US2294372A - Phase modulation - Google Patents

Description

Span l, 19.42. Y 1'.. E. BARTON 2,294,372

PHASE MoDULAT'IoN Filed Oct 31. 1941 -Ffa 1.

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Er mm) 3nventor Loy Barton Cttorneg Patented sept. 1, 1942 [BASE MODULATION Loy Barton, Collingswood, N. J., as'signor to Radio Corporation of America, a corporation of Delaware Application october' vr31, 1941, serial No'. 417,385

s claims. `(ci. 17g-171.5)

My invention relates to radio transmitters or the like and, particularly, to the art of Yphase modulating or frequency modulatinga Ycarrier wave.

An object of the invention improved method of and means for phase modulating or frequency modulating a carrier wave.'

A further object of the invention is to provide a simplified circuit for phase modulating the output of a stable oscillator.

A further object of the invention is to provide an improved method of and means for shifting the phase of ka carrier wave over a wide angle. v

In a preferred embodiment of the invention, the output of acrystal oscillator or the like is ^applied to the input circuit of a modulating tube through a phase shifting circuit including a condenser andA to the plate circuit of the tube I through a resistor, the said resistor and the plate to ground capacity of the tube forming a second phase shifting circuit. The rst phase shifting is lto provide an the plate side of the tuned circuit I3 and ground. The resulting lagging voltage appearing across the condenser CI is applied through a coupling `condenser 26 to the control'gr'id I8 of the modulator tube. Since the tube produces a phase shift of 180 degrees, this voltage appears at the plate 22 as a leading voltage y(an inductive component).

. Carrier wave current from the oscillator is also fed through a resistor R2 and the plate capacity C2, these two impedances also being in series with each other and connected between the plate side of tuned circuit I3 and ground. Thus a capacitive component appears across C2.

The audio signal or other modulating signal is applied to one of the grids of the modulating tube I6. It preferably is applied to the control grid I8 through grid resistors 21 and 28.

The tube I6 is biased by means of a cathodel circuit introduces an inductive reactance into the Y plate circuit of the tube since the tube produces a 180 degree phase shift. The negative bias on the modulating tube is adjusted to obtain onehalf useful conductance. Upon the -application of a modulating signal, if it makes the tube more conducting, the inductive componentA becomes more effective in shifting the phase of the carrier wave and, if it makes the tube less conducting, the capacitive component becomes more effective. Thus, a maximum phaseshift ofvnearly 180 degrees is possible.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure luis a circuit diagram ofv one embodiment of the invention, and

Figure 2 is a vector diagram that is referred to in explaining the invention.

Referring to Fig. 1, the invention is shown applied to a radio transmitter in which the carrier wave is produced by a stable oscillator I0 comprising a vacuum tube II which has af piezoelectric crystal I2 in its input circuit and a tuned circuit I3 in its plate circuit. A by-passccndenser is indicated at I 4.

The modulator tube is\shown at 16 as a pentode, by way of example, havinga cathode Il, a control grid I8, a screen grid I 9,- a suppressor grid 2|, yand a plate 22. 'I'he plate to ground capacity of the tube I6 is indicated atlC2.

'Carrier wave current from the oscillator is fed through a resistor RI and a condenser CI which 'plate 22 of the modulator tube by the voltage denser 3i, to obtain one-half the useful mutual conductance of the tube when no signal is being applied. As shown in Fig. 2, with this adjustment, the reactive voltage Eer produced at the drop across condenser CI balances the reactive voltage Een produced by current flow through the capacity C2; thus the carrier wave voltage Eiat plate 22 is in phase with thevoltage across tuned circuit I t. I

Thevaction when the modulating signal is applied is as follows: If the signal makes the control grid IB less negative, the output voltage of the modulator tube decreases and shifts towards Erima). When the grid I8 is made more negative by the signal, the `output voltage also decreases, but shifts towards Enma). Thus, a limit of a plus or minus QO-degree phase shift is possible. v

The linearity of the shift in phase with changes in control grid voltage is determined to a large extent by the proper choice of resistance for resistor R2 and the tube characteristic. In general R2 should have` a resistance which is large compared with the reactance of the capacity C. Also, resistor RI preferably has high resistance compared with the reactance of C'I so that the network RI--CI will, like the network R2-C2, produce vsubstantially a degree phase shift. I

I claim asmy invention:

1.\In combination a source of carrier wave ento said anode, a phase shifting network con,-

are connected in series with each other'between 55- nected between said sourceand the input circuit 2 aaagsra off said tube. saidphase shifting network being v designed to produce a phase-shift at said anode that is opposite `tol the phase shift produced thereat by said resistor and said capacity to ground, means for varying the mutual conduct,

ance of ,said tube in accordance with a 4modulating signal, and means for coupling said anode toa signal transfer circuit.

2. The invention according to claim 1' wherein y nected in series with each other and between ground and said point on said source, said control grid being connected to the junction point of said second resistor and condenser, means for varying the mutual conductance ,of said tube in accordalice with a modulating signal to produce a phase modulated signal at saidA anode, and means for coupling said anode to a' signal transfer circuit.

4. In combination, a stable oscillator having an output terminal, an electric discharge tube comprising a control grid and an anode, said anode having capacity .to ground, a resistor connecting said terminal to said.anode, a second resistor and a condenser connected in series with each other and between saidterminal and ground, said control grid being connected to the junction point of said second resistor and condenser, means for varying the mutual. conduct ance of said .tube in accordance with a modulating signal, andmeans for coupling said anode to a signal transfer circuit.

5. In combination, a stable oscillator having an output terminal at which appears a carrier wave of constant frequency, an electric discharge vtube comprising a control grid and an anode,

said anode having 'capacity to ground, a resistor connecting said terminal to said anode and' having a'resistance which is large compared with the reactance of said capacity latsaid constant frequency, a secondresistor and. condenser connected in series with each other and between said terminal and ground, said second resistor having a resistance that is large compared with the reactance of said condenser atv said frequency,

said control grid being connected to the junction point of said second resistor and condenser",`

.means for varying the mutual .conductance of said tube in accordance with a modulating signal,

,and means for coupling said anode to a signal transfer circuit. i

- LOY E. BARTON.

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