US2158961A - Means and process for the amplification of radiant energy - Google Patents

Description

,Miy16,1939. AL Y 2,158,961

MEANS AND PROCESS FOR THE AMPLIFICATION OF RADIANT ENERGY Filed oci. 24, 1927 JOS CL rrley.

Patented May 16, 1939 UNITED STATES MEANS AND PROCESS FOR THE AMPLIFICA- TION OF RADIANT ENERGY Joseph J. Daley, Boston, Mass, assignor, by mesne assignments, to Research Products Corporation, Boston, Mass, a corporation of Massachusetts Application October 24, 1927, Serial No. 228,249

10 Claims.

This invention relates to a novel method of amplification of radiant energy and the avoidance of such currents as produce undesired oscillation in the amplifier circuit. Heretofore, the oscillations produced. by these currents were largely the limiting factor in radio frequency amplification, and it was found necessary to suppress them by resorting to external means to produce other currents in opposition, or to introduce high resistance into the circuit. Either method was undesirable since the introduction of resistance materially reduced the efficiency of .the circuit, making it less sensitive and less selective; while the method depending upon the production of an opposing current not only reduced the overall efiiciency of the amplifier, but was in itself effective only over a .very limited range of frequency. v r

Heretofore all systems of reception and amplification of radiant energy were built around the conception that these disturbing currents and their consequent oscillations were inevitable. Certain systems sought to force these oscillations further, to produce a form of amplification in connection with the detector tube but this gave rise to very serious distortion and undesirable noises. When true amplification at high frequencies was attempted these oscillations, as

. stated above, became the limiting factor and had to be damped and suppressed before any appreciable degree of amplification could be obtained. It has been found that when these undesired oscillatory currents have been suppressed to a degree that permits of reasonable amplification, the desired and useful oscillatory currents in the circuit have also been suppressed to a very considerable degree, thus reducing the efiiciency of the entire circuit.

- I have found that between the zone of forced oscillations and the zone of damped oscillations there exists a critical point at which there is no flow of disturbing current and consequently no undesired oscillations. In my invention I have brought about this condition of true non-regeneration, never before realized, by a novel arrange.- ment of inductances and capacities which in themselves constitute the amplifier circuit. The electrical relation of the various parts of the circuit is such that this condition of true non-regeneration is automatically maintained for any desired frequency; and since no undesired oscillations can now exist, all necessityfor their suppression has been eliminated. This novel arrangement of inductances and capacities more specifically described below produces a higher degree of amplification per stage than has been obtainable by any other system and eliminates entirely the distortions and noises set up when undesired oscillations are present.

I have also found that distortion and unstable operation in an amplifier may be present even when the undesired oscillatory currents are not present. This condition is brought about by the flow of currents, desirable in themselves, in a path where they do not belong. In other words, to obtain a high degree of efficiency in amplification without distortion, the circuit must contain only the useful and desirable currents and their flow must be restricted to their proper and useful paths. The means by which I accomplish this object are described in detail below.

Thus this invention makes possible full and efficient amplification at any desired frequency and equal amplification at all frequencies without disturbing currents.

Since the energy transfer due to electromagnetic coupling increases with an increase of frequency, and since the magnetic coupling remains constant at its optimum value, the point is quickly reached at which the tube will go into violent oscillation, thereby destroying all reception or amplification. In my invention, however, the energy transfer trakes place not only by means of electromagnetic coupling, but also by means of electro-static coupling simultaneously. The value of energy transfer through static coupling is not a function of frequency, and if the value of the static coupling were constant, the combination of magnetic and static coupling must still vary with frequency in approximately a straight line ratio. If the value of the static coupling could be made to varycoincidentally with changes in received frequency but in the inverse ratio, the combination of magnetic and static coupling could be made to produce, by a proper selection of values, the maximum transfer of energy without permitting at any time the existence of disturbing ourrents which produce uncontrolled oscillation in In this electro-static leg, the tuning condenser is to the coupling condenser in about the ratio of 1 to 20, and is variable. Therefore, as the system is tuned to a higher frequency, the value of the tuning condenser is reduced, thereby reducing the where C1 is the variable tuning condenser, and C2 is a capacity of fixed value. For any desired band of frequencies, the value of C1 must be such as to produce the proper tuning with its associated inductance, and at the same time its variation for the purpose of tuning must be of a magnitude that the change in the total capacity (C will be inversely proportional to the change in Value of the magnetic coupling due to change of frequency.

When the proper values have been obtained, the act of tuning will automatically maintain the proper balance between the electromagnetic and electro-static legs, thus maintaining the maximum energy transfer at all frequencies, and preventing the production of any disturbing currents to cause undesired oscillation.

In addition, all other undesired currents :are excluded from the circuits, and all undesired transfers of energy from one part of the circuit to another is eliminated by means of choke coils and condensers as shown hereinafter.

The inductances used in the magnetic leg of this amplifier circuit take the form of transformers. I have found as a result of a long series of experiments that the introduction of a direct current into the primary of such a transformer is extremely detrimental. The radio currents impressed upon the primary of such a transformer are necessarily of a very low intensity and are modulated for example by voice frequencies, music or other modulating frequencies. It is desired that the current induced in the secondary winding of the transformer retain without any change the modulation characteristics of the original current although there may have been a certain definite increase in voltage. If any direct current is allowed to flow in the primary coil, the magnetic field intensity is inevitably increased. This field intensity may increase until its results are comparable to the phenomenon known as core saturation in iron core transformers. Its effect is to dampen or suppress the fine variations of the modulated current, in fact it may entirely eliminate some of the weaker modulations. As a result of this, the current induced in the secondary of a transformer in which direct current is allowed to flow in the primary, does not contain a true reproduction of the modulations existing in the radio current originally impressed on the primary.

Since these modulations represent and are produced by the original voice, music, etc., and on them, after rectification, depends the reproduction of that voice or music, it is obvious that if they are changed or suppressed or eliminated to any degree in transit, the resulting reproduction must be untrue and distorted. To meet this condition I have introduced into the plate circuit a capacity so arranged as to prevent all direct current from flowing into the primary of the transformers, but at the same time, permitting free flow of the modulated pulsating radio frequency current into the said primaries.

It must be noted that the interposition of such a capacity will result in a change of phase in the current flowing in the primary of the transformer so therefore I reverse the direction of the winding of the primary coil in order that the current in it may be again restored to proper phase.

When direct current is allowed to flow in the primary of the transformers the resulting intensification of the magnetic flux also greatly enlarges the external field of the coil. Thus it becomes increasingly difficult to prevent undesired energy transfer through inter-stage coup-ling. If shielding is used the shields for each stage must be made so large as to be unpracticable, otherwise the entire efiiciency of the amplifier is greatly reduced as a result of the large eddy currents set up. By eliminating all direct current from the transformers, as I have done in my invention, the external field is so reduced that small close shields may be used and all interstage coupling removed. In fact the external field is so small that in many instances shielding may be dispensed with.

I have also found that the voltage drop across the high resistance of the common source of plate current supply created by the passage of the pulsating current flowing back from the plate may effect a coupling between stages or a feed back to the grid circuit. I have placed choke coils of such values and in such a position in the plate circuit of each stage and thereby eliminated entirely this very detrimental effect.

The drawing forming part of this specification illustrates in diagram the circuits embodying my invention. The drawing shows two stages of radio frequency amplification although the invention is not restricted to that number. One is in the antenna circuit and each stage consists preferably of an air core radio frequency trans former having a minimum of dielectric losses, of which I is the primary and 2 is the secondary. This transformer is tuned by two condensers or other capacities, one of which, 3, is variable, and 4 is fixed; the condenser 4 being in series con nection electrically with the condenser 3, and both being in shunt connection across the terminals of the secondary coil 2, thus making the combination of capacities 3 and 4 variable when 3 is varied. The circuit also contains an electronic tube having grid 5, plate 6 and filament l.

The filament I is connected to its battery in the usual manner, and has in its circuit a suitable resistance 8, preferably in the negative side, to maintain the proper operating'condition. The grid 5 is connected to one end of the secondary coil 2; the other end of the secondary constituting the grid return being connected into the negative side of the filament circuit at a point between the resistance 8 and the battery.

The plate 6 is connected to its battery through a radio frequency choke coil 9, and to the primary I of the next following radio frequency transformer through a condenser I0.

In this way, while the direct component of the plate battery may pass readily to the plate 6 through the choke 9, it can never flow into the primary l of the radio frequency transformer because of the interposition of the condenser I0. On the other hand, the electromagnetic component on the plate being of a modulated pulsating nature will flow readily into the primary coil I through the condenser 10 where it is desired,

but is effectively checked from flowing further into the plate battery circuit or through it into adjacent stages of amplification where it is not desired, by the interposition of the choke 9. The primary coil I has its one end connected to the plate of the preceding tube through the condenser IO, or to the antenna in the case of the first stage, and its other end connected to the common connector between the rotor plates of the variable condenser 3 and one side of the fixed condenser 4.

Thus the variations in the electromagnetic side (the coils I, 2) due to change of frequency are compensated for in the electro-static side which is made up of the condensers 3 and 4, since there exists between the primary l and the secondary 2 not only magnetic coupling but also static coupling through the condenser 4 which is itself in series with the condenser 3, and variable with it.

It is essential for the operation of this circuit that the coil I be always in phase with the coil 2, and since the condenser I 0 serves to reverse the phase of the input to the following primary I, this primary must be in itself reversed in phase so that the resulting current is once more brought into proper phase with the current in the coil 2.

What I claim as my invention is:

1. A system of amplification of radiant energy comprising in combination an electronic device, the input of which consists of a transformena variable capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the variable capacity and said series capacity combination being connected in shunt across the secondary of the transformer; an output circuit comprising in combination a transformer, a capacitive self-impedance connected in series with the plate of the electronic device and the following primary of said transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, the series capacity combination being connected in shunt across the secondary of the transformer, said secondary providing output terminals for the system; and the plate of the electronic device being connected to a source of direct current through an impedance placed in series between the plate and the source of direct current for the purpose of preventing the flow of alternating current back through the source of direct current supply, but allowing the free flow of the modulated alternating currents from the plate through the primary of the transformer.

2. A system of amplification of radiant energy comprising in combination an electronic device, the input of which consists of a transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the variable capacity and said series capacity combination being connected in shunt across the secondary of the transformer; an output circuit comprising in combination a capacitive selfimpedance connected in series between the plate of the electronic device and the following primary, a transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, the series capacity combination being connected in shunt across the secondary of the transformer, combined with one or more successive stages of amplification, each stage comprising in combination an electronic device whose grid input is connected across the terminals of the secondary and whose output circuit is comprised of the elements of the output circuit above mentioned; and each plate of the electronic devices being connected to a source of direct current through an impedance placed in series between each plate and the source of direct current for the purpose of preventing the flow of alternating current back through the source of direct current supply, but allowing the free flow of the modulated alternating currents from the plates through the primaries of the transformers.

3. A system of amplification of radiant energy comprising in combination a first and a following electronic device, said first electronic device having input means, and an output circuit consisting of a transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the variable capacity, and both capacities being connected in shunt across the secondary of the transformer, the high potential end of said secondary being connected to the grid of the following electronic device and the low potential end of the secondary being connected to ground or the filament of the following electronic device or some common terminal; and another capacity connected in series between the plate of the first electronic device and the primary.

4. A system of amplification of radiant energy comprising in combination an electronic device, having input means, and an output circuit consisting of a transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the variable capacity, and both capacities being connected in shunt across the secondary of the transformer, and furthermore a capacity connected in series between the plate of the electronic device and the primary. 5. A system of amplification of radiant energy consisting of elements as set forth in claim 4 the output circuit elements of which provide capacities to form an electrostatic path of energy transfer whose value is definitely variable, and inductances comprising a transformer to form an electromagnetic path whose value is naturally variable with changes of frequency; the electrical relationship of these two paths and their impedance values, associated with the self-impedance values, being such that a maximum transfer of energy is obtained at every desired frequency.

6. A system of amplification of radiant energy consisting of elements as set forth in claim 4 wherein the capacity connected between the plate of the electronic device and the primary has for one of its purposes, in conjunction with its associated capacities, the prevention of the appearance of direct potential at the primary of the transformer, but permitting the free flow of the modulated alternating currents from the plate through the primary of the transformer and said plate being connected to its source of direct current through a high frequency impedance placed in series between the plate and the source of direct current for the purpose of minimizing the flow of alternating current back through the source of direct current supply, but permitting the flow of direct current from its source to the plate.

7. A system of amplification of radiant energy consisting of elements as set forth in claim 4,

combined with one or more additional stages, each stage having a capacity of suitable value connected between the plate of the electronic device and the following primary, and having a suitable source of direct current connected in shunt to a point in the circuit between said plate and the above mentioned capacity, and having a high frequency impedance of suitable value interposed in series in the above-mentioned shunt between the source of direct current and the plate, for the purpose of separating the current on the plate into two components, one of which is a modulated alternating component'wnich is allowed to pass freely into the transformer of such stage, but is highly impeded in its flow 'back through the common source of direct current supply, the other component being a direct current component which is allowed to pass freely from the direct current source to the plate, but is not allowed to appear at the primary of the transformer of such stage.

8. A system of amplification of radiant energy consisting of elements as set forth in claim 4, the output circuit of which comprises an electromagnetic mutual path and an electrostatic mu tual path of energy transfer, the impedance values of which are variable automatically by the act of tuning.

9. A system of amplification of radiant energy comprising an electronic device, the input of which consists of a transformer, a variable capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the variable capacity, and said series capacity combination being connected in shunt across the secondary of the transformer, and an output circuit consisting of a transformer, a variable capacity, a capacity connected in series between the primary and secondary of said transformer, said capacity being also in series with the variable capacity and both capacities being connected in shunt across the secondary of the transformer and furthermore a capacity connected in series between the plate of the electronic device and the primary, and the impedance values, both self and mutual, of said inductances and capacities being so selected and so related to each other as to result in a condition of energy transfer which is maintained constant at its maximum value at every desired frequency.

10. A system of amplification of radiant energy comprising an electronic device the input of which consists of a transformer, a variable capacity, a capacity connected in series betwee the primary and secondary of the transformer said capacity being also in series with the variabl capacity, and said series capacity combination,

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