Патент USA US2121427код для вставки
June 21, 1938. L. T. FOWLER 2,121,427 SENSITIVITY CONTROL SYSTEM FOR AUTOMOBILE RADIO RECEIVERS Filed April 50, 1957 2,121,27 Patented June 21, 1938 ~ UNITED STATES PATENT orrior , ‘ , ‘ 2,121,427 , ~ . 1 ‘SENSITIVITY CONTROL‘ SYSTEM FOR. ‘ = ‘AUTOMOBILEI‘RADIO Lester RECEIVERS ' > I Fdwler, Oaklyn, N. J., assignor to Radio ; Corporation of America, a corporation of, JDela-f ware Application April so, 1937, SerialNo.‘ 140,064" 10 Claims. (01. 25o_20)' . . "The present‘ invention‘ireIa'tes to a sensitivity connection with the cathode circuits of any of control‘ system for automobile radio receivers and the ampli?er tubes, whereby interference pick-up thelikegwhichiare normally subjected to ignition is vreduced to a minimum. - tended control circuit from‘the receiving appa stood from theT'following‘ description,»when con- 5 sidered in connection with the accompanying drawings, and its scope ‘will be pointed out in the ratus and which does not introduce interference appended claims,‘ signals into the receiving apparatus. Inthe drawing, Figure 1 is a‘ schematic circuit diagram of a portion of a'ra‘dio receiver for auto- 10 mobiles ‘and the like provided with a sensitivityv control system embodying‘the invention, and ‘ the character referred to‘which permits of an ex ll) I‘Sin'ce'the sensitivity control for automobile re ceivers and the like must be‘ ‘extended to the in strument panelof the automobile, the control circuit is external to the receiver and'is connected thereto ‘by ‘a‘cable: ‘The usual method of pro viding a sensitivity control for such receivers in cludes ‘the use of a variable resistorlin the cathode to ignition interference ‘and the extension of such having a cathode ‘8, a detector diode anode 9 to prevent picking up ignition and» other inter ‘ connected with the tuned‘ secondary circuit iii of v the transformer 6, an automatic volume ‘control diode anode ll connected with the tuned primary > Cathode. resistor control» of the intermediate 25 frequency ampli?er tubes alone is unsatisfactory, although’ less sensitive to interference. Control of the ‘intermediate-‘frequency 'ampli?er'tube or tubes‘ requires biasing to such a'wi'cle degree that the‘itubeslose ‘sufficientlpower to *drive the diode .30 recti?er-or second; detector. Also, with this meth od of control, the distortion increases andv addi-‘ , tional second harmonic signals are generatedin the plate circuitv of' the intermediate frequency am pli?er tube ortubesa This causes the beat note condition to be. worse than normal, so that ‘addit tional ?ltering is necessary to suppressthe‘ beat notes. I i‘ i‘ ' - “‘ “ It is, therefore, a further object of the‘ present invention to provide a sensitivity control system .40 foruautomobile radio. receivers and the like which effectively overcomes substantially all of the above disadvantagesrand. which'is at the‘ same tim easily p'r‘ovidedat low cost. ‘ In 1a ‘radio. receiving "system, the automatic ‘ volume control circuit is provided with suitable ?lters comprising series- resistors and by-pass ca pacitors for decoupling the controlled grids from the automatic volume-controlbias source‘. It is, therefore, a-‘furtherob'ject of-the present‘inven ‘ tion‘ to provide ‘a‘ sensitivity control‘system‘ for automobile’radio receivers and the‘llke having a ?ltered automatic'volume, controli‘circuit which is applied ‘to the return ‘circuit of the‘ automatic control means to take advantage of the inherent I‘ ?ltering and without resulting in any control ‘1 an intermediate‘ifrequency coupling transformer '6 with a‘second detector’ and ampli?er tube 1. The latter is of the double-diode, triode type, . circuits involves additional ‘?lters and ‘shielding ‘ v Referring‘ to‘ Fig. 1, 5 is an‘intermediate fre quency ‘ampli?er tube ‘which iscoupled through tector tube.“ Suchg tubes 'are‘essentially sensitive ference. ‘ Figure 2 is asimilar schematic circuit diagram, being a portion of the circuit of Fig. 1‘, showing a modification of the sensitivity control circuit. 15 circuit»=of“0ne ormoreof the radio or‘intermediate frequency ampli?er tubes, as wellas'the ?rst de 35 i The invention will, however, be better under and other‘interferencaand has‘for its object to provide an improved sensitivity control system of circuit‘ |2 of theitra‘nsformer 6 through a coupling capacitor I3, and having‘a control grid l4 and an output anode 15 for the triode ampli?er portion thereof." The cathode B is connected to chassis or ground I 6, which isalso the automatic volume control return circuit, through a self bias‘ or cathode resistor comprising three sections l1, l8 and I9 providedwitha by-pass capacitor 20. The control grid I4 is arranged to receive‘ audio frequency signals‘ from the "detector ,diode 9, through a diodevoutput resistor 2| and a shunt 35 ‘ Volume. control resistor 22,“conneced therewith through a couplingl‘capacito'r 23. The grid It receives a biasing potential‘ from a tap 24 between the resistor sections l8 and I9, to which tap point the volume ‘control resistor 22 is connected at its 4.0 low potential‘end‘, asshown‘. i ' _ > ' The output‘L anode “l5'lo'f the‘ triode section is coupled" through" suitable resistance coupling means‘ 25 withv‘a ?rst audio frequency ampli?er v tube26,‘ in the‘ output anode circuit 21 of'which 45‘ an ‘output coupling device 28 is provided for con nection with additional ampli?er stages or other output devices-(not shown). The ampli?er stage 26 is‘provided witha tone control means com prising a capacitorfSU ‘connected to the output 50 circuit 21 and having‘ a control lead 3| connected through a lead 32 ‘in an extension cable 33, with atone control resistor 34 adapted for mounting on the instrument panel of the automobile. A ground lead‘35‘connected‘ with the chassis I6 is 55 2 2,121,427 extended through a lead 36 in the cable 33 to a manually adjustable tone control contact 31 in connection with the resistor 34, whereby the tone is controllable in a well known manner, the re sistance in circuit with the capacitor 30 being ireduced to reduce the high frequency response sistance for such self bias use by an amount such that the cathodes of the controlled tubes, such as the cathode 50, may have a positive potential with respect to ground or chassis su?icient to provide the grids, such as the grid 48, with a of the capacitor across the signal circuit. The automatic volume control circuit is con drop in potential through the self bias or cathode resistor 52 is therefore greater than the‘ drop in normal negative bias in the absence of signals, of the ampli?er by the increased shunting action ~ whereby maximum sensitivity is obtained. The _10 nected with the diode anode II, which receives signals from the primary of the transformer B and is thereby more broadly responsive than the secondary. The diode circuit is provided by a diode output resistor 40 connected between the potential through the ?xed potential source in 10 the automatic volume'control return circuit at l9, whereby the predominating bias potential on the grid is negative by the desired amount over provided by the drop through the resistors 11 the positive bias set up‘ in the potential source i 9. If, now, the automatic volume control return 15 terminal 24 is connected to chassis or ground I6, it will be seen that the grids of the controlled tubes will become more negative with respect to and I8. It will be noted that a lesser delay 20 potential is placed on the diode anode 9 for the their cathodes by the amount of the potential 4 provided by the resistor I9 and the over-all sensi 20 diode anode H and the terminal 24 or other suitable tap along the cathode resistor. This places a delay potential on the diode anode ll detector through the connection of the detector output resistor 2| with a tap point 4| between the resistor sections I1 and i8. " for receiving local signalsrwithout' interference. The automatic volume control potentials de veloped across the resistor 40 are applied to an automatic volume control lead "for the preced ing ampli?er tubes, through a series ?lter resistor 43 and a second ?lter resistor 44, for which by pass capacitors 45—45 are provided. ' v 30 ' The controlled ampli?er tubes, represented by ‘the intermediate frequency ampli?er tube 5, are connected with the automatic volume control lead 42 through suitable leads indicated at 46, and 41. In the present example, the control grid 48 of the ampli?er 5 is connected through the input circuit 49 with the lead 46, While the cathode 50 is connected to chassis or ground 5!’ through a self bias resistor "52. Other-ampli?er tubes (not 40 shown) are'connected in a similar manner to the chassis and automatic .yolume 'control' lead 41, whereby the chassis provides the automatic volume control return circuit connection. . Intermediate frequency signals are applied to the second detectorand automatic Volume con 45 trolmeans included in the tube ‘land associated ,circu'its, through the ampli?er} from an inter mediate frequency input transformer 53, the secondary of which is included'in the input cir , cuit 49 and the primary 54 of which may be 50 included in the anode output circuit of either the ?rst detector or apreceding intermediate fre quency ampli?er tube (not shown), as is well understood. ' ' , ‘ - tivity of the receiver-will be reduced accordingly, to some desired lower value, suitable, for example, I ' The automatic volume control lead 41 may be 55 connected with any of the preceding gain con trol tubes as normallyused in 1a receiver such as the usual’ radio frequency ampli?er, ?rst detector, and other intermediate frequency ampli?er tubes, This control maybe e?ected by extending a. lead 60 from the terminal 24, through a cable lead 6| 25 in the cable 33. to a switch 52 representing any suitable control device for grounding the lead 6|. In the present case, the switch serves to connect the lead 6! to ground through the leads 36 and 35. Because of the connection provided with the 30 ground return circuit of the automatic volume ' control system as shown, interference. from ignition ,orother sources introducedinto the ex tension leads 36 and 6! have no effect upon the receiving circuits because of the ?ltering in the 35 automatic volume control circuit, and, the fact that the controlled potential source is connected adjacent to ground; ' ' ' " - Theextensible control circuit shown may be connected with the receiver through terminals 40 indicated ‘at 63‘ and the control leads may in certain, cases‘ be grounded-at R. F. and I. F. potentials to the cable shield 33 and ground or chassis 64 andg65 through suitable high frequency by-pass capacitors 66 and 61 at the receiver ter 45 minals. The by-pass connections at this point are effective in' removing ultrahigh frequency disturbances from the internal circuits of the receiver and in further isolating the same elec trically' from the external-circuits connected 50 therewith: Y‘ 1 I Y i ' The circuit shown has been found to be ‘satis factory in connection with automobile receivers operating in the presence of heavy ignition and other interference potentials. Furthermore, the 55 two-point sensitivity control is effective to pro vide what may be termed local and distance re ceiving conditions; depending upon the particular the connections being asshownifor the tube 5. tubes used, andthe amount of potential change 60 In this circuit, the biasingpotential between grid 'required, for reducing the sensitivity for local 60 and cathode'is provided-by the automatic volume receiving conditions. control diode output resistor 40 and thecathode -The range vof control is determined 'by-the resistor [9 as two potential ‘sources, together‘with potential established. across the auxiliary or the ‘potential source provided by 'the self bias sensitivity control resistor l9 provided asthe 65 resistor 52 at the ampli?er tube. The polarity 'of ?xed potential source in the automatic volume 65 these sources is indicated adjacent thereto. The bias circuit arrangement is such that the automatic volume ‘control diode resistor 40, in stead of being returned‘ directly to ground or 70 chassis I6, is returned thereto through the poten~ tial source l9 which‘is positive at ‘the terminal ’ 24 with respect to ground or chassis by an amount determined by the degree of sensitivity control which is desired. The self bias resistors, such as 75 the resistor 52, are of a higher than ‘normal re‘ control circuit return lead to ground or chassis. In case, as is desirable, the ?xed potential source for the sensitivity control is provided as'a part of the cathode resistor of the combined second detector and ampli?er-tube, the resistance 70 of the resistor section I 9 should be relatively'low with respect to the resistance of the remainder of the resistor comprising sections i7 and I8, in order that as the sensitivity control section is short-circuitedithe change in the bias on the 76 3 2,121,427 triode section‘of‘ the detector ampli?er and'auto ‘Iqclaim as my‘ invention: matic volume control tube‘l imay‘not be too great for its proper operation. However,"t any suitable ?xed source of biasing potentialumay'be utilized in place of the cathode resistor 7section‘ 19 in a ‘ LR'I'he combination with an automobile radio . V receiving systemhaving automatic volume con‘—' trol ‘means, of» an extensible sensitivity control circuit‘ for said system comprising a chassis ground lead and a ground return lead for said receiver. ‘ ‘ If variable control of the sensitivity is desired, automatic volume control means, means provid the automatic volume’control lead to the source ing a controllable connection between said leads at a point remote from said receiving system to control the sensitivity between predetermined 10 at the terminal 2'4 may be made variable, or the I9 maybe extended externally of‘ the re “10 section ceiver and a‘variable return connection may be limits, and means providing a source of poten tial between said leads in circuit with said auto matic volume control means and in opposition to made therewith as shown‘in' Fig. 2, to which at tention is now directed, and in which like circuits 'and circuitvelements as in Fig. 1 are designated by the same reference numerals. In‘this case, the terminal 24 and the ground the biasingpotential provided by said automatic volume control means in response to signals, the 15 potential of said source being of a predetermined [6 ‘are connected through the leads GI] and 35 value determining the'range of sensitivity‘ control with the cableleads 6| ‘and_36, respectively, as ef‘fective- at said remote control point.~ _ 2.‘ The combination with an automobile radio receiving system having automatic volume con beiore, which‘termin‘ate in a’ potentiometer re 2o sistor 10 having a movable contact ‘H connected through a cable lead 12 with a leadl3 in the re . trol means, of a remote control system having an ceiver for the automatic volume ‘control ground extensible control circuit comprising a chassis return from the automatic volume control diode output resistor 40, whereby the said lead is vari 25 ably connected with the potential source‘ l9. It will be seen‘that movement of the potentiometer contact ‘H permits a varying ‘potential to‘be ap plied to the automatic volume control circuit in opposition to the higher‘ than normal ‘biasing po 30 tential provided in connection with- each‘ampli ?er tube by the ‘self bias‘ grounded cathode re sistors, thereby permitting the sensitivity to be reduced gradually from‘a maximum to a‘mini mum determined by the range“ of' potential varial ‘ tion available across the source l9.‘ In certain cases, where interference is less=severe,i the re sistor l9 may be omitted and the resistor 'Hl‘may provide the potential droprequired-‘for-the range of sensitivity control. ‘i 1» i‘ 1 ‘ ‘ ‘ In ‘the present case, the tone control'connec 40 tion is omitted, although ‘it "mayil‘be' "applied . through the cable connection‘ in the‘ same manner as shown‘ in the circuit of Fig.v 1.v The present circuit, however, reduces the number of leads re quired in the'cable which is extended to anysuit able‘ location for the sensitivity control ‘device. In either of the embodiments shown in ‘Figs. 1 and 2, the‘ operation of the automatic volume control means isi’not impaired, since'the poten tials set up across'the diode ‘output resistor‘ 40, to ground lead, a tone control circuit including said lead,'and a ground return lead for the automatic volume control system, means for connecting said 25 leads at a point remote from said receiving sys tem to control the sensitivity and tone between predetermined limits, and means providing a source of potential between said ground and ground return leads in opposition to a normal 30 biasing potential provided by said automatic vol ume control means and of a predetermined value determining the range of sensitivity control effec tive at said remote control point. 3. The combination with anvautomobile radio 35 receiving system having automatic volume, con trol means, of an extensible sensitivity control cir cuit for said system comprising a chassis ground leadand a ground return lead for said auto matic volume control means, means providing a controllable connection between said leads at a point remote from said receiving system to con trol the sensitivity between predetermined limits, means providing a sourceof potential between said leads in circuit with said automatic volume 45 control means and in opposition to biasing po tential provided by said automatic volume con trol means in response to signals, the potential of‘ said source being ‘of a predetermined value determining the range of sensitivity control effec in the presence of ‘signals, serve further to in crease the negative bias oi the controlled tubes,‘ and therefore reduce the gain Whether the sen sitivity is' set for maximum or minimum or any tive at said remote control point,‘said automatic volume control means including a diode signal intermediate position by‘ either‘of the means tem, each of said tubes having a control grid shown in Figs. 1 and“ 2. connected with the negativeend of said output ‘ ‘ “ i In either circuit, the sensitivity control'iis ap 40 recti?er having an output resistor and a plurality of signal ampli?er tubes in said receiving sys resistor, a ?lter in said connection, and said plied in the ground return connection for the ' ground return lead for the automatic volume automatic volume control circuit, the ‘latter being control‘sys‘tem being'connected with the opposite provided with sui?cient ?xedrnegat‘ive rbiasing po tential on the controlled tubes to overcome a receiving system having automatic volume con trol means, of a sensitivity control system having trol desired for changing ther'receiving system - an extensible ‘control circuit comprising a chassis from a condition of maximum ‘sensitivity to a ground lead and a ground return lead for, the automatic volume control system, means for con necting said leads at a point remote from said receiving system to'control the sensitivity 'be tween predetermined limits, means providing a condition of reduced sensitivity‘for‘ the reception r of local signals.‘ ‘ With this arrangement, the series automatic volume control source" of ‘variable potential may operate effectively to control the gain‘loc'ally‘un der-‘any c‘onditio'n‘of ‘s‘ensitivity‘an‘d theexternal ‘ circuits from the receiver are eifectively' isolated from the receiving circuits through the normal ?lter provided inthe automatic‘ volume control circuit. ‘ ‘ ‘ i ' ~' 1“ " ' 60' ‘ 4. The combination with an automobile radio a value‘ representing‘ the ‘range 1 of ‘ biasing ‘con series‘?xed opposing ‘positive ‘biasing potential ‘of 76 end o'fsaid output resistor. sourceof potential between said leads in opposi tionto biasing potential provided by‘said auto 70 matic volume control means in response to sig nals and of a predetermined value determining the‘range of sensitivity control e?ective at said remote control point, ‘said automatic volume 75, . 4 2,121,427 control means including a diode signal rec ti?er having an output‘resistor and a plurality of signal ampli?er tubes in said receiving ‘sys tem, each of said tubes having a self bias resistor connected with said chassis ground providing a potential in excess of the potential of said source maticvolumeicontrol potentials, of an output re sistor'for said recti?er having a negative ter minal; an automatic volume control circuit con nected therewith,.?lter means in said connection including a series high resistance element and by an amount to provide maximum sensitivity in the absence of received signals, each of said tubes by-pass capacitor, means providing a ?xed bias ing potential in said last named circuit in series having a control gridconnected with the negative with said output resistor connected between the opposite end thereof and ground in said system, 10 a plurality of ampli?er tubes controlled by said automatic volume control means, each of said control tubes having a self bias resistor means providing a biasing potential greater than said ?rst named potential by a predetermined amount 150 and in opposition thereto, and remote control means for reducing the elfect of said ?rst named potential in said automatic volume control cir cuit comprising a circuit control device and cir cuit leads connected therewith and with said ?rst 20 10 end of said output resistor, a ?lter in said con nection, and said ground return lead for the automatic volume control system being connected with the opposite end of said output resistor. 5. The combination with a radio receiver hav ing an automatic volume control circuit provided with a grounded chassis return connection, of means providing a ?xed source of positive bias ing potential for said circuit in said ground re: turn connection of a potential value correspond 20 ing to a desired change in sensitivity between a condition of maximum and minimum sensitivity, means in said automatic volume control circuit providing a negative biasing potential in excess of and in opposition to said ?rst named potential 25 by an amount su?icient to provide a predeter mined maximum sensitivity, and means con nected with said ?rst named potential source for reducing said ?rst named potential thereby to decrease the sensitivity of the receiving system from maximum, an extensible control circuit for said last named means connected with the auto matic volume control circuit, and ?lter means in said automatic volume control circuit for isolat ing said extensible circuit from the, receiving 35 diode'signal recti?er adapted to provide auto system. . ' 6. In a radio receiving system, the combination with automatic volume control means and a plu rality of ampli?er tubes controllable, thereby, of an automatic volume control‘ circuit comprising means providing a control’ potential responsive to variations in received signal strength, ‘means providing a return lead to aichassis ground for said circuit, means in said lead providing a ?xed source of biasing potential for said tubes, means 45 providing a second ?xed source of biasing poten tial for said tubes,-the magnitude of which po tential is in excess of the potential provided by said ?rst named source and in opposition thereto by an amount to provide a condition of maximum named potential source. 9. In a radio receiving system, the combination of an interstage ampli?er coupling transformer having a primary winding and a secondary Wind ing, a signal recti?er device including a cathode 25 and an anode, means for connecting said anode with the primary winding to receive signal energy therefrom, an output resistor for said signal recti ?er, means providing a common chassis ground connection for said receiving system, a cathode 30 circuit resistor connected between said cathode and said common chassis ground and having a connection at the cathode end thereof with the positive terminal of said output resistor, an auto matic volume control circuit having a negative 36 biasing supply lead connected with the negative terminal of said output resistor, ?lter means in said connection comprising a series resistor and a by-pass capacitor to the chassis ground from said lead, means for applying direct current to 40 said cathode circuit resistor to cause a pre determined potential drop therethrough to effect a predetermined change in sensitivity of said re ceiving system, a pair of shielded control leads connected with said cathode circuitresistor, and 45 remote control means connected with said leads and operative to connect the positive end of the signal rectifier output resistor to chassis ground to; the exclusion of said cathode circuit resistor, sensitivity for said‘ receiving :system, sensitivity thereby to change the sensitivity of said receiving 50 control leads extending from-said ?rst named» system through a predetermined range dependent source of biasing potential, and means connected upon said potential. with said leads for connecting said automatic 10. In a radio receiving system, the combina 55 volume control return lead'to said chassis ground. '7. In a radio receiving system, the combination with automatic volume control means and a plu rality of ampli?er tubes controllable thereby, of an automatic volume control circuit comprising means providing a controlling potential responé 60 sive to variations in received signal strength, a chassis ground connection therefor, means in said connection providing a ?xed source of biasing potential, means providing a second ?xed source of biasing potential for said controlled ampli?er 65 tubes,'the magnitude of which last named poten , tial is in excess of the potential provided bysaid ?rst named source and in opposition thereto ‘by an. amount to provide a condition of maximum sensitivity for said receiving system,v sensitivity 70 control leads’extendingirom said ?rst named source of ?xed-biasing potential, and means con nected with said leads forvariably connecting said automatic volume control circuit to ground. 8. In a radio receiving system, the combination with automatic volume control means including a tion with automatic volume control means includ ing a diode signal recti?er adapted to provide 65 automatic volume control potentials, of an out put resistor for said recti?er having a negative terminal, an automatic volume control circuit connected therewith, ?lter means in'said connec tion, an ampli?er having a cathode circuit in~ 60 eluding a resistor providing a ?xed biasing po tential in series with said output resistor and connected with the opposite positive terminal of said output, resistor at a point on said cathode circuit resistor which is positive with respect to 65 ground, said ground providing a common return connection for said automatic volume control circuit, a plurality of ampli?er tubes connected with said automatic volume control circuit to re ceive biasing potential therefrom in response to 70 signals and from said ?xed biasing potential, each of said control tubes having a self bias resistor means connected between cathode and ground and providing a biasing potential greater than said ?rst ?xed biasing potential in opposition 75 2,121,427 ' thereto and by a predetermined amount sufficient to effect substantially maximum sensitivity, means for reducing the effect of said ?xed biasing potential on said automatic volume control cir cuit comprising a circuit control device and ex tended circuit leads connected therewith and with 5 said ?rst named potential source, and means'for ' shielding said leads including by-pass paths of low alternating current impedance at the ter minal of said leads at said receiving system. LESTER T. FOWLER.