US1656987A - Ultrahigh-frequency generator - Google Patents

Description

Jan. 24, 1928. I 7 1,656,987

7 R. s. OHL

ULTRAHIGH FREQUENCY GENERATOR Filed Dec. 24, 1924 INVENTOR E (5: 01% BY /%& 6 ATTORNEY Patented den. 24, 1928.

I UM'lED stares t an? ra-"rnu 'r RUSSELL S. OHL, OF NEW YORK, N. Y., ASSIGNOR T AMERICAN TELERHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ULTRAHTGH-FREQUIENCY GENERATOR.

Application filed December at, 19.24. Serial No. 757,920.

to energy is fed back from the output circuit to the input circuit to maintain the production of oscillations. The vacuum tube generators ot' the prior'art have been satisfactory where the frequency requirements have not been to very high; that is to say, not above 5,000 lrllocycles. With the improvements being rapidly made in radio signaling, particularly, along the lines of directional control, it is desirable to produce oscillations of relatively 2o short wave length, for example, of the order of magnitude of meters or less.

This invention resides in a vacuum tube generator capable of producing ultra-high 'tre uency oscillations. By the term ultra-.

at big frequency is meant a frequency higher than 5,000,000 cycles per second.

The invention will be apparent from the following description when read in connection with the attached drawing showing an schematically a form of embodiment of the invention.

Tn the drawing, the vacuum tube 1 is of the well known three-electrode type comprising a filament 2, a grid 3 and a plate 4. For the my purpose of carrying out this invention the tube employed in the generating circuit should have low internal loss at the frequencies of oscillation. The filament 2 is connected with the source of filament-heatin an current 5, one pole of which is grounde The connection between the source 5 and the filament includes the choke coils 6 and 7 which should be so proportioned as to have extremely high impedance at the oscillating tre uency. The grid 3 is connected with one of t e filament leads, the connection including a high frequenc choke coil 8, a resistance 9 and a con enser 10, the said resistance serving as the grid leak. The plate o 4 is connected with the positive pole of the source 11 of plate potential. the negative pole of which is grounded. The connection between the plate a and the source 11 includes a high frequency choke coil 12. Cont5 nected between the grid 3 and the plate 4 ground. The possibility of such is a variable condenser 13 which determines the frequency of oscillation of the circuit.

The base of the vacuum tube, namely, the

part designated w supporting the glass coutainer, which base coact's with a receptacle to hold the tube in correct position, should,

in eflect, be connected to ground in order to avoid the dissipation ofthehightrequency energy through its ca acity to dissipation will be apparent when it is considered that the base, consisting of a relatively large mass of metal, is in close juxtaposition to the space in which the high frequency oscillations are being set up and has, also, fairly large capacity to ground. A preferred method of grounding the base consists in connecting it with the filament-heating circuit between said filament and a choke coil, for example, 6, so that the choke coil acts in the same manner with respect to the base as to the filament circuit. The leads to the cathode and the grid should have as lowtinductance and capacity as practicable in the construction of vacuum tubes.

The radiating element of a vacuum tube generator of the type described consists of a rod of copper or similar metal of such diameter as to cause the rod to remain in a fixed position without appreciable vibration. Such a rod should be ungrounded and its length should be one-half the length of the generated wave. The rod should be placed in close juxtaposition to the source of oscillations and should have a thermoammeter inserted midway between the ends of the rod. As thus placed the rod will absorb most of the power. output of the vacuum tube generator when the resonant circuit or the tube is attuned to the naturalperiod of the rod.

The manner in which the circuit functions to produce the ultra-high frequency oscillations is as follows: The grounded source of plate potential 11, which for example,

may be of the order of magnitude of 1,000

leak 9. It will be apparent therefore that there will be a charge and discharge ofthe condenser 13, and the rate of charge and discharge will depend upon the magnitude of the condenser andof the constants of the tube. The connecting circuits do not appreciably affect the rate of oscillation because the choke coils 6, 7, 8 and 12 have been so chosen as to prevent the passage of high frequency currents through the circuits in which the coils are placed. The oscillations produced within the tube will be transferred to the antenna and radiated therefrom. The connection of the base w of the tube to the grounded lead of the filament heating cirof 5,000 ohms; the tube was of 51 watts capacity; the source 5 was of 10 volts and the source 11 was 1,000 volts. With such an arrangement it was found that the power output efliciency was comparable with that of a vacuum tube generator producing much lower frequencies.

While this invention has been disclosed as embodied in a particular form it is to be understood that it is capable of embodiment in other forms without departing from the spirit and scope of the appended claim.

WVhat is claimed is:

A generator of ultra-high frequency oscillations, comprising a vacuum tube having a plate, a grid and a filament, an evacuated vessel enclosing such electrodes and having a metallic base supporting said vessel, a condenser-coupling between said plate and grid, a grounded source of plate potential, a grounded source of filament-heating current, and a connection between the said metallic base and the grounded side of the source of filament-heating current.

In testimony whereof, I have signed my name to this specification this 23rd day of December, 1924.

RUSSELL S. OHL.

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