US1763380A - Electric coupling system - Google Patents

Description

June 10,1930. c. E. TRUBE 1,763,330

I ELECTRIC COUPLING SYSTEI Filed July 14. 1928 2 Sheets-Sheet 1 INVENTOR ATTORNEYS June 10,1930. c. E. TRUBE 1,763,330

' ELECTRIC COUPLING SYSTEI Filed July 14, 1928 2 Sheets-Sheet 2 INVENTOR (br/ E @056 0M, 777 ZWQ ATTORNEYS the stability and the selectivity.

Patented June 10, 1930 PATENT OFFICE .UNITED STATES CARL E. TRUBE, OF ORANGE, NEW JERSEY, ASSIGNOR TO HAZELTINE CORPORATION, OF JERSEY CITY,'NEW JERSEY, A CORPORATION OF DELAWARE ELECTRIC courtme SYSTEM Application filed July 14, 1928, Serial No. 292739, and in Great Britain July 2, 1926.

This invention relates to electric coupling systems especially adapted for use with radio-frequency vacuum tube amplifiers, and more particularly to circuit arrangements which operate most effectively over a relatively wide range in frequency. Such systems are discussed more generally in my copending application for U. S..Letters Patent Serial No. 120,045, filed July 2, 1 926, of

which the present application is a continuation in part; Figs. 2 and 5 of this present application being the same as Figs. 6 and 8' of the prior application, and present Fig. 1 being the same as prior Fig. 2 except forthe substitution of a radio-frequency selfinductance for the choke coil described in the prior specification.

- The mentioned prior application discloses various forms of coupling systems so arranged as to give a voltage ratio that varies automatically with the frequency. The present application is confined to'such coupling systems in which the variation in voltage ratio is accomplished in a primary circuit which includes a fixed self-inductance effectively in parallel with one or more fixedcircuit is resonant at a frequency lower (but preferably not greatly lower) than the lowest frequency within the range of the CO2- pling system. I

The voltage ratio' in an inter-tube coupling system affects the degree of amplification, At each frequency there is a particular ratio o'f-output voltage to input voltage that will give the best compromise design. This ratio varies rapidly with the frequency, being relatively high at high frequencies. This invention provides means for securing substan- .tially the most desirable ratio at all freby which direct voltage is removed from the fixed capacities.

Fig. 5 illustrates a form of this invention in which a self-inductance coil (L of the preceding figures, is electromagnetically coupled to the transformer.

Fig. 6 illustrates a modification of Fig. 5.

Fig. 7 illustrates another modification of Fig. 5.

The coupling system of Fig. 1 is tuned by a variable condenser C connected across the primary coil L and the secondary coil L in series. Ordinarily L should have much fewer turns than L so that there is a hi h step-up voltage ratio between them. e path through the primary coil L from the plate of the vacuum tube to the filament includes also the fixed capacity G which is ex ternal to the main resonant circuit C L L In parallel with this path is a second path including the self-inductance L the value of which is so chosen that its circuit (completed through C and L is resonant at a frequency lower, but not greatly lower, than the lowest frequency within the range of condenser C The circuit of L being completed through C and L is thereby coupled to the main resonant circuit C L L so that part of the current of C and L will flow through C and L this part of the currentrbeing limited mostly by the reactance of L Since the reactance of L varies directly with the frequency while that of C varies inversely with the frequency, the voltage across C will rapidly fall off relative to the voltage across L as the frequency rises. For a given output voltage E the voltage across L is very. nearly independent of frequency, due to the electromagnetic coupling between L and L Hence the voltage E between the plate and the filament, being the sum of the voltages of indicated, being such voltage across 0 alone. This is the condition which is desired and which results in the maintenance of a high degree of stability over the frequency range, together with high sensitivity and selectivity.

The operation of the circuit of Fig. 2 is essentially the same as that of Fig. 1, but here the circuit of L parallel paths, that through C and that through C and L As before, this circuit L C C L should be made resonant at a frequency lower, but not greatly lower, than the lowest frequency within the range of C As described in the above-mentioned prior application, the voltage ratio E /E in Fig. 2 is obtained from a double step-up, first between C and the combination of G and C and then between L and L and, with the resonant condition just given, this voltage ratio will automatically vary with the frequency in the same manner as in Fig. 1.

Fig. 3 differs from Fig. 2 only in that the primary coil L is not included in the main resonant circuit. Coil L should here have the same number of turns as in Fig. 2; while the secondary coil L should have the same number of turns as L Fig. 2. The remaining relations are the same as in Fig. 2.

In Fig. 3 the direct voltage of the plate battery B exists across condensers C and G which is disadvantageous in that these condensers may break down. This difficulty is obviated in Fig. 4 by connecting the lower terminals of condenser C and coil L to the lower terminal of coil L instead of to the common lead at the bottom of the diagram. This connection does not aifect the alternating-current relations of Fig. 4, which are identical with those of Fig. 3.

In Figs. 1 to 4, the coupling between the circuit of coil L and the main resonant circuit C L L or C L. is effected through the coil L together with its electromagnetic couplin to coil L However, it is possible to couple t e circuit of L directly with the main resonant circuit by coupling L electromagnetically to L One method of accomplishing this is illustrated in Fig. 5, whose elements correspond to those ofFig. 1 and are denoted by like reference characters. Fig. 5 also differs from Fig. 1 in isolating the primary system C L L from the secondary system 0 L in a way similar to that shown in Fig. 4. As in the circuit arrangement of the preceding figures, L of Fig. 5 should ordinarily have much fewer turns than L and the circuit of L including L and 0,, should be made resonant at a frequency somewhat lower than the lowest frequency within the range of C The proper relative polarities of coils L and L; are as that the terminal .of E connected to one side of C is of opposite polarity to the terminal of L connected to is completed through two- 1 The operation of Fi and L combined, in

the other side of C the word polarity here referring to the polarity of the respective terminals when the coils are on open circuit. As before, there is in Fig. 5 a path from the plate to the filament whichincludes in series the fixed condenser C and the primary coil L With the relative polarities just stated,

the voltages across L and C are additive, due to the fact that at frequencies higher than the resonant frequency of the circuit C L the terminal voltage of L is reversed with respect to the voltage induced in L; by the current in L 5 are thus similar to those of the preceding figures, although the mathematical equations diiier slightly in form.

As the self-inductance of coil L in Fig. 5 should be made much greater than that of coil L (which ordinarily has but few turns) it will make very little difference whether the lower terminal of L is connectedto the upper terminal of L as in Fig. 5, or to the lower terminal of L as in Fig. 6, so long as the correct polarity relations are maintained. 6 is qualitatively identical with that of ig. 5 and can be made qllllantitatively identical by slight chan es in t e values of the circuit constants. s before, the circuit of coil L which is completed through condenser C is resonant at a freqiliency lower, but not greatly lower, than t e lowest frequency within the range of 0 Since the circuit of L does not now include the coil L it is necessary to couple it to the secondary circuit C- L by electromagnetic coupling between the coils L and L In cases where the natural capacities to ground of coil L and condenser C, are objectionable, it may be desirable to interchange the order of this circuit and L in Fig. 6, giving the arrangement of Fig. 7. Except for the minor effects of these capacities to ground, the operation of Fig. 7 is identical with the operation of Fig. 6 if the relations of the parts are otherwise the same as in Fig. 6.

The use of electromagnetic coupling between coils L andL in Figs. 5, 6 and 7 results in a more gradual variation with frequency of the voltage ratioE /E and there'- fore of the performance, i. e., of the stability, sensitivity and selectivity. The coeflicient of coupling between L and L should be neither very close nor very loose; a coupling of the order of 30% being satisfactory. It is to be understood that as many radio-froquency stages as required, similar to those .herein described, may be connected in cascade-the output terminals of one stage connected to the input terminals of the next-in order to obtain the advantages ofthis invention in a multi-stage amplifier.

I claim: 1. In a radio amplifier stage including a vacuum tube having a filament, a grid'and a The voltage relations of Fig.

plate, an electric coupling system which coniprises a main resonant circuit including as elements a secondary coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency,

a second circuit coupled to said resonant circuit, including a fixed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, whereby said secondcircuit is resonant at a frequency lower than the lowest frequency within said range, a primary coil electromagnetically.

coupled to said secondary coil, and a path through said coupling system between said plate and said filament includingin series said primary coil and at least aportion of said fixed capacity, whereby in the operation of the amplifier stage there is developed in said main resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automaticall rises when said adjustable element is adjusted for higher frequencies.

2. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including a xed secondary coiland an adjustable condenser adapted to tune the coupling system over a rangein frequency, a circuit coupled to said resonant circuit, including a fixed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, whereby said second circuit is resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, a primary co-il electromagnetically coupled to said secondary coil and having few turns relatively thereto, and a path through said coupling system between said'plate and said filament including in series said rimary coil and at least a portion of said xed capacity, whereby in the operation of the amplifier stage there is vdeveloped in said main resonant circuit a resonant voltage high compared with the voltage between the plate and the filament, and whereby the ratio of said resonant voltage to the voltage between the plate and the filament automatically rises rapidly when said adjustable condenser is adjusted for higher frequencies.

3. In a radio amplifier stage including a vacuum tube having a filament, a grid'and a plate, an electric coupling system which comprises a main resonant circuit including a fixed secondary coil and an adjustable condenser adapted to tune the coupling system over a range in frequency, a fixed coil electromagnetically coupled to said secondary coil, a circuit including said fixed coll andja fixed capacity effectively inparallel, said N fixed capacity being external to said main resonant circuit, a primary coil electromagnetically coupled to said secondary c011, and a path through said coupling system between said plate and said filament including in series said fixed capacity and said primary coil, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the-filament automatically rises when said adjustable con denser is adjusted for higher frequencies.

4. In a radio amplifier stage including a vacuum tube having a filament, a grid and'a plate, an electric coupling system which comprises a' main resonant circuit including a fixed secondary coil and an adjustable condenser adapted to tune the coupling system over a range in frequency, a fixed coil electromagnetically coupled to said secondary coil, a circuit including said fixed coil and a fixed capacity effectively in parallel, and having a resonant frequency lower than the lowest frequency within said range, said fixed-capacity being external to said main resonant circuit, a primary coil electromagnetically coupled to said secondary coil, and a path through said coupling system between said plate and said filament including in series said fixed capacity and said primary coil, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable condenser is adjusted for higher frequencies.

fixed secondary coil and an adjustable condenser adapted to tune the coupling system over a range in frequency, a fixed coil electromagnetically coupled to said secondary coil, a circuit including said fixed coil and a fixed capacity effectively in parallel, said fixed ca pacity being external to said main resonant circuit, a primary coil electromagnetically coupled to said secondary coil, and a path 'through said coupling system-between said plate and said filament including in series said fixed capacity and primary 0011, said primary coil having such polarity relative to said fixed coil that the terminal of the stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable condenser is adjusted for higher frequencies.

6. In-a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including a fixed secondary coil and an adjustable condenser adapted to tune the coupling system over a range in frequency, a fixed coil electromagnetically coupled to said secondary coil, a circuit including said fixed coil and a fixed capacity e liectivelyin parallel and having a resonant frequency lower than the lowest frequency within said range, said fixed capacity being external to said main resonant circuit, a primary coil electromagnetically coupled to said secondary coil, and a path through said coupling system between said plate and said filament including in series said fixed capacity and said primary coil, said primary coil having such polarity relative to said fixed coil that the voltages across said primary coil and said fixed capacity are additive, whereby in the operation of the amplifier stage there is developed in said resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable condenser is adjusted for higher frequencies.

7. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a second circuit coupled to said resonant circuit including a fixed self-inductance efiectively in parallel with fixed capacity external to said main resonant circuit, whereby said second circuit is resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, a circuit element having a substantially fixed voltage ratio relative to said main resonant circuit, and a path through said coupling system between said plate and said filament including in series said circuit element and at least a pbrtion of said fixed capacity, whereby in the operation of the amplifier stage there is developed in said main resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable element is adjusted for higher frequencies.

8. In a radio amplifier stage including a vacuum tube having a filament, a grid and a plate, an electric coupling system which comprises a main resonant circuit including as elements a coil and a condenser, at least one 'of which is adjustable to tune the coupling system over a range in frequency, a second circuit coupled to said resonant circuit including a fixed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, whereby said second circuit is resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range,-said fixed self-inductance being electromagnetically coupled to said resonant circuit, a circuit element having a substantially fixed voltage ratio relative to said main resonant circuit, and a path through said coupling system between said plate and said filament including in series said circuit element and at least a portion of said fixed capacity, whereby in the o ration of the amplifier stage there is deve oped in said main resonant circuit a resonant voltage whose ratio to the voltage between the plate and the filament automatically rises when said adjustable elements is adjusted for higher frequencies.

9. A radio-frequency coupling system having input terminals and comprising a main resonant circuitincluding as elements a coil and a condenser, at least one of which is adjustable to tune the coupling system over a range in frequency, a second circuit coupled to said resonant circuit including a fixed self-inductance effectively in parallel with fixed capacity external to said main resonant circuit, whereby said second circuit is resonant at a frequency lower, but not greatly lower, than the lowest frequency within said range, a circuit element having a substantially fixed voltage ratio relative to said main resonant circuit, and a path through said coupling system between said input terminals and including in series said circuit element and at least a portion ofsaid fixed capacity, whereby there is developed in said main resonant circuit a resonant voltage whose ratio to the voltage between said terminals automatically rises when said adjustable element is ad usted for higher frequencies.

In testimony whereof I afiix my si CARL E. TR BE.

ature.

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