US1770525A - Radio receiving apparatus - Google Patents

Description

July 15, 1930. 1.. L. JONES RADIO RECEIVING APPARATUS Filed July 15, 1927 2 Sheets-Sheet l S m R O ML N r I e l. L w n L2 -C Lo 02mm W. A J L B 7 OL.PIOU @CZQJDU g ATTORN EYS July 15, 1 930. L. JONES RADIO RECEIVING APPARATUS Filed. .July 15, 1927 2-5hoets-Sheet 2 ATTORNEYS atented July 15, 1930 UNITED STATES PATENT OFFICE LESTER Ia. JONES, OF ORADELL, NEW JERSEY a RADIO RECEIVING APPARATUS 7 Application. filed July 15, 1927. Serial No. 205,934.

This invention relates to radio receiving as I am aware, the amplifier circuits emapparatus, and relates more particularly to bodied a construction which reacte upon radio receiving apparatus embodying sepathe said first tunable input circuit in a manrate selective and amplifying systems wherener to cause with change of frequency a tranby the selection of the electrical oscillations sition from an unstable oscillatory condition 65 q of a desired frequency is accomplished prior which created distortions of tone to a dampto amplification thereof; and has special refing reaction which distinctly .destroyed the erence to the provision of an improved amselectivity of the selective circuit. Such prior plifying system especially adapted to be art amplifier circuits, incausing these changei 10 coupled to a separate selective system of such able or transitory reactions, are ill adapted 60 radio receiving apparatus. for practical use in receiving apparatus A prime desideratum of my present invenwhere separate systems or instrumentalities tion centers about the provision of an imare used for accomplishing the selection and proved electron discharge tube amplifying the amplification of the received energy.

system of the so-called untuned type having A prime object of my present invention 65 a selective or tuned input circuit; and the therefore resides in the provision ofan aminvention has for its object the production of plifier system embodying preferably a plua high and reasonably constant degree of amrality of untuned electron amplifiers arranged plification over a wide range of radio frein cascade which is adapted for connection quencies in such an amplifying system havto a highlyselective input circuit or a hi hly 7 ing fixed circuit adjustments, and especially selectiveselector system in which all of the without producing those reacting effects on reactions at'the input terminals of the' first the sharply tuned selective input circuit circuit of the amplifier are neutralized over which tend to change the selectivity thereof the whole wave length range of the receiver.

to values other than those that correspond to As is well known, the most common type of 7 the natural damping of the input circuit radio receiving apparatus employed in comalone.' merce is the so-called tuned radio frequency It is now well known that clear reception system which comprises a series of tuned ms of broadcast transmissions depends largely caded circuits, each circuit of the series emupon maintaining the tunable circuits at suitbodying an audion or electron discharge de- 80 able degrees of selectivity so that on the vice, the audion stage being coupled together one hand they will not be so'broad as 'to and to the energy receptor (antenna) by pick up several different transmissions simulmeans of tuning elements. In these tuned rataneously, nor on the other hand be so sharpdio frequency systems each stage of the cirly tuned as to discriminate between radio frecuit series functions as a frequency selector 5 quencies comprising a single IQH P and energy amplifier of the signal impressed In an elec r discharge tulle p y s 37 upon the energy receptor or antenna. The f havlng fixed cll'cult adlllstnflents d P building, design or construction of tuned ra- W f b selfmtllfe first l dio frequency receivers throughout the dey 40 t 1S rfiqtuslte to 't the Stabll' velopment of the art has been beset with nuof and elfmutate 2 getwtlons upon title merous difliculties requiring scientific and en- 323353 3 g gig g g f giff zggg z gineering development; and such difficulties selectivity of the system. Where, as in the g Increased fi tig s q this f as 45 ideal cas the optimum selectivity isf disired A izg igf fii ig g g r sgggai g a o Over the whole Wave length range 0 t 8 re The difiiculties encountered have multiplied ceiver, the reactions at the tuned input circuit must be eliminated or neutralized at all almost geometrlcauy Wlth the number of frequencies over the Wave length band, In tuned stages required, so that the physical 50 prior untuned amplifying systems, as far limitations of tunedradio frequency circuits have imposed a limit to the selectivity and sensitivity achievable.

By my present invention I propose to deviate from this prior practice of cascading tuned radio frequency audion stages wherein the selectivity and amplification of the energy are simultaneously accomplished, and I propose to utilize separate instrumentalitles or systems for accomplishing the selection of the frequency and the amplification of the energy, these separate selector and amplifying systems functioning to produce a highpowered receiver of great selectivity.

To accomplish this general object, I have found that the selector system, devoid of electron discharge devices or separate energy sources, should be organized so as to constrain the flow of energy through each of the cascaded circuits of the selective system, and so as to prevent any but the first circuit of the series from receiving energy from an extraneous source. I have further discovered that these circuits of the selective system may be so operated as to effect a maximum transfer of energy with a minimum energy loss in the transmission of the energy; and that when so organized a maximum and full geometric selection of the energy is effected. A selective system embodying organized circuit instrumentalities for accomplishing these results is generically described in the present application, but is more specifically described and broadly claimed in my copending application filed herewith, Ser. No. 205,935, of July 15, 1927.

I have further discovered that to produce a successful radio receiver in which the frequency selecting equipment or system is separated from the energy amplifying system, the amplifier (of the electron discharge tube type) must be designed so as to prevent any disturbing reactions from reaching the selector system as aforesaid, and that Such an amplifier should be associated with the selective system to operate upon only the selected energy coming from the selector system. This inter-relation between the selective SYSQQ J and the amplifying system is described specifically in the present application, and is broadly claimed herein.

While I show the improved untuned amplifying system of my present invention associated with a separate selector system of the type in which selectivity is accomplished by geometric progression, producing in combination a radio receiving apparatus of the character referred to, I desire it to be understood that the amplifying system is capable of and adaptable for use with a single selective circuit or may be associated with other selective circuits following the amplifying apparatus, all as will be clear from a consideration of these disclosures.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other, as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show the preferred embodiment of my invention, and in which:

Fig. 1 is a diagrammatic view showing the combination of the selector and amplifying systems forming a radio frequency receiver of my present invention. Figs. 2 and 3 are graphs of the characteristics and eflects of the circuits of the amplifier explanatory of some of the principles of my invention.

Fig. 4 is a graph showing the effect upon an input circuit of the characteristics of an output circuit built in accordance with some of the principles of the invention, and

Figs. 5 and 6 are graphs of the requirements of certain circuits of the amplifier for producing the non-reacting condition at the first input terminals of the amplifier over the Whole wave length range for which the amplifier is built.

Referring now more in detail to the drawings and having reference first to Fig. 1 thereof, I show a radio receiving apparatus comprising a selective system generally designated by the bracket S and also by the legend Selector and an audion amplifying system generally designated b the bracket A and also designated by the egend Amplifier, the selector system S comprising a plurality of circuits in cascade tunable to effect selectivity in geometric progression, and the amplifier A comprising untuned audion or electron discharge tube stages coupled to the last selective circuit of the selector system S. I

The structure of and specific functional inter-relations between the parts of'the selector system S are particularly described in my aforesaid copending application filed herewith Serial No. 205,935, of July 15, 1927; and in the present application I will confine the description of the selector system to the broad structural features of and functional inter-relations between the parts thereof.

This selector system comprises three or more tuned or selective circuits S1, S2 and S3, coupled together preferably inductively by variable coupling means 12I and 13-I the elements 12 and 13 comprising the adjustable coil units which are simultaneously adjustable for the purpose of producing similar or like degrees of coupling in the adjustable coupling means between the circuits S1S2 and S2S3, the simultaneous and similar adjustment being indicated by the arrowed lines 14 and 15 diagrammatically shown as connected together and controlled by a single dial 20.

The first selector circuit S1 is coupled to an energy receptor ant by means of the coupling condenser 10 and the last selector circuit S3 is coupled to the filament rid circuit of the first tube of the amplifier Each of the selective circuits is tunable preferably capacitively, said circuits being provided for this purpose with tuning condensers designated as C with an exponent corresponding to the circuit of which it forms a part; and the first selector circuit is provided with an inductance I of magnitude similar to those incorporated in the other selector circuits. Where the tuning condensers C, C and C are desired to be simultaneously adjusted for uni-control, the additional capacity added by the antenna ant and its coupling condenser 10 is made equal to the tube input capacity effective at the output terminals of the selective circuit S3 and a small fixed condenser 11 equal to this capacity. is placed in shunt with the variable condenser C of the circuit S2.

The three selector circuits S1 to S3 are capacitively and inductively shielded or decoupled from each other except for the adjustable'energy coupling means P12 and P13; and to accomplish this the main inductances I, I and I are made astatic, these inductances being either of the binocular type or of the concentric astatic type described and claimed in my patent to coil system, No. 1,608,560, of Nov. 30, 1926, the construction being such that there is freedom from magnetic and electrostatic coupling between these inductances. The condensers of the circuit are preferably of the grounded rotor type, so that there is freedom from intercapacitive coupling between these elements. The low potential side of each selective circuit is grounded as at 16, 17 and 18 respectively, and each of the circuits is made highly efficient by the use of Litz wire coils and dielectric mountings of low loss.

With this construction the first and third selector circuits are capacitively and induc tively decoupled from each other so that the energy transferred from the first to the third circuits of the-series is constrained to flow through the second or intermediate circuit of the series, and all of the selector circuits save the first-is prevented from picking up energy from an extraneous source. This decoupling is diagrammatically represented by the broken dotted line 19 in Fig. 1 of the drawings. Each'of the tuned circuits of the series therefore contributes its share to and forms a full component in the selectivity of the system, since that coupling between a circuit and a non-adjacent circuit which results in virtually eliminating an intermediate circuit of the series as a selector component is effectively prevented. The similar and preferably simultaneous adjustment of the adjustable couplingmeans produces a maximum energy transmission with a minimum energy afore-related, so as to inhibit over the Whole wave length range of the system any reactions upon the selector system which tend to destroy the selectivity thereof. Other important requirements of the amplifier are that the various input circuits of the amplifier should possess inherentstability, that is, no

instability or oscillation in any stagethereof, that the amplifier as a whole should be prevented from picking up any energy except that fed thereto from the selector system, and that the amplifier should desirably be sufficiently powerful to increase the signal to a volume suitable for operating the audio system even though the couplings in the selector system be made quite loose, this so as to permit said loose couplings to, be used and realize the full'geometric selectivity of the system.

To accomplish these results, my invention is directed to the provision of an amplifier embodying a' series of electron discharge tubes and having a pair of tubes first in the series which are so organized as to eleminate all damping reactions and oscillating creating tendencies at the input terminals of the first tube of the series. I have discovered, as

aforesaid, that in the prior art amplifying systems there existed a transition from an unstable oscillatory condition at the input terminals of the first tube, which created distortions of tone, to a damping reaction, at such input terminals which distinctly destroyed the selectivity of the selector circuit or system; and therefore to eliminate these reactions and the transition'from an oscillatory condition to a damping reaction, the cascade audion amplifier A of the invention is equippedwith a pair of tubes T1 and T2 of the triode or three-electrode type coupled to-, gether and to subsequent circuits of the series in such a way as to eliminate or balance all of the reactions at the input terminals of the tube T1 throughout the wave length range of the receiver.

Each of the tubes T1 and T2 comprises the usual grid, plate and filament g, p and f respectively, the filaments of the tubes being connected by means of filament circuits to the loss in the transmission of the energy through A battery designated A Both filament circuits may be suitably provided with fixed resistors such as r, 1'. The B battery designated -B+ is connected in the usual way to the A battery and to the output circuits 5 of each of the tubes T1 and T2, a bypass condenser 21 being employed connecting the plus side of the B battery to the minus side of the A battery. The input and output circuits 11, 0, and 0 of -.he tube stages T1 and T2 are connected to the tube electrodes and batteries as shown in the drawings.

To balance the reactions at the input terminals of the first input circuit 2'', the circuit network of the amplifying tubes T1 and 15 T2 are, generically speaking, so organized as to cause such network to act or behave as a pure reactance, either capacitive or inductive. To permit of uni-control for the selective system S, this amplifier circuit network should further be designed so as to produce a constant reactance at the input terminals of the first input circuit i. In the construction exemplified in Fig. 1 ofthe drawings, this reactance is capacitive. \Vhen the circuit network of the amplifier A is made to react thus as a pure capacitance over the whole wave length range. (all positive and negative resistances effective on the input circuit 2" being eliminated for the whole wave length range), I have found that the selectivity of the selector system S, or more generically of the selective circuit S3, remains unimpaired and is capable of optimum operating results; and when such a capacitance is maintained constant, uni-control of the selector system S may be accomplished.

To attain this balance or neutralization of the reactions at the input terminals of the first tube T1, I first fix the constants of the output circuit 0 in accordance with the principles described and claimed in my copend ing application Serial No. 51,569 of Aug. 21, 1925, now Patent No. 1,713,132 of May 1 1, 1929, or in my Patent No. 1,620,661 of Mar. 15, 1927, the natural frequency of this output circuit in connected circuit being greater than the highest frequency of the whole frequency range through which the input circuit I" is tunable. By the natural frequency of this output circuit, I mean the natural frequency of the impedance network hanging onto the plate of the tube or the natural frequency of the impedance L of the output circuit 0 in connected circuit. \Vith this char- 55 acteristic imposed upon the output circuit 0,

-there are produced feed-back reactions from the output circuit 0 to the input circuit 2" for the whole frequency range of the receiver.

The reason for this may be explained by 60 reference to Fig. 2 of the drawings. If the output impedance network has a natural frequency at a point within the range of the frequencies of the wave length band of the system, as in structures of the prior art, the 66 output circuit possesses characteristics which may be represented by the resonance curve 0 of the graph of Fig. 2 of the drawings, this resonance curve having its peak within the wave length range (200 to 600 meters) of the receiver. The section ab of the curve 0 produces a capacity reactancc, and has the effect of producing a damping in the input circuit of the tube; while the section be of the curve O produces an inductive reactance and has the effect of producing a feedback reaction in the said input circuit of the tube, the point 5 being the point of transition from damping to feed-back. To eliminate the transition point and to fix the reactions to a feed-back reaction which may subsequently be eliminated or neutralized, I select the natural frequency of the output so as to be comparable with or preferably greater than the highest frequency of the whole frequency range, so that the resonance curve of the output circuit is shifted to the position shown by the curve P of Fig. 2 of the drawings. Inspection of the curve P will show that the inductive reactance or feed-back-creating section bc' thereof lies wholly within the wave length range of the receiver, and there results an oscillation creating tendency in the input circuit over the whole wave length range which is then capable of being neutralized.

For neutralizing this feed-back reaction, I employ resistance means in the plate circuit of the tube-T1, which resistance means is selected of such a magnitude as to cause a feed-forward action from the input to the output circuit equal to the feed-back action produced by the output circuit through the capacitive coupling of the tube structure, which resistance functions, even though fixed in magnitude, for neutralizing this feed-back reaction over the whole wave length range. This resistance, represented as R in Fig. 1 of the drawings and arranged preferably between the plate and the inductive component of the output circuit, may be of the order of 1600 ohms, and is selected in accordance with the laws or rules described, for example, in my aforementioned application Serial No. 51,569, now my said Patent No. 1,713,132, or in my Patent No. 1,620,661, as well as in my application Serial N o. 742,-

342, of Oct. 8, 1924, now Patent No. 1,713,130,

patented May 14, 1929. This resistance may, for example, be about 1600 ohms.

The output circuit 0' with this determined characteristic is then coupled to the input circuit i by means of a coupling condenser K and an inductance M, the condenser K being tapped at a midpoint of the resistance R as shown in the drawings, the capacity K and inductance M when taken in series having preferably a natural frequency lower than the lowest frequency of the band to be transmitted through the amplifier. Preferably also the plate side of the resistance R is shunted by means of an inductance N and a condenser D. The inductance M may be loosely coupled to the plate inductance L, but preferably is closely coupled thereto.

5 an example of suitable magnitudes of these constants, the section of resistance R between the plate and the intermediate tap may be 920 ohms, the remainder of the resistance R about 707 ohms, the coupling condenser K about 250 mmfs., the inductance N 22 microhenrys, and the condenser D, 150 mmfs. The inductance M is preferably divided into two sections, one section transformer coupled to the inductance L and the other a free section, the free section being about 485 microhenrys and the transformer coupled section about 150 microhenrys, both arranged so as to inductively aid each other. The transformer coupled parts are preferably bifilarly wound after the manner described and claimed in my copending application Ser. No. 195,631 of June 1 1927, to transformer and coil system.

I have found that while neutralization at the input terminals of the tube T1 can'be effected by the means thus far described over the whole wave length range of the receiver, that there are residual variations in the exact balance of the feed-forward and feedback reactions over the wave length range due largely to feed-back reactions from the tube T2 (distant stage feed-back as distinguished from adjacent stage feed-back of tube T1), these variations being of the order of magnitude of about 5% of the reaction due to an adjacent stage feed-back. It is, however, desirable in a system having its selectivity determined only by the constants of the tuned circuits, to approach more exactly to theexact balance of feed-forward and feedback over the entire wave length range. I have discovered that this most exact balance can be obtained over the wave length range by producing slight variations in the input capacity of the second tube of the couple, the tube T2. This I accomplish by predetermining the characteristics of the second output circuit 0 of the amplifying tube pair.

More specifically, I have found that the residual reactions which, as stated, are due largely to a distant stage feed-back, may be eliminated first by selecting the constants of the output circuit 0' so as to just neutralize on the long waves, this producing a residual over-damping for the short Waves, and by then neutralizing these residual damping re actions by producing varying input capacity for the second tube T2,this input capacitybeing effective as a varying capacity across the output 0 of the tube T1. The input capacity should rise or increase at the longer wave lengths, so as to neutralize said increasing damping reaction at the short wave lengths.

This rising input capacity for the tube T2 I- efl'ect by selecting the output circuit 0 to have a natural frequency of the order of and preferably lower than the lowest frequency of the wave length band. Thus the output circuit 0 of the tubeTl is organized so that over the wave length band there is produced an energy feed-back reaction from the out-put circuit to the input circuit through the grid-plate capacitive coupling of the tube neutralized except for a residual feed-back reaction at the long waves of the wave length band; and the output circuit 0 of the tube T2 is organized so as to be effective for producing a rising input capacity of the second tube at the longer wave lengths for neutralizing this residual feed-back reaction.

The characteristic of this output circuit 0 and its effect upon the input capacity of the tube T2 is diagrammatically represented by Fig. 3 of the drawings. In this figure, in part similar to Fig. 2, the curve OX represents the resonance curve of the output transformer or impedance when the same is selected to have a natural frequency Within the wave length range of the receiver. The section at of this curve produces a capacity reactance and has the effect of causing a rising input capacity with increasing wave length in the input circuit ofthe tube with which the output circuit is associated, the curve be producing an inductive reactance and having the effect of causing a decreasing input capacity with increasing wave length. Now it will be seen that where it is desired to have a rising input capacity with increasing wave length over the whole wave length range, the curve OX should be shifted to the right and be transformed into a curve PX,

with the section (17) thereof (producing the rising input capacity) within the full operative range of the receiver.

The efiect on the input capacity of the tube (T2) of the output characteristics of such tube, is shown by the graph of Fig. 4 of the drawings, wherein the abscissae represent the wave lengths in meters and the ordinates the capacity in mmfs. between the grid and filament terminals of the input circuit. It will be noted from this curve that by suitably selecting the output characteristics as described, a rising input capacity from about 15 mmfs. to 60 mmfs. may be secured over a wave length from 200 to 600 meters.

In Figs. 5 and 6 are representative graphs showing values of input capacities (of tube T2) which I have found should be added over the wave length range to obtain the exact balance of feed-forward and feed-back reactions at the input terminals of the tube T1. Fig. 5 shows two curves giving the values of the input capacity for the tube T2 when the inductance L has a value of 124 microhenrys used with a standard type of electron relay having an input capacity of 10 mmfs., an amplification constant of 8, and a plate circuit resistance of about 10,000 ohms. Two

iso

curves are shown, one for a resistance R of 1100 ohms and the other for a resistance R of 1250 ohms. These curves show the input capacity of tube T2 which it is neces sary to obtain in orderto cause the feedforward reaction due to resistance R to exactly neutralize the feed-back reaction of the inductance L and its associated capacities. From these curves it will be seen that a slight diminution of input capacity is necessary as the frequency is increased. These curves also show that a decrease of resistance It must be accompanied by an increase of capacity from plate to ground to maintain the balance of. reactions.

In Fig.6 I have shown two other curves for the input capacity of tube T2 necessary to maintain the exact balance of reactions for the wave length range. In this case, however, the inductance L is shown increased to a value of 143 michrohenrys. The tube used is the same as that described for Fig. 5. Both of the inductance values for L produce resonant frequencies in the non-tunable output circuit which are higher than the highest frequency to which the tunable circuit S3 may be tuned. (In this case 200 meters wave length.) In the latter case, however, the inductance produces a resonant frequency in the non-tunable output R, L which is much closer to the highest frequency to which circuit S3 can be tuned; and in this case the variation of the following tube input capacity for the condition of no reaction is sharper over the wave length range.

Now by comparison of the input capacity requirement of Figs. 5 and 6 with the input capacity derivable from the output characteristics as shown in Fig. 4, it will be readily seen that the non-tunable transformer or output circuit 0 may be given a natural frequency so as to produce a desired variation.

of the input capacity of the tube preceding the same. The method of procedure preferably is to select L and R in accordance with the directions already given. A variable condenser is then connected in place of the grid and filament of the tube T2. This is adjusted at each wave length to secure the exact freedom from reaction of the tube T1 on the selector circuit S3. The curve relating these condenservalues with the frequency will be a curve such as shown in Figs. 5 and 6. This curve gives a picture of the variation of the input capacity of tube T2 required for creating the exact balance of feed-forward and feed-back reactions in the tube T1. The next step is to design the non-tunable transformer of the circuit 0 so as to give this relationship. In the embodiment of the invention shown, the transformer p -8 of the output circuit 0 is a bifilarly wound transformer of about 415 turns and having a natural frequency in connected circuit of about 625 meters.

By the provision of this construction I first stabilize the adjacent'stage reactions of the tube Tl, then neutralize the feed-back reactions in this stage, and finally impose a varying input capacity characteristic on the input of the second tube T2 by predetermining the characteristic of the output circuit of the tube T2; and by this combination of means I balance over the whole wave length range the feed-back and feed-forward reactions at the terminals of the first tube T1.

The amplifying system A is desirably shielded by an enclosing shield 23 so that any stage of the same is prevented from picking up any extraneous energy, the reception of the energy to be amplified being confined to the transmission of the selected energy from the circuit S3 to the input of the tube T1.

The balancing of all of the reactions at the first input terminals of the amplifier system, in eliminating over the wave length range all damping resistance in excess of the normal damping of the input circuit, has a two-fold effect on the selectivity of the selector system S. The absence of damping resistance over the whole range in the last stage of the selective system results in the production of a high and selective resonance point over the range and the absence of such resistance has the effect on the cascade selector as a whole of permitting a greater amount of energy transfer at lesser degrees of coupling between the circuits, so that the optimum condition of selectivity is efi'ectuated. Thus the improved amplifier of the invention permits of the maintaining of the highest geometric selectivity as well as the greatest amplitude of selectivity of the selector system.

The amplifier coupling tubes T1 and T2 described also possess an amplification characteristic which increases with the wave length. This characteristic is extremely desirable in connection with the cascaded capacitively tuned circuits preceding these tubes, and especially when such circuits are used in connection with the loop type of receiving antenna. It has been found experimentally that in'radio receivers of this type there is a considerable loss of sensitivity at the longer wave lengths as compared to that obtained at the shorter wave lengths. This loss of sensitivity is in part due to the lower reception efficiency of the loop at long waves. and in part due to the less favorable ratio of L/C which is obtained at the longer waves with capacitively tuned circuits. Although each tuned circuit shows a relatively small drop in amplification, of the order of 3 to 1. the cascading of these circuits causes a geometric increase in the ratio which again compounds with the drooping characteristic of the loop so that where three tuned circuits are used in cascade with the loopreceptor. the relative-sensitivities at the extremes of the wave length range are widely variable. The

. length range.

of a pair of untuned amplifier tubes (T1 and T2) having a sharply rising sensitivity with wave length tends to correct for the decrease in sensitivity and produces a receiver which responds much more uniformly to signals at the Various wave lengths within the range. I have found that the non-tunable transformer p s having the resonant frequency described will tend to produce a sharply rising amplification characteristic desired. The rising amplification characteristic of this untuned transformer is compounded with the rising amplification characteristic due to the circuit KM which couples the output 0' and the input :5 this coupling apparatus and its function to produce the rising amplification being described and claimed in my copending application Ser. No. 182,220 of April 9, 1927.

I have further found that in order to secure the input capacity characteristic de sired, that the second or short wave mode of oscillation of the transformer .9 must be either entirely eliminated or moved to a frequency range higher than the highest frequency to which the tunable input circuit may be adjusted. -In addition to this, it is also desirable that this transformer have the highest possible efliciency over the wave I have discovered that it is possible to secure this combination of conditions by constructing the transformer bifilarly as described and claimed in my aforesaid application Ser. No. 195.631 to transformer and coil system. Briefly considered. this transformer is wound with a pair of wires twisted together with a pitch relatively large compared to the wire diameter. One of these wires forms the primary winding and the other the secondary winding, and similar ends of the two windings connect with the plate voltage supply and filament connections of the tube. The bifilar winding is preferably random wound in a relatively narrow slot so as to form a coil of relatively small distributed capacityand of relatively high.

inductance. vThe inductance is made suitieiently great to give a natural frequency to the transformer in connected circuit as aforedescribed. I

Following the coupling tubes T1 and T2,

the amplifier A is made to comprise a plurality of so-called untuned audion amplifiers T3, T4 and T5 followed by a detector tube Deli, which latter is connected to the audio amplifying system.

While I have termed the tubes T3, T4 and T5 untuned amplifiers, in accordance with their designation of the prior art, I construct these tube stages in accordance with the prin ciples described and claimed in my copending application Ser. No. 198,061 of June 11, 1927, the said amplifying stages functioning for producing what I prefer to call an automatic tuning effect, causing the production of high and eflicient amplification over a considerable or relatively, wide wave length range or band.

As described in this copending application Ser. No. 198,061, now Patent No. 1,673,287 of June 12, 1928, the constants of the sequential circuits of the amplifying tubes (T3, T4 and T5) are selected so as to produce a self-tuning or automatic tuning of the system as a whole. This I accomplish more specifically by coupling the tube structure T3 and T4 with a transformer p 8 having a natural wave length of about 318 meters, then coupling the tube structures T4 and T5 by means of a transformer p 8* having a natural wave length of about 343 meters and coupling the tube structure T5 with the detecting tube Det. with a transformer 19 8 having a natural wave length of about 650 meters. Each of these transformers is preferably a bifilar tiansformer of the kind afore-described, the first being wound with about 210 turns, the second with 225 turns, and the third with 450 turns. The inductive component of the input circuit of the detector is also provided with a free section of inductance 25 which is ar-.

ranged with respect to the secondary s so as to have the mutuals aid. These circuits are connected to the A and B battery as shown, the B battery being preferably 90 volts and the A about 5 volts.

' The principle underlying this arrangement of amplifying tubes (T3, 4 and T5) is that the higher selected natural wave length of the last transformer of the series (3) a has the effect of producing a rising input capacity change with increasing wave length for the last amplifying tube T5 which is suited or made to coincide with that desired characteristic of the input circuit of said tube T which would cause the said input to vary its resonance frequency and thus to automatically tune itself over a considerable wave length band. This same relation is carried out in the coupling of the tube T4 to the tube T3, the natural wave length of the transformer 12*, a being greater than the natural wave length of the transformer 12 8 The interrelations between the circuits inseries should i also be considered. Thus the output of tube T4, being tuned to 343 meters, is tuned to a wave length that this output would have if the next tube T5 had no relay action. However, when tube T5 has relay action, its tube input capacity is higher than the geometric capacity by an amount due to the reaction of the output of T5. This causes a rise in the natural wave lengths of the 343'mete'r transformer, bringing it up to the region of 450 meters. The tube input capacity curve of T4 is therefore not like thetube input capacity curve of T5, because the output of T4, instead of having a single resonant frequency, has a group' of resonant frequencies which are determined by the automatic tuning efiect of T5 on the 343 meter transformer. The output of tube T3, which is designated as a 318 meter transformer, is acompromise for the capacity characteristic of tube T4. Generally speaking, the output of T3 by the arrangement shown is -automatically tuned to be held resonant over a wave length band of 320 to 450 meters, while the output of T4 is automatically tuned to be resonant over a range of 350 to 550 meters. Thus the three tubes are in effect two pairs of tubes, each pair control. lin the automatic tuning over a given and di erent wave length band, and both pairs covering the desired fullrange of frequencies.

The method of constructing and the operation of a radio receiving system embodying the principles of my present invention will be fully apparent from the above detailed description thereof. The numerous advantages in the combination of the selector system, coupling tubes and unturned audion amplifier stages. as well as in these instrumentalities considered apart from the combination and capable of use in other relations and other combinations, will also be apparent from the above description. It will also be apparent that while I have shown and described my invention in the preferred form, many changes and modifications may be made in ,-the structure disclosed Without departing from the spirit of the invention, defined in the following claims.

I claim:

1. An amplifier embodying an electron tube having input and output. circuits,' and means in the output circuit for causing a predetermined uni-directional variation in the input capacity of the tube with a variation in wave length, said uni-directional va- .riation being effective over the whole wave length range over which the amplifier is operative.

2. An amplifier embodying an electron tube operative for amplifying currents of fre uencies over a given wave length band, sai tube having input and output electrodes, and an impedance output circuit network connected to the output electrodes, the said impedance output circuit network having a natural frequency outside of the range of frequencies of said wave length band so as to be effective with the change in frequency over said wave length band for causing a uni-directional variation in the input capac- :ity of the tube over saidwave' length band,

said uni-directional variation being effective over the wave length range for which said tube is operative.

3. An amplifier embodying an electron tube operative for amplifying currents of freql'lencies over a given Wave length band having input and output electrodes, and an impedance output circuit network connected to the output electrodes, the said impedance output circuit network having a natural frecreasing input capacity of the tube being ef- 1 fective over the wave length band for which said tube is operative.

4. An amplifier embodying an electron tube operative for amplifying currents of frequencies over a given wave length band having input and output electrodes, and an impedance output circuit network connected to the output electrodes, the said impedance output circuit network having fixed constants and having a natural frequency corresponding to the lowest frequency of said wave length band so as to be effective with the change in frequency over said wave length band for causing the input capacity of the tube to increase with increasing wave lengths over said wave length band, said increasing input capacity of the tube being effective over the wave length band for which said tube is operative.

5. An amplifier comprising an electron tube operative for amplifying currents of frequencies over a given wave length band and having an input circuit and an output circuit capacitively coupled by means of the tube structure to the input circuit, the said output circuit being untuned and embodying a non-tunable impedance network for coupling the output circuit to a subsequent circuit, means for fixing over said wave length band the reactions of said untuned output circuit on the input circuit due to the said capacitive coupling and for neutralizing such fixed reactions,'said means being selected so as to produce ,a residual reaction on one side of the wave length band, and means for neutralizing said residual reactions whereby the reactions are balanced over the whole wave length band.

6. An amplifier comprising an electron tube having an input circuit and an output circuit capacitively coupled by means of the tube structure to the input circuit, mechanism for tuning the input circuit over a iven wave length band, the said output circuit being untuned and embodying a nontunable impedance network for coupling the output circuit to a subsequent circuit, means for fixing over said wave length band the reactions of said untuned output circuit on the tuned input circuit due to the said capacitive coupling and for neutralizing such fixed reactions, said means being selected so as to produce a residual reaction on one side of the wave length band, and means for neutraliz'ing said residual reactions whereby the reactions are balanced over the whole wave length band.

7 An amplifier comprising an electron tube operative for amplifying frequencies over a given wave length band having an input cir cuit and an impedance output circuit capacitively coupled by means of the tube structure to the input circuit, means for producing over said wave length band-an energy feed-back reaction from the output circuit to the input circuit due to the said capacitive coupling and for neutralizing such energy feed-back reaction, said means being selected so as to produce a residual feed back reaction on the long waves of the wave length band, and means for neutralizing said residual reaction whereby the reactions are balanced over the whole ivave length band.

8. An amplifier comprising an electron tube operative for amplifying frequencies over a given wave length band having an input circuit and an output circuit capacitively coupled by means of the tube structure to the input circuit, mechanism for tuning the input circuit, the said output circuit being untuned and embodying a non-tunable impedance network for a coupling the output circuit to a subsequent circuit, means for producing over said wave length band an energy feed-back reaction from the untuned output circuit on the tuned input circuit due to the said capacitive coupling and for neutralizing such reaction, said means being selected so as to produce a residual feed-back reaction on the long waves of the wave length band, and means for neutralizing said residual reaction whereby the reactions are balanced over the whole wave length band.

9. An amplifier comprising an electron tube operative for amplifying frequencies over a given wave length band and having an input circuit and an output circuit, sa1d output circuit having a natural frequency comparable with the highest frequency of said wave length band whereby an energy feed-back reaction from the output circuit to the input circuit is produced for the whole frequency range, means in said output circuit for neutralizing said feed-back reaction, the constants of said output circuit being selected so as to produce a residual feed-back reaction on one side of said wave length band, and means for neutralizing said residual reaction whereby the feed-back reactions are balanced over the whole wave length band.

10. An amplifier comprising an electron tube operative for amplifying frequencies over a given wave length band and having an input circuit and an output circuit, said output circuit having a naturual frequency greater than the highest frequency of sa1d wave length band whereby an energy feedback reaction from the output circuit to the input circuit is produced for the whole frequency range, means for neutralizing sa1d feed-back reaction, the constants of said output circuit and said means being selected so as to produce a residual feed-back reaction on one side of said wave length band, and means for producing a rising capacity with increasing wave length effective across said 7 -tube operative for amplifying frequencies over a given wave length band and having an input circuit and an out-put circuit, means for tuning said input circuit, said output circuit including an untuned impedance network having a natural frequency comparable with the highest frequency of said wave length band whereby an energy feed-back reaction from the output circuit to the input circuit is produced for the whole frequency range, resistance means in said output circuit for neutralizing said feed-back reactions, the constants of said impedance circuit and resistance being selected so as to produce a residual feed-back reaction on one side of said wave length band, and means for producing a rising capacity with increasing wave length effective across said output circuit for neutralizing said residual reaction whereby the feed-back reactions are balanced over the whole wave length band.

12. An amplifier comprising an electron tube having an input circuit and an output circuit capacitively coupled by means of the tube structure to the input circuit, means for neutralizing the feed-back reactions due to the capacitive coupling between the circuits, and means for producing a rising capacity with increasing wave length effective across said output circuit for neutralizing residual feed-back reactions effective on said input circuit.

13. An amplifier comprising an electron tube having an input circuit and an output circuit capacitively coupled by means of the tube structure to the input circuit, means for tuning the input circuit, the output circuit including an untuned impedance network, means for neutralizing the feed-back reactions due to the output circuit and the capacitive coupling between the circuits, and means for producing a rising capacity with increasing wave length effective across said output circuit for neutralizing residual feedback reactions effective on said input circuit.

14. An amplifying system comprising a pair of electron discharge tubes each having input and output circuits, the output circuit of the first tube being coupled by non-tunable means to the input circuit of the second tube, means for producing an energy feedback reaction from the non-tunable coupled circuits to the input circuit of the first tube for the whole frequency range of the system, means for neutralizing said feed-back reaction, and means in the output circuit of the second tube for neutralizing a residual feedback reaction effective on the input circuit of the first tube.

15. An amplifying system comprising a pair of electron discharge tubes each having. input and output circuits, means for tuning the first input circuit over a predetermined frequency range, the output circuit of the first tube being coupled by non-tunable means to the input circuit of the second tube, means for producing an energy feed-back reaction from the non-tunable coupled circuits to the input circuit of the first tube for the whole predetermined frequency range, means for neutralizing said feed-back reaction, the output circuit of the second tube being untuned and having constants for neutralizing a residual feed-back reaction effective on the input circuit of the first tube.

16. An amplifying system comprising a pair of electron discharge tubes each having input and output circuits, the output circuit of the first tube being coupled inductively to the input circuit of the second tube, means for producing an energy feed-back reaction from the output circuit to the input circuit of the first tube for the whole frequency range of the s stem, means for neutralizing said feed-baclz reaction, and means in the output circuit of the second tube for neutralizing a residual feed-back reaction effective on the input circuit of the first tube.

17. An amplifying system comprising a pair of coupled electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, the output circuit of the first tube and the input circuit of the second tube being non-tunably coupled together, means for neutralizing the energy feed-back reaction from the first output to the first input circuit, and means in the outut circuit of the second tube for neutralizmg residual feed-back reactions effective on the input circuit of the first tube.

18. An amplif ing system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, means for neutralizing the energy feed-back reaction from the first output to the first input circuit, the output circuit of the second tube having means for causing the input capacity of such second tube to increase with increasing wave lengths for neutralizing residual feed-back reactions effective on the input circuit of the first tube.

19. An amplifying system comprising a pair of electron discharge tubes operative or amplifying currents of frequencies over a given wave len th band, each having input and output circuits, means for neutralizing the energy feed-back reaction from the first output to the first input circuit, the output circuit of the second tube having a natural frequency comparable with the lowest frequency of said band so as to be effective for producing a rising input capacity of the second tube at the longer wave lengths for neutralizing residual feed-back reactions effective on the input circuit of the first tube.

20. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and out ut circuits, the output circuit of the first tube having a natural frequency comparable with the highest frequency of said Wave length band whereby an energy feed-back reaction from such output circuit to the first input circuit is produced for the whole frequency range, means for neutralizing said feed-back reaction, the constants of said first tube output circuit and the second tube being such as to produce a residual feed-back reaction effective on the first input circuit, and means in the output circuit of the second tube for neutralizing such residual reaction whereby the feed-back reactions on the input circuit of the first tube are balanced over the whole wave length band.

21. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, the output circuits of the first tube having a natural frequency comparable with the highest frequency of said wave length band whereby an energy feedback reaction from such output circuit to the first input circuit is produced for the Whole frequency range, means in said first output circuit for neutralizing said feedback reaction, the constants of said first tube output circuit and the second tube circuits being such as to produce a residual feed-back reaction effective on the first input circuit, the out ut circuit of the second tube having means or causing the input capacity of such second tube to increase with increasing wave lengths for neutralizing the residual reaction on the first tube.

22. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, means for tuning the first input circuit, the output circuit of the first tube having a natural frequency comparable with the highest frequency of said wave length band whereby an energy feedback reaction from such output circuit to the first input circuit is produced for the whole frequency range, means for neutralizing said feed-back reaction, the constants of said first output circuit and the second tube circuits being such as to produce a residual feed-back reaction effective on the first input circuit, the output circuit of the second tube having a natural frequency comparable with the lowest frequency of said wave length band so as to be effective for producing a rising input capacity of the second tube at the longer wave lengths for neutralizing the residual reaction on the first tube.

23. An apparatus for selecting and amplifying high frequency oscillations, comprising a selector circuit operative for receiving high frequency oscillating energy and for selecting energy of the desired frequency from such received energy, an untuned amplifier circuit network coupled to the selector circuit for receiving such selected energy and operative for amplifying the same, said untuned amplifier circuit network comprising electron discharge tube coupled stages having fixed constants and effective over a given wave length band for maintaining said stages automatically resonant over said given band, and means associated with the coupling between the selector circuit and the amplifier circuit network for eliminating the selectivity disturbing reactions of said amplifier circuit network on said selector circuit.

24. An apparatus for selecting and amplifying high frequency oscillations comprising an untuned amplifier including electron discharge tube coupled stages having fixed constants predetermined to maintain the stages automatically resonant over a given frequency band, a tunable selector clrcuit connected to and feeding into the input terminals of said untuned amplifier, and means for stabilizing the untuned amplifier to eliminate the selectivity disturbing reactions of said untuned amplifier on said selector circuit.

25. An apparatus for selecting and amplifying high frequency oscillations comprising an untuned amplifier including electron discharge tube coupled stages having fixed constants predetermined to maintain the stages automatically resonant over a given frequency band, a tunable selector circuit connected to and feeding into the input terminals of said untuned amplifier, and means for causing the untuned amplifier to act as a pure reactance at" the said input terminals over a given range of frequencies.

26. An apparatus for selecting and amplifying high frequency oscillations comprising a selector circuit network embodying a plurality of tuned circuits arranged in cascade and operative for receiving high frequency oscillating ener y and for geometrically selecting energy 0 adesired frequency therefrom, an amplifier circuit network embodying a plurality of untuned stages of electron discharge tubes also arranged in cascade for receiving such geometrically selected energy and oiperative for amplifying the same, said ampli er circuit network including electron discharge tube coupled stages having fixed constants and effective over a given wave length band for maintaining said stages automatically resonant over said band, the

output terminals of said selector circuit network feeding into the input terminals of said amplifier circuit network, and means for eliminating the selectivity disturbing reactions of said amplifier circuit network on said selector circuit network.

27. An apparatus for selecting and amplifying high frequency oscillations comprising a tunable selector circuit, an untuned electron discharge tube amplifier having fixed constants effective for maintaining resonance in said amplifier over a given frequency range, and means for coupling said untuned amplifier to said tunable selector circuit.

28. An apparatus for selecting and amplifying high frequency oscillations comprising a tunable selector circuit, an untuned electron discharge tube amplifier having constants effective for automatically maintaining resonance in said amplifier over a given frequency range, means for coupling said untuned amplifier to said tunable selector circuit, and means for stabilizing the tunable selector circuit and said untuned amplifier for preventing other than negligible reactance and resistance components from being reflected into the selector circuit for the whole frequency range for which the tunable selector circuit 1s operated.

29. An apparatus for selecting and amplifying high frequency oscillations comprising a tunable selector circuit, anuntuned electron discharge tube amplifier having fixed constants effective for maintaining resonance in said amplifier over a given frequency range, and an electron discharge tube stage coupling said untuned amplifier to said tunable selector circuit also having fixed constants and effective for producing a resultant pure reactance at the output terminals of said selector circuit over said frequency range.

30. An apparatus for selecting and amplifying high frequency oscillations comprising a tunable selector circuit, an untuned amplifier embodying a plurality of electron discharge tube stages, said stages having fixed constants effective for maintaining resonance in said amplifier over agiven frequency range, an untuned amplifier tube network coupling said untuned amplifier to said tunable selector circuit, and means for stabilizing said untuned amplifier tube network.

31. An electron discharge tube system comprising in combination with an electron discharge tube having input and output electrodes, an input circuit connected to the input electrodes and an impedance output circuit network connected to. the output electrodes, the said impedance output circuit network having fixed constants for causing a predetermined uni-directional variation in the input capacity of the tube with variation in wave length, said uni-directional variation being effective over the wave length range for which said tube is operative.

32. An electron discharge tube system comprising, in combination with an electron discharge tube having input and output electrodes, an input circuit connected to the input electrodes and an impedance output circuit network connected to the output electrodes, the said impedance output circuit network having fixed constants for causing a rising variation in the input capacity of the tube with increasing Wave length, said rising input capacity variation being effective over the wave length range for which said tube is operative.

An amplifying system comprising a pair of electron discharge tube stages operative for amplifying currentsof frequencies over a given Wave length band, each having input and output circuits, means coupling the output circuit of the first tube stage to the input circuit of the second tube stage, means for predetermining the reaction of the second tube stage effective through the grid-plate channel of the first tube on the input circuit of the first tube stage, and means in the said coupling means for combinedly neutralizing over the whole wave length range the said predetermined reaction produced by the second tube stage and the reaction of the coupled circuits efiective through said channel on the input circuit of the first stage.

34. An amplifying system comprising a pair of electron discharge tube stages operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, means non-tunably coupling the output circuit of the first tube stage to the input circuit of the second tube stage, means in the second tube stage for producing a damping reaction effective on the input circuit of the first tube stage, and means in the said coupling means for combinedly neutralizing over the whole wave length range the said damping reaction produced by the second tube stage and the feed-back reaction of the coupled circuits on the input circuit of the first stage.

35. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and output circuits, means coupling the output circuit of the first tube to the input circuit of the second tube, non-tunable means inthe output circuit of thesecond tube for producing a predetermined reaction effective on the input circuit of the first tube, and means in the said coupling means for neutralizing over the wave length band said predetermined reaction and for neutralizing reaction on said input circuit of the first tube due to the structure of the output circuit of the first tube and said coupling. means.

36. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of fre uencies over a given wave length band, eac having input and output circuits, non-tunable means coupling the output circuit of the first tube to the lnput circuit of the second tube, means for producing a predetermined reaction of the second tube e ective on the input circuit of the first tube, and means in the output of the first tube for neutralizing over the wave length band said predetermined reaction and for neutralizing reaction on said input circuit of the first tube due to the structure of the output circuit of the first tube and said coupling means.

37. An amplifying system comprising a pair of electron discharge tubes operative for amplifying currents of frequencies over a given wave length band, each having input and'out ut circuits capacitively coupled by means oi the tube structure, means associated with the first tube of the pair for neutralizing energy feed-back reaction taking place through the grid-plate channel of the first tube from the first output circuit to the first input circuit, means associated with the second tube of the pair for producing a predetermined variation of in ut capacity on the second tube of the pair e ective through said channel to produce a given reaction on the input circuit of the first tube, the said means in the output circuit of the first tube of the pair being organized and connected to the input circuit of the second tube so as to neutralize said given reaction due to the second tube.

38. An amplifying system comprising a plurality of electron discharge tubes operative for amplifying currents of frequencies over a iven wave len h band each havin 3 0 input and output circuits, means non-tunably coupling the first output circuit to the second input circuit, means associated with the first tube for neutralizing energy feed-back reaction taking place through the grid-plate channel of the first tube from the first output circuit to the first input circuit, means in the output of the second tube for producing a predetermined input capacity on the second tube effective through said channel to produce a given reaction on the input circuit of the first tube, the said coupling means being organized so as to neutralize said given reaction due to the second tube over the whole wave length range of the system.

Signed at New York city, in the county of New York and State of New York this 12th day of July A. D. 1927.

LESTER L. JONES.

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