US2633537A

US2633537A - Coaxial line oscillator

Info

Publication number: US2633537A
Application number: US634097A
Authority: US
Inventors: William R Rambo
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-12-10
Filing date: 1945-12-10
Publication date: 1953-03-31
Anticipated expiration: 1970-03-31

Description

09H0/ gm rfa/1 Q40/ am @0g/@WLan 2,63 ,sang/vf W. R. RMBO COAXIAL LINE OSCILLATOR .Filed im. 1o, 1945 1N VEA/Ton WILLIAM RAMBO MQ/rv.

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Patented Mar. 31,1953 *C* 1 COAXIAL LINE OSCILLATOR William R. Rambo, Cambridge, Mass., assignor to the United States of America as represented by the Secretary of War Application December 10, 1945, Serial No. 634,097

(Cl. Z50- 36) 4 Claims. 1

,same time as a frequency tripler.

The upper frequency limit at Which a conventional triode vacuum tube will oscillate at its fundamental frequency is limited by the physical structure of the vacuum tube, the transit times of the electrons between the cathode and the plate, and increases in power loss through structural materials and dielectrics at the higher frequencies. Accordingly it is an object of this invention to extract radio frequency energy from a conventional triode Vacuum tube operatingas an oscillator at frequencies beyond its normal Working range.

The above object will be satised if the plate tank circuit of the oscillator is resonant at the fundamental frequency and at the same time at the third harmonic of the frequency of oscillation. It is a further object to provide a device of the required function cited above in which the tuning may be made not too critical.

Other objects, features and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention taken in connection with the accompanying drawing in which:

Fig. 1` is a cross sectional view of an oscillator-tripler circuit using a conventional triode vacuum tube and resonant coaxial line tank circuits; and

Fig. 2 is a schematic diagram of the oscillatortripler circuit shown in Fig. 1.

Referring more specically to Fig. 1 there is shown therein a pictorial View of a conventional triode vacuum tube I which may be of the lighthouse type. Triode I0 includes a cathode II, control, grid I2 and anode pillar I3, each separated by a suitable insulating material I4 Center conductor 20 of a coaxial line associated with the triode Ill is connected to outer shell 42 of triode I0 which in turn is capacitively coupled to cathode I| through a small thickness of dielectric material 43. Outer conductor 2| of the aforesaid coaxial line is joined to control grid I2 through metal disk 22. Center conductor 20 and coaxial outer conductor 2| form a resonant coaxial line between the cathode and the control grid of triode I0. Cathode II is connected to center conductor 20 2 through bias resistor 44. The terminating en of the grid-cathode resonant cavity is short-circuited by means of an adjustable annular piston 23.

One end of center conductor 30 of another coaxial structure is connected to anode pillar I3 and the opposite end is connected to a suitable source of positive potential, designated herein as B+.

One end of coaxial conductor 3|, the diameter of which is greater than that of center conductor 30, contacts center conductor 30 by means of sliding contact 32. The opposite end of coaxial conductor 3| is connected to an insulating collar 33 surrounding center conductor 30. Insulating collar 33 contains a screw 36 which projects vthrough slot 34 cut in a second coaxial conductor 35. 'Ihe diameter of coaxial conductor 35 is greater than the diameter of coaxial conductor 3|. Adjusting nut 3l on screw 36 allows the insulating collar 33 and coaxial conductor 3| assembly to be adjusted relative to center conductor 30.

One end of coaxial conductor 35 is joined to a metal disk 38 which in turn is screw-connected to metal disk 22. A second insulating collar I1 surrounding center conductor 30 is attached to the opposite end of coaxial conductor 35.

The electrical terminating end of coaxial conductor 35 is short-circuited for radio frequencies to the electrical terminating end of coaxial conductor 3| by means of an annular piston I5, surrounding coaxial conductor 3|. The sliding member of annular piston I5 which contacts coaxial conductor 3| is separated from the sliding member which contacts coaxial conductor 35 by a piece of dielectric material I6. This prevents the plate potential from being shorted to the control grid of the triode vacuum tube and allows the radio frequency potential to be bypassed. The position of the annular piston I5 is adjustable by means of a rod such as 40 attached thereto and projecting through insulating collars 33 and I1 to the outside. Center conductor 30, coaxial conductor 3| and coaxial conductor 35 form a resonant coaxial line between the control grid and anode pillar of the triode.

Feedback between the grid-plate and the gridcathode resonant coaxial lines is provided by a small feedback probe 45 projecting through a hole containing an insulating material 4I in disks 22 and 38.

Power is extracted by a pickup probe 46 which projects through a hole I8 in coaxial conductor 35 and is applied through a high pass filter 41 to the apparatus which utilizes the output of the illustrated device.

For a more detailedexplanation of the operation of this circuit, reference will now be made to Fig. 2 which is an equivalent schematic diagram' of the device shown in Fig. 1. All elements designated in Figs. 1 and 2 by the same reference numbers are identical in function and purpose. In this oscillator circuit the vtube gridplate capacitance is tuned by the inductive irnpedance of the anode pillar and the two lengths of the coaxial lines, all coacting in series. The inductive impedance formed by the anode pillar within the tube envelope is shown as Z1 in Fig. 2. The inductive impedance formed by the first section of coaxial line, Z2, also shown in Fig. 2, is adjusted through motion of the sliding contacts at 32. The inductive impedance formed by the second section of coaxial line, Za, also shown in Fig. 2, is adjusted through motion of the annular piston I relative to the sliding contact at 32.

. The characteristic impedance of the two scctions of coaxial lines differ from one another since each center conductor is of a different diameter. For a given set of characteristic impedances, a combination of line lengths can be found that will resonate the resonant coaxial lines at both the fundamental and at the third harmonic frequency of oscillation. Viewed from the anode pillar of the vacuum tube, the effective impedance offered to the fundamental frequency must be three times that offered to the third harmonic frequency in order that the above resonant conditions will exist. The electrical length of the grid-anode resonant cavity is there.. by dependent upon the frequency applied to it.

The cathode-grid resonant coaxial line is a single-characteristic impedance coaxial line, end loaded with the tube capacitance. It is therefore impossible that it be resonant at both the fundamental frequencies and at three times the fundamental frequency. The annular piston in the grid-cathode resonant coaxial line is adjusted so that it will be resonant at the fundamental frequency of oscillation.

The feedback is designed to operate efficiently at the fundamental frequency in developing a driving voltage across the resonant cathode-grid impedance. There is therefore no significant third harmonic feedback into the grid-cathode resonant coaxial line. The tube oscillates as an oscillator at a frequency 1A; that of the desired output frequency.

While there is a wide range of line lengths and characteristic impedances that can satisfy the tuning requirements insofar as the fundamental is concerned, simultaneous tuning to the third harmonic is somewhat critical. This sharpness of tuning is accentuated as the terminating capacitance of the vacuum tube is increased or, for a xed capacitance, as the frequency is increased. For a given capacitance and frequency, tuning is least critical when the characteristic impedances of the two lengths of concentric lines, Z2 and Z3, are widely separated in value.

Power is capacitively coupled from the gridplate resonant circuit by the probe 46 which is placed in the line at a point where the third harmonic voltage signal is at a maximum, this being at a distance M4 (at the third harmonic) from annular piston I5 as shown in Fig. 2. The probe 46 feeds the load through a T-section high-pass filter that attenuates the fundamental and passes the third harmonic, This limits the 94 output to energy of the desired high frequency.

Since the oscillator is essentially underloaded on the fundamental frequency (except by the driving impedance), high amplitude alternating voltages exist that provide suicient excitation and also bias across bias resistor 44 and capacitance coupling 43 to permit shortening the electrical angle of plate current now to values conducive to the generation of harmonics.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as set forth n the appended claims.

The invention claimed is:

1. In combination, an electron discharge device having at least a cathode and a control grid and an anode, a first resonant coaxial line connected between said control grid and said cathode, a means for adjusting the physical length of said first resonant coaxial line so that it will be resonant at a particular radio frequency, second and third resonant coaxial lines of different radial dimensions and coacting in series to form a fourth resonant coaxial line between said control grid and said anode, means for independently adjusting the physical lengths of said second and third resonant coaxial lines so that said fourth resonant coaxial line is simultaneously resonant at both the fundamental and the third harmonic of said radio frequency, and means for extracting radio frequency energy of substantially said third harmonic frequency from said fourth resonant coaxial line.

2. An ultra-high frequency oscillator comprising an electron discharge device having a cathode and a grid and an anode, a first resonant coaxial line coupled to said grid and cathode and tuned to a given radio frequency, a second resonant coaxial line coupled to said grid and anode, said second line including a pair of coaxial lines of different radial dimensions connected in series, means for independently adjusting the length of said last-mentioned Icoaxial lines so that said second coaxial line simultaneously tunes the grid-to-plate interelectrode capacitance of said tube to said given radio frequency and to a third harmonic thereof, coupling means in said second line at a point where energy of said third harmonic is a maximum`and energy of said given frequency is substantially less than that of said third harmonic for providing output energy of said third harmonic, and means coupling said first line to a point in said second line at which energy of said given radio frequency is a maximum and energy of saidthird harmonic is substantially less than that of said given radio frequency for supplying feedback energy of said radio frequency to said first line.

3. An ultra-high frequency oscillator comprising an electron-discharge device having at least a cathode and a control -grid and an anode, a first resonant coaxial line connected between said control grid and said cathode, means for adjusting the length of said rst coaxial line so that it will be resonant at a given radio frequency, a second coaxial line with a given spacing between conductors coupled at one end to.

said grid and said anode, a third coaxial line with a given spacing between conductors smaller than that of said second coaxial line and coupled at one end to the other end of said second line and short-circuited at its other end, means:

for independently adjusting the lengths of said second and'y third lines so that the coaxial line formed by said second and third lines is simultaneously resonant at said given radio frequency and at the third harmonic of said radio frequency, means in said third line at substantially a quarter of a Wavelength of said third harmonic from said short-circuited end for obtaining output signals of said third harmonic, and means coupled between said first line and a point in said second line at which energy of said given radio frequency is a maximum and energy of said third harmonic is substantially less than that of said given radio frequency for providing feedback energy of said given radio frequency to said first 15 2,476,725

coaxial line.

4. An oscillator according to claim 3 in which said output coupling means includes a high pass filter for attenuating said given radio frequency and for passing said third harmonic.

WILLIAM R. RAMBO.

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

UNITED STATES PATENTS Number Name Date 2,379,952 Heedene July 10, 1945 2,408,355 Turner Sept. 24, 1946 Gurewtsch July 19, 1949