US1383807A - Power modulation for radiotransmission - Google Patents

Power modulation for radiotransmission Download PDF

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US1383807A
US1383807A US51762A US5176215A US1383807A US 1383807 A US1383807 A US 1383807A US 51762 A US51762 A US 51762A US 5176215 A US5176215 A US 5176215A US 1383807 A US1383807 A US 1383807A
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circuit
antenna
impedance
frequency
current
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US51762A
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Raymond A Heising
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AT&T Corp
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Western Electric Co Inc
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    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03CMODULATION
    • H03C1/00Amplitude modulation

Description

R. A. HEISING. POWER MODULATION FOB RADIO TRANSMISSION.
APPLICATION FILED SEPT. 21-19I5.
. 1 383,807; Patented July 5, 1921.
W/fn ealses:
D7 v e'ni'or RAYMOND A. HEISING, OF EAST ORANGE, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A COR- DURATION OF NEW YORK.
POWER MODULATION FOR'RADIOTRANSMISSION.
ssasor.
Patented July 5, 1921.
Application filed September 21, 1915. Serial No. 51,762.
To all whom it may concern:
Be it known that I, RAYMOND A. IIEISING, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Power Modulation for Radiotransmission, of which the following is a full, clear, conclse, and exact description. I
This invention relates to theuse of highfrequency currents in radio signaling, and particularly to the use of these currents for radio telephony. The object of thisinvention is to provide means for modulating the high-frequency power used in wirelesstelephony or telegraphy in accordance w1th the thisresult without requiring the passage of' heavy currents directly through the tele phone transmitter or other signaling device.
In this invention it is proposed to secure the modulation of the total high-frequency power by varying the impedance of a vacuum tube placed in the antenna circuit. It has been found that thermionic vacuum tubes, particularly of the audion type, are well adapted for this purpose because 0 their relatively high impedance, and because of the fact that this impedance can be varied by means ofa signaling device, in particular a telephone transmitter, which is required to handle only a limited amount of power.-
In general, however, a thermionic device is unilateral, and, in order to permit the passage of both halves of the high-frequency oscillations, it is necessary to make the system symmetrical by usingtwo such thermionic impedances suitably connected, or by using a specially constructed impedance of this character which is symmetrical. The invention will be best understood by reference to the following specification:
Referring to the drawings, Figure 1 shows a transmitting station imrorporating the invention; Fig. 2 shows a modification of F 1g. 1; Fig. 3 shows a further modification. In these figures, 1 represents any suitable high: frequency generator of large power, such as is necessary for radio signaling. This generator is inductively connected by means of the transformer 6 to the antenna 7 which may be the usual elevated conductor, or any other suitable radiating system or energy transmitting or translating element.
In Fig. 1, there is shown in series with the Y secondary of the transformer 6 a thermionic amplifier 10 of the audion type having the usual heated element 12, grid 13 and plate 14k, the output circuit 12, 1 1 of the amplifier being connected to the antenna circuit. In parallel to this thermionic amplifier 10, is placed a similar amplifier 11 which has similar electrodes 15, 1.6 and 17. This amplifier 11, however, is connected in the reverse direction to 10. This reversal of direction is for the purpose of rendering the antenna system bilateral, in order that oscillations may take place in either direction, well known, positive current can flow only from the plate 14 to the filament 12, or from the plate 17 to the filament 15. .lonnected to the input circuit of the amplifier 10 is the tenna, is grounded in the usual manner at 18.
The operation of the system is as follows: High-frequency oscillations of uniform amplitude are generated by the generator 4,
and are impressed upon the radiating antenna. The amplitude of these oscillations is determined by the impedance or effective resistance of this antenna. If this impedance is varied or modulated in accordance with signals, the oscillations will be similarly modulated. When signals, or control impulses, are impressed upon the microphone 24, low-frequency currents of low power are impressed upon the input circuits of 10 and 11 by means of the three-winding transformer 20, 21, 22. The changes in the potentials of the grids 13 and 16 bring about a relatively large change in the impedance of these thermionic amplifiers, and accordingly the oscillations in the radiating system are modulated in the same manner.
Fig. 2 shows a modification in which the two amplifiers of Fig. 1 are combined in a single tube. In this case the plates 1.4 and 17 are unnecessary, and accordingly the thermonic impedance comprises merely a for, as is tube inclosing the heated electrodes 31 and 32, and the grids 33 and 34. In view of the fact that both 31 and 32 are heated elements, this device is bilateral, that is, current may flow in either direction. A threecoil transformer 40, 41 and 42 with, microphone 44 and battery 43 is connected to the input circuits in precisely the same manner as shown in connection with Fig. 1.
In view of the fact that theseimpedances shown have a very large resistance, there results the introduction of a large resistance into the antenna. A circuit arrangement by which this dilficulty is overcome is shown in Fig. 3. A winding of a transformer is introduced into the antenna circuit, and'the secondary of this transformer, consisting of a large number of turns, is connected by a circuit including a variable condenser 51 to such a modulating device as is shown in Fig. 2. It is obvious that in place of this modulating device the one shown in Fig. 1
' may be used in the arrangement of Fig: 3.
In using this transformer 50, the apparent resistance introduced into the antenna may be made ofany desired value.
In general, the antenna is tuned to the sending frequency, which is the frequency .of the generator 4 and the value of the current flowing in the antenna circuit will depend only upon the voltage impressed and the sum of the resistance of the antenna, the coil and the resistance introduced by the tubes.
the effective reslstance in the antenna circuit, which variation is due to the variations of the tubes. For complete modulation it is, therefore, necessary that the resistance introduced by the tubes be large enough to reduce the highv frequency current in this circuit to'zero when the low frequency input to the modulating device has its maxi-- mum negative val u e. It is also necessary for efficiency that the resistance of the tubes become very small when the low frequency output has its maximum positive value.
By complete modulation, as used above,
is such modulation that the maximum negative value of the low frequency input shall just reduce the modulated high frequency oscillations to zero amplitude. In this case the high frequency oscillations are just large enough to 'carry the maximum of the low frequency oscillations. lu other words, the picture of the low frequency oscillations, as shown in the envelop of the high frequency oscillations, just comes down to the zero line, having none of the picture cut off by this zero line, and, on the other hand. leaving none of the high frequency between the envelop and the zero line unused.
It is important that the transformers 20, 21 and 22 be so connected that both grids are at all times of the same sign with rcga rd In all the modifications shown, the. modulation is produced by the variation of to their respective filaments. When this sign is positive, the flow of electrons from filament to the corresponding to a decreased resistance of the tube to current in this direction. Current cannot, however, flow in the opposite direction in the tube. onsidering a half cycle of the high frequency in which the antenna is positive with respect to the ground, it is apparent that the current will, duringthis time,fiow through the tube 11 but not through the tube 10. When the antenna is negative with respect to the ground, current will flow through the tube 10 but not through the tube 11. The action of the positive part of the low frequency cycle being to make the grids positive with respect to the filament in both tubes, the high frequency currents will flow readily through the circuit which offers a low resistance to it. hen, however, the grids are made negative with respect to the fila-' ments, the current will be impeded in both tubes, giving the effect of an increased resistance in the antenna circuit. It is thus evident that the device will modulate the high frequency oscillations, and it is further evident that in order that both half cycles of the high frequency may be treated alike, it is necessary that the tubes 10 and 11 have the sameconstants. In the case of Fig. 2, the modulation is again effected by the introduction of a proper impedance in the antenna circuit. In this case, as well as in the other. it is necessary that the grids both take the same sign with regard to their respective filaments.
Although this invention has been described as being particularly adapted for wireless telephony, it is to be understood that it may be used equally well in, radio signaling of any kind or in ordinary telephony or wire signaling. In the ease of wire signaling the antenna is replaced by the usual transmission circuit.
lVhat is claimed is:
1. A source of substantially constant high frequency electromotive force, a circuit upon which substantially all of said electromotive force is impressed, a modulator comprisin two constantly operative asymmetric conducting devices connected in opposition in said circuit, signaling means controlling'said devices. substantially all of the current induced in said circuit by said electromotive force passing through said devices and means for transmitting the energy of said induced current.
2. In a wireless signaling system, a gem erator of high frequency high power oscillations, a radiating antenna connected therewith, two constantly active unilateral impedanccs cowluctively connected in replate will be made easier,
source of low frequency variations and means whereby said impedances are similarly controlled by said low frequency va-' riations.
3. In a wireless signaling system, a generator of high-frequency, high-power oscillations; a radiating antenna inductively connected therewith; two constantly active thermionic amplifiers of the audion type connected in reverse directions in said antenna and in parallel to each other and means for similarly modulating the impedance of said amplifiers in accordance with signalsto be transmitted.
4. In a wireless signaling system, a generator of high-frequency, high-power oscil-. lations; a radiating antenna inductively connected therewith; two constantly active thermionic amplifiers of the audion, type connected in reverse directions in said antenna and in parallel to each other and a telephone transmitter assoc'ated with said amplifiers, for modulating the oscillations .in said antenna in accordance with signals to be transmitted. i I
5. In =,a wireless signaling system, a generator of high-frequency, high-power oscillations; a radiating antenna inductively connected therewith; two thermionic amplifiers of the audion type, connected in "reverse directions in said antenna by means of the output electrodes and connected in parallel to each other a circuit containing a battery and a telephone transmitter, said circuit being inductively connected to the input circuits of the amplifiers, whereby the impedance f the antenna is varied in accordance with the signals to be transmitted.
6. In a wireless signaling system, a generator of high frequency high power oscillations, a radiating antenna connected there-. with, ing constantly active sources of electronstreams, said conductors being conductiv'ely. connected in reverse directions tosaid antenna and in parallel with each other, and means for impressing upon said sources similar variations in accordance with the signals to be transmitted.
7. In a wireless signaling system, a generator of high frequency high power oscillations, a radiating antenna connected therewith, constantly active thermionic impedances connected in reversedirections in said antenna and in parallel to each other, and means for impressing low frequency variations of similar phase upon said impedances, whereby the impedance of said antenna is varied in accordance with said low frequency variations.
8. In a wireless signaling system, a generator of high frequency high power oscillations, a radiating antenna connected therewith, two constantly active thermionic impedanccs connected in reverse directions in two asymmetric conductors compris said antenna by means of the output electrodes and connected in parallel to each other a source of low frequency variations adaptedto impress oscillations of similar phase upon said impedances, whereby the impedance of said antenna is varied in ac cordance with said low frequency variations. r
9. An antenna, two constantly active ther-' mionic inipedances connected in parallel in reverse directions between two points in and means for varying each.
said antenna,
impedance 'inaccordance with signals.
10. A circuit, two constantly active asymmetric impedances oppositely connected between the same points in said circuit, means for impressing a high frequency electrometive force upon said circuit, and means for transmitting to a work circuit, the energy of the resultinghigli frequency current flowing through said impedances in said circuit. 11. The method of-signaling comprising causing a high frequency current to traverse a constantly active, symmetrically conducting thermionic impedance, varying the value of said current by varying the magnitude of said impedance in signals, and transmittingtheenergy of said .varied current. I f i 1 12. A source of high frequency electrometive force, 'a circuit upon which substantially all of said electroinotive force ,is impressed, a modulator comprisingltwo constantly operative. asymmetric conductors connected in opposition in branches of said circuit, an
accordance with element in said circuit fOfllljlllZlIlg current therein, substantially all of the current" m- ..cluce(l in said circuit by said electromotive [force passing through said element and sai modulator, and signaling means controlling said modulator. a
13. In combination, means for supplying a high frequency electro-motive force, con- Ystantly active thermionic discharge means for symmetrically conducting electrical energy, a translating element and means connecting said electro-motiveforce supply means, said discharge means and said translating element in a series circuit.
14. In combination, means for supplying a high frequency current, an impedance device comprising two'constantly active asymmetric impedances' having the. terminals of the one respectively connected to unlike terminals of the other, .a translating element and means connecting said high frequency current supply means, said impedance device and said translating element in a series circuit.
l5. In a series circuit, symmetrically conducting means for permitting electrical energy to pass only by electron discharge, means for impressing an alternating electromotive force upon said circuit, means for varying the impedance of said conducting means substantially proportionally to the individual variations of speech currents,
and means for transmitting to a distant .oass by electron dischar e means for impressing a. high frequency electro-motive force upon said circuit, and means for varying the impedance of said conducting means in accordance with control currents.
17. In a series circuit, constantly active electron discharge means for symmetrically conducting electrical energy, means for im pressing a high frequency electro-motive force .upon said circuit, means for controlling theimpedance of said electron discharge means, and means for transmitting to a distant point the energy of the current traversing said electron discharge means.
18. In combination, a circuit, means for impressing a high frequency electro-motive force upon said circuit, a constantlyactive symmetrically gconduct-ing {thermionic impedance in series With said means, means for varying the magnitude of said impedance in accordance with control currents, and
means for transmitting the energy of the resulting current.
19. A circuit including a constantly active symmetrically conducting thermionic impedance, means in series with said impedance for impressing a high frequency electro-motive force upon said circuit,means for controlling the value of-said impedance in accordance with signals, and means for transmitting to a distant point the energy of t 1e current traversing said impedance.
In Witnesswhereof, I hereunto subscribe my name this fifteenth day of September RAYMOND A. YHEISING.
til
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