US1328610A - Method of and means for controlling high-frequency alternating currents - Google Patents

Description

Q Voltage 0f Genefator or- Amplifier W/bd/hg E. F. W. ALEXANDERSON.

METHOD OF AND MEANS FOR CONTROLLING HIGH FREQUENCY ALTERNATING CURRENTS.

APPLICATION FILED JAN. 21, 1916.

1,328,610. I Patented Jan. 20, 1920.

AAAAAAA "Iv" Inventor 1 His Attornel UNITED STATES PATENT OFFICE.

ERNST F. W. ALEXANDERSON, OF SCI-IENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

METHOD OF AND MEANS FOR CONTROLLING HIGH-FREQUENCY ALTERNATING I CURREN'IS.

Specification of Letters Patent.

Patented Jan. 20, 1920.

Application filed January an, 1910. Serial No. 73,443.

To all whom it may concern:

Be it known that 1. Elmer F. Vt. ALFX- ANDERSON, a citizen of the United States, residing at Schenectadv. Schenectady, State of New York, have invented certain new and useful Improvements in Methods of and Means for Controllin Hi h-Frequency Alternating Currents, 0 which the following is a specification.

My present invention relates to improvements in apparatus for controlling alternating electric currents, and more especially for controlling alternating currents used in wireless signaling systems.

The object of my invention is to provide means for efficiently controlling and varying the amplitude of a high frequency current flowing in a signaling circuit in accordance with variations'in the amplitude of a signaling current of much lower frequency and amplitude.

In carrying my invention into effect 1 make use of electromagnetic apparatus of a kind which I term magnetic amplifiers, such, for example, as are described in my U. S. Patent No. 1,206,643. By varying the circuit arrangements used inadapting a magnetic amplifier to asignaling system over those which have heretofore been employed, and by using in conjunction therewith suitable condensers in a way which will be more fully set forth in the description which follows, I am able to accomplish the object of my invention.

The novel features which I believe to be characteristic of my invention are pointed out with particularity in the appended claims. The invention itself, however, with further objects and advantages will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a simple diagrammatic representation of the apparatus and circuit connections which may be employed in carrying my invention into effect; Fig. 2 shows diagrammatically the preferred form of magnetic amplifier used with the arrangement of the magnetizing winding thereon; Fig. 3 is agraphic representation of the volt ampere characteristics of the amplifier under different conditions" of operation; Fig. 4 shows the combined volt ampere characteristics of a high frequency inthe county of alternator and of a magnetic amplifier with different values of control current; Fig. 5 is a diagrannnatic representation of a modification in the apparatus and circuit connections which may be used and Fig. 6 is a diagram showing how the system of Fig. 1 Inlay be modified so that it may be used for to egraphy instead of telephony.

As indicated in Fig. 1, the armature wind ing 1 of a high frequency alternator, the rotor 2 of which is driven by a motor 3, is inductively connected by means of the transformer A with the antenna 5. Coils 6 and 7 of a magnetic amplifier are connected in shunt to the secondary of transformer 4 and in parallel to each other. A variable condenser 8 is connected in series with both coils and condensers 9 and 10 are connected in series with coils 6 and 7 respectively. A condenser 11 may also be connected in shunt to the two coils. By varying the current flowing through coils 6 and 7, the electromotive force at the terminals of the secondary of transformer 4 may be varied and the amplitude of the current flowing in the antenna will be varied accordingly. The means for varying the current flow in coils 6 and comprises two controlling coils 12 and 13. Coil 12 is supplied with a constant direct current from the source 14 and the value of this current required to give the magnetic circuit of the amplifier a desired degree of saturation may be adjusted by the variable resistance 15. The winding 13 is supplied with the signaling-current which in the present example is furnished by the secondary of transformer 16, the primary circuit of which includes a telephone trans mitter 17 with the usual local battery 18. A high inductance 19 is preferably inserted in the circuit of coil 12 in order that this circuit shall offer a. high impedance to the flow of currents induced therein from the coil 13. It is also desirable that the circuit of coil 13 shall be resonant to the most common frequency of the current in that circuit and for this purpose a variable condenser 20 in series with the circuit may be employed. This condenser will preferably be shunted by resistance 21 in order that the circuit shall not be too highly resonant.

By the organization which I have thus described it is possible by means of the small methods.

'an amplification of the current variations in the telephone transmitter having. a ratio equal to the ratio between the frequency of the high frequency current flowing in coils 6 and 7 and that of the current which is to be amplified. While the systei'n here shown is especially adapted for wireless telephony,

it may, by suitable imidification, equally well be employed for transmitting telegraphic signals.

()ne manner in which this maybe accomplished is indicated in Fig. (l in which the coil 13 is included in the circuit with a telegraph key 31 and battery 32.

In Fig. 2, I have shown a magnetic structure which is especially suitable for a magnetic amplifier. In this case two magnetic cores 22 and 23 carry the coils 6 and 7. The windings are so arranged that the flu produced by the high frequency current in the coils is in opposite directions in the two cores and as a result this flux is confined to the two cores and the small portions 24 of the structure adjacent the cores. The winding 25 which carries the controlling current is wound around both of the cores as indicated. Theflux produced by this winding traverses the two cores in the same direction and also traverses the outer legs 26 of the magnetic structure. It will be apparent that each turn of the controlling winding is threaded by the flux 1n the cores 22 and 28 in opposite dlrections so that any electrometive forces induced in the winding bythe high frequency flux are neutralized in each turn. While I have shown a single controlling winding this may be divided into two separate parts as indicated in Flg. 1.

Magnetic amplifiers of the type which I employ may be operated by two distinct In case the-two high frequency coils are connected in series, as shown in my U. S. Patent #1,206,643, the current in those coils is forced to be equal at any moment and the resulting flux is allowed to adjust itself in accordance with the permeability of the iron so that the Voltage appearing at the terminals of the high frequency wlnding becomes a variable function depending upon the current distribution. In case the two coils are connected in multiple as I have indicated in Fig. 1, the relation of the currents in the two coils is indefinite but the flux variation in the two branches of the core is forced to be equal. In Fig. 3, curve A shows the volt ampere characteristic of the coils with the. first method of opmeans greater sensitiveness and a lower curvature means that larger currents can be carried without causing instability, as will be explained later.

With the multiple connection the flux variations are forced by the circulating current flowin in the short-circuit between the two multip e coils. The induced current in this short circuit tends to oppose any changes in the average flux and thus a tele phone current in the control winding would simply cause a corresponding short circuit between the two high frequency coils withoutproducing the desired flux variations. This difficulty, however. can be overcome by taking advantage of the fact that the high frequency winding needs to operate only at radio frequencies which are very much higher than the frequency of the telephone current. It is, therefore, possible to find a value for the condensers 9 and 10, such that this circuit acts as a short circuit for the radio currents and ractically as an open circuit for the telep one current.

The current in' the hi h frequency winding has a tendency to (epress the average average flux of the high frequency coil although the control excitation is kept constant. It has also been shown above that the degree to which the short circuit opposes changes in the average flux can be modified by the introduction of suitable condenseis.

In order to show how by other modifications the magnetic amplifier may be utilized to advantage for controlling the voltage of an alternator, reference may be had to the alternator characteristics shown in Fig. 4. The alternator voltage is plotted against the current in the shunt circuit and curves G, G and G" represent the alternator characteristic. for different outputs. The magnetic amplifier is used in the control shunt circuit and the volt ampere characteristics of the i citation in the controlling winding. The

intersections between the sets of curves give the alternator voltages at the corresponding amplifier excitations.

These curves show that the alternator voltage approaches zero as the amplifier excitation increases and it is possible to'obtain effective control of telegraphy in this way without exceeding the current carrying capacity of the control winding of the amplifier. However, these results are'not all that'is to be desired for telephony because there is a lack of linear proportionality between the alternator voltage and amplifier control current. The improvements in the characteristics of the amplifier that are described have the eifect not only of securing this linear proportionality but also a much higher degree of sensitiveness. The nature of these improvements can be explained by further reference to the volt ampere characteristics. These characteristics are a set of curves radiating from the origin, each of which represents a certain control excitation. For the complete control. of the alternator, to vary its voltage from zero to a'maximum, it would be desirable that the first curve should coin: cide with the Y-axisand the last coincide with the X-axis, and that the other curves should be distributed. uniformly between these limits. Instead of this, however, the amplifier characteristics all fall within a certain angle covering only a little more than one-half the desired sweep. This disadvantage may be overcome to a large ex tent by neutralizing part of the voltage of the amplifier windmg by a suitable series condenser 8 so that the circuit becomes resonant when the radiation from the antenna is a minimum and neutralizing part of the current by a suitable shunt condenser 11 so that the circuit which includes the coils and the shunt condenser become resonant when the radiation from the antenna is a maximum. If the condenser is chosen so that it exactl neutralizes the inductance of the ampli er winding at some definite value of excitation, the resulting impedance at this excitation becomes a m1nimum and the impedance at any lower excitation is determined by'the difference between the inductive reactance of the amplifier coil and the capacity reactance of the series condenser. The smaller this difference, the lower will be the amplifier excitation. which gives minimum impedance vand the corresponding minimum. of alternator voltage. This means that the sensitiveness of the amplifier I is increased because a smaller excitation is needed to reduce the alternator voltage. The increase of sensitiveness which can be obtained in this way is, however not unlimited. If the minimum impedance is obtained as a result of a large inductive and a large capacity reactance, the core in my prior application, Serial No. 873,110,

filed November 20, 1914.

The voltage which results from the combination alternator and amplifier can be determined by the intersection of the alternator and amplifier characteristics. When these curves have a definite sharpintersection point, a definite alternator Voltage results from each excitation of the amplifier. If on the other hand the curves have such a shape that the alternator and amplifier characteristic curves become parallel or tangent in some place, the intersection becomes indefinite and the result is instability and generation of self-excited oscillations. The conditions which lead to the instability may be illustrated by the curves-shown in broken lines in Fig. 4. If a series condenser is used which has such a value that it has the voltage characteristic indicated by the curve C, the resultant characteristic of the shunt circuit for different values of excitation will be represented by the difierence between this curve and the curves H, H, etc. For example, curve H will be brought down so that it occupies a position H and curve H"" will be practically coincident with the X-axis. All of the new characteristics will have definite intersection points with the generator characteristics and the operation will, therefore, be stable under all conditions of load which are indicated. If, however, a condenser is used which is of such capacity that it has the voltage characteristic indicated by the curve C, the resultant of curve H wlth this condenser curve will be the curve H It will be seen that this curve becomes tan ent to the generator characteristic G and, t erefore, operation with this generator output and this particular value of excitation will be unstable. With higher degrees of excitation, it will be apparent that the point of instability will be reached with lower generator outputs. f

In Fig. 5 I have shown an arrangement which is the equivalent of that shown in Fig. 1, only in this case a separate winding 27 on thehigh frequency alternator supplies current for the operation of a second amplifier 28. The circuit through the coils of this amplifier is controlled in the same manner as the current in the amplifier coils in the organization shown in Fig. 1. The variable indicated but one controlling winding in dicated in the supply connections for the controlling winding 31 of amplifier 28.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination in a wireless signaling system of an antenna, a source of high.

frequency alternating current) connected to said antenna, an electromagnetic device comprising a pair of wmdmgs connected m shunt to each other and included in a circuit with said high frequency source, a pair I of parallel cores magnetized by said windings in such a way that the flux produced therein flows in opposite directions in said cores, a controlling winding surrounding said high frequency windings so as to produce a flux in the same direction through both of said cores, means fol-supplying said controlling winding with a variable current, the variations of which are of comparatively low frequency in com arison with the frequency of the current in the high frequency circuit, a condenser in series with said high frequency winding. to neutralize part of the voltage of said windings, a condenser in shunt with said high frequency windings for neutralizing a part of the'current therein, and condensers in the closed circuit formed by the high frequency windings of such capacity that the circuit offers a' low impedance to high frequency currents but.

a high impedance to currents of the frequency of the controlling current.

2. The combination in a wireless signaling system of an antenna, a source of high frequency alternating current connected to said antenna, an electromagnetic devicecomprising a pair ofwindings connected in shunt to each other and included in a circuit with said high frequency source, a air of parallel cores magnetized by said windings in such a way that the flux produced therein flows in opposite directions in said cores, a controlling winding surrounding said high frequency windings so as to roduce a flux in the same direction throug both of said cores, means for supplying said controlling winding with a variable current, the variations of which are. of comparatively low frequency in comparison with the frequency of the current in the high frequency circuit, a condenser in series with said high frequency windin s to neutralize part of the voltage of sai windings and a condenser in shunt to said high frequency windings for neutralizing part of the current therein.

3. The combination in a wireless signaling system of an antenna, a source of high frequency alternating current connected to with said high frequency source, a

said antenna, an electromagnetic device comprising a pair of windings connected in shunt to each other and included in a circuit air of parallel cores magnetized by said windings in such a way that the flux produced therein flows in opposite directions in said'cores, a controlling winding surrounding said high frequency windings so as to roduce a flux in the same direction .throug both of said cores, means for supplying said controlling windin with a varlable current, the variations 0 which are of comparatively low frequency in comparison Wit the frequency of the current in the high frequency circuit, a condenser in series with said high frequency windings to neutralizepart of the voltage of said windings and condensers in aclosed I circuit formedby the high frequency windings of'such capacity that thecircult offers a low impedance to high frequency currents but a high impedance to currents of the frequency of the controlling current.

4. The combination in a wireless signaling system of an antenna, a source of high frequency alternatin current connected to said antenna, an e ectromagnetic device comprising a pair of windings connected in shunt to each other and included in a circuit with said high frequency'source, a pair of parallel cores magnetized by said windings in such'a way that the flux produced therein flows in opposite directions in said cores, acontrolling winding surrounding said high frequency windings so as to produce a flux in the same direction through both of said cores, means for supplying said controlling windin with a varlable current, the varlations'o which are of comparatively low frequency in comparison with the frequency of the current in the high frequency circuit, a condenser in shunt to said high frequency windings for neutralizing a and condensers In a closed circuit formed by the high frequency windin of such capacity that the circuit offers a ow impedance to high frequency currents and a high impedance to currents of the frequency of the controlling current. I I

5. The combination in a wireless signaling system of an antenna, a source of high frequency alternating current connected to said antenna, an electromagnetic device comprising a pair of windings connected in shunt to each other and included in' a circuit with said high frequency source, a pair part of the current therein,

rent, the variations of which are of comparatively low frequency in comparison with the frequency of the current in the high frequency circuit, and a condenser in series with sand high frequency winding'to neutralize part of the voltage of said wind- 1ngs.-

6. The combination in a wireless-signaling system of an antenna, a source of high frequency alternating current connected to said antenna, an electromagnetic device comprising a pair of windings connected in shunt to each other and included in a circuit with said high frequency source, a pair of parallel cores magnetized b said Wllldings in such a, way that the ux produced therein flows in opposite directions in said cores, a controlling winding surrounding said high frequency windings so as to produce a flux in the same direction through both of said cores, means for supplying said controllin windin with a variable current, the varlations 0 which are of comparatively low frequency in comparison with the frequency of the current in the high frequency circuit, and a condenser in shunt with said high frequency windings for neutralizing a part of the: current therein.

7. The combination in a wireless si aling system of an antenna, a source of igh frequency alternating current connected to said antenna, an electromagetic device comprising a pair of windings connected in shunt to each other and included in a circuit with said high frequency source, a pair of parallel cores magnetized by said windings in such a way that the flux-produced therein flows in opposite directions in said cores, a controlling winding surrounding said high frequency windings so as to produce a flux in the same direction through both of said cores, means for supplying sald controlling winding with a variable current, the variations of which are of comparatively low frequency in comparison with the frequency of the current in the high frequency circuit, and condensers in a closed circuit formed by the high frequency windings of such capacity that the circuit offers a low impedance to high frequency currents but a high impedance to currents of the frequency of the controlling current.

8. The combination in a wireless signal-" ing system of an antenna, a source of high frequency alternating current connected to saidantenna, an electromagnetic device corn-- prising windings included in shunt to each other in a circuit with said high frequency source and a condenser in series with said windings'to neutralize of said windings. s

9. The combination in a wireless signaling system of an antenna circuit, a source with sai part of the voltage comprising a pair of windings included in shunt to each other in a circuit with said high fr'eguency source, a condenser in series frequency windings, for neutralizing part of the current therein.

high frequency windings to neu-.

11. An elctromagnetic device for controlling the flow in an electric circuit of high frequency current comprisng a pair of windings connected in shunt to each other and included in the high frequency circuit,

a condenser in series with said high frequency windings to neutralize part of the voltage of said windings, and a condenserin shunt with said high frequency windings for neutralizing part of the current therein.

12. Means for controlling the flow of high frequency current in an electric circuit complying said controlling winding with the controlling current and a condenser in series with said high frequency windings to neutralize part of-the voltage of said windings.

. l3. Means for amplifying a variable current comprising a source of alternating current, the frequency of which is high in comparison with'the frequency of the variationsin the current to be amplified, an electromagnetic device comprising a pair of windings connected in shunt to each other and included in the circuit of the high frequency current, a pair of parallel cores magnetized by said windings in such a. way that the flux produced therein flows in opposite directions in said cores, a controlling winding surrounding said high frequency windings so as to produce a flux in the same direction through both of said cores, means for supplying the variable current which is to be ampllfied to said controlling winding,

and,condensers in a closed circuit formed I by said high frequency windings of such capacity that the circuit offers a low impedance to high frequency currents but a high impedance to currents of the fre uency of the current which is to be amplifie 14. The method of controlling the flow in an electric circuit of a high frequency alternating current which consists in cansing the current to flow through a pair of circuit supplied with energy from sa-id'electric circuit in such a way that it reaches a state of resonance when the output of the main circuit is a minimum.

16. The method of controlling the flow in an electric circuit of a high fre quency 'al- 'ternating current which consists 1n continuously varying the inductance of an auxiliary circuit by varying the magnetic permeability of the circuit and neutralizing part of the inductance by electrostatic capacity so that theauxiliary circuit reaches a state of resonance when the output of the main circuit is a minimum.

. 17. The method of controlling the flow in an electric circuit of a high frequency alternating current which comprises vary ing an inductance included 'in two auxiliary circuits associated with the main circuit and neutralizing a part of the inductance by electrostatic capacities in both of the auxiliary circuits in such a way that one of the auxiliary circuits reaches a state of resonance when the output of the main circuit is a minimum and the other reaches a state of resonance when the output of the main circuit is a maximum.

18. The method of controlling the flow in an electric circuit of a high frequency alternating current which comprises tuning difierentially two auxiliarytcircuits associated with the main circuit in such a way that one of the auxiliary circuits reaches a. state of resonance when the output of the main circuit is a minimum and the other reaches astate of resonance when the output of the main circuit is a maximum.

19. The combination in a wireless signaling system of an antenna circuit sup liedbya source of high frequency alternating current, a reactance and a variable condenser connected in-shunt to saidhigh frequency source and to said antenna circuit, a second circuit including a magnetizing winding inductively related to sald reactance in such a manner that the impedance of the antenna circuit may be varied by varying the current flowing in said magnetizing winding,

and means for causing a variable current to flow in said second circuit.

20. Means for controlling the flow of a radio frequency alternating current in an electric circuit comprising a pair of magnetic cores, a pair of windings for magnetizing said cores which are connected in shunt to each other and supplied with current from said .circuit, means for producing a low frequency controlling flux in said cores in such a way that at any given instant the'controlling flux and the radio frequency flux are in the same direction in one coreand in opposite directions in the other core, a condenser in series with said windings for neutralizing a part of the voltage of said windings and condensers in the closed circuit formed byv said windings of such capacity that the circuit offers a low impedance to radio frequency currents but a high imped- ,ance to currents of the frequency of the controlling flux. i

21. Means for controlling the flow of a radio frequency alternating current in an electric circuit comprising a pair of magnetic cores, a pair of windings magnetizing said cores which are connected in shunt to each other and supplied with current from said circuit, means for producing a low frequency controlling flux in said cores in 811011 a way that at any given instant the controlling fiux and the radio frequency flux are in the same direction in one core and in opposlte directions in the other core, and a condenser in series with said windings for neutralizing part of the voltage of said windings.

2?. Means for controlling the flow of a rad1o frequency alternating current in an electric circuit comprising a 'pair of magnetic cores, a pair of windings for magnetizing said cores which are connected in shunt to each other and supplied with current from said circuit, means for roducing a low frequency controlling flux 1n said cores in such a way that at any given instant the controlling flux and the radio frequency flux are in the same direction in one core and in opposite directions in the other core, and condensers in' the closed circuit formed by said windings of such capacity that the circuit offers a low impedance to high frequency currents but a high impedance to Eurrents of the frequency of the controlling 23. Means for controlling the flow of a radio frequency alternating current in an electric circuit comprising a pair of magnetic cores, a pair of windings for magnetiz= ing said cores which are connected in shunt to each other and supplied with current from said circuit, means for roducing a low frequency controlling flux 1n said cores in such a way that at any given instant the I controlling flux and the radio frequency flux I windings, the closed circuit formed by said windings being'so arranged that it offers a low impedance to the radio frequency cur- I rents and a high impedance to currents of the controlling flux.

the frequency of the controlling flux.

24.'Means for amplifying a variable current comprising a source off-alternating current the frequency of which is high in comparison with the frequency-of the variations in the current to be amplified a pair of magnetic cores, apair of windings for magnetizing said cores which are connected in shunt with each other and supplied from said source of alternating current, means for producing by the'current to be amplified a flux in said cores in such away that at any given instant, the flux produced by the variable current and the high frequency flux are in the same direction in one core and in opposite directions in the other core, and condensers in the closed circuit formed by said windings of such capacity that the circuit offers a low impedance to high, frequency currents but a high impedance-to the currents of the frequency of the current which is to be amplified.

25. The combination in a Wireless signaling system of an antenna, a source of radio frequency alternating current connected to said antenna, a pair of magnetic cores, a pair of windings for magnetizing said cores which are connected in shunt to each other and included in a shunt circuit to the antenna circuit, means for producing a low frequency controlling flux in said cores in such away that at any given instant the controlling flux and the radio frequency flux are in the same direction in one core and in opposite directions in the other core, means for neutralizing a part of the voltage of said windings and condensers in the closed circuit formed by saidiwindings of such ca,- pacity that the circuit offers a low impedance to radio frequency currents but a high impedance to currents of the frequency of ciated therewitlia secondary circuit which I "comprises a variable inductance and a series 26. Means for controlling the flow of radio frequency current in an electric circuit comprising a variable inductance having a shunt and a series capacity associated therewith, the capacities being so chosen that at one value of the inductanceit is neutralized by the series capacity at a desired frequency and at a second value of the inductance it isneutralized by the shunt capacity at the same frequency, and means for varying the inductance between said two values.

27. Means for controlling the flow of radio frequency current in an electric circuit comprising a variable inductance having a shunt and a series capacity associated therewith, the capacities being so chosen that at one value of the inductance it is neutralized by theseries capacity at a desired frequency and at a second value of the inductance it is neutralized by the shunt capacity at the same frequency.

I 28. A radio signaling. system comprising an antenna which is resonant to a desired frequency supplied by a. source of radio frequency continuous current and having assocapacity and a third circuit which comprises the variable? inductance and a shunt capacity, the second circuit being so proportioned that it becomes resonant to the desired frequency at one value of the variable inductance and the third circuit beingv so proportioned that it becomes resonantto the desired frequency at a second value of the variable inductance.

29. The method of operating a radiating antenna system which comprises a variable inductance which is common to two oscillating circuits which consists in varying the value of said inductance in such a way that under one condition of operation one of the oscillating circuits becomes resonant to a desired frequency and under another condition of operatlon the other oscillating circuit becomes resonant to the desired frequency.

In witness whereof I have set my hand .this 20th January, 1916.

. ERNST F. w. ALEXANDERSON.

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