US2001107A - Phase modulating system - Google Patents

Description

May 14, J. sAwA 2,001,107

PHASE MODULA TING SYSTEM Filed July 31, 1934 FIG.

INVEN TOR J. 05A WA A r romysr Q ing the operation of the system of Fig. 1.

Patented May 14, 1935 a i I w 2,001,107

UNITED STATES PATENT OFFICE 'Juichi Osavva, Mita, Shibaku, Tokyo, Japan, assignorto Western Electric Company, Incorporated, New York; N. Y., a corporation of New York 7 Application July 31, 1934, Serial No. 737,696 I H In Japan August 24, 1933 I 6 Claims. (Cl. 179-171) This invention relates to modulating systems with sections 6 and 1 andmidpoint 8. A feedandparticularly to those in'which the phase of back transformer 9 has one winding connected 2. carrier wave is varied in accordance with to the grid of tube I and the other connected signals. I I between the plate and cathode of tube I through 5 The general object of the invention isto transaseries tuning condenser I0. A signal source II 5 latea signal wave into a succession of phase is connected to the grid of tube I by means of variations in a carrier wave. an input transformer I2. The grid circuit of A specific object isto diminish amplitude vaamplifier 3 is connected between the grid of tube riations of the carrier Wave in the process of I and the transformer midpoint 8. The output 10' phase modulation. r circuit of amplifier 3 is coupled to the antenna 10 Existing systems of "phase modulation which system 4 in an entirely conventional manner. insure a close correspondence between phase va- In the operation of the system of Fig. l, the

-riation and signal amplitude show very little carrier generator 2 develops a carrier voltage amplitude variation provided the phase change across the secondary windingsfi and 'I,the value is relatively small. If this range be exceeded, the of which voltage in each winding is denoted by 5 accompanying amplitude modulation may be E/2. In the absence of feedback, the entire great. voltage E is impressed between the grid and In accordance with H the invention, a carrier cathode of tube I. With the feedback circuit wave of substantially fixed amplitude and vaconnected, as shown, a carrier current, denoted riable phase is generated by means of a vacuum by IP, in the plate circuit develops a feedback 20 tube having a reactive feedback connection be-' voltage, denoted by EM, acrosstransformer 9. tween its plate and grid circuits. The voltage The carrier voltage between grid and cathode, fed back to thegrid circuit is in fixed quadrature designated Ec, is modified by the feedback, but relation with the grid voltage. The resultant is always determined by the equation. p

vectorial value of the sum of the grid voltage and v 25 the feedback voltage is always substantially equal E= E -l- E (1) r to the impressed carrier. voltage, which latter T may be supplied from'a constant voltage source. in which each voltage is required to be expressed The grid and feedback voltages may be varied as a vector quantity.

by means of a-source of signal waves but the The plate circuit of tube I may be tuned to 30 quadrature relation of the voltages will hold the carrier frequency by means of the condenser throughout the variation. Furthermore, the load Ill. At resonance the onlymaterial impedance. impedance offered by the vacuum tube'to the of the plate circuit is the internal plate-to-cathcarrier source is not materially affected by the ode resistance which is herein designated R0 introduction and operation of the signal source. andhas a conductance value equal to the re- 35 The locus of the grid potential is given in'the ciprocal of R0 which will be called S. The carvector representation by a circular arc. The rarier plate current I]? is then given by the equadius vector, which corresponds to the voltage betion tween the grid and the midpoint of the carrier E source, has the properties here desired. Ac- I K (2) 40 cordingly, the output wave is taken from across 1 s p thus insuring a phase modulated where ,LL is the amplification factor of the tube. W free from amplitude modulation- The voltage across either the transformer 9 or The invention Will be morefully understoodthe condenser II! is in quadrature with the plate from the following detailed description in 6011 current and proportional thereto. In the system 45,

J c i with the drawing, of hi illustrated, the feedback voltage is taken from g- 1 shows a Preferred embodlment of h the transformer and is proportional to its mu- Ventwn? and tual impedance. The feedback voltage is then Fig. 2 is a vector diagram useful in explaindetermined by the equation In Fig. 1, a modulator tube I is shown con- E =jwMIp, (3) necting a carrier source 2 to an amplifier 3 and an antenna system 4. The carrier source is conwhere :i is the operator indicating quadrature,

nected to the grid of tube I by means of a transto is 21r times the carrier frequency and M is the former 5 having a divided secondary winding mutual inductance of the transformer 9. 55

Substantially Equation (2) in Equation (3) gives E =jwM E S,

which indicates that EM and EG are always in quadrature with each other although their relative values may vary. Since the vector sum of EM and EG is always equal to the impressed voltage E, it is evident that the locus of the grid potential must lie upon a circular arc in the vector field. This relation is shown in Fig. 2 wherein EG and EM are plotted at right angles and of such relative magnitudes as to sum up vectorially to the value E. The phase angle between EG and E is denoted by b. Vfnile this angle is variable by changing either E6 or EM, the latter by varying S, the vector EG always terminates upon the semi-circular are having E as the di-. ameter.

Inspection of Fig. 2 reveals that the radius vector lies between the midpoint of the diameter and the junction of Ed and EM. This vector has a constant length /2E and a variable phase angle 5. The vector corresponds to the voltage generated in the system of Fig. 1 between point 8 and the grid of tube l. The voltage between these points is denoted E and is impressed between the grid and cathode of amplifier 3. In this way a voltage of constant amplitude and variable phase is impressed on the amplifier 3 and delivered in amplified form to the antenna system 4 The phase is varied by means of the signal source i I shown connected to the grid circuit of tube I in a well known manner to vary the plate circuit conductance in accordance with a signal wave.

What is claimed is:

1. A phase modulating system comprising a vacuum tube with a cathode, an anode and a control grid, a divided carrier source with accessible midpoint, the outer terminals of said source being connected respectively to the grid and the cathode of the tube, means to feed back a carrier wave from the anode circuit to the grid circuit in quadrature with the instantaneous carrier voltage between the grid and the cathode, a load circuit bridged between the midpoint of the carrier source and the grid of the tube, and a signal source adapted to vary the anode current of the tube, whereby the phase of the carrier voltage across the load circuit is varied at a signal rate while the amplitude of said carrier voltage is rendered substantially independent of the signal.

2. A phase modulating system comprising a vacuum tube with a cathode, an anode and a control grid, a divided carrier source with accessible midpoint, the outer terminals of said source being connected respectively to the grid and the cathode of the tube, an anode circuit including a branch series resonant to the carrier frequency, means to transfer into the grid cir cuit a voltage developed across one element or" said series resonant branch, a load circuit connected between the grid of the tube and the midpoint of the carrier source, and a signal source adapted to vary the anode current of the tube, whereby the phase of the carrier voltage across the load is varied while the amplitude of said carrier voltage remains unchanged.

3. A phase modulating system comprising a vacuum tube with a cathode, an anode and a control grid, a divided carrier source with an accessible midpoint, the outer terminals of said source being connected respectively to the grid and the cathode of the tube, an inductance and a capacitance connected in series between the anode and the cathode of the tube, said inductance and capacitance being resonant to the carrier frequency, inductive coupling means to couple said inductance with the grid of said tube, a signal source adapted to vary the anode current of the tube, and a load circuit connected between the grid of the tube and the midpoint of the carrier source, whereby phase modulation of the carrier source is effected substantially without amplitude modulation.

4. A phase modulating system comprising two vacuum tubes, each having a cathode, an anode and a control grid, a divided carrier source with an accessible midpoint, the outer terminals of said source being connected respectively to the grid and the cathode of the first tube, means to feed back a carrier wave from the anode of the first tube to its grid in quadrature with the instantaneous carrier voltage between said grid and cathode, a signal source adapted to vary'the anode current of the first tube, said second tube having its grid and cathode terminals connected respectively to the grid of the first tube and-the midpoint of the carrier source, whereby the anode current of the second tube is phase-modulated without material amplitude modulating effect.

5. A phase modulating system comprising a vacuum tube with a cathode, an anode and a control grid, a transformer with a divided secondary winding, a carrier source connected to the primary winding of the input transformer, the extremities of the secondary winding being connected respectively to the grid and the oathode of the tube, means to feed back a carrier wave from the anode to the grid in quadrature with the instantaneous carrier voltage between the grid and the cathode, a load circuit connected between the grid of the tube'and the midpoint of the secondary winding of the transformer, and a signal source adapted to vary the anode current of the tube, whereby the phase of the carrier current in the load is' varied at a signal rate while the amplitude of the carrier current is substantially constant.

6. A phase modulating system comprising a vacuum tube with a cathode, an anode and a control grid, a divided carrier source with an accessible midpoint, the outer terminals or" said source being connected respectively to the grid and the cathode of the tube, meansto feedback a carrierwave from the anode to the gridin quadrature with'the carrier voltage existing between the grid and the cathode, a load circuit bridged between the midpoint of the carrier source and the grid of the tube, and a signal source adapted to change the internal anodecathode resistance of the tube, whereby phase modulation free from objectionable amplitude modulation is effected.

JUICHI OSAWA.

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