US2007099A - Modulation - Google Patents

Description

July 2 1935. G. L. ussELMAN MODULATION Filed Sept. 16, 1932 GEORGE L. lELMAN A'TORNEY INVENTOR Patented July 2, 1935 MODULATION George Lindley Usselman, Port Jeerson, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application September 16, 1932, Serial No. 633,431 zzfclaims. (ci. 17o- 171) This invention relates to signalling means and in particular to'I means whereby the characteristics of high frequency oscillations other than amplitude are varied in accordance with signals '-5 to be transmitted.

' It has been found that ordinary amplitude modulated highfrequency'oscillations in transmission from the sending station to the receiving station are subject to what is known as fading effects. In particular, "the transmission of telegraph signals in the pastwas attendant by detrimental fading at thev receiver Where the diversity receiving system was not in use. This is a decided disadvantage since it introduces dropouts and errors in the signal. It lwas Alater found that if the frequency band of the transmitted signal Were spread out or made wider the effect of this fading Was reduced.

` In the prior art the carrier frequency band was made Wider by modulating the amplitude of the carrier energy at some desirable rate, usually in the neighborhood of 500 cycles per second. This produced side bands at, say," 500 cycles above and-500 cycles below the carrier frequency. The signal band was in this case 1000 cycles wide. Amplitude modulation of a telegraph transmitter `makes it necessary to reduce the power output' to a great extent.

It has been found that the carrier can be modulated in phase to spread thefrequency band of the transmitted signal. This produces side bands on each side of the carrier frequency, which also reduces the effects'of fading at the receiver. Y

I have found that if the high frequency oscillations are modulated in phase or in frequency in accordance Withv the telegraph signal to be transmitted they are less subject to the effect of fading than amplitude modulated Waves, assuming like amounts of power are utilized in the transmission. Also the reason Whylphase or frequency modulated oscillations in telegraph transmission are subject to a less extent to fading efffects than oscillations modulated otherwise is that a greater amount of the transmitter -power is available for transmission. In other Words, a transmitter can operate at full power with phase or frequency modulated telegraph signals, While it is necessary to reduce the power output to labout one quarter-for amplitude modulation of the same signals If We assume equal power output, reduction of fading should be slightly'greater Where the oscillations are modulated in phase or frequency than when they are modulated otherwise.

l' When a high frequency carrier is modulatedA in phase or frequency in accordance with telegraph signals, such modulation of the-,carrier is usually accomplishedfin a stage following the carrier frequency generator; which is usually a crystal control oscillator, or a long linerrcrystal control oscillator, or any other kind of oscillation generator. Furthermore, the keying of the trans'- mitter in accordance With the telegraphy signals,

is usually accomplished in a stage subsequent to the modulator stage. Any standard method of keying may bev used.

'In each of my United States applications, Serial No. 623,558,'led July 20, 1932, serial'No. 616,026, filed June 8, 1932, Serial'No. 602,487, filed April 1, 1932, and Serial No.v 607,932, filed April 28, i932, I have shown means for varying at signal frequency the characteristics other than the amplitude of a carrier frequency. In each of these arrangements the carrier frequency is impressed through phase shifting Vmeans on the control grids of a pair of 'thermi- Yonic tubes which have their anodes connected inV parallel-to a common tank circuit and their internal impedances varied in phase opposition by the signal wave. In each of these arrangements the phase modulator stagel comprises two tubes having their input electrodes symmetrically connected `and energized as indicated above, and a common tank circuit connected in parallel to the anodes of said pair of tubes.l

In my United States applications Sen No. 633,955, filed September' 20, 1932 and Ser..No. 637,923, filed October 15, 1932, I have shownimproved transmitters of the type referred to above. more thermionic tubes are used to accomplish phase modulation of the carrier frequency.

The present invention relates to an improved and simplified modulating means by which the characteristics of a carrier Wave other than amplitude maybe variedv at any desirable frequency to be transmitted by the use of a single thermionic tube. 1

More in detail, this invention relates tov an improved modulating means to reduce fading in a signal wherein the modulator stage comprises a single tube having a control grid coupledjalternately to a source of high frequency oscilla- An apparent advantage to be gained by the use of the present invention results fromthe In each of these transmitters one or fact that the carrier frequency and modulating Waves are applied to the thermionic modulator through a purely mechanical means of simple and durable nature. This results in low rst cost and economic upkeep.

The novel features of my invention have been pointed out with particularity in the claims appended hereto.

The nature of my invention and the operation thereof will be best understood from the following detailed description thereof and therefrom when read in connection with the drawing, throughout which like reference numerals indicate like parts, and in which:

Figure 1 illustrates a specific embodiment of the invention; ywhile,

Figures 2 and 3 illustrate a detail and a modication of the arrangement of Figure l.

The practice in prior art has been to use vacuum tubes to shift the phase in a phase modulator stage to phase modulate a telegraph transmitter. To reduce fading in telegraph signals by phase modulation it is only necessary to modulate the phase of the carrier frequency 4of the transmitter at some desirable but uniform frequency, usually between 300 and 1000 cycles per second. The'present invention does this simply with a phase splitting circuit and a motor driven rotary condenser. The way in which' this is` accomplished is described below in connection with the drawing.

A specific embodiment of my invention is shown schematically in Figures l, 2 and 3. Referring to Figure l, the motor A drives the shaft S of rotary condenser C-XC through the insulated shaft coupling Y. The upper part C of the rotary condenser is connected to the grid G of tube V through the phase shifting inductance coil D while the lower part of the rotary condenser is connected to grid G of tube V through the phase shifting capacity or condenser E. Tube V is shown as the screen grid or four element type, but by using a neutralized circuit a three element tube may be used.

vDirect current biasing potential for the grid G of tube V is supplied by way of choking inductance Q (a resistor may be used if preferred) from a potentiometer 5 connected as shown in parallel with a portion of source I 0. A low impedance path for alternating currents passing through Q is provided by condenser 6 connected as shown between Q and the grounded lead of the heating circuit for cathode F. Alternating current in tank circuit YM is shunted around source l0 by means of a by-pass condenser 8 connected as shown. Charging poten- ,tial for the screen electrode I2 of tube V is provided by a lter circuit comprising a lead 8 tapped to a point on potentiometer resistance I4 and a condenser connected as shown.

The output of tube V and tank circuit M is connected by a line R to stage N, which may be a limiter, a frequency multiplier, an amplier, or all three combined. Stage N is coupled to stage O by lines S-S. Stage O may be a frequency multiplier, an ampliiier, or both. The output of stage O is connected to a load circuit, which is the transmission line and antenna P in this case. The oscillator B is connected to therotatable element X of the rotary condenser by the sliding contact Z which rests on the element which rotates the plates X.

Figure 2 shows an end view of the rotary condenser used in the modulator of Figure l. As shown here, the `movable plates X, which are connected with the high frequency oscillator, are driven by an element S relative to the xed plates C' and C. The plates C and C are conductively connected as shown to the phase shifting elements D and E respectively.

The transmitter keying means has not been shown but it may be keyed or modulated by any of the well known methods. The modulating or keying of the energy may be accomplished in any stage following the phase modulator, as indicated in the drawing.

The operation of the phase modulator will now be set forth. In the following statement cf the operation assume that the motor A is driving the shaft S and the rotating element X of the rotary condenser X-C-C at a speed to give the desired rate or frequency of phase shift or modulation. We may assume this speed gives, say, 50) cycles per second modulation. If the oscillator B is delivering constant high frequency energy, say 2,000,000 cycles per second to X by way of contact Z and the shaft S of the rotary condenser, the two stationary halves C' and C will become excited with high frequency energy alternatingly at a rate of 500 cycles per second (assumed). The insulator Y prevents this excitation from B from escaping to ground through the motor A. The excitation from C passes to the grid G through the phase retarding inductance D. The excitation from C passes to the grid G through the phase advancing capacity E. Since C and C are alternately excited at a 500 cycle rate, the phase of the high frequency excitation reaching the grid G will be retarded and advanced in phase at a 500 cycle rate. Consequently the phase of the carrier frequency transmitted or radiated by the antenna will be phase modulated at a 500 cycle rate or at a rate determined by the speed of the rotary condenser C-X-C. Amplitude limiters or frequency multipliers may be used in the transmitter before the signal is finally amplified and radiated by the antenna. Consequently the signal characters radiated from the transmitter will be modulated in phase at the assumed 500 cycle rate.

The operation of the rotary condenser is simply to capacitively couple the oscillator B alternately to the excitation phase retarding element D and the excitation phase advancing element E, from which elements the excitation energy is conducted to the grid G of tube V. The anode current of tube V causes the oscillations in tank circuit M to be phase modulated and from this circuit the radio frequency in the following stages of the transmitter is phase modulated at a regular rate. The carrier energy of the transmitter may be keyed or modulated by the signal with any suitable means before it is radiated by the antenna. This keying or interrupting of the phase modulated carrier energy may be accomplished in any stage of the transmitter. Preferably, keying, modulating, or interrupting of the phase modulated carrier is accomplished in any stage subsequent to the modulator stage. For example, this operation may be accomplished as indicated either in stage N or O.

When it is desired to obtain a higher modulating frequency without increasing the speed of the motor A an arrangement as shown in Figure 3 may be used. In this compound rotary condenser of Figure 3 the rotatable element X takes the form of a disk with teeth fastened to the pe riphery of the rotating disk which is mounted on a shaft S for rotation by themotor A. The plates C, C are "mounted adjacent the pathof rotation of the teeth of X so that the capacity between the disk X and the plates C', C alternately increase and decrease. Thisalternate increase and decrease ofV coupling is Ytransferred by way of phase shifting means D and C to the control electrode G of tube V, the same as 'in Figure l. Due to the fact that.v there area plurali'ty of teeth X on the disk 14, a lsingle rotation of the shaft S alternately Vincreases and decreases. the coupling lbetween the lrotatable disk I4 and the fixed plates C', C anumber of times. The capacity X-C-C' maycomprise a single disk X and single platesC', Cor a plurality of disks X and a pair of xed plates C', C located adjacent the periphery of each of the disks X so that the coupling between the disk X and the plates C', C will alternately increase and decrease as the teeth` of the disk X move toward the iates-CQ C.

Having thus described my invention and the operation thereof, what I `claim is:

` 1. Phase modulating means comprising la source of high frequency oscillations, a-fthermionic tube, a rotatable condenser, a connection between one armature-of said condenser and the control electrode of said tube, a connection `between the other armature of said condenser and said source of high frequency oscillations, and a motor for rotating said condenser at a modulating frequency rate.

2. Phase modulating means comprising a sourceof high frequency oscillations, a thermionic tube, parallel variable capacities connected in series between the control, electrode of said tube and said high frequency oscillation source, and means for varying said capacities in opposite sense at a modulating frequency rate.

' 3. Modulating means comprising a source of high frequency oscillations, a thermionic tube, parallel variable condensers connected in series between the control electrode of said tube and said high frequency oscillation source, and means for alternatelyV increasing and decreasing the capacity of said condensers atv a modulating n frequency note.

control electrode of said tube, and mechanical means for coupling said conductors to said' source of oscillations and for changing ythe value of the coupling between the respective conductors and said source betweenr predetermined maximum and minimum values in a complementary sense. v

6. Modulating means comprising a thermionic tube, a work circuit connected between ythe output electrodes of said tube, a pairl of paths of different electrical characteristics connected to the control electrode of said tube, the other terminals of said paths'being connected tothe statorplates oi a condenser, a source of high fre- "of, said condenser, andfmeans for rotating the vrotatable plates of said condenser at a rateof the order of 1an audible frequency.

7. Signal modulating means comprising -a source oi high frequency oscillations, a thermif' .onicrelay tube, Va tuned circuit connected ,be-

tween the output electrodes of said tube, a pair of paths, of different `electrical characteristics connected to the control electrode of said tube,

`the otherterminals of said paths being connected :to the stator plates of a condenser havingtwo stators and a rotor, means for connecting said source of high frequency oscillations to the r0- tor plates of said condenser, and means for rotating the rotatablefplates of said condenser.. Y;

8. Signal modulating means comprising ra source of high frequency oscillations of constant frequency, a thermionic tube, a tuned tank circuit connected between Vthe output electrodes of said tube; a pair of paths connected-to the control electrode -of said tube, one of said paths including a phase retarding element, the other of said paths including a phase .advancing element, means for connecting the other terminal of each of said paths ,to a stator of ay condenser having two stators and ya rotor, means for connecting said source of high frequency oscillations to .the rotor of said condenser, and means for rotating the rotor. of said condenser at a desired modulating frequency rate.

9. Signal modulating means comprising a thermionic tube having input and output electrodes, a work circuit connected to the output electrodes of said tube, a pair of transmission channels of different electrical characteristics connected to Ythe input electrode of said thermionic tube, a

compound condenser comprising a pair of fixed plates'anda set of rotatable plates, aconnection between each of said transmission channels and one of said iixed plates, a source of high frequency oscillations connected to said rotatable plates, and means forY rotating said rotatable plates at a desiredfrequency rate.

10. The combination of a frequency multiplier, a thermionic relay tube having its output electrodes connected thereto, a compound condenser comprising a .movable plate, a pair of fixed plates, reactances of different character' lconnecting said fixed plates to the input elec-v trodes of said thermionic relay tube, said movable plate being .adapted to be rotated at a rate equal'to an audible frequency, and a high frequency oscillator connected to said movable plate. f.

11. Phase modulating means comprising in combination a thermionic tube, a variable capac- Y ity having a pair of Xed elements and a rotatable element, said fixed elements each being connected through series reactances to the input electrodes of said tube, a source of high frequency oscillationsconnected to vsaid rotatable element, `and means .for driving said rotatable element. i

, l2. The combination of afrequency multiplier, an amplitude limiter connected thereto, a thermionic tube having its output electrodes connected to said limitera 4condenser comprising a pair of fixed plates: connectedto the input electrodes of saidthermionic relaytube said Vcondenser also comprising a rotatable plate of mechanical means for Vrotating said ,rotatable plate, and a high'frequency oscillator connected to said rotatable plate.

13. Signal modulating'. :means comprising a quency oscillations connected to the rotor plates: -themoll tube having input and Output 2160-775 trodes, a tank circuit connected to the output Ielectrodes of said tube, a pair of `transmission channels connected to the input electrode of ksaid `thermionic tube, one of said channels being lcalgzacitive inv character, the other of said chan- -nels being inductive in character, acondenser comprising a pair Vof fixed plates and a movable plate, a connection between each of said transmission channels and one of said fixed plates, a source of high frequency oscillations connected to said rotatable plate, means for vrotating said rotatable yplate at a low frequency rate, means -for .tuning said tank circuit to a frequency which is a multiple of the frequency of said source, and means for keying or modulating the resulting phase modulated high frequency energy at signal frequency.

14. Signal .modulating means comprising a thermionic tube having input and output yelectrodes, a tank circuit connected to the output electrodes of said tube, a pair of transmission channels `connected to the input electrode of said thermionic tube, one of said channels being capacitive in character, the other of said chanfrequency, and radiating means coupled to said .tank circuit.

15. Wireless telegraphy means comprising a source of high lfrequency oscillations, means for wobbling the phase of said oscillations comprising a. vthermionic tube, said tube having input .and output electrodes, capacities connecting the input electrode of said tube to said source of high frequency oscillations by way of reactances of unlike character, means for varying said capacities at a rate equivalent to an audible frequency and keying means connected with the output of said tube.

16. Telegraphy signalling means comprising, a thermionic tube having input and output electrodes, a pair of conductors of diierent electricalcharacteristics connected to the input electrode of said tube, means for applying high frequency oscillations to said conductors, said oscillations being alternately applied at a rate equivalent to an audible frequency, a work circuit coupled to the output electrodes of said tube, and keying means interposed between said vwork circuit and the output electrodes of said tube.

17. Telegraphy means comprising a thermionic tube having rinput and output electrodes, a pair of conductors of different electrical characteristics connected to the input electrode of said tube, means for alternately applying high frequency oscillations to said conductors, said oscillations being alternately applied at low frequency rate, a tank circuit connected between Vthe output electrodes of said tube, said tank circuit being tuned to a multiple of the frequency ofthe applied high frequency oscillations, a utilization circuit, and relaying means includin keying means connecting said tank circuit to said utilization circuit.

, .18.111 a telegraph .transmitter 'the .combina- Vacca-co9 tion of, phase modulating means, frequency multiplying means and amplifying means coupled thereto, said phase modulating means comprising Aa thermionic tube having input and output electrodes, a pair of conductors of different electrical characteristics connected to the input electrode, means for alternately applying high frequency oscillations to said conductors, said oscillations being applied at a low frequency rate, and means coupled to the output electrodes of said tube for keying or modulating the phase modulated carrier energy in accordance with the signals to be transmitted.

19. Signal modulating means comprising, a thermionic tube having an output circuit con nected between its output electrodes and a direct current circuit including an impedance and a source of potential connected between its input electrodes, a condenser comprising a pair of xed plates and a stator plate mounted adjacent said xed plates, a motor and a source of high frequency oscillations connected to said stator plate, a capacity having one terminal vconnected to the control grid of said tube and an inductance connecting the other terminal of said capacity to one of said xed plates, and a capacity connecting said other terminal of said condenser to the other fixed plate of said condenser.

20. Signal modulating means comprising, a thermionic tube having an input electrode, a pair of high frequency conductors of different electrical characteristics connected to the input electrode of said thermionic tube, a compound condenser comprising a pair of xed plates and a movable plate, a connection between each of said transmission lines and'one of said fixed plates, a source of high frequency oscillations connected to said movable plate, and means for moving said movable plate relative to said fixed plates at a modulating frequency rate.

21. A transmitting system comprising a source of high-frequency oscillations, an inductive circuit for said oscillations, a capacitive circuit for said oscillations, means to continuously (cause, alternately, maximum energy to flow from said source through said circuits, means combining the energy fiowing through said circuits, said combined energy being in the form of oscillations continuously varied in phase, means to impress a signal to be transmitted upon said phase-varied oscillations, and means for transmitting said oscillations bearing said phase variations and said signal.

22. In a transmitter for reducing fading effects, a source of high-frequency oscillations, aninductive circuit, a capacitive circuit, each of said circuits being connected to said source, means for increasing the iiow of oscillations from said source through said inductive circuit while decreasing the flow of oscillations from said source through said capacitive circuit, and for decreasing the flow of oscillations from said source through said inductive circuit while increasing the flow of oscillations from said source through said capacitive circuit, means for combining the oscillations ilowing through said circuits whereby said combined oscillations form oscillations continuously varying in phase, means for amplifying said oscillations varying in phase, means for impressing a signal on the amplified oscillations, and means for transmitting said oscillations bearing said signal.

`GEORGE LHTDLEY USSELMAN.

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