US2105849A - Phase modulation - Google Patents

Description

Jan. 18, 1938. G. Ussl-:LMAN

PHASE MODUL'ATION Filed Nov. 12, 1954 IAAAAA 'VVIIV Patented Jan. 18, 1938 UNITED STATES PATENT oFFicE Application November 12, 1934, serial No. 752,629

8 Claims.

This invention relates to a method of and means for impressing phase modulations on radio waves or oscillations for signaling purposes. In particular this invention relates to anim'- proved method of and means for accomplishing phase modulation by the use of a pair of tubes having their input electrodes connected in substantially push-pull relation toa source o-f carrier waves to be modulated, their cathodes modulated as to potential differentially by the modulating potentials, and their anodes connected in Y push-pull relation by a common output circuit. l In modulators of the priorV art it has been general practiceto apply the modulating potentials to the anodes or control grids or other grid or anode like electrodes. In the present invention by applying the modulating'potentials to the cathodes much of the distortionl inherently accomplished in modulators known heretofore is eliminated. This advantage and others will be apparent from the specication which follows.

The phase modulator of the present invention may also be readily altered to produce amplitude modulation in place of phase modulation. Moreover, the circuit arrangement of the present invention may be operated to produce phase read "in connection with the drawing in which' thefsin'gle figure shows for purposes of illustration only a phase modulator circuit arrangement including the features essential to my invention. It will vbe understood-that the arrangement 'shown may be departedfrom considerably' without de'- parting from the spirit of the `present invention.

The phase modulator stage comprises a pair ofr thermionic tubes V1 and V2. The control grids of the tubes V1 and V2 are connected as shown by way of phase shifting reactances L and C and stopping condensers land 2 respectively to an'I inductance in a tuned resonant circuitA whichy maybe coupled to any source of carrier wave oscillations. Preferablyl the tuned circuit A is connected as shown to a source of oscillationsv O.

The control grids of the tubes V1 and V2 are con- `v`nectedto the electrical center of the heating circuits for the cathodes F1 and F2 by Way of re-l sistances R1 and R2 respectively as shown. The anodes ofthe tubes V1 'and V2 are connected in push-pullfrelation to a tuned tanlrcircuit B- comprising an inductance 6 and a variable condenser arrangement'i."'Condensers l, 2,3, and 4 are direct 'current blocking condensers. Condensers 3 `and 4 are connected as' shown between the cathode ends ofresistances R1 and R2 and ground respectively. `The"lectrical centers of the filamerits F1 and F2 are"connected as'shcwn to the Vterminals of a secondary winding W2 of a transformer-T1. lThe primary winding of the trans` former'T1 may b'e connected as shown by a switch Sito the source ofsignal' modulations E. A resistor R3 is connected across/thesecondary winding'of the transformer T1. The center tap of resistor R3 and'winding W2 of transformer T1 is connected tothe anode of an additional thermionic tube V3 and to a contact associated with switch S2.` The electrical center of the cathodey F3' of tube V3 is connected to ground. The grid of y tube V3 is connected to a biasing source I by Way of the secondary 'winding W4 of a transformer T2. The primary winding Wa of the transformer T2 is connected to a contact which also cooperates with the switch S1. The 'contact member of the switch S1 is of suiiicient length to complete either or'both of thel primary winding circuits. The switch S2 when closed short circuits the impedance between the anode and cathode" of the tube V2. The anodeipotential forthe tub'es`V1 and V2 is supplied by way of a plate rectifier D having its positive terminal connected to thevelectrical center of the inductance 6 and its negative terminal connected to ground and tothe electrical'ce'nter of the cathode F andinov the movablec'ontact of switch S2. In 'pointing'outthe operation of the device it will rsrt blassumed that oscillator O is supplying powerl at' constant frequency' to the circuit A; Oscillations will` be set up in tank circuit A, the tuning or response of vwhich is determined by the inductance and capacitythereof. Excitation voltage at constant frequency will be supplied from the Ycircuit A through inductance Land condenser C to the grids of' tubes V1 and V2 respectively in substantially phase opposition or in push-pull fashion.' However, the phaseof the voltage excitation appliedhtol the 4grid of modulator'tube V1. willfbe retarded to some extent by the inductance Lwhilethe phase of the voltage excitation applied to the grid of modulator tube V2 willfbe advanced to some extent by the capacity C.` 'I'he amount of retardation and advancement in the' phase of the excitation applied to the grids of these ftubesrrifayv be varied and will dependup'on thev retarding or inductive value'giyen to the inductanceli and the' 'advancing or capaci,-

tive value given to the condenser C and also on the value of the resistors R1 and R2 respectively. The impedance in each side of the grid circuit should be balanced, then if modulator tubes V1 and V2 have the same direct current bias on their control grids, which is the case when no modulation energy is supplied from E, the power supplied by each modulator tube to the circuit B will be equal and the potential oscillations in circuit B willhave a constant phase which will coincide with the average phase position of the excitation voltage.

Now, if we assume that audio frequency modulations are produced in E and applied through the transformer T1 by way of switch S1 to the cathodes F1, F2 of tubes V1 V2 respectively, the bias applied to the said cathodes will vary in phase opposition and the tubes having the lower bias at any particular instant will supply the most power to the circuit B. Since the radio frequency excitation to the grids of the two tubes V1 and V2 respectively has a phase difference, the power supplied to the circuit B by the anodes of the two tubes V1 and V2 willV have a phase difference. The phase of the oscillations appearing in circuit B will change or approach that of the tube supplying the most power. The amount of phase change in the circuit B will be substantially proportional to the difference in power delivered by the tubes V1 and V2 to the circuit B. It is obvious however that there may be no greater phase shift in the circuit B than there is phase diiference of excitation applied to the grids of tubes V1 and V2 respectively.

When the device is operated as described above, to accomplish phase modulation, the switch S1 is moved to a position suchthat the winding W1 only is energized. The switch S2 is preferably closed to short circuit the impedance between the anode and cathode of V3 so that this tube impedance is not included in the anode-cathode direct current circuit of the tubes V1 V2.

When the device is to be used as an amplitude modulator the switch S1 is moved into a position such that the winding W3 of the transformer T2 only is energized. Switch S2 is now open. The anode and cathode impedance of Va is now connected in series with the direct current anode-cathode circuit of tubes V1 V2. Ihe amplitude modulating potentials are applied from the anode of V3 in phase or co-phaseally to the cathodes F1 and F2. Due to this co-phaseal application of the modulating potentials and substantially anti-phaseal application of the carrier wave potentials to the tubes V1 V2, carrier frequency waves of substantially constant phase and of variable amplitude will be produced in the circuit B from which they may be utilized.

A combination of phase and amplitude modulation may be accomplished by moving the switch S1 in a position such that modulating potentials are supplied to both primary windings W1 and Wa. In this case the switch S2 is moved into an open position so that the impedance between the anode and cathode of V3 is included in the direct current anode circuit of tubes V1 V2. Now modulating potentials are applied in push-pull and in phase to the cathodes F1 and F2 while carrier wave oscillations are applied in substantially phase opposition by inductances L and C. The output energy in B will be modulated as to phase and as to amplitude simultaneously in accordance with the modulating potentials.

The output circuit B may be tuned to the fundamental frequency or to an harmonic thereof. The circuit B may b cii'pied to any ioad circuit but is preferably coupled to a radiating circuit by way of an amplitude limiter or an arnplier `or a frequency multiplier or one or more of said devices.

Where necessary, the anode to cathode capacity of tubes V1 and V2 may be neutralized as shown by neutralizing condensers N1 and N2 as shown. My invention contemplates the use of any known type of tubes. All that is essential is that the tubes include at least the three electrodes. Where screen grid tubes are utilized the neutralizing capacities N1 N2 may not be neces-- sary.V

In any event, the biasing resistances R1 and R2 serve the double purpose of effecting the phase of the radio frequency potentials applied to the control grids and also as a means for supplyingl biasing potentials to said control grids.

When the device is operated as a phase modulator, the phase modulated energy appears in the tank circuit B but the amplitude modulated component is balanced out.

When the device is operated as anamplitudef gized by modulating'potentials, said transformerv having a secondary winding, a connection between a point on the secondary winding of said transformer and a point on one of said impedances, a connection between another point on the secondary winding of said transformer and a point on the other of said impedances, an additional electron discharge device having an anode,'a cathode and a control electrode, a circuit including 2, source of direct current potential and the anode to cathode impedance of said additional electron discharge device connecting, the anodes of Said'pair of tubes to the cathodes of said pair of tubes and a circuit for applying modulating potentials to the control grid and cathode of said additional electron discharge de vice to produce additional modulation of thecarrier wave of a different character in said pair of tubes.

2. A phase modulating means comprising a pair of electron discharge tubes each having an anode, a cathode and a control grid, a circuit adapted to be energized by oscillations of carrier wave frequency, phase changing means connecting different points on said circuit to the control grids of said tubes, a tuned circuit connected between the anodes and cathodes of said tubes, resistive means connecting the control grid of each tube to the cathode of the respective tube,

a source of modulating potentials connected inl y carrier wave frequency, phase shifting means connecting different points on said circuit to the control electrodes of said tubes, a source of modulating potentials, and switching means and circuits for applying modulating potentials from said source in phase opposition to the cathodes of said tubes or in phase to the anodes of said tubes, or both in phase opposition to the cathodes of said tubes and in phase to the anodes of said tubes.

4. In a signalling system, a source of oscillations, a pair of thermionic tubes each having an anode, a cathode and a control electrode, connections between different points on said source of oscillations and the control electrodes of said tubes, a phase shifting reactance in each of said connections, a circuit connecting the anodes of said tubes in push-pull relation, a source of modulating potentials, a biasing and phase shifting impedance connected between the control electrode and cathode of each tube, and transformer means for impressing the modulating potentials from said source in phase opposition on the terminals of said impedances adjacent the cathodes of said tubes, to vary the potential of said cathodes oppositely in accordance with signals to thereby vary the amount of energy supplied by each of said tubes to said circuit.

5. In a phase modulation system, a pair of thermionic tubes each having an anode, a cathode and a control electrode, a symmetrical circuit adapted to be energized by oscillations of high frequency, phase shifting means of unlike character connecting points of high frequency potential on said circuit to the control electrodes of each of said tubes to excite the same in phase displaced relation, a biasing and phase shifting impedance connecting the cathode of each tube to the control electrode of the same tube, neutralizing means coupling the anode of each tube to the control electrode of the other tube, an alternating current circuit connecting the anodes of said tubes in push-pull relation, and a source of modulating potentials connecting the cathodes of said tubes in phase opposition to vary thepotential of said cathodes oppositely in accordance with modulating potentials to thereby vary the amount of energy supplied by each of said tubes to said alternating current circuit.

6. In a transmitting system, a source of oscillations of carrier wave frequency, a pair of electron discharge tubes each having an anode, a cathode, and a control electrode, separate circuits connecting said source of oscillations substantially in phase opposition to the control electrodes of each of said tubes, phase shifting means in each of said circuits, a circuit connecting the anodes of said tubes in push-pull relation, a source of modulating potentials, an impedance connected to said source of modulating potentials, connections between different points on said impedance and the cathodes of said tubes to apply modulating potential in phase displaced relation from said impedance to said cathodes, a phase shifting and grid biasing impedance connecting the c-ontrol electrode of each tube to the cathode of each tube, and a connection including a source of potential between the cathodes of said tubes and the anodes of said tubes.

7. In a signalling system, a source of carrier wave oscillations, a pair of electron discharge tubes Ieach having an anode, a cathode, and a control electrode, circuits for applying oscillations from said source in substantially phase ropposition to the control electrodes of said tubes, an alternating current circuit connected to the anodes and cathodes of said tubes, a direct current circuit connected to the grid and cathode of each tube, a, circuit for impressing modulating potentials in phase opposition on the cathodes of said tubes, and a circuit for impressing modulating potentials on the anodes yof said tubes.

8. In a signalling system, a source of oscillations of carrier wave frequency, a pair ci electron discharge tubes each having an anode, a cathode, and a control electrode, phase shifting reactances of different character for applying oscillations from said source to the control electrode of eachV of said tubes, an output circuit connected to the anodes and cathodes of said tubes, neutralizing means interconnecting the anodes and the control electrodes of said tubes, a circuit for impressing modulating potentials on the anodes of said tubes, and a circuit for impressing modulating potentials in phase opposition on the cathodes of said tubes.

GEORGE LINDLEY USSELMAN.

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