingulshing between fluctuating currents of the same frequency but different amplitudes, which comprises impressing the currents upon a eurrenttranslating circuit and upon a control path upon the magnitude of Whose reactance depends the magnitude of effect in said translating circuit, and rendering said reactance periodically of small magnitude for Withholding from said translating circuit effects of said current of greater amplitude.

3. The method of distinguishing between fluctuating currents of different amplitudes, which comprises impressing the currents upon a current-translating circuit and upon; a control circuit including inductive and capacitative reactances, and impressing upon said control circuit a fluctuating current for rendering its reactance periodically of reduced magnitude for withholding from said translating circuit effects of the current of greater magnitude.

4. The method of distinguishing between fluctuating currents of the same frequency but difi'erent amplitudes, which comprises impressing the currents upon a currenttranslating circuit and upon a control circuit including inductive and. capacitative reactances, and impressing upon said control circuit a fluctuating current for rendering its reactance periodically of reduced magnitude for withholding from said translating I desired signal and oscillations of the same.

frequency-but of greater amplitude representing a disturbing effect, which comprises impressing both sets of oscillations upon a slgnal-translatmg circuit and a control 011- cu1t including inductlve and capacitative reactances and adapted upon reduction of magnitude of its reactance to withhold en erg from said signal-translating circuit, an impressing upon said control circuit a' periodic current of different frequency.

7. The method of distinguishing between I radio frequency oscillations representing adesired signal and oscillations of the same frequency but of greater amplitude repre. senting a disturbing effect, which comprises impressing both sets of oscillations "upon a signal-translating circuit and a control circuit including inductive and capacitative reactanees and adapted upon reduction of magnitude of its reactance to withhold enrent-translating means,

ergy from said signal-translating circuit, and impressing upon said control circuit a periodic current." I

8..Apparatus for distinguishing between fluctuating currents of difierent amplitudes, comprising a winding and. associated cura reactance related to said winding for withholding energy therefrom upon reduction of said reactance, a reactance of different type associated with said reactance for effecting reduction of said first named reactance to small value when said reactances are traversed by substantial current, means for impressing the currents of different magnitudes upon said winding and upon said first named reactance, and means for impressing upon said reactances a periodic current.

,9. Apparatus'for distinguishing between fluctuating currents of the same frequency but different amplitudes, comprising a winding and associated current-translating means, an inductive reactance related to said winding for withholding energytherefrom upon reduction of said reactance, a .capacitative reactance associated with said inductive reactance for effecting reduction of said inductive reactance to small value when'said reactances are traversed by substantial current, means for impressing the currents of different magnitudes upon said windingand said inductive reactance, and means for impressing upon said reactances a periodic current:

10. Apparatus fluctuating currents of the same frequency but different amplitudes, comprising a winding and associated current-translating means, an inductive reactance related to said winding for withholding energy therefrom upon reduction of said reactance, a capacitative reactance associated with said inductive reactance for effecting reduction of said inductive reactance to small value when said reactances are traversed by substantial current, means for impressing the currents of different magnitudes upon said winding and said inductive reactance, and means for impressing upon said reactances a periodic our rent of different frequency. r

11." Radio receiving apparatus for distinguishing between oscillations of radio frequency representing a desired signal and oscillations of the same frequency but greater amplitude representing a disturbing effect. coniprimfng a winding, signaltranslating means associated therewith, an .inductive reactance related to said winding .for withholding energy therefrom upon reduction of said reactance, a capacitative reactance associated with. said inductive reactance for effecting reduction of said in-. ductive reactance to small value when said reactances are traversed by substantial current, means for impressing the oscillations for distinguishing between comprising a winding of different amplitudes upon said winding and said inductive reactance, and means for impressing uponsaid reactances a periodic current.

12. Radio receiving apparatus for distinguishing between oscillations of ra'dio frequency representing a desired signal and oscillations of the same frequency but greater amplitude representing a disturbing effect, comprising a winding, signaltranslating means associated therewith, an inductive reactance related to said winding for withholding energy therefrom upon reduction of said reactance, a capacitative reactance associated with said inductive reactance for effecting reduction of said inductive reactance to small value when said reactances are traversed by substantial cur rent, means for impressing the oscillations of different amplitudes upon said winding and said inductive reactance, and means for impressing upon said reactances a periodic current of a frequency different from the frequency of said oscillations.

13. Radio receiving apparatus. for distinguishing between oscillations of radio frequency representing a desired signal and oscillations of the same frequency, but greater amplitude representing 'ing effect, comprising a winding, signaltranslating means associated therewith, an inductive reactance related to said win ding for withholding energytherefrom upon reduction of said reactance, a capacitative reactance associated with said. inductive reactance for effecting reduction of said inductive reactance to small value when said reactances are traversed by substantial current, means for impressing the oscillations of difierent amplitudes upon said winding and said inductive reactance, and means for impressing upon said reactances a periodic current of a frequency differing from the frequency of said oscillations by an amount offecting beats of inaudible frequency.

' 14:. Apparatus for distinguishing between fluctuating currents of different amplitudes,

and associated current-translating means; a reactance related to said winding for withholding energy therefrom upon reduction of said reactance, a reactance of different type associated. with said reactance for effecting reduction of said first named reactance to small value when said l'eactances are traversed by substantial current, means for impressing the currents of different magnitudes upon said winding and upon said first named reactance, means for impressing upon said reactances a periodic current, and means for adjusting the magnitude of said periodic current.

15. Apparatus for distinguishing between fluctuating currents of different amplitudes, comprising a winding and associated current-translating means, a reactance'related a disturbl ili lilt lint

to said winding for withholding energy therefrom upon reduction of said reactance, a reactance of different type associated with said reactance for efiecting reduction of said first named reactance to small value when said reac tances are traversed by substantial current, means for impressing the currents of different magnitudes upon said winding and upon said first named reactance, means for impressing upon said reactances a periodic current, and means for adjusting the magnitude of said periodic current to an amplitude corresponding substantially with the amplitude of the weaker of said currents. y

16. The method of distinguishing be- T tween fluctuating currents of different amof said currents.

17. The methodof distinguishing between fluctuating currents of the same frequency but different amplitudes, which comprises impressing the currents upon a currenttranslating circuit and upon a control path upon the magnitude of Whose reactance depends the magnitude of effect in said translating circuit, and impressing on the control path a fluctuating electro-motive-force for periodically changing' the magnitude of said reactance for periodically withholding to diflerent degrees from said translating circuit the effects of said currents of different amplitudes.

18. The method of distinguishing between fiuctu ating currents of different amplitudes, which comprises impressing the currents upon a current-translating circuit and upon a control circuit including inductive and capacitative reactances, and impressing upon said control circuit a fluctuating current for periodically changing its reactance for periodically withholding to different degrees from said translating circuit the effects of said current of different amplitudes.

19. The method of distinguishing between fluctuating current of the same frequency but different amplitudes, which comprises impressing the currents upon a currenttranslating circuit and upon a control circuit'including inductive and capacitative reactances, and impressing upon said control circuit a fluctuating current of different frequencyj for periodically changing its reactance for periodically withholding to different degrees from said translating circuit trol path for periodically withholding to different degrees from said signalstranslating circuit the effects of both sets of said oscillations.

21. The method of distinguishing between radio frequency oscillations representing a desired signal and oscillations of the same frequency but of greater amplitude representing a disturbing effect, which com-v prises subjecting to the influence of both sets of oscillations a signal-translating circuit and a control path including inductive and capacitative reactances, and impressing upon said control path a periodic current of different frequency for periodically varying the reactance of said control path for fects of both sets of said oscillations. I

22. The method of distinguishing between' sustained radio frequency oscillations representing a desired signal and decadent oscillations of the same frequency repreperiodically withholding to different degrees from said signal-translating circuit theef senting a disturbing 'efiect, which comprises" influencing by both sets of oscillations a signal-translating circuit and a control path including inductive andcapacitative reactances, and impressing upon said control path a current of different frequency for periodi cally'varying the reactance of said control path for periodically withholding to different degrees from said signal-translating circuit the efiects 6f both sets of said oscillations. v

23. The method of distinguishing between radio frequency oscillations repre-' senting a desired signal and oscillations of the same frequency but of different ampli-j tnde, which comprises subjecting to the influence of both sets of oscillations a signaltranslating circuit and a control path in eluding-inductive and capacitative reactances, and impressing upon said control path a periodic current for varying the reactance of said control path for withholding to different degrees from said signal-translating circuit the effects of both sets of oscillations.

24. The method of distinguishing between radio frequencyv oscillations representing a desired signal and oscillations of the same frequency butof different amplitude, which comprises subjecting to the influence of both sets of oscillations a signaltranslating circuit and a control path inof said control path for Withholding to diffrom said signal-translating ferent degrees circuit the effects of both sets of oscillations, and varying the amplitude of said impressed current to a magnitude more closely approaching the amplitude of the oscillations of one of said sets than the amplitude of the oscillations of another of said sets.

25. The method of distinguishing between sustained radio frequency oscillations representing a desired signal and decadent oscillations of the same frequency representing a disturbing effect, whichcomprises subjecting to the influence of both sets of oscillations a signal-translating circuit and a control path including inductive and capacitative reactances, impressing upon said control path a periodic current of different frequency for periodically varying the reactance of said control path for periodically Withholding to diflerent degrees from said signal-translating circuit the eflects of both sets of oscillations, and varying the amplitude of said impressed current to a magnitude more closely approaching the amplitude of said sustained oscillations than the amplitude of said decadent oscillations.

26. Radio receiving apparatus for distinguishing between oscillations of radio frequency representing a desired signal and oscillations representing a disturbing eflect, comprising signal-translating means influenced by both sets of oscillations, a control path including capacitative and inductive reactances and so disposed that changes in the reactance of said path cause said sets of oscillations to influence said signal-translating means to different degrees, and means for changing the reactance of said control path 27; Radio receiving apparatus for distinguishingbetween oscillations of radio frequency representing a desired signal and oscillations representing a disturbing effect, comprising signal-translating means influencedvby both sets of oscillations, a control path including capacitative and inductive reactances and so disposed'that changes in the reactance of said path cause said sets of oscillations to influence said signal-translating means to different degrees, and means for periodically changing the reactance of said control path.

28. Radio receiving apparatus for distinguishing between oscillations of radio frequency representing a desired signal and oscillations representing a disturbing eflect, comprising signal-translating means influenced by both sets of oscillations, a control path including capacitative and inductive reactances and so disposed that changes in.

the reactance of said path cause said sets of oscillations to influence said signal-translating means to different degrees, and means for impressing upon said control path a periodic current for changing its reactance.

29. Radio receiving apparatus for distinguishing between oscillations of radio frequency representing a desired signal and oscillations representing a disturbing effect, comprising signal-translating means influenced by both sets of oscillations, a control path including capacitative and inductive reactances and so disposed that changes in the reactance of said path cause said sets of oscillations to influence said signal-translating means to different degrees, and means for impressing upon said control path a periodic current of different frequency for periodically varying its reactness.

In testimony whereof I have hereunto affixed my signature this 13th day of November, 1922.

DAVID Gr. MCGAA.

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