US2169018A - Electric wave reception - Google Patents

Description

heet

G. L., BEER?? Aug.V '8, 1939.

ELECTRIC WAVE RECEPTION Original Filed April l? v LQIS 3 Sheets-S Mmmm nnJ-km G. LA BEERS Aug. 8, 1939.

ELECTRIC WAVE RECEPT ION Original Filed April 16, 1928 3 Sheets-Sheet 2 lNvENToR eO/fg'e 56ers.

ATTORN Augc 3, 1939. e. L. BEERS ELECTRIC WVE RECEPTION Original Filed April 16, 1928 3 Sheets-Sheet 3 WITNSSES:

ff/M A ATTORNEY Patented Aug. 8, 1939 ELECTRIC WAVE RECEPTION George L. Beers, Haddonfield, N. J., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Original application April 16, 1928, Serial No. 270,285. Divided and this application May 14, i937, Serial No. 142,559

7 Claims. (Cl. 250--20) This application is a division of my copending application, Serial No. 270,285, led April 16, 1928, Patent No. 2,082,478, dated June 1, 1937, and assigned to the assignee of this applicaof grid-biasing potentials from the anode-potential source.

Another object of my invention is to provide an eiiicient volume-control device for a radio retion. ceiving system. 5

My invention relates to electric wave reception A superheterodyne receiving system, constructand it has particular relation to the reception ed and arranged according to a preferred emand amplication of electric waves at radio-frebodiment of my invention, COmpriSeS a plurality quencies. of thermionic devices of the equipotential-cath- 10 Although certain phases of my invention are ode type interconnected in cascade through tuned l0 capable of broad application to radio receiving COllplng-trarlSfOrmerS and Supplied With aIlOde systems of many types, the invention, considered petentials and grid-biasing peterltialS frOm a as an entity, may be regarded as primarily directrectifying device that may be erlergiZed from ed toward improving superheterodyne receiving any convenient source of alternating current.

systems of the type disclosed in the patent to The rSt amplifying tube 0f the Series iS arl5 Armstrong, 1,342,885. ranged to be coupled to an energy-collecting de- One object of my invention is to provide e, vice through a substantially non-inductive resuperheterodyne receiving system that shall have SiStOr 0f Suieerlt magnitude t0 prevent the animproved selectivity characteristics. tenlla I'OIII radiating energy from the lOCal 0S- Another object of my invention is to provide cillator. The resistor does not affect the sen- 20 a superheterodyne receiving system in which the SitiVity 0f the System. so-called image-frequency response sha1] be The thermionic devices comprised in the interminimized, mediate-frequency amplifying stages are cou- Another object of my invention is to provide pled together thrOugh tuned transformers of a a superheterodyne receiving system that shall be nOyel tyDe- Considered frOm an eleetrieal Starld- 25 substantially incapable of radiating the locally point, the intermediate-frequency transformers generated oscillationsl are so proportioned that they are somewhat anal- Another object of my invention is to provide, OgOuS t0 band-Dass filters; CODSidered from a mein a superheterodyne receiving system of the uni- Chahieal StahdpOiht, they are SO mounted in incontrol type, means whereby the tuning of the OliVidual Shielding deVieeS, and S0 DI'OVided With 30 oscillator stage shall be unaffected by changing tuning eehdeuSerS having easily aeCeSSilOle adthe thermionic tube comprised therein. justing elements that they may be accurately Another object of my invention is to provide, calibrated and tuned before being mounted in a in a radio receiving System 0f the aforemencomplete receiver, with complete assurance that tioned type, improved inter-tube coupling transthe precalibration will not later be changed. 35 formers between the thermionic tubes comprised Volume-Control iS aCCOmPliSheCl by Varying the in the intermediate-frequency amp1ifergrid-biasing potential applied to all of the high- Another object of my invention is to provide, frequency amplifying tubes, SuCh potential being in a superheterodyne receiving system, improved derived from the anode'potentlal Supply through 40 means for securing the proper frequency re1a a resistor-network, and the. various` .thermionic 40 tion between the tuning of the oscillation genertubes Compnsed m the entire recelvtng system ator and the tuning of the radio-frequency amare so grollpd Wlth respfect. to the said' netwrk pufymg Stages that a variation of the biasing potentlal applled Another object of my invention is to provide agg hlgl'frqlllencyltue ds not grfatly 45 an improved circuit network for so intercontues e p0 en la apple o e remammg nectlng' a plurality Of -tl'iermlomc del/ICES com' I nd it preferable to connect all of the main pused m a will? recewmg system to, a sourfe tuning condensers together for simultaneous of anode potentlal therefor that varlatlonsl ln Control and it is accordingly necessary that the said anode-potential source shall be substantlalfrequency of the oscillations generated by the 50 ly ineffective to cause variations in the output from said receiving system.

Another object of my invention is to provide an improved circuit network of the aforesaid type that shall comprise means for deriving a plurality local oscillator shall not be aieoted when different thermionic tubes of the same type are substituted therein. I provide for this condition by coupling the frequency-determining circuit of the local oscillator, in which is included one of the said maintaining condensers, very loosely to the grid and cathode of the oscillator tube, in order that the grid-cathode capacity of the tube shall be negligible in fixing the frequency to which the said circuit is resonant.

In addition, I have provided a novel arrangement of series and shunting condensers in the frequency-determining circuit of the local oscillator, by the proper adjustment of which a variable tuning condenser of the ordinary concentric-plate type may be utilized to maintain a constant-frequency difference between the local oscillation frequency and the frequency of the incoming signal.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and additional advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken kwith the accompanying drawings, in which:

Figure l is aschematic wiring diagram of a complete radio receiving system comprising a preferred embodiment of my invention;

Fig. 2 is a diagram illustrating the manner in which the various thermionic devices comprised in my improved radio receiving system are supplied with grid-biasing and anode-potentials according to my invention;

Fig. 3 is a perspective View of one of the intermediate-frequency transformers, a portion of the shielding container thereof being broken away;

Fig. 4 is an end elevationalview of the transformer shown in Fig. 3;

Fig. 5 is a top plan View of the coil-and-con- Y denser-supporting element of the transformer assembly illustrated in Fig. 3;

Fig. 6 is a cross-sectional View taken along a line corresponding to the line VI-VI in Fig. 5;

Fig. '7 is a plan View of the under surface of the supporting element; and

Figs. 8 and 9 are modifications of the circuit of Fig. 2.

The radio receiving system illustrated in Fig. 1 comprises a thermionic coupling tube l, a radiofrequency amplifying tube 2, a first detector tube Z5, a plurality of intermediate frequencyamplifying tubes and 5, a second detector vtube 5, an audio-frequency-amplifying tube l, and an oscillator tube Allof the tubes, with the exception of the audio-frequency amplifier l, are of the equipotential cathode type illustrated in the patent to Nicolson, No. 1,459,412, and,reach tube, excepting the said audio-frequency ampliiier, is provided with a grid Q, an anode Ill, an equipotential cathode il, and a heater-element i2. All of the heater elements l2 are connected in parallel, by means of a plurality of conductors i3 and M, to the terminals of a secondary winding l5 of a power transformer it, the primary winding l of which may be enerii gized from any convenient source of. commercialand those of the first and second intermediate-- frequency-amplifying tubes and 5, are connected together through a conductor 23 which terminates in an intermediate point 2d on a resistor 25, in order to fix their potential with respect to they grids of the several devices and the ancdes thereof, in a manner hereinafter specifically described.

The cathode li of the first detector tube 3 is connected to the cathode l i of the oscillator tube 3 over a circuit including a conductor 26 and a coupling-coil Zi, the said cathodes, as well as the cathode of the second detector tube 6, being maintained at the same direct-current potential by a common connection 23 to one end of the resistor 25.

The coupling-coil 2l is positioned in inductive relation to an inductor Sii which is comprised in the frequency-determining input-circuit of the oscillator tube 8. A main tuning condenser 3i, a Vernier condenser 32 in shunt thereto, and a small variable condenser 33 are connected in shunt relation to the inductor Sil. The grid of the oscillator tube is variably connected to the inductor t@ through a grid condenser 34 and a stabilizing resistor 35, and a grid-leak 36 is provided to maintain the grid at the proper operating potential.

inode-potential for the oscillator tube E is derived from the positive terminal of a rectifying device later to be described in more detail, the supply circuit including a feed-back inductor 3l', positioned in inductive relation to the input inductor 3% which provides the necessary transfer of energy to maintain oscillations therein.

By reason of the inclusion of the inductor 2l in the connection between the cathode of the oscillator tube and the cathode of the rst detector tube, the local oscillation frequency is impressed on the first detector tube by causing the potential of its cathode to Vary with respect to the potential of the grid, instead of causing the grid potential to vary with respect to the cathode, as is usual. The stability of the system seems to be improved to some rextent by this v phase of my invention, since I am thereby enl.

abled to so modify the capacity-displacement curve of the main tuning condenser 3i that a constant-frequency difference may be maintained between the tuning of the oscillator and the tuning of the radio-frequency stages of the t.

amplifier without altering the shape of the oscillator tuning-condenser plates or without shifting the rotor thereof with respect to the stator.

The effective minimum capacity of the tuning condenser may be adjusted by the shunt condenser while the maximum effective capacity of the tuning condenser is determined by the ratio of the series condenser 33 to the total capacity of. the tuning condenser and the shuntV condenser. By properly adjusting the two added condensers, the curve expressing the relation between the total capacity effective to tune the frequency-determining circuit and the movement of the main tuning condenser may be made to quite closely approximate a predetermined shape. The great utility of the adjusting condensers 32 and 33 will be more apparent hereinafter.

rihe antenna-coupling tube I is provided with an input circuit comprising a resistor 38, one end of which is permanently connected to a grounded conductor 40 which terminates inI a variable contact device 4| associated with the biasing-potential supply resistor 25. The other end of the input resistor 38 is provided with a connection whereby the said resistor may be included serially in an energy-collecting circuit including anI antenna 2 and a ground connection 53. When the resistor 38 is included in the antenna-ground circuit, the antenna is rendered substantially incapable of radiating energy imparted thereto from the local oscillator, either through the coupling tube or through the space outside of the container in which the entire receiving system is mounted.

A variable contact device 44 may be provided to permit the grid of the coupling-tube to be so connected to the input resistor that the signalvoltage applied to the tube may be altered at will to secure a measure of volume-control.

Signal-energy from the couplingi tube is applied to the input circuit of the radio-frequency amplifying tube 2 through a transformer 45, which is provided with a high-inductance primary constructed according to the disclosure in my copending application, Serial No. 151,722, filed November 30, 1926, which has issued as Patent #1,907,478 of May 9, 1933, and a secondary winding having a variable tuning condenser 46 connected in shunt thereto.

Regeneration in the amplifying tube is controlled through the agency of a feed-back circuit comprising an inductor 41 coupled to the secondary winding of the inter-tube transformer 45, and a small variable condenser 48 connected between the inductor 41 and the anode |13 of the amplifying tube.

The amplifying tube 2 is coupled to the first detector tube 3 through a transformer 50 having a high-inductance primary winding and a secondary winding 52 shunted by a variable tuning condenser 53 and a fixed condenser 513 in series. The high-inductance primary winding 5| in the output circuit of the amplifying tube causes a certain amount of damping in the input circuit of the said tube, as explained in my aforementioned copending application, which accounts for the necessity of supplying the aforementioned feedback circuit to bring the amplification therein up to the proper value.

The first detector tube 3 is coupled to the rst intermediate-frequency amplifying tube 4 through a transformer 55 having a primary winding 55 shunted by a tuning condenser 5l and a secondary winding 58 shunted by a tuning condenser 6D. Oscillation in the first intermediate-frequency amplifying tube is prevented according to the method disclosed in the patent to Rice, No, 1,334,118, a small condenser 6|, connected between the anode of the tube and the lower end of the secondary winding 58, being utilized to supply the proper anti-oscillation potentials.

The first intermediate-frequency-amplyfying tube 4 is coupled to the second intermediatefrequencymamplifying tube 5 through. transformer 62, similar to that interposed between the first detector and the first intermediate-frequency amplifier, and the second intermediatefrequency-amplifying tube 5 is coupled to the second detector tube 6 through another analogous transformer G3. The three transformers 55, G2 and sing structurally alike, the several constituent parts of each have beenv similarly numbered in the drawings. Each transformer is totally enclosed by the non-magnetic shielding material, indicated by the dotted rectangles, to minimize interaction between the several amplifying stages.

There is no tendency toward regeneration in the second detector 6, and, for that reason, the neutralizing condenser 5|, which is a constituent part part of the transformer-assembly 63, when manufactured, is not needed for neutralicing, and it may, accordingly be connected in shunt relation to the tuning condenser 59, as shown.

The second detector tube 6 is coupled to the audio-frequency power-amplifying tube through an audio-transformer I of any well known type, and the output circuit of the power amplifier may be coupled to a loud-speaker through a biocking condenser i2, as illustrated, or through an output-transformer (not shown).

The tuning condenser 46, comprised in the input circuiti of the radio-frequency amplifying tube 2, the tuning condenser 53 in the input circuit of the first detector tube 3, and the tuning condenser 3| in the frequency-determining circuit of the oscillator tube 8, are all connected together, as indicated by the dotted lines 1,3, for simultaneous actuation, and the rotors thereof are connected to the grounded conductor 45.

In order to improve the selectivity of my receiving system, and to minimize the so-called image-frequency response, i have chosen an intermediate frequency of 180 kilocycles, and it is, accordingly, apparent that the frequency of the oscillator must always differ from the frequency of the desired signal by that amount, Manufacturing cost is lessened by giving the same Contour to the rotor plates of all the tuning condensers, and by assembling the rotors of the tuning condensers on one shaft but, previous to my invention, this method of construction rendered it substantially impossible to so adjust the system, after assembly thereof into a completed set, that a constant frequency-difference could be maintained over the entire tuning range.

By providing the aforementioned adjusting condensers 32 and 33, however, the effect of the tuning condenser 3| on the frequency of the oscillations generated by the oscillator may be so materially modified that the desired frequencydifference may be achieved, and maintained over the tuning range, without changing the value of the input inductor 33 or altering the position of the rotor of the oscillator-tuning condenser 3| with respect to the stator thereof, as was the procedure previous to my invention.

If the oscillator, instead of being tuned to a frequency higher than that of the incoming signal, is tobe tuned to a lower frequency, the adjusting ccndensers 32 and 33 are associated with the input circuits of the radio-frequency amplifier tubes and the first detector tube, and not with the oscillator tube input circuit, as illustrated.

Anode potentials, grid-biasing potentials, and cathode potentials for thevarious thermionic tubes are supplied from a rectifying device 8G over a network which is arranged according to an important phase of my invention. The rectifying device Sii is of the full-wave rectifying type, having a plurality of anodes 8|. The device may be provided with a thermionic cathode 82, supplied with operating potential from a secondary winding B3 on the power transformer I6, or it may be of the cold-cathode type which functions by virtue of gas-action, since the specific rectifier constitutes no part of my invention.

i-iigh potential for the anodes of the rectifying device is supplied from a secondary winding Sd on the power transformer, a connecting 85 to an intermediate point on the said winding constituting the negative output-terminal of the rectifier. The positive output terminal of the rectifier, which is constituted by the cathode 82, is directly connected to the anode of the audio-frequency amplifier l, through a plurality of choke-coils t5, 'i and 38 and a conductor 9%. A plurality of by-pass condensers Si and 92, of relatively large capacities, are connected in shunt to the rectifier output terminals, and provide, together with the choke-coils, a filter circuit to exert a smoothing action on the rectied current.

Anode potential for the coupling tube i, the radio-frequency amplifying tube 2 and the intermediate-frequency amplifying tubes i and 5, i suppiied from the positive terminal of the rectifier over a circuit including a resistor` ESG and a common conductor lill. Anode potential for the first detector tube 3 and the oscillator tube ii is from the positive terminal of the recover a circuit including a conductor 982 and a resistorl @D3 of greater magnitude than the resistor tilt, while anode potential for the second detector tube ii is supplied from the positive tern minal ci the rectifier over a conductor iiii.

In order that the manner in which the rectifier uw"rushes anode and grid-biasing potentials for tr us thermionic devices may be more cleariy understood, attention should also now be directed to Fig. 2 of the drawings in addition to it will be noted that the positive terminal oi the rectifier is directly connected to the anode of the audio-frequency ampliiier tube l, and to the anode of the second detector tube 5, thus supplying these tubes with maximum anode potential. Anode potential for the oscillator tube and the first detector are supplied over theresistor iii, one end of which is connected to the conductor 9%.

The cathodes of the oscillator tube, the first -r-r: 1 Eig. i..

detector tube, and the second detector tube are conductively connected, by the conductor 28, to terrnediate point on a resistor m5 arranged .':it to the secondary winding 20, to an intermediate point on a resistor lili arranged in shunt to the heater-Winding l5 and to one end of the previously referred to bias potential resistor The resistor preferably comprises a plurality of fixed resistor elements itl and 08 and a portion llil with which is associated the movable contact device M, one end of the portion i being directly connected to the negative ter'- minal B5 of the rectifying device.

rihe sum of the space currents in the oscillator tube, the rst and second detector tubes and the audio-frequency amplifying tube, therefore, flows through entire resistor ili'a, and causes a fail in potential thereacross, the end nearest the rectiier terminal 85 being obviously the negative end. Since the cathodes of the tubes just referred to are ail connected to the positive end of the f' 25, the grids of the tubes may be given appcp, .c negative biasing potentials by connecting tnem to points along the resistor element as illustrated. It is preferable, however, to .so arrange the oscillator that no initial bias be applied to the grid thereof and the grid resistor t, therefore, is connected directly toV the cathode il.

The cathode of the coupling tube, the radiofrequency amplifying tube and the two intermediate-frequency amplifying tubes are connected to a point on the resistor 25 intermediate the sections lll'l and |38, and a resistor |20 is connected in shunt to the space-current paths of the said tubes. The fall in potential across the resistor sections IUS and ll is accordingly in part xed by the current fiowing through the resistor E25, in part by the space-current in the high-frequency amplifying tubes I, 2, 4 and 5, a

and in part by the space-current in the remaining tubes. By choosing proper values for the resistor i243 and the resistor section S08, the potentiai of the contact-device il may be maintained highly negative, notwithstanding marked variation in the space currents from the several tubes.

The contact device 4l may, accordingly, be utilized to vary the magnitude of the negative potential applied to the grids of the high-frequency amlifying tubes l, 2, l and 5, for volume-control purposes while the system is in operation, with the full assurance that an ample negative potential is always available.

In some instances, particularly when my improved receiving system is operated relatively close to a powerful broadcasting station, it is necessariJ for complete volume-control, to provide whereby the grid of the coupling tube l may be given a more negative bias than the grids of the succeeding amplifying tubes. This may be accomplished by providing a separate variable connection Elli from the cathode of the coupling 'tube to the resistor 25, whereby upon movement of the contact device ll i toward the negative end of the resistor element l It, the said variable connection is caused to simultaneously move toward the posi'- tive end of the resistor. Another way in which I may accomplish the same result is to connect the shunting resistor i229 with` thermionic tubes l and 2 alone, and to supply the tubes Il and 5 with anode potential across a separate sistor H5, at the same time retaining the remain-- ing connections as illustrated in Fig. The mcdn ied circuit is illustrated in Fig. 9.

in either event, the shunting resistor i2@ has the very important function of preventing an undue increase in the plate potential applied to the high-frequency amplifying tubes when they are so negatively biased as to diminish the space f currents therein.

Thus it is clear from the above description that the resistor l2@ is of such a value as to maintain a substantially unvarying anode potential upon the anodes of the tubes I and '2 during changesI of grid bias, and in order that the circuit should function in the desired manner, namely, to cbtain a greater change in amplification in the preceding tubes of the cascade arrangement than the succeeding tubes, it naturally foliows that the A7- changes in the grid bias of the succeeding tubes substantial changes in the voltage impressed on the plates.

A bypass condenser |30 is connected in shunt with the resistor I 20 in order that potential iuctuations impressed thereacross shall not be effective to interfere with the action of the succeeding devices in the series.

A similar bypassI condenser |3| is connected in shunt with the space-current paths or" the oscillator and first detector tubes for an analogous purpose.

Additional bypass condensers |32, |33 and |34 are provided for the purpose of forming lowimpedance paths around the resistor assembly.

The variable contact device I I I, or volume control, is provided with a connection to ground, and to the chassis of the set, for safety purposes.

An important phase of my invention is concerned in the construction and arrangement of the intermediate-frequency coupling transformers 55, 62 and 63, which are shown in detail in Figs. 3 to 7, inclusive, of the drawings, in order that the intermediate stages may have the requisite selectivity and yet not be so sharply tuned that the quality of the signals is impaired.

Each of the intermediate-frequency transformers comprises an insulating plate Edil which rests upon, and is supported by, two of the upper edges of a metallic shielding container |4I. The container, which is preferably rectangular in form, is provided with a plurality of upwardly-extending ears |42 adapted to be inserted upwardly through openings in a metallic frame element incorporated into the chassis of the set (not shown), and bent over to maintain the container firmly in position.

The primary winding 56 and the secondary winding 58 are coaxially mounted on an insulating form |50 which is suspended from the covel` plate |40 by means of a plurality of angularly bent arms |5I. The coupling between the windings may be varied within the limits of the length of the form for a purpose hereinafter described more in detail.

The fixed primary tuning condenser 5l is mounted on the upper surface of the insulating plate and is fastened thereto in any desired manner, the said condenser being connected across the terminals of the primary winding by means of a plurality of conductors |52 and |53.

In addition to the xed tuning condenser, the variable secondary tuning condenser 60 and the variable neutralizing condenser 6| are also carried by the cover plate, being mounted on opposite sides thereof.

Referring specifically to Figs. 5, 6 and 7, the variable tuning condenser 60 comprises an immovable plate |54 held to the upper surface of the cover-plate |40 by a plurality of solid rivets |55, and a flexible element |56, one end of which is affixed to the cover-plate by means of a hollow rivet |57. The upper end of the hollow rivet extends through an opening in the bottom of a small cup |60, thus holding the cup and the end of the flexible element firmly in contact.

The Variable neutralizing condenser 6| comprises an immovable plate IBI held to the undersurface of the cover-plate |40 by a plurality of solid rivets |62, and a flexible element |53, one end of which is aixed to the cover-plate by means of a hollow rivet |64 having an interior thread.

An adjusting screw |65 extends downward through the hollow rivet which holds the end of the upper movable plate |56 in position and cooperates with a nut |65 affixed to the free end of the lower flexible element |63 to provide adjusting means therefor.

A small cup |67, having an opening through the bottom thereof, is amxed to the free end of the upper flexible element |55 by a hollow rivet |68 through which extends an adjusting screw |16 thatv engages the interiorly threaded surface of the rivet I 64, thus holding the end of the lower flexible element in position. The upper movable element of the condenser may, accordingly, adjusted with reference to the fixed plate thereof by rotating the said screw.

The terminals of the tuning condenser 60 and the neutralizing condenser 6I may be connected to lugs li mounted on the edges of the coverpla-te, or to the proper terminals of the primary and secondary windings, as shown in Fig. l.

The small cups 35 and |67 are filled with sealing-wax, or an analogous material, after the have been properly adjusted, which partially prevents subsequent tampering with the adjustment. Tampering with the condenser adjustment is still further prevented by the novel manner in which the shielding containers are mounted beneath the chassis of the set, as hereinbefore described.

When both the primary winding and the secondary winding oi' the transformer are properly tuned, and the coupling between the windings adjusted, it is found that the resonance curve thereof has a suiiiciently wide peak to permit the efficient amplification of the side-band frequencies, a feature that is noticeably lacking in aircore intermediate-frequency transformers constructed previous to my invention.

Insofar as I am at present aware, it has not been previously suggested that economy of space and convenience in adjustment could be obtained by so mounting a plurality of variable condensers on the casing of an intermediate-frequency transformer that each of said condensers could be separately and independently adjusted from the exterior of the said casing. In addition, since the condensers are completely shielded electrically from other parts of the receiving system,

when the container is mounted in place beneath the chassis, the opportunity for inter-circuit coupling, and consequent regeneration, is eliminated.

-The space between the transformer windings and the inner walls of the shielding container is preferably filled with an insulating compound, a mixture of beeswax and resin having been found very desirable for this purpose.

I have determined, by careful experiments, that, byl utilizing my improved intermediatefrequency transformers in a superheterodyne receiving system, the amplification obtainable is greatly increased. Many factors enter into the improvement in amplification, the shortness of leads, the tuning of both primary and secondary, the complete shielding, and others which I have not, as yet, fully determined. Since the amplification, however, is improved, I am enabled to employ an intermediate frequency of the ord-er of 180 kilocycles with good results, instead of the usual 40 kilocycle frequency, and the use of the high intermediate frequency very greatly reduces` the image-frequency response of the system. By image-frequency response is meant the response of the system to an undesired signal which differs in frequency from the desired signal by twice the intermediate frequency. If, therefore, the intermediate frequency is high, the selectivity of the radio-frequency stages of the system will be such as to greatly reduce, in amplitude, any signal which differs from the desired signal by twice the said intermediate frequency.

It will, accordingly, be apparent that the several phases of my invention coperate to enable the production of a superheterodyne receiving system that is superior, in many respects, to analogous receiving systems` constructed according to the teachings of the prior art.

I am aware that many modifications of my invention may be suggested to persons skilled in the art, and that many other specific embodiments thereof are possible. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l.. In combination, a source of fluctuating unidirectional potential, a thermionic device arranged to amplify electric currents at high frequencies, a resistor, connections whereby said resistor and the space-current path in said device are serially included in shunt to said source, a thermionic device arranged to amplify electric currents at audio-frequencies also having its space-current path connected in shunt to said source, and an impedance device interposed between the point of connection of said rst-mentioned device to said source and the connection of said second-mentioned device to said source, whereby said first mentioned device tends to materially reduce the fluctuating component of the potential applied to said second-mentioned device.

2. In combination, a source of fluctuating unidirectional potential, a thermionic device arranged to amplify electric currents at frequencies higher than audio-frequencies, a resistor, connec'- tions whereby said resistor and the space-current path in said thermionic device are serially included in shunt to said source, a second resistor connected in shunt to said space-current path, a thermionic device arranged to amplify electric currents at audio-frequencies, an impedance device, connections whereby said second-mentioned thermionic device and said impedance device are serially included in shunt to said source, and means for deriving a grid-biasing potential for said rst-mentioned device from the space current therein and from the space current in said second-mentioned device.

3. In an electric-current-amplifying system, a plurality of thermionic devices interconnected through tuned transformers and adapted to amplify electric currents at frequencies higher than audio-frequencies, a plurality of thermionic devices arranged to function as demodulators, a thermionic device arranged to function as an oscillation generator, a thermionic device arranged to amplify the output of one of said demodulators, and means whereby the space current flowing in said demodulators, said oscillation generator and said audio-frequency amplier is utilized to provide grid-biasing potentials for said first-mentioned thermionic devices.

4. In an amplifying system employing electron discharge devices in cascade, said devices having control grid and other electrodes, the method of controlling ampliiication which comprises increasing the negative bias on the control grid electrodes of certain of said devices to produce a decrease in amplification and simultaneously increasing the positive voltage on another electrode of one of said tubes tending to increase amplification.

5. The method of operating an amplier system constitutedby a plurality of Yamplifying devices connected in tandem, which comprises applying a gain control potential to said devices, applying a second gain control potential to a lesser number of said devices than said first gain control potential, causing the first-mentioned potential to vary and causing the second-mentioned potential to simultaneously vary with variations in the first-mentioned potential.

6. In an amplifying system employing electron discharge devices in cascade, said devices having control and other electrodes, the method of controlling ampliication which comprises increasing the negative bias on the control electrodes of certain of said devices to produce a decrease in amplification and simultaneously increasing the ainplication of a lesser number of devices beyond the rst device in said cascade by increasing the positive voltage on another electrode of said lesser number of devices.

'7. The method of operating an amplier system constituted by a plurality of amplifying devices connected in tandem, which comprises applying a gain control electrical quantity to said devices, applying a second gain control electrical quantity to certain of said devices after the first, causingthe first gain control quantity to vary the amplification of said devices in one direction and simultaneously causing said second gain control quantity to vary the amplification of said certain devices in the opposite direction.

GEORGE L. BEERS.

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