US1926173A - Radio receiving system - Google Patents

Description

Sept. 12, 1933,

s. w. PLACE 1,926,173

RADIO RECEIVING SYSTEM Filed Jan. 21, 1931 IN V EN TOR.

ATTORNEY.

Patented Sept. 12, 1933 FFEE 1,926,173 RADIO RECEIVING SYSTEM Samuel W. Place, Norristown, Pa., assignor to Atwater Kent Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania Application January 21, 1931. Serial No. 510,149 16 Claims. (Cl. 25020) My invention relates to radio receiving systems, particularly those involving amplification by thermionic tubes of the screen or shield grid type for amplification of radio frequency energy in one or more stages;

In accordance with my invention there is effected, by adjustment of a single device, more specifically a single contact or brush a resistance or potentiometer, variation of the amplification by one or more amplifier tubes of 1 upon or of the aforesaid screen grid type, by variation of screen grid voltage or bias to vary t cation factor of the tube or tubes, with simultaneous variation of the magnitude of transfer of radio frequency signal energy to said tube or tubes, or from oneor more of succeeding tube or tubes.

My invention resides in a method them to a and apparatus of the character hereinafter described'and claimed.

For an understanding of my inv ention and for an illustration of some of the forms it may take, reference is to be had to the accompanying drawing, in which:

Fig. 1 is adiagrammatic view of receiving apparatus embodying a stage of radio frequency amplification, and utilizable for pra 'formof my invention;

Fig, 2 is a diagrammatic View of a cticing one erodyne radio receiving system embodying a further form of my invention.

absorbs the electro-radiant energy from a natural medium. Through a condenser K, which is antenna system and at the same time to provide a low reactance path for the incoming radio frequency energy, the antenna A is con,-

' nected to the contact or brush 1 movable along the resistance R, whose one terminal connects through a stopping condenser K1 with one terminal of the primary 1? of a radio frequency transformer T, and whose other end connects with the other terminal of the primary P. The

second terminal of the resistance R a nd primary P connects to earth or counter capacity E through the resistance R1; and to the cathode c of amplifier tube V of the screen grid type. The cathode is, which may be an incandescent filament or a cathode raised in temperature by a heater, is connected to ground or earth through a condenser K2, of lowv reactance for radio frequency current, in shunt to the resistance R1;

superhetupon the potentiometer resistance R. utilized tokeep the direct current voltage off the 7 Connected across the terminals of the secondary S of the transformer T is the variable tuning condenser C for tuning the input circuit of thetube V to the various radio frequencies of a suitable range, for example, to tune to the broadcast frequencies now commonly employed. One terminal of the tunable loop SC is connected to the control grid g of the tube V while its other terminal is connected to earth or, in effect, to the cathode lc' through the condenser K2. In" the grid'lead may be inserted a damping resistance T, which generally may be omitted, though of advantage in event of feedback or regenera- 7 tion through capacity, generally substantially entirely external to the tube V exising between theplate or anode a and the grid g. v,

The positive treminal 2, of the B source, not shown, or source of uni-directional or direct current for supplying the anode or plate circuit of the tube V, is connected to one terminal of the resistance R, while its other terminal is connected to ground E. Current accordingly flows from theB source through the resistances R and R1 in series. From the contact or brush 1, there is a connection to the screen grid or shield grid s through aradio frequency choke coil 3; and from a point between the coil 3 and the screen grid 3 there is a connection to ground E through the condenser K3, exhibiting low reactance for currents of the radio frequency range involved.

The positive potential impressed upon the screen or shield grid sof the tube V is varied as the contact 1 is moved to diiferent positions The movement of the contact or brush 1 along the resistance R has the further and simultaneous effect of varyinglthe amount of the received radio frequency or signal-representing energy impressedupon the transformer primary P, and thence upon the input of the tube V..

As the brush or contact 1 is moved downwardly along the resistance R the amplitude of the received radio frequency or signal representing energy impressed upon the input of the tube V is reduced; and'simultaneously'the positive po.-

tential or bias of the screen grid s is reduced,

causing in effect a reduction in the" magnitude of the amplification factor of thetube V thereby diminishing the amplification of the radio frequency energy, and thereby-reducing the amount of signal-representing or radio frequencyenergy impressed upon the succeeding circuit, not

shown, through any suitable coupling means generically represented by the transformer primary P1.

The signal representing energy transferred by the coupling, represented by the coupling Pl, may then be further amplified if desired; impressed upon a demodulator or detector, and the audio frequency current in the output of I the detector then may be amplified by one or more amplifier tubes and impressed upon .a. signal translating instrument such as a loud speaker.

If the volume is controlled only by reduction of the positive bias on the screen grid, and carried to an extent Where the positive potential of the screen grid is reduced to substantially zero, the plate current is also reduced to substantially zero; Under such circumstances incoming radio frequency energy, having great modulation, will nevertheless cause some plate current to flow on strong signals while little or no plate current will flow with weak signals. Large and serious distortion will result when such reat reduction of volume is effected solely by reduction of screen grid potential. a

- To overcome the foregoing difiiculty, it has been proposed to apply a second and independent volume control which reduces the amount of the radio frequency signal-representing energy transferred from the antenna or impressed upon the radio frequency amplifier, or which reduces the amount of radio frequency signal-representing energy transferred from one vacuum tube amplifier to another vacuum tube of or within the radio receiving system; and it has been proposed to effect the separate controls of screen grid bias and transfer of radio frequency signalrepresenting energy by operating their adjustable elements mechanically ,in unison.

In accordance with my invention, however, the two electrical efiects are accomplished by one andthe same electrical devicejsuch as a single potentiometer or adjustable resistance.

As the brush or contact 1 is moved from the upper toward the lower end of the resistance R, its effect, in reducing the amount of radio frequency signal-representing energy impressed upon the input circuit of the tube V, is at first small, and then becomes rapidly greater and greater, thereby more rapidly decreasing the signal-representing voltage impressed upon the input of the tube V, and therefore the volume,

as the contact 1 approaches the lower end of the resistance R,

The combined action, therefore, is such that as the contact 1 is moved from the upper toward the lower terminal of the resistance R, the volume control is at first predominantly by virtue of decrease of positive bias upon the screen grid, and during the latter part of the downward movement, of the contact 1 the further volume reduction is predominantly due to reduction of signal-representing voltage impressed upon the input of the tube V.

In brief, the action is such that the amplification factor of the'tube V is immediately reduced with resultant reduction in amplification due to the first part of the downward movement of the brush 1, and this action continues throughout the range of possible movement. Simultaneously the radio frequency shuntingaction of the adjustable resistance R, effectively in shunt to the primary P, is'at first, however, slight or gradual, but increases rapidly as the amplification factor of the tube V is further reduced by reduction of the potential of the screen grid s.

it is apparent from the foregoing that the same electrical device or means accomplishes both functions 'of control of screen grid 'poten-- tial and control of magnitude of voltage impressed upon the input circuit of the amplifier tube; amplification is varied simultaneously with diversion of input of signal energy by one and the same electrical device.

Fig. 2 is a diagram of a superheterodyne radio receiving system in which, between the antenna or absorption structure A and the first radio frequency amplifier tube V1, of the screen grid type, is a preselector system 4 comprising a plurality of cascaded circuits tunable to any of the frequencies within a range, such as that prevailing in present broadcasting practice. The plate circuit of the screen grid amplifier V l is coupled through suitable coupling means including the transformer T1, whose secondary is tunable by the variable condenser-C1, to the'input circuit of the first detector tube D1, of the screen grid type.

O is a vacuum tube utilized as a local oscillator for producing oscillations of a frequency difi'erent from those representing the received signals, speech or music, to produce therewith in the input circuit of detector Dl beats of preferably constant and lower or intermediate radio frequency. The output of the detector D1 is coupled to the input of the intermediate freuency amplifier tube V2, of the screen grid type, whose output in turn is" coupled to the iii-- put of the second detector tube D2. These two last mentioned couplings are preferably fixedly tuned to the constant'or fixed intermediate frequency. The output of the detector D2 is suitably coupled to the input of the audio frequency amplifier V3 whose output is suitably coupled to the push-pull amplifiers at whose output, amplified audio frequency current, is de-- 'livered through a socket 5 to a loud speaker,

such as an electro-dynamic loud speaker, whose voice coil connects with the output of the tubes V4 through the socket 5 through which latter current is delivered also to the field coil of the speaker.

' The power supply 6 is of any suitable type, and is here represented as comprising a rectifierfilter, well understood in the art. My invention is applied to the system of Fig. 2

generally'in accordance with the principles illustrated by Fig. 1.

Between the positive terminal 2 of the B source or power supply 6 and earth or ground E to which the negative terminal of the power supply is connected, are serially connected the resistances R2, R3, R4 and'RS through which uni-directional current from the B source 6 continuously flows While the set is in operation. 7 These resistances, or any suitable one thereof, as R3, may be considered in association with its adjustable contact or slider 1 an adjustable resistance or a potentiometer. Between one of the. resistance R3 and the adjacent end of the resistance R4 is included a radio frequency choke coil 3 which prevents radio frequency si nalrepresenting current from flowing through resistances R4 and R5 to ground E. The choice coil offers high impedance to radio frequency I currents but permits the direct current from the B source 6 readily to flow through all of the resistances mentioned.

j Sincethe contact 1 does not engage or move along the resistance R2, that resistance serves to limit the maximum positive voltage which may be impressed upon the screen or shield grids s of the tubes V1, D1 and V2, all of which grids are connected to the contact 1 through the conductor '7. The resistances R4 and R5 to- 5 gether smilarly limit the minimum positive potential which may be applied to the same screen grids s of the three tubes aforesaid. ,The conductor 8 impresses upon the control grids g of the tubes V1 and V a fixed or constant negative potential or bias of a magnitude determined by the resistance R5.

The resistance R3 is in effect a potentiometer which permits by adjustment of the slider or brush 1 variation of the positive grid bias applied to the screen grids s of the tubes V1, D1 and V2; adjustment of the slider 1 determines the amplification factors and the amplification effected by the tubes in question, movement of the slider 1 from left toward the right reducing volume by reduction of-amplification. The variable portion of the resistance R3 between the slider 1 and the point 9 determines the shunting effect of that variable portion of the resistance 'to divert radio frequency energy from, or reduce the amountthereof impressed upon, the primary P of the coupling transformer T1, by virtue of connection of the point 9 throughconductor 10 to the upper terminal of the primary P whose lower terminal connects through the condenser K4 to ground E and thence through condenser K5 and conductor. 7 to the movable contact 1. Movement of the contact 1 from left toward the right thereby increases the shunting effect upon the primary P and therefore reduces the radio'frequency signal-representing energy impressed from the output of the tube V1 upon the input of the detector tube D1. Each of condensers K4 and K5 has a capacity of the order of .1 microfarad; in any event each of these condensers offers very low reaotance to the radio frequency current. The condenser K4 serves to prevent short circuit of the direct current from the B source 6' flowing through the resistances R2 to R5 inclusive.

Simultaneously with reduction of amplification by movement of slider l from left toward the right on resistance R3, the shunting effect upon the primary P increases, whereby the volume of reproduction by the loud speaker is.

controlled by the conjoint action of the two effects which, however, are produced by 'one and the same electrical instrument as a variable resistance, a potentiometer, or any equivalent means.

As in the case of Fig. l, the reduction of amplification by movement of the slider 1 operates immediately upon movement of the slider from the left end of the resistance R3 and continues throughout its possible range of movement, further to reduce the amplification, which, however, cannot be'reduced. substantially to zero because the positive potential of the screen grids may not be reducedbelow a certain magnitude as determined by the potential difference across the resistancesR4 and R5 in series. Simultaneously, the reduction of radio frequency input, or the diversion of radio frequency from the input of a tube, or from .a coupling between tubes, is effected, first at very low rate, adjacent the left end of the resistance R3, and then at very rapidly increasing rate as the slider lapproaches the right end of resistance R3.

By .way of example merely it may be stated senting energy, 1

"2. In a radio receiver, a thermionic tube of said resistance in a path whose resistance determines the transfer of radio frequency signalthat when the voltage of the B source 6 is of the order of 150 to 200 volts the resistance R2 may be 20,000 to130,000-. ohms; R3, 50,000 to 100,000 ohms; R4, 10,000 to 15,000 ohms; and R5 about 200 ohms. These proportions have been found to give suitable potentials as impressed upon the screen grid s of the tubes V1, D1 and V2,'when' of the present type [IX-224; and for effecting by resistance R5a constant or fixed negative bias of substantially three volts upon the control grids of the tubes V1 and V2.

What I claim is: I

1. In a radio receiver, a thermionic tube of the screen grid type, a resistance,.means for passing uni-directional current therethrough, means for varying the amount of resistance between a point and a connection to the screen grid of said" tube for varying the potential thereof, and connections-for including the resistance between said point and connection in a signal transfer system of the receiver for simultaneously varying the transfer. of signal-reprethe screen grid type, a resistance, means for passing uni-directional current through said resistance, means for effecting connection wi'th saidresistance at a plurality of points thereon and in circuit with the screen grid of saidtube for varying the potential thereof, and connections for including a portion of said resistance so varied in a path traversed by the signal energy for varying the transfer of said energy in said system. 7

3. In a radio receiving system, a thermionic tube of the screen grid type, a resistance, a source of current for the anode circuit of said tube passing current through said resistance, means for effecting connection with said resistance at a plurality of points thereon and in circuit with the screen grid of said tube] for varying the potential thereof, and connections for including a portion of said resistance so varied in a path whose resistance determines the transfer of signal-representing energy in said system.

quency amplifier tube of the screen grid type, a resistance, means for passing uni-directional current through said resistance, a contact movable along'said resistance for varying the po-' tential of the screen grid of said tube, andcon nections for including the variable portion of representing energy in said system.

5. 111 2. radio receiving'system, a radio Ire quency amplifier tube of the screen grid type, a

resistance for diversion from saidtube of radio frequency signal-representingenergy, means for passing uni-directional current'through said resistance, and a-contact movable along said rer sistance for simultaneously varying the diversion aforesaid from, and the potential of the screen grid of, said tube, for simultaneously varying the volume of reproduction in the same senses and cumulatively throughout the range of movement of said contact. l V

6. A radio receiving system comprising a plurality of thermionic tubes in cascade, at least one of which is of the screengrid type, a-resistance, means for passinguni-directional current therethrough, means for effecting connection with said resistance'at a" plurality of points '.thereon and in circuit with the screen grid of at least one ofsaid tubes: for varyingthe potential thereof to -vary the volume of reproduction,. and means for 'efiecting simultaneous Cumulative volume variation comprising-connections for including a portion of said resistance so varied in an inter-tube coupling system for varying the transfer .ofsignal-representing. energy from said one of said tubes to another tube of said system- 7. In a radio receiving systenn a detector of the screen grid type, a resistance, means for passing uni-directional current through said resistance, means for effecting connection with said resistance at a plurality of points thereon and in circuit with the screen grid 'of'said detector for varying the potential thereof, and connections for. including a portion of said resistance so variedin a path traversed by signal energy for varyinggthe transfer thereof in said system.

8. In a radio receiving system, an amplifier tube of the screen grid type, in. a later stage a a resi stance, means for passing uni-directional current through said resistance, means for effecting connection with said resistance ata plurality of points thereon andin circuit: withjthe screengrids of said tubes for varying the potentials thereof,; and connections for including a portion of said resistance, so varied in a path whose resistance determines the transfer of signal-representing energy in said system.

10. In a heterodyne receiving system, a radio frequency amplifier tube ofv the screen gridtype, an oscillator; a detector tube of the screen grid type, means for coupling-the output of saidfirst named-tube totheinput of said detectortube, a resistance, means for passing uni-directional current through said resistance, means for effecting connection with said resistance at aipluralityof points thereon and in circuitwith the screen grids of said tubes for varying the potene -tials thereof, and connections for including a portion of said resistance so varied in circuit with said coupling means for-varying the trans fer of signal-representing energy. v

v 11. In a superheterodyne receiving system, a radio frequency vamplifiertube; of the screen grid type, an oscillator, a first detector tube of the screenggrid type,ran intermediate frequency amplifier of the screen grid-type, a resistance means for passing uni-directional current through said resistance, means for effecting con necticn with-said resistancaat' a plurality of points thereon and in circuitwiththe screen grids of said tubes. for varying the potentials thereof, and connections for including a portion of said resistance so varied in-a pathwhose resistancedetermines thetransfer of signal-representing energy in said system. i,

12. In a radio receiving system comprising. one or more amplifying tubes. of the screen grid type, the method of, controlling the ,volume of reproduction which comprises varying a resistance to vary-the screen grid potential of at least one of said tubes to vary its amplification, and

simultaneously, by the same variation of said resistance, varying the transfer of signal-,representing energy. 7

13. In a radio receiving system comprising one ormore tubes of the screen grid type, a coupling for transferring signal-representing energy, and a resistance for affecting said coupling in its transfer of said energy, the method of controlling the volume of reproduction whichv comprises passing uni-directional current through said resistance, adjusting a contact along said resistance to .vary the screen grid potential of at least one of said tubes to effect one component of the volume control varying in the same sense throughout adjustment of said contact, and simultaneously by adjustment said resistance by said contact varying the transfer of signal-representing energy by said coupling to effect another component of the volume control. varying in the. same sense with said first named component. 14. In a radio receiving system, a thermionic tube of the screen grid type, a coupling for transferring signal-representing energy, a ,resistance in shunt to said coupling and in circuit with the screen grid of said tube, means for passing unidirectional current through said'resistance, and a ,contact adjustable along said resistance for, varying the potential of the screen said tube to. effectlone component of a volume control carying in the same sense throughout said adjustment, and simultaneously to vary the transfer of signal-representing energy effected by said coupling to effect another component ofthe volume control varying in the same sense, with said firstqnamed component.

l5.'In a radio receiving system, a thermionic tube of the screen grid type, a magnetic -cou=- pling for transferring signal-representing energy, a resistance in circuit with the screen grid of said tube, capacity in series with said resistance inshunt with said coupling, meansfor passing uni-directional current through said resistance, and a contact adjustable along said resistance for varying the potential of the screen gridof said tube to effect one component of a volume control varying in the same sense throughout said adjustment, and simultaneously to vary the transfer of signal-representing energy effected by said coupling to effect another component of thevolume control varying in the same sense with said first-named component.

'16. In a radio receiving system, a thermionic tubepf the screen grid type, ascurce of unidirectional current, a resistance traversed by current"from said source, a radiofrequency choke coil connecting sections of said resistance for excluding radio frequency current from one sectionthereof, a coupling for transferring signal-representing energy, a connection to said one of. said sections of said resistance for biasing a control grid of a tube of said system, and means for controlling the volume of reproduction comprising a contact movablealong another of .said sections of said resistance to vary the potential of the-screen grid of said tube'for effecting.one...component of the volume control, and connections to said coupling for causing said adjustment of said contact along said other of SAMUEL w. PLACE,

CERTIFICATE 0F (IQRRECTION.

Patent No. 1,926,173. September 12, 1933.

SAMUEL W. PLACE.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 72, for "treminal" read terminal; page 4, line 60, claim 11, insert a comma after "resistance"; and line 106. claim 14, for "carying" read varying; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Sign d and sealed this 21st day of November, A. i). 1933.

F. M. Hopkins (Seal) Acting Commissioner of Patents.

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