US2113340A

US2113340A - Ultrahigh frequency oscillator

Info

Publication number: US2113340A
Application number: US41540A
Authority: US
Inventors: Evans John
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1935-09-21
Filing date: 1935-09-21
Publication date: 1938-04-05
Anticipated expiration: 1955-04-05

Description

April 5, 1938. J. EVANS ULTRAHIGH FREQUENCY OSCILLATOR Filed Sept. 21, 1935 IIII IN vB/v'roR John Evans Witness.- 00 '7 HT'I'OHNEY Patented Apr. 5, 1938 UNITED STATES PATENT OFFICE John Evans, Collingswood, N. J assignor to Radio Corporation of America, a corporation of Delaware Application September 21, 1935, Serial No. 41,540

8 Claims.

My invention relates to ultrahigh frequency thermionic devices. More particularly, my invention is an ultrahigh frequency oscillator employing thermionic tubes in which the anodes are a virtually at ground potential.

I am aware of numerous circuits for generating high frequency oscillations. Some of the proposed circuits will generate ultrahigh frequencies but the frequency is far from constant. Other circuits have been devised which generate oscillations of high and constant frequency but it is impossible to extend the range to frequencies exceeding fifty megacycles. Beyond these high frequencies the thermionic tube elements and the leads within the tubes assume electrical lengths of proportions which interfere with the higher frequency ranges.

One of the objects of my invention is the generation of oscillatory currents of ultrahigh frequencies.

Another object of my invention is to reduce the effect of the anode load on the input circuits of a thermionic tube.

A further object is to place the anodes of a pair of push-pull oscillator tubes at virtually ground potential.

Additional objects will appear in the following specification and claims.

Figure 1 is a schematic diagram of an ultrahigh frequency oscillator in which the anodes are at ground potential, and

Figure 2 is a diagram of an oscillator embodying one form of my invention.

It is well known to those skilled in the art that the characteristics of the input circuit of a 'triode are dependent on the load in its output circuit. Although this efiect may not be of great importance at low frequencies, it is of extreme importance at high frequencies.

ample, with one type of tube which has an input capacity of about 28 micromicrofarads with a zero plate circuit load, the effective input capacity will be approximately three times as great with an external load of 100,000 ohms. The output load may be inductive, capacitive or resistive and in each case the effective capacity or reactance of the input circuit will be effected.

The input reactance may be efiected in either a positive or negative sense. 7

Although these effects are not always deleterious, I have found that at ultrahigh frequences the plate circuit load will limit the range of oscillation and ultimately limit the highest oscillatory frequency which can be reached. At frequencies of the order of. megacycles and lower,

By way of ex-- depending mainly on the tube construction, the circuit of Figure 1 may be used.

In Figure 1 a pair of triode tubes l-3 are connected in push-pull relation. The grids 5-l are connected to the conductors 9ll of a transmission line l3. A bridging member I5 is adjusted on the 'lines 9-H until a quarter wave length characteristic is obtained. The center I! of the bridge is grounded through a grid leak resistor Hi. The cathodes 2l-23 may be energized by any suitable source; for example batteries 25-21 or alternating current. In practice the capacity of the batteries or other source of cathode heating energy must be considered. Either filter networks or concentric lines should be employed between the batteries and the cathodes as will be described below. The batteries 25-21 in Fig. 1 are shown as directly connected to the cathodes 2|, 23 merely for convenience of illustration.

Conductors 293l of a second transmission line 33 are connected to the cathodes 2 l-23. An adjustable bridging member 35 is connected to the transmission line at about a quarter wave length position at which the tuned grid, tuned cathode will cause oscillations. The center 3! of the cathode bridging member is grounded. The anodes 394l are connected together with the shortest. possible leads. The center 43 of the leads between anodes is connected to ground through a suitable capacitor 45. The center is also connected to a radio frequency choke coil 41. The choke in turn is connected to the positive terminal of the anode current source 49. The negative terminal of the anode current supply 49 is grounded.

In the arrangement shown in Figure 1, if the length of the leads between the anodes is very short, the anodeswill be maintained at ground potential for radio frequency currents because of the low reactance of the capacitor 45 which virtually grounds the anodes. Under favorable circumstances the anode output circuit will have substantially zero impedance and the effective input capacity will be relatively low and permit the generation of oscillatory currents of a frequency of the order of 50 megacycles. However, as the frequency is gradually increased, the leads between the anodes, and particularly the leads within the tube envelopes, will assume sub- 0 The proper length of the transmission put circuit and effect the characteristics of the input circuit as explained above.

I propose to overcome this difliculty by arranging an output circuit which will have substantially no effect on the oscillation frequency and which will place the anodes at virtually ground potential at the highest frequencies. In

Figure 2 a diagram of a circuit employing anodes at virtual ground potential is shown. A pair of triode thermionic tubes 5 1-52 are connected as a push-pull oscillator. The grids 53-55 are connected respectively to the conductors 5'l--59 of a transmission line 6|. The line is adjustedto a quarter wave length by moving a bridging member 63 to the required position. The center 65 of the bridging member is connected to ground through the grid leak resistor 61.

The cathodes 69--'H are each energized by batteries 'l3l5 or other suitable source. Radio frequency choke coils Ill, 12 are connected "in" each of the leadsbetween the

batteries

13, 15 and the cathodes 69- 11. The batteries are eachgrounded. Ag-pairof capacitors 14 and 16 are connected in series across each of the cathode leads. The junction of one pair of capacitors 14,

i4 is connected to one of the conductors ll of a transmission ,-line 8|; pair of capacitors I6, 16 is connected to the other conductor of the transmission line. Although I have shown the filter network between the batteries and the cathodes, .it is equally effective to make the transmission line 8| a pair of hollow conductors. One wire is connected within each conductor from the battery to the cathode and the hollow conductors are used for the return wires from each cathode to the battery. The cathode leads are by-passed by a suitablecapacitor. In either type of connection, it is preferable to make the transmission lines straight, parallel and of equal length.

line to sustain oscillations is found by moving the bridging member 83 whose center point 85 is grounded. The anodes 8'l--89 are connected to the conductors 9l93 of a transmission line 95. Across the end of the transmission line opposite the anodes is placed the bridging member 91. The center 99 of the bridging member 91 is grounded through a capacitor lfll whose reactance is low to the currents generated b-y the push-pull oscillator.

The center. 99 of the bridging member is also connected through'a radio frequency choke I03 to the positive terminal of the anode current supply. N15. The negative terminal of this supply is grounded.

If the bridging member 91 is carefully adjusted so that the transmission line is effectively a half wave length long, the anodes will be virtually at ground potential for the highfrequency currents. The effect of the virtually grounded anodes is to make the output load of the anode circuit substantially zero and to remove the effects of this circuit on the input circuit. Using RCA type .852 tubes in push-pull relation with tuned input and tuned cathode-circuits, I have been .able to gener- The junction of the other 1. In an ultrahigh frequency oscillator of the thermionic tube type in which the inductance of the anode electrode lead has sufficient reactance at said ultrahigh frequency to prevent grounding the anode electrode within the tube, a pair of thermionic tubes, each of said tubes including grid. cathode and anode electrodes, 2. ground connection, a grid circuit connected between said gridelectrodes and said ground, a cathode circuit connected between'said cathode electrodes and said ground, means for tuning said grid and cathode circuits with reference to the frequency of the oscillations to be produced, an anode circuit connected to said anode electrodes, means for grounding said anode circuit, and

means for tuning said anode circuit to effectively a half wave length of said ultrahigh frequency oscillation wherebysaid grid and cathode circuits determine the oscillatory frequency of said -'oscillator and said anode circuit establishes an ultrahigh frequency groundhpotential on said anode. electrodeswithin said envelope.

2..In an, ultrahigh frequency oscillator of the thermionic ,tube type in which the anode lead offers a reactance at the frequency of operation which prevents directly groundingthe anode electrode within said tube, a pairof thermionic tubes, including, within. an evacuated envelope grid, cathode and anode electrodes, arranged to operate on opposite phases of oscillatory currents; a ground connection, a grid circuit connected between said grid electrodes and'ground, a cathode circuit connected between saidcathode electrodes and ground, means for tuning said grid and cath- OdQ'CiICUItS to said frequency of operation, means for impressing a positive direct current potential with respect to said cathodes on said anodes, and means for establishing, an ultrahigh frequency ground potential on said anodes within said envelope.

3. In an ultrahigh frequency oscillator of the type, in which the anode lead of a thermionic tube offers sufficient reactance to the frequency of operation to prevent directly grounding, the

anode within said tube, a pair of thermionic tubes including within an evacuated envelope grid,

' cathode and anode electrodes and arranged to operate on opposite phases of their generated currents, a ground connection, a grid circuit connected between said-grid electrodesand ground, a cathode circuit connected between said cathode electrodes and ground, means for tuning said grid and cathode circuits to said-frequency of opera-,-

tion,;means for impressing -a positive direct current potential between said anode and cathode electrodes, and means: for establishing an ultrahigh frequency ground potential within said envelope on said anodes with respect to said ground connections.

4.1m a push-pull ultrahigh frequency thermionic oscillator of the type in which the anode lead offers a reactance at the frequency of operation which prevents directly grounding the anode within said tube, a pair of thermionic tubes having inputfanode and cathode electrodes; a ground connection, a transmission line of substantially one quarter wave length connected between said input electrodes and ground, a second transmission line of substantially a quarter wave length connected between said cathode elec-. trodes and ground, and means .for maintaining said anodes at points within said thermionic tubes at ground potential with respect to said ground connection for ultrahigh frequency currents and at positive direct current potential with respect to said cathode electrodes.

5. In a push-pull ultrahigh frequency thermionic oscillator of the type in which the anode lead oiiers a reactance at the frequency of operation which prevents directly grounding the anode Within said tube, a pair of thermionic tubes having grid, anode and cathode electrodes, a ground connection, a transmission line of substantially one quarter wave length connected between said grid electrodes and said ground, a second transmission line of substantially a quarter wave length connected between said cathode electrodes and said ground, and a third transmission line of substantially a half wave length connected to said anode electrodes at one end and to ground at the other end and tune whereby the first mentioned end of said third transmission line is substantially at the potential of said ground connection with respect to high frequency currents, and a source of anode current supply, having a grounded negative terminal and a positive terminal connected to the second mentioned end of said third line.

6. In an ultrahigh frequency thermionic oscillator of the type in which the anode lead offers a reactance at the frequency of operation which prevents directly grounding the anode within said tube, a thermionic tube having an evacuated envelope including grid, cathode and anode electrodes; a ground connection, a grid circuit connected between said grid electrodes and ground, a cathode circuit connected between said cathode electrodes and ground and an anode circuit connected between said anode electrodes and ground, means for tuning said grid and cathode circuits to generate oscillations at said operating frequency, means for adjusting the effective electrical length of said anode circuit to a half wave length at said operating frequency whereby said anode electrode within said envelope will be at ground potential for said high frequency oscillations, a direct current supply and connections therefrom for positively biasing said anode electrode with respect tosaid cathode.

7. In a device of the character described in claim 4, means for adjusting the effective length of said transmission lines.

8. In a device of the character described in claim 5, means for adjusting the effective length of said transmission lines.

JOHN EVANS.