US1462038A - Modulating system - Google Patents

Description

July 17, 1923. 1,462,038

R. v` l.. HARTLEY MODULATING SYSTEM Original Filed Dec. 30, 1916y 2 Sheets-Sheet l July 17, 1923. 1,462,038

R. v. L.. HARTLEY MODULATING SYSTEM Original Filed Deo. 30, 1916 2 Sheets-Sheet 2 frequency Patented July 17. 1923.

UNITED STATES RALPH V. L. HARTLEY, OF SOUTH ORAN GE, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OIF NEW YORK.

MODULATING SYSTEM.

Application led December 30, 1916, Serial No. 139,784. Renewed October 25, 1922. Serial No. 596,899. l

To all whom 'it may concern.:

Be it known that I, RALPH V. L. HARTLEY, a citizen of the United States, residing at South Orange, in the county of Essex and State of New Jersey, haveinvented certain new and useful Improvements in Modulating Systems, of which the following is a full, clear, concise, and exact description.

The invention relates to modulating systems, or systems for supplying a high frequenc wave which varles in amplitude in acc'or ance with the wave form of a signal to be transmitted.

It is well known that a wave of the high f modulated in accordance with the signal frequency a, where a is the instantaneous' value of the signal frequency, may be considered as composed of three components having the frequencies f, f-I-a: and f-a. Considerable power is wasted in radiating the unmodulated component of frequency f, and it is desirable for efficient transmission to radiate only the pure modulated waves of frequencies f-l-a and f-a, the unmodulated component being restored in any suitable manner at the receiving station..

An object of the 'present invention is to provide a modulating system for transmitting a pure modulated wave.

The invention makes use of reactance modulators of the transformer type for controlling the high frequency out put by varying the mutual inductance between the primary and secondary windin s of the transformer in accordance with a signal to be transmitted. The amplitude of the high frequency currents radiated depends upon the coupliny between the primary and secondary windings and by varying this coupling, i. e., the mutual inductance, in accordance with the signal, a vmodulation of the carrier wave is effected. The variation in coupling is effected by varying the permeabilities of the transformer cores in accordance with the signal currents.' The secondary windings of the two transformers are connected to the antenna in opposition to each other, so that no high frequencyt power is radiated in the absence of signalin currents. The effect of signaling currents 1s to increase the permeability'of one transformer core, and to decrease the permeabillty of the other trans- .former core. This disturbs the balance of the opposed secondary windings, and modulated high frequency power is radiated.

former has three similar components with the same frequencies. The two opposed unmodulated components of frequency f are not varied in amplitude by the signal current of frequency a, and these components are always balanced out so that no unmodulated power is transmitted. The pure modulated waves of frequencies f-l-a and f-a. developed in the transformers by the signal currents, agree in phase and so reinforce each other.

Another object of the invention is to prevent the induction of radio frequency currents in the excitation winding. This is accomplished by providing two paths in opposition for the high frequenc flux, the excitation winding being linke by both fluxes so that the effect of the opposed fluxes is to induce no resultant E. M. F in the excitation winding.

A source of steady current is used to bring the permeability of the cores to the desired point about which the permeability is changed by the signaling currents,

A further object of the invention is to use a single excitation winding for each transformer, which is to be supplied by both the steady source and `the signallng source, the

currents from these sources aiding in one winding and opposing in the other, and to prevent the currents supplied by each source from being short-circuited through the other source. To this end the invention provides an impedance coil in circuit with the steady source and a condenser in circuit with the signaling source. The steady current cannot traverse the condenser, while the variable signaling currents cannot pass through the impedance coil, so that both currents are properly supplied to the single excitation winding.

It has been determined that best results are obtained when the modulators are energized by a nerator which acts as a pure resistance. lil order to provide such a generator the reactance of the same is neutralized by a reactance of opposite characteristics. For instance, if the generator has lnductance, then a capacity is provided to neutralize the inductance of the generator which accordingly acts as a pure resistance.

For further details of the invention reference may be made to the drawings, in Which- Figs. 1, 2 and 3 show diagrammatically systems embodying the invention.

In Fig. 1 the reactance modulators or transformers3 and 4 are connected between the source of radio currents 5 and the antenna 6. The transformer 3 has a toroidal core 7 with the crossbar 8. Disposed on the toroidal core 7 at either side of the crossbar 8 are the two halves 9 and 10 of the primary winding. The secondary windings 11 and 12 are similarly disposed on either side of the cross bar 8. The transformer 4 also has a toroidal core 13 with a crossbar 14, and a similar division of the primary windings 15 and 16, which are in circuit with the high frequency source 5 and the'primary windings 9 and 10. The secondary windings 17 and 18 are disposed half on either side of the crossbar 14, and are connected in opposition to the secondary windings 11 and 12. The secondary windings 11 and 12, 17 and 18, are in circuit with the antenna 6, which is tuned by means of the induetance 19 to the frequency to be radiated which may be one or both of the side frequencies f-l-a, f-a. The circuit including the primary windings and condenser 20 is tuned to thel frequency supplied by the source( 5 by means of the condenser 20 which is variable. As explained above it has been determined that for maximum sensitiveness the generator 5 should act as a pure resistance. If the generator 5 has inductance, then means, such as condenser 50, is provided to counterbalance its inductance. If the generator 5 had an equivalent capacity then the element 50 should be an inductance.

In order to bring the permeabilities of the cores 7 and 13 to a desired point, the excitation winding 21, arranged on cross bar 8, and the excitation winding 22 upon the crossbar 14 are supplied through the adjustable rheostats 23 and 24 from a source of steady current 25. In order to vary the permeabilities of the cores 7 and 13 in accordance with a signal to be transmitted, the winding 26 on crossbar 8 and the winding 27 on crossbar 14 are connected through transformer 28 to the signaling device 29. It will be noted that the core 7 and crossbar 8 provide parallel magnetic paths, the primary and secondary windings being disposed artly in each path and the windings 21, 26 eing common to both paths. lf the coils 21 and 22 are so connected to the battery 25 as to supply fluxes in the same direction, as shown in the drawings, then the flux from the winding 2-6 will oppose the flux produced by winding 21 at the instant that the flux produced by winding 27 is aiding the Hux produced by winding 22. In

the drawings, the relative direction of the fluxes is shown by arrows, each arrow indicating the direction of the flux produced by the winding enclosing that arrow. When there are no signaling currents no high frequency power will be radiated, as the secondar'y windings ofthe two transformers are balanced in opposition. When signaling currents are supplied to the transformers, the differential action of the windings 26 and 27 produces additive effects in the secondary circuit, so that a modulated wave is transmitted by the antenna system. As explained above` the unmodulated components supplied by the two transformers are balanced out and only a pure modulated wave is transmitted. Since the primary and secondary windings are equally distributed at each side p of the crossbar, the high frequency flux takes a circular path through the toroidal core and none of the hie-h frequency flux traverses the crossbar. sidered that the high frequency fluxes do traverse the crossbar 8 but traverse it in opposite directions so that no resultantelectromotive force is induced in the excitation windings. This makes it unnecessary to insulate the windings 21, 22, 26 and 27 for high voltage high frequency electromotive forces which might otherwise bc induced in these windings by the high frequency flux.

In Fig. 2 the signaling currents supplied by the signaling device 30 may, if desired, be amplified by one or more amplifiers 31 of the audion type. Instead of using four windings on the crossbars of the two transformers as in Fig. 1, only two windings 32 and 33 are used in the system of AF ig. 2. The steady current for the windings 32 and 33 is supplied b v the battery 34, one terminal 35 of which is connected t0 terminal 36 of winding 32 and to terminal 37 of winding 33. The other terminal 38 of the battery is connected through rheostat 39 and an impedance coil 40 to the other terminal 41 of winding 32. Terminal 38 of the battery is also connected through rheostat 42 and impedance coil 43 to the other terminal 44 of winding 33. Signaling currents are supplied by the transformer 45 over the lines, 46 and 47 to the terminals 41 and 44, respectively. ln the lines 46 and 47 are connected condenscrs 48 and 49 respectively to prevent currents supplied by t e battery 34 from traversing the secondary winding of transformer 45. The currents supplied by the signaling source and the battery 34 produce fluxes in the crossbars 32 and 33 which are additive in one of these crossbars and differential in the other, as is the case in Fig. 1. The impedance r it may be-conlll) lll)

l'll) coils 40 and 43 .prevent the signaling cur- The condensers 48, 49 insure that the secondary winding of transformer 45 will not short-circuit the windings 32, 33 for direct current from battery 34;. and the impedances 40. 43 prevent the lines including the resistanees 39 and 42 from short-eircuiting the windings 32, 33 as to signaling currents.

The transmission of a pure modulated wave by the system of Fig. 2 is effected in the sairie manner as explained in connection with Fig. l.

In the system shown in Fig. 3, the transformer cores of Fig. 2 are replaced by the four toroidal cores 51, 52, 53 and 54.

The arrows in Fig. 1 show the opposing magnetic paths provided by the unitary cores in Figs. 1 and 2. In Fig. 3 each high frequency flux path is provided in a separate core, the primary and secondary windings being disposed in these paths as before and the excitation windings 32 and 33 each encircling two high frequency paths for opposed fluxes, so that no high frequency E. M. F. is induced in the excitation windings. The arrangement of cores in Fig. 3 has the advantage that the primary, secondary and excitation windings may be uniformly distributed about their cores.

In regard to all of the figures, the resonance of the local circuit including the condenser 20 and the primary windings of the transformers. is effected by` the inductive relation of the primary to the secondary windingsl This inductive relation depends upon the variable permeabilities of the cores which ar@ controlled by the signaling currents. rPhe variable condenser 20 is so adjusted, when the signaling currents are zero, that the local circuit including the condenser 20 and the primary windings of the transformers is timed to the frequency supplied hy the carrier current generator 5. Since the primary windings 9, 10. 15. 1G and the condenser 20 are in shunt to generator 5 and arc tuned to the frequency supplied by generator 5. the windings 9. 10, 15, 16 and condenser Q0 form a path which. except for the effect of its resistance component, offers infinite impedance to currents of the carrier frequency, The closed oscillation circuit 9,v

10, 15, 1G is accordingly termed a loopresonant circuit and it is opaque to currents of the carrier frequency. The circuit 9, 10, 15. 16 being timed as described, insures that no power except the negligible amount necessary to supply the RP and core loss will be drawn from the generator 5 when the signaling currents are Zero, which is of advantage as it prevents a waste of the high frequency power. The effect of signaling currents however is to vary the inductance in the circuit 9, 10, 15, 1G, 20 which disturbs and upsets the resonance condition of the loop-resonant circuit and draws more' or less power from the generator 5 in accordance with the signaling currents.` As illustrating one of the modifications that may be made in the systems shown, it may be mentioned that in Fig. 1, for instance, transformer 4 may be dispensed with and an ordinary transformer or alito transformer may be substituted therefor. This amounts to iiiductively relating the primary coils 15, 16 to the secondary coils 17, 18 in the usual manner, the coils 27 and 22 being dispensed with so that transformer 28 supplies only coil 2G and battery 25 furnishes current only to coil 21.

Although this invention has been illustrated and described in connection with radio signaling, it is to be understood that it is applicable aswell to transmission of energy waves over conducting circuits.

What is claimed is:

1. The combination of a source of high frequency currents, a line 'selectively responsive to modulated currents of said high frequency, means associated with said source and said line for modulating said high frequency currents,said means comprising two transformers having primary windings connected to said source and secondary windings connected in series opposition in said line, and signaling means for differentially controlling said transformers whereby a pure modulated wave is transmitted by said line. c

2. The combination of two transformers each having niagnetizable means with primary -and secondary windings thereon, a source of high frequency currents for supplying said primary windings. a line selectively responsive to modulated currents of said high frequency associated with said secondary windings, said secondary windings being balanced in opposition and connected in series in said line to normally restrain the transmission of energy from said source to said line, and signaling means controlling said magnetizable means for disturbing the balanced condition of said windings whcreby said high frequency currents are modulated in accordance with the signal to he transmitted.

A signaling system comprising a source of high frequency currents. a line selectively responsive to modulated currents of said high frequency, means between said source and said line for modulating said high frequency currents, said means comprising two transformers having primary windings connected to said source and secondary windings balanced in opposition in said line, and signaling means for differentially controlling said transformers whereby a pure modulated wave is transmitted.

4. In a signaling system, a high frequency circuit including a source of high frequency current and magnetic control means in series therewith in said circuit, an excitation winding for said control means, a source for supplying a steady current to said winding, a source of signaling current for said winding, means for preventing said signaling current from passing through said first mentioned source, and means for preventing said steady current from passing through said signaling source.

5. ln a, signaling system, a high frequency circuit including a source of high frequency current and magnetic control means in series therewith in said circuit, an excitation winding for said control means` a source for supplying a steady current to said winding, a

' source of signaling current for said winding,

an impedance coil for preventing said signaling current from passing through said first mentioned source, and condensive reactance for preventing said steady current from passing through said signaling source.

6. ln a system for the modulation of high frequency currents, the combination of two excitation windings, a source for supplying a steady current to said windings` means for independently adjusting the current in each ofusaid windings. a. source of signaling current for supplying said windings-` lmeans for preventing said signaling current from passing througlL said first mentioned source, and means for preventing said steady current from passing through said signaling source.

7. A signaling system comprising two excitation windings, a source of current. for supplying said windings, an impedance coil anda rheostat in circuit with each of said windings, a source of signaling current for supplying said windings. leads for connecting said signaling source to said windings, and a condenser in each of said leads, the currents from said sources aiding in one of said windings and opposing in the other of said windings.

8. In a signaling system, a modulator consisting of two transformers balanced in opposition each transformer comprising primary and secondary windings and magnetizable means providing two magnetic pat-hs, said primary and said secondary windings be- .ing disposed part in one of said paths and part in another of said paths. an excitation winding disposed about a common portion of said paths a source of alternating current to be modulated connected to said primary winding and a transmission circuit tuned to the frequency of said modulated alternating current connected to said secondary winding.

9. In a signaling system. a modulator consisting of two transformers balanced in opposition each transformer comprising primary and secondary windings and magnetizable means, and an excitation winding for varying the permeability of said magnetizable means, a source of alternating current to be modulated connected to said primary Winding, a source of current for said excitation Winding, said excitation winding being so disposed as to prevent the same from becoming a source of currents of the frequency supplied to said primary winding and a translation circuit connected to the secondary windings and tuned to the frequency of the modulated alternating current.

10. A modulating system comprising a source of unmodulated oscillations and means for modulating said oscillations in accordance with signals including a reactance conductor in series with said source for supplying energy to a line, and means in shunt to said conductor having a reactance equal in value but opposite in kind to that of said reactance conductor with respect to oscillations of the frequency supplied b v said source.

l1. A reactance modulator comprising a line, a high frequency circuit, magnetic means connecting said line and said circuit, an oscillation generator connected to said high frequency circuit, said line being tuned to a frequency differing by approximately mean speech frequency from that of the oscillations produced by said generator and signaling means for varying the impedance which said high frequency circuit offers to said generator.

12. An oscillation generator, and a series circuit connected thereto comprising means having a reactance equal in value and opposite in kind to the reactance of said generator, a closed loop circuit tuned to the fre- 'quency of said generator and a work circuit arranged to be supplied with current from said loop circuit.

13. A signaling system comprising means for supplying high frequency oscillations, a modulator having primary and secondary windings associated with a core of magnetic material, said primary windings being adapted to be energized by said means and a high frequency line for transmitting modulated currents of the carrier frequency supplied by said means and adapted to be energized by said secondary windings, a condenser in series with said means, and another condenser in shunt to said primary windings.

14. In a signaling system for transmitting a pure modulated wave, a transformer comprising primary and secondary windings and magnetizable means having two magnetic paths, said primary and said secondary windings being disposed part in one of said paths and p art in another of vsaid paths, and an excitation winding common to both of said paths. a similar transformer, a signaling device in circuit with the excitation windings of said transformers, a source of high frequency currents for the primary windings of said transformers` the secondary windings of one of said transformers being connected in opposition to the secondary windings of the other of said transformers, and a high frequenc line adapted to be supplied by said secon ary windings.

15. The combination of a source of high frequency oscillations, a line tuned to a frequency differing by approximately mean speech frequency from that of said oscillations and two reactance devices having primarywindings connected to said source, and secondary windings balanced in series opposition in said line.

16. The combination of two transformers each having primary, secondary and excitation windings, a generator of carrier waves for supplying said primary windings, a source of steady current and a source of signaling current for supplying said excitation windings, a high fre uency line adapted to be differentially supp ied by said secondary windings, and means for tuning said high frequency line to a frequency differing from that of said carrier waves by the frequency of said signaling current.

17. The combination of two transformers eacli having primary, secondaryl and excitation windings, a generator of carrier waves, means for neutralizing the reactance of said generator, said generator being in circuit with said primary windings, tuning means associated with said primary windings, a source of direct current for supplying said excitation windings, signaling means for controlling the inductive relation of said primary to said secondary windings, a .high frequency line adapted to be. differentially supplied by said secondary windings, and means for tuning said line to the frequency to be transmitted.

18. The combination of a carrier current generator, a modulator comprising a condenser and primary windings in series circuit with said generator, secondary windings associated with said primary windings and connected in series opposition, signaling means controlling the inductive relation of said primary and secondary windings, and a high frequency circuit connected to said secondary windings to receive modulated carrier current energy therefrom and tune-d to one of the principal frequencies of said modulated carrier current.

19. The combination of a high frequency generator, a condenser and primary windings in series circuit therewith, secondary windings inductively associated with said primary windings, signaling windings associated with said primary and secondary windings to produce modulation of the current supplied by said primary windings to said secondary windings, and a high frequency circuit tuned to a principal frequency of said modulated current connected to said secondary windings.

20. The combination of a high frequency generator, a condenser and primary windings quency from that of sai carrier current, the

.secondary windings of said transformers being connected in opposition to said line.

22. In a signaling system for transmitting a pure modulated wave, two transformers each .comprising primary and secondary windings, a source of carrier frequency currents forthe primar windings of said transformers, a line tune to a frequency differing by approximately mean speech frequency from that of said carrier current, the secondary windings of said transformer being connected in opposition to said line, and means for controlling the energy which said transformers transfer to said line.

23. In a signaling system the combination of asource of high frequency oscillations, a transmission circuit, a magnetic modulator connecting said source to said circuit, and means conductively connected to said source for preventin substantially any current flow from sai source during non-signaling periods.

24. The method of variably controlling the transmission of an alternating current from a source to a utilization circuit which comprises subjecting rthe current flowing from said source to the impedance offered by a loop-resonant circuit and varying the impedance offered to said current by said loop resonant circuit in accordance with signals and in such manner that the impedance offered by said loop-resonant circuit is a maximum at the instants of minimum transmitted current.

25. A source of high frequency current, a circuit directly ccnnected thereto and containing a closed loop having inductive react- -ance and capacity reactance so proportioned as to offer substantially infinite impedance in said circuit to current from said source, a source of modulating waves, an outgoing circuit containing impedance and arranged to be normally substantially out of effective energy transfer relation with said loop, and means for setting up effective energy transfer relation between said loop and said outgoing circuit in accordance with the instantaneous amplitudes of said modulating waves.

26. A source of high frequency currents,

lll

a circuit connected thereto and containing a. parallel branched path which oil'ers substantially infinite impedance to the current from said source, a source of modulating waves coupled to one branch of said. path to vary the impedance of said circuit 1n accordancc with variations of said modulatlng waves and an outgoing circuit coupled to one branch of said path in a manner to have large amplitude current impressed thereon at the instants when the impedance of said patli is of relatively small amplitude and vice versa.

2T. In a modulating system, a source of oscillations to be modulated, a capacity and an inductance connected to said source in parallel with each other to form a loop-resonant circuit tuned to the frequency ot' said source, said inductance being comprisedln two parts, a pair of separate windings inductively related respectively to the two parts of said inductance and connected 1n opposition in an outgoing circuit, and means for simultaneously varying the mutual inductance between each portion of said inductance and its inductively related Winding in accordance with signals to be transmitted. 28. In a modulating system, a source ot' sustained oscillations possessing reactance, a reactive element of opposite kind to the reactance of said source and of a magnitude to neutralize the reactance of saidsource, an inductance and a capacity connected in parallel with each other and connected to said source and reactive element 1n series, said inductance and capacity together forming an anti-resonant circuit to the oscillations from said source, said inductance being comprised in separate portions, a corresponding number ot' windings each inductively related to a different one of said inductance portions and connected in an outgoing circuit to normally apply respectively opposlte potentials to said circuit, whereby when no signals are being sent substantially no oscillations from said source reach said outgoing circuit, and means for simultaneously Varying the mutual inductance between each of said inductance portions and its associated winding to vary in opposite scuse the oppositely applied potentials to said outgoing circuit in accordance with signals to be sent.

29. In a modulating system comprising a generator of oscillations and an outgoing circuit, means for preventing transmission of the oscillations to said circuit during nonsignaling periods comprising a pair of transformers having primary windings con nected to said generator and secondary windings connected in said outgoing circuit in opposition to each other, means for reducing the load drawn from said generator during non-signaling periods comprising a capacity in shunt of said primary windings and forming with said transformer inductanccs a loop-resonant circuit of very high impedance to the oscillations from said generator, and means to vary the mutual inductance ot' at least one of said transformers in accordance with signals.

30. In a modulating system, a source of oscillations, an outgoing circuit having impedance, a, loop-resonant circuit connected to said source and offering substantially infinite impedance to the oscillations from said source during non-signaling periods, said loop-resonant circuit having substantially zero net Inutual inductive Arelation with said outgoing circuit, and means acting in response to impressed signals for setting up a net mutual inductive relation between said loop-resonant and said outgoing circuit to an extent substantially proportional to the instantaneous amplitudes of the signals, whereby the impedance offered by said loopresonant circuit to oscillations from said source is decreased and signal modulated oscillations are impressed on said outgoing circuit.

In witness whereof, I hereunto subscribe Amy name this 29th day of December A. D.

RALPH V. L. HARTLEY.

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