US2434400A - Pulse modulated oscillator - Google Patents

Description

Jan, 13, 1948- A. EASTON PULSE MODULATED OSCILLATOR Filed ma 21, 1945 Q'IIII'LI'IIIIII.

WWQSO INVENTOR ALLAN EASTON BY ATTORNEY Patented Jan. 13, 1948 PULSE MODULATED OSCILLATOR Allan Easton, Longlsland City, N. Y., assignor to Emerson Radio and Phonograph Corporation,

New York, N.'Y., a corporation of New York Application May 21, 1945, Serial No. 595,030

3 Claims.

The object of my invention is to provide a pulse modulated oscillator which may be used to produce a train of oscillations in which all oscillations, including the first, are of equal amplitude and to do this simply, efiiciently, and economically even at high frequencies.

Various ways are known for getting constant amplitude oscillations, but these ways become expensive with increase in frequency. The reason for this is that the voltage across the tuning coil of an oscillator, E, is approximately equal to where I is the current through the tuning coil, L is the inductance of the tuning coil, and C is the shunt capacity of the tuning coil and connected thereto. It is possible to make the voltage large by using a relatively large inductance at low frequencies. it is necessary for various reasons to reduce the size of the inductance. In order to get suflicient voltage across the coil it is therefore necessary to increase the current and such increase of current is usually expensive.

With the present invention the current I is increased by the use of a thyratron tube which will draw large amounts of current momentarily, but will remain in a ready condition while drawing something like 1 milliampere.

It is therefore a further object of this invention to produce a pulse modulated oscillator in which the oscillations of high frequency are of equal amplitude, and of higher amplitude than obtainable by other means, using comparable input power.

In the drawing, the single figure is a circuit diagram illustrating my invention.

The drawing illustrates my invention as applied to an oscillator which may operate at megacycles and in which the voltage of the constant amplitude pulse modulated oscillations may be approximately 50 volts.

In one typical embodiment of my invention it involves the use of three tubes l, 2. and 3. These are respectively, a shock tube l which may be a thyratron of the 2D21 type, a clamp tube 2 which may be of the 604 type, and an oscillator 3 which may also be of the 604 type. The shock tube I has the well known characteristic of being able to pass a large amount of current, on the order of 2 amperes, and of rema ning in a ready state with the passage of a small amount of current, on the order of 1 milliampere. The clamp tube 2 has the well known characteristic that its im- As the frequency goes up, however,

I pedance from cathode'to ground, which is inpatallel with the tuning coil of the oscillator, is very high when the tube is non-conducting and very low, on the order of 300 ohms when thetubeis conducting. Oscillator tube 3 and its circuit is permitted to oscillate, and prevented from oscil lating by the tube 2. This occurs by reason of the fact that the tuning coil 8 is connectedinthe circuit of the tube 2 between cathode and ground. When the tube 2 is not conducting the impedance looking into the cathode is very high so that the tube 3 is permitted to oscillate. When the tube 2 is conducting the impedance looking into the cathode is approximately 300 ohms and this low impedance is in shunt to the oscillator coil. Tube 3 is therefore prevented from oscillating when the tube 2 is in a conducting state.

In operation, my circuit in the ready state will be passing a small amount of current through the thyratron l and this will charge condenser 4. When it is desired to set off a train of oscillations, all of equal amplitude, a positive pulse of voltage will be applied to the grid of tube I through condenser 5 and across resistance 6, while a negative pulse of voltage will be applied simultaneously to the grid of tube 2 through condenser l. Tube 2 will accordingly cease conducting and permit the oscillator 3 to start oscillating. Tub-e I will also have its resistance abruptly lowered so that the condenser 4 will discharge through the tube and momentarily pass several amperes of current through it. This current will pass through the resistance I0 and primary l I which is couoled to the oscillator coil 8. The oscillations will therefore not have to build up from low amplitude gradually, but the first oscillation, due to the current in tube I, can be equal in amplitude to all of the succeeding oscillations. When the negative pulse on the clamp tube 2 ends the clamp tube begins to draw current and provides a low resistance path in shunt to the tuning coil 8 of the oscillator, oscillations stop and the wave train ends. A small amount of current will continue to flow throu h the thyratron, maintaining it in a ready state. and plate resistor 4 will be charged in preparation for the next train of oscillations.

As may be seen from the drawing, my circuit consists of an input terminal connected through a condenser 5 to the grid of tube l, the grid also being connected to a 22 volt negative bias source from resistance 6. The cathode of tube I is connected to ground through the resistance l0 and coil II. The anode of tube l is connected to ground through the condenser 4. It is also connected through resistance I2 to a source of anode voltage supply marked with the plus symbol and which will be referred to herein as B+. 3+ is connected through resistance l3 to the grid of tube 2 which grid is also connected to condenser 1. 3+ is also connected through resistance I4 to the anode of tube 2. Thecathode of tube 2 is connected to ground through the condenser 9 in parallel with which is the coil 8 and. is also connected to the grid of tube 3. 3+ is connected to the anode of tube 3 through the resistance I5. The cathode of tube 3 is connected through the variable resistance IE to a tap on the coil 8.

The circuit here disclosed has been tried out at a frequency of 10 megacycles. The envelope of the oscillations was substantially flat and the circuit worked well.

It will be understood by those skilled in the art that my invention is capable of various modifications and I do not therefore desire to be restricted to the particular details shown and described but only within the scope of the appended claims.

What is claimed is:

l. A pulse modulated oscillator comprising a shock tube, a clamp tube and an oscillator tube, means for operating said clamp tube to cause sa d oscillator tube to oscillate and discontinue oscillating, and means whereby a surge of current from the shock tube is added to said oscillations at the beginning thereof.

2. A pulse modulated oscillator comprising an oscillator tube and circuit, a clamp tube, and a shock tube, means for operating said clamp tube to start and stop the production of oscillations by said oscillator tube and circuit, and means for operating said shock tube to add current to said oscillations at the beginning of each operation of said oscillator.

3. A pulse modulated oscillator comprising a gaseous, grid controlled rectifier type shock tube, a clamp tube, an oscillator tube and circuit, an oscillator coil connected in the circuit of said oscillator tube and also connected in the cathode to ground circuit of said clamp tube, a second coil coupled to said oscillator coil, said second coil being in the cathode to ground circuit of said shock tube.

ALLAN EASTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,223,058 Christ Nov. 26, 1940 2,370,685 Rea et al Mar. 6, 1945

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