US2419793A

US2419793A - Ultra high frequency electron discharge device circuit

Info

Publication number: US2419793A
Application number: US525542A
Authority: US
Inventors: Charles A Rosencrans
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1944-03-08
Filing date: 1944-03-08
Publication date: 1947-04-29
Anticipated expiration: 1964-04-29
Also published as: GB598159A

Description

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April 29, 1947.

C. A. ROSENCRANS Filed Mach 8, 1944 ULTRA HIGH FREQUENCY ELECTRON DISCHARGE DEVICE CIRCUIT 2 sheets-sheet 2 AMPLIFIER OUTPUT 1.45 l

esclu/won OUTPUT INVENTOR CHARLES A. ROSENCRANS BY l ATTORNEY Patented Apr. 29, 1947 ULTRA HIGH FREQUENCY ELECTRN DIS- CHARGE DEVICE CIRCUIT Charles A. Rosencrans, Haddoneld, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 8, 1944, Serial No. 525,542

11 Claims. l

The present invention relates to electron discharge device circuits for use over a relatively wide range of ultra high frequencies.

Heretofore, in employing oscillators and ampliers for use over a range of frequencies, it has been conventional practice to require, for the oscillator stage, both feedback and anode circuit controls as a minimum, and for the ampliiier stage, input and output circuit controls as well as a neutralizing control (particularly in the case of a push-pull amplifier). The present invention simplifies the electron discharge device circuits and minimizes the number of controls.

One object of the present invention is to provide a simple electron discharge device circuit which may be made to act either as an amplifier or an oscillator having a high degree of stability With a minimum number of controls.

A second object is to provide an electron discharge device stage for use as an amplifier having a very small amount of regeneration so as to permit a relatively high power gain over a wide band of operating frequencies.

Another object is to provide a transmitter employing vacuum tube triodes for the oscillator, buffer amplifier and power amplifier, and capable of operating uniformly over a range of approximately 264 to 372 megacycles without the need for feedback or neutralizing controls.

A further object is to provide an electron discharge device stage for use as an amplifier over a range of high frequencies and whose impedance from cathode to ground is low and capacitive over the entire range of operating frequencies.

A still further object is to provide a push-pull electron discharge device stage for use over a relatively wide range of high frequencies, employing a pair of triodes whose grids are connected together by an electrical connection of eX- tremely lovi7 inductance, the value of this inductance being such as to make the net impedance between cathode and anode of each tube very high through the interelectrode capacities of the tubes,r this impedance being a capacitive reactance over the entire operating range and approaching iniinity at some frequency higher than the highest desired operating frequency.

A feature of the invention is a triode amplifier with an anode tuned circuit but with no neutralizing control, which can operate over a wide range of frequencies, the remainder of the circuit components of the amplifier being arranged to permit either regeneration, degeneration or oscillation. An advantageous characteristic lies in the fact that once the triode is set up to operate in a particular condition, this condition Will hold over a Wide range of operating frequencies, with only a variable adjustment in the anode circuit.

' body the principles of the present invention;

Fig. 2 shows the equivalent electrical circuit for the ampliiiers of Fig. 1; and

Fig. 3 shows the equivalent electrical circuit for the oscillator of Fig. 1.

Referring to Fig. l, there is shown only that portion of a television transmitter Whose stages embody the principles of the invention. These stages are the oscillator, buffer amplifier and power amplifier which are labeled appropriately and each illustrated as being of the push-pull type. It should be understood, however, that the invention is not limited to push-pull stages, since it is equally applicable to a single ended stage.

The oscillator comprises a pair of vacuum tube vtriodes IA and 2 whose grids are connected together by a connection 3 of extremely low inductance. The anodes are connected to one end of a tunable parallel conductor system L5 which is tuned by a slider S. The filament terminals of the two tubes are connected together by means of choke coils L2 and Lll to whose center points H, I-I is connected the filament heater supply. Negative bias for the grids is provided by a grid resistor 4.

The buffer amplifier and the power amplifierl each comprise a push-pull stage having a pair of

vacuum tubes

5, 6, the grids of which are connected together by means of a connection 3 of extremely lov/ inductance. The grid resistor 4 supplies negative bias to the grids. The three inductance coils L2, L4 and L3 connect together the iilament terminals and the filament center taps, respectively. The input circuit or cathode line comprises a parallel conductor system LI which inductively couples the iilaments to the anode tuned circuit L5 of the previous stage. The amount of excitation in the parallel conductor system LI is adjustable by means of a slider Sl. Of course, the degree of excitation of each driven amplifier stage primarily depends upon the tightness of the coupling between the cathode line Ll and the anode tuned circuit L5 of the previous (or driving) stage. The slider SI is not employed for tuning the frequency but merely Referring to the amplifier of Fig. 2 the excitation on the cathode Ll is adjustable by means of slider SI. Once this adjustment of slider SI has been set for a desired excitation, it remains stationary for the entire frequency range. The frequency adjustment is eiected by means of the. slider S in the anode tuned circuit L5 which adjusts the stage for the desired carrier frequency in the normal manner. At the desired frequency of adjustment, the anode line L5 will be electrically one-quarter wavelength long. The grid connector 3' has an extremely low inductance, and inpractice may constitute a short metal strip whose dimensions are determined by experiment. The Value of the inductance of con'- necto-r 3lV is such as to makevthe net impedance between cathode and anode of each tube extremely high at all operating frequencies, the net impedance approaching infinity at some frequency higher than the highest operating frequency. The effective capacity between thegrid and anode at this condition is extremely small compared to the normal grid-to-anode interelectrode capacity. A change in the operating frequency can be had by a cha-nge in the inductance of conductor 3, due to a change in its dimensions.

The cathode line Ll must be longer than a certain length at which oscillations will occur at the lowest operating frequency. The length of Ll is such that the net impedance .between cathode-to-cathode (or between cathode and ground in a single ended tube circuit) is capacitive over the entire frequency range. The correct value of Li is best found through trial and error (i. e. through experiment). Thus, the cathode line LI serves a two-fold. purpose. First, it provides thev necessary capacitive reactance in the gridcathode circuit over a wide range of frequencies, and. secondly it provides av means by which the amplifier may be inductively coupled to the preceding radio frequency stage. The net result is a stable regenerative amplifier capable of operating over about a two-to-one frequency range.

The three inductance coils L2, L3 and L4 in theV filament circuit are not critical as to inductance but must be large enough so that the net impedance Z looking into the system Ll, L2, L3, L4 from the filaments of the vacuum tubes has a low value of capacitive reactance over the entire frequency range. If this requirement is not fulfilled, it will be found that although the amplier may not oscillate, it will not be possible to modulate it properly. The precaution should be taken not to permit the above impedance Z to become a pure resistance.

The foregoing requirements apply both to the power ampli-fier and to the buffer, although it is possible to obtain a higher power gain in the buffer by permitting the above net. impedance Z to have a considerably higher value of capacitive reactance by suitable selection of the three filament inductance coils L2, L3 and L4. A

practical operating condition has been found in which the buffer system will oscillate very weakly when the driving excitation from the oscillator is removed. When the buffer is coupled to the oscillator, then the bulier does not oscillate but acts as a regenerative amplifier.

Fig. 3 illustrates the equivalent electrical circuit for the oscillator of Fig. 1. Similar principles of operation apply to the oscillator. Although the cathode line LI utilized for the buffer and the power amplifier is not shown in Fig, 1, it may, if desired, be employed-in which case it will occupy the position shown by the dash lines in Fig. 3. If line L! is used in the oscillator, it should be sufliciently long to provide a capacitive reactance much less than in the case of the buier and power amplifier over the entire frequency range. The grid connection 3 for the oscillator may bemade longer; i. e., its inductance is increased relative to the same connection employed in the buffer and power amplifler. If cathode line L! is omitted, as sho-Wn in Fig. 1, then for the same values of L2 and L4, oscillations can be obtained over a wide range of frequencies.

Ancde line L5 controls the frequency of operation by suitable adjustment of slider S. If the inductance of the grid connection 3 is increased beyond that necessary to obtain the desired uniformity of operation over a wide range of frequencies, then the efliciency of the oscillator will be improved but the frequency range will be reduced. The situation may be improved by replacing Ll, if used, with a very small adjustable capacity whose value must be changed from time to time as the oscillator is tuned over the operating range by means of the anode tuned circuit L5.

In one experimental embodiment of the invention successfully tried out in practice, the three push-pull stages each employed a pair of RCA 8025 tubes. The transmitter as a whole (used for television purposes) operated in the range of 264 megacycles to 372 megacycles, although not limited to these particular frequencies or to this frequency range width. The tuned anode circuit sliders S were adjusted by means of Bakelite insulating screws linked to the centers of the tuned circuits.

One advantage of the present invention resides in the stable triode amplifier circuit arrangement which is capable of operation over a wide frequency range without employing conventional neutralization schemes. Another advantage lies in the simplified circuit arrangements which reduce to a minimum the number of controls required in the oscillator and amplifier stages.

What is claimed is:

1. A stable electron discharge device stage operatingA over a wide range of radio frequencies, comprising a Vacuum tube having a grid, a cathode and an anode, a connection from said grid to ground, a line coupled to said cathode having such length that the cathode-to-grid impedance is capacitive over the entire frequency range, said line being longer than the length at which oscillations will occur at the lowest operating frequency, inductance coils in the legs of said cathode having such inductance that `the net impedance looking into said coils and line from said cathode has a low value oi" capacitive reactance over the entire frequency range, and a tuned circuit coupled to said anode for controlling the frequency of operation of said stage.

2. A stable electron discharge device stage op erating over a range of radio frequencies, comprising a vacuum tube having a grid, a cathode and an anode, a connection from said grid to ground, a line coupled to said cathode having such length that the cathode-to-grid impedance is capacitive over the entire frequency range, inductance coils in the legs of said cathode and in the center tap for said cathode, said coils having Such inductance that the net impedance looking into said coils and line from said cathode has a low value of capacitive reactance over the entire frequency range, and a tuned circuit coupled to said anode for controlling the frequency of operation of said stage.

3. A stable regenerative electron discharge device amplifier stage capable of operating over approximately a two-to-one ultra high frequency range, including a vacuum tube triode having a grid, a center tap cathode and an anode, a con.- nection from said grid to ground, a line coupled to said cathode having such length that the cathode-to-grid impedance is capacitive over the entire frequency range, inductance coils in the legs of said cathode and in the vcenter tap for said cathode, said coils having such inductance that the net impedance looking into said coils and line from said cathode has a low value of capacitive reactance over the entire frequency range, and a tuned line circuit coupled to said anode for controlling the frequency of operation of said stage.

4. A stable electron discharge device stage operating over a relatively wide range of radio frequencies, comprising a vacuum tube having a grid, a cathode and an anode, a direct current connection from said grid to ground, inductance coils in the legs of said cathode, a tuned line circuit connected to said cathode, the parameters of said cathode circuit being such that the net impedance looking into said coils and line circuit from said cathode is capacitive over the entire frequency range, said tuned line circuit having a length which is longer than the length at which oscillations will occur at the lowest operating frequency .and a tunable frequency controlling circuit coupled to said anode.

5. A stable electron discharge device stage operating over a relatively wide range of high radio frequencies, comprising a vacuum tube having a grid, a center tap cathode and an anode, a direct current connection from said grid to ground, inductance coils in the legs of said cathode and in said center tap, condensers across the terminals of said inductance coils, a source of heating current for said cathode connected to the mdpoints of the inductance coils in the legs o-f said cathode, the parameters of said cathode circuit being such that the net impedance looking into said inductance coils from said cathode is capacitive over the entire frequency range, and a tunable line circuit coupled to said anode for controlling the frequency of operation of said stage.

6. An electron discharge device stage operating over a wide range of radio frequencies comprising a, pair of vacuum tubes each having a cathode, a grid, and an anode, a connection of extremely low inductance connecting the grids of said tWo tubes together, a connection from said grids to ground, inductance coils connecting the corresponding legs of said cathodes together, a parallel conductor line having one end connected to said cathodes, said line having such length that the net impedance between cathode to cathode is capacitive over the entire frequency range, said line having a length which is longer than the length at which oscillations will occur at the lowest operating frequency, said inductance coils having such inductance that the net impedance looking from said cathodes into the system comprising said inductance coils and line has a low value of capacitive reactance over the entire frequency range, and a tunable parallel conductor circuit connected between said anodes for controlling the frequency of operation of said stage.

7. An electron discharge device stage operating over a relatively Wide range of radio frequencies, comprising a pair of triode vacuum tubes each having a center tap cathode, a grid and an anode, a connection of extremely low inductance connecting the grids of the two tubes together, a bias connection for said grids, inductance coils connecting the corresponding legs and center tap connections of said cathodes together, a source of heating current connected to the midpoints of those inductance coils which are connected between the legs of said cathodes, by-pass condensers across the terminals of said inductance coils, a parallel conductor line having one end connected to said cathodes, said line having such length that the net impedance between cathode to cathode is capacitive over the entire frequency range, said inductance coils having such inductance that the net impedance looking from said cathodes into the system comprising said coils and line has a low value of capacitive reactance over the entire frequency range, and a tunable parallel conductor circuit connected between said anodes for controlling the frequency of operation of said stage, and a source of positive anode polarizing potential connected to the electrical center of said tunable parallel conductor circuit.

8. An ultra high frequency transmitter operating over a relatively wide range of radio frequencies comprising a pair of vacuum tubes each having a cathode, a grid and an anode, a connection of extremely low inductance connecting the grids of said two tubes together, said connection having such value as to make the net impedance between cathode and anode 4of each tube eXtremely high at all operating frequencies and approaching infinity at some frequency higher than the highest operating frequency, a connection from said grids to ground, inductance coils connecting the corresponding legs of said cathodes together, a parallel conductor line having one end connected to said cathodes, said line having such length that the net impedance between cathode to cathode is capacitive over the entire frequency range, said inductance coils having such inductance that the net impedance looking from said cathodes into the system comprising said coils and line has a low value of capacitive reactance over the entire frequency range, and a tunable parallel conductor circuit connected between said anodes for controlling the frequency of operation of said stage, a source of positive anode polarizing potential connected to the electrical center of said tunable parallel conductor circuit, a by-pass condenser connecting said electrical center to ground, said parallel conductor cathode line being inductively coupled to the output of a preceding radio frequency stage, and a slider for adjusting the effective length of said cathode line to thereto vary the excitation on said cathode line.

9. An oscillation generator capable of oscillating uniformly over a wide band of ultra high frequencies, comprising a vacuum tube having a grid, a cathode and an anode, a direct current connection from said grid to ground, inductance coils in the legs of said cathode between said cathode and a source of cathode heater supplys the parameters of said cathode circuit being such that the net impedance looking into said coils from said cathode is maintained capacitive over the entire frequency range, and a tunable frequency controlling circuit coupled to said anode.

10. An electron discharge device stage operating over a relatively wide range of radio frequencies, comprising apair of triode vacuum tubes each having a, center tap cathode, a grid and an anode, a connection of extremely low inductance connecting the grids of the two tubes together, a bias connection for said grids, inductance coils connecting the corresponding legs and center tap connections of said cathodes together, a source of heating current connected to the mid-points of those inductance coils which are connected between the legs of said cathodes, by-pass condensers across the terminals of said inductance coils, a parallel conductor line having one end connected to said cathodes, said line having such length that the net impedance between cathode to cathode is capacitive over the entire frequency range, said inductance coils having such inductance that the net impedance looking from said cathodes into the system comprising said coils and line has a low value of capacitive reactance over the entire frequency range, and a tunable parallel conductor circuit connected between said anodes for controlling the frequency of operation of said stage.

11. A stable electron discharge device stage operating over a range of radio frequencies, cornprising a vacuum tube having a grid, a cathode and an anode, a connection from said grid to ground, an input line circuit coupled to said cathode and having such length that the cathode-to-grid impedance is capacitive over the entire frequency range, inductances in the legs of said cathode and in the center tap for said cathode, a heater supply coupled to the leg inductances of said cathode, said inductances having such values that the net impedance looking into said inductances and line from said cathode has a low value of capacitive reactance over the entire frequency range, and a tuned circuit coupled to said anode for controlling the frequency of operation of said stage.

CHARLES A. ROSENCRANS.

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

UNITED STATES PATENTS Number Name Date 2,315,296 Strutt Mar, 30, 1943 2,052,888 Lndenblad Sept. 1, 1936 2,168,924 Dow Aug, 8, 1939 2,267,520 Dow Dec. 23, 1941 OTHER REFERENCES Journal of the A. I. E. E. for April 1920, an article by Heising, page 365. Copy in Library.