US2086195A

US2086195A - Radio receiving system

Info

Publication number: US2086195A
Application number: US678410A
Authority: US
Inventors: Rogers M Smith
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-06-30
Filing date: 1933-06-30
Publication date: 1937-07-06
Anticipated expiration: 1954-07-06

Description

July 6, 1937.. R. M. SMITH RADIO RECEIVING SYST EM Filed June 30, 1933 2 Sheets-Sheet-l /.s flTTOEl/EX 'July 6, 1937. R. M. SMITH RADIO RECEIVING SYSTEM 2 Shets-Sheet 2 Filed June 50, 1935 smtk Patented, July 6, 1937 UNlTED STATES PATENT- OFFICE to Radio Corporation of America, a corporation of Delaware Application June 30, 1933, Serial No. 678,410

I I 23 Claims.

The present invention relates to radio receiving systems, and more particularly, to radio receiving systems wherein one or more electric discharge devices or electronic tubes are caused to function in a plurality of signal conveying circuits. Such systems are of. increasing commercial importance in connection with midget radio receivers, automobile receivers and the like, wherein certain definite requirements in regard to size, current consumption and cost must be met.

In automobile receivers, in particular, it is important that current consumption be kept at minimum value while at the same time maintaining a high level of sensitivity. Accordingly, it

is desirable to reduce the number of current consuming devices, and in particular, the number of tubes employed in such apparatus without correspondingly reducing the operating efficiency.

To this end, a single electric discharge device or vacuum tube may be arranged to function as an element of a plurality of signal conveying circuits.

Radio receiving circuits and the like, wherein an electronic tube performs two functions, as in a refiexed amplifier, are known, as well as circuits wherein further functions are provided, though attended often by undesirable complicaticn of said circuits or of the circuit arrangement. It is conceivable, however, that if a further combination of functions may be given to one vacuum tube, without introducing undesirable circuit complications, the number of tubes necessary for use in a given receiving circuit may be greatly reduced and to good advantage.

It is, therefore, an object of the present invention to provide an improved receiving system embodying a single electric discharge amplifier device wherein a reduction in operating current is efiected with increased amplification and wherein said device performs a plurality of functions in separate signal circuits thereof.

It is a further object of the present invention merits, namely a cathode, a control grid, an

anode, and screen and suppressor grids, whereby a greater amplification is obtainable therefrom and, in addition, at least .one and preferably two 5 anodes or plates also associated with the cathode,

independently of the other electrodes, for diode rectification of signal currents.

' It is a still further object of the present invene tion to provide a radio receiving system wherein, in a single tube amplifier device of the character above described, the combined functions. of high frequency amplification, detection, low frequency amplification, and automatic volume control may be provided through simple circuit means.

In this connection, the present invention is,

therefore, particularly adapted for use with.

superheterodyne type receivers to provide a combfned intermediate frequency amplifier-second detector-automatic volume control-audio frequency amplifier system, the vacuum tube amplifier devicepreferablybeing of the pentode type. Such a device provides, in an amplifier, a rela-' tively high amplification factor with correspondingly low operating potentials and a stable operating characteristic. The use of such a device and circuit in a battery or automobile receiver results in high gain with an appreciable reduction in the current consumption and battery drain.

The invention, however, is not limited to superheterodyne receivers of the battery type, nor to a second detector circuit of a superheterodyne receiver, but may be applied to any detector circuit which is associated with and interposed between high frequency and low frequency amplifier circuits and in conjunction with automatic Volume or gain control means for the system in which the detector is located.

The use of a separate and additional diode plate for supplying control potentials or current to other circuits, such as automatic volume control circuits, may be desirable in certain receiving systems, and accordingly, it is a further object of the present invention to provide an improved circuit of the character above described, wherein a diode rectifier function and an automatic volume control function are separated.

It is a still further object of the present inven- In accordance with one embodiment of the invention, a diode detector is supplied with signal energy from the anode or output'circuit of a pentode type amplifier, both the detector and amplifier beingjprovided in a single envelope and having "a common cathode, and the audio fre quency signal output, therefrom is reflexed, by, resistance or impedance coupling, for example,'

preferably onto the pentode grid then back through the pentode, and the pentode output circuit, to the utilization system or to a further amplifier, whereby both the control grid and the anode of the pentode serveto carry both high and low frequency signals, suitably filtered input and the detector circuit or indirectly from a separate rectifier circuit in connection with a separate anode, whereby as hereinbefore stated, the device is provided preferably with two diode plates.

The invention will, however, be better understood from the following description when taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a schematic circuit diagram of a radio receiving system embodying the invention; and

Figs. 2, 3 and 4 are similar diagrams of modifications of the system shown in Fig. 1.

Referring to Fig. 1, a high frequency amplifier 5 and a low frequency amplifier 6 having an output device 1 provide the usual signal channel of a receiver, with a detector circuit or system 8 therebetween havinga plurality of functions in accordance with the invention, and as hereinbefore pointed out.

In the present example, a superheterodyne type of receiver is indicated, wherein a radio frequency amplifier device 9 and a combined detector and oscillator device I6 are provided in the high frequency amplifier 5 and connected in customary cascade relation through suitable coupling circuits I I between a high frequency input or antenna circuit I2 and a high frequency output circuit I3.

This apparatus is preferably electrically shielded as indicated by the dotted rectangle enclosure therefor, having a ground lead or base indicated at I4. The ground lead may not necessarily be connected to ground, but represents the low potential lead or circuit connection of the apparatus. 'A cathode return lead I5 for the two devices 9 and II is connected to the ground lead I4 as indicated, and includes a self bias resistor I6. Additional biasing potentials for volume control purposes are supplied to the devices 9 and I0 through a supply lead indicated at 11. This lead includes a high frequency filter provided by suitable series resistors I8 and bypass condensers I9. This circuit connection will further be described hereinafter.

An anode potential supply lead also for this portion of the receiver is indicated at 20. For the reason that the construction and circuit arrangement of this portion of the receiver does not concern the present invention, further description is believed to be unnecessary, and for the sake of simplicity and clearness in the drawings, the remainer of the circuits have been omitted.

Likewisa'the audio frequency amplifier 6 represents any suitable low frequency amplifier having an electric discharge amplifier device or vacuum tube 2| connected between a suitable input circuit 22 and an output circuit 23 leading to the output device ,1. Audio or low frequency coupling transformers are indicated at 24 and 25 to provide a cascade connection through the amplifier for signal potentials delivered to the input circuit 22. Since the audio or low frequency amplifier and the output device represent any suitable utilization means for the low frequency signals, and do not form part of the present invention, further illustration of the same and a further description are believed to be unnecessary. The amplifier is indicated as being enclosed in a suitable casing or container, by the dotted rectangle 6, and is provided with suitable anode potential supply and return ground leads 26 and 21, respectively.

The high frequency output circuit I3, which may be taken as representing any source of high frequency modulated radio signals, is coupled to the circuit 8, which, in turn, is coupled to the low frequency input circuit 22 to complete the signal channel of the receiving system. The modulated signal current, in passing through the circuit 8 between the high frequency signal output circuit I3 and the low frequency signal input circuit 22, is caused to pass through a plurality of transformations, including amplification at high frequency, diode detection, amplification at low frequency, and rectification for providing direct current control potentials for automatic volume control purposes.

In providing the several functions in this transformation, a single electric discharge or vacuum tube device 28 is utilized in the circuit 8, such device having a single cathode 29, at least one diode plate or anode 30 and preferably at least one other anode electrode 31, a first or inner grid 32, an output anode 33, a screen or second grid 34, and preferably a third or suppressor grid 35, although such device may function in the circuit of the present example without such suppressor grid. With an indirectly heated cathode in a device as illustrated, a heater element 36 is also provided for the cathode. Such a device will be termed a duplex diode pentode.

The cathode 29 is associated with the diode plates 30 and SI and also with the remaining pentode electrodes or elements 32 and 33. The screen grid 34 serves to decouple, in a well known manner, the last-named triode elements which serve as control grid and anode, respectively.

As will hereinafter be seen, a tube of this character provides the advantage that the electron stream of a portion thereof which is utilized as an amplifier may be separated from the electron stream of another portion which provides a diode rectifier, both the amplifier and rectifier being within the same electric discharge device 28 and with the common cathode, thereby permitting separation of the amplifier circuits from the rectifier circuits.

The source of high frequency signal potentials, rep-resented by the high frequency output circuit I3, is coupled to the control grid 32 through a high frequency input circuit 31. The input circuit includes a suitable high frequency input impedance or coupling device such as the tuned secondary 38 of a coupling transformer 39. The grid receives a suitable biasing potential through this circuit and through a low potential supply lead 40 therefor, connected to the ground lead I4 through a coupling resistor 4|. The biasing potential is supplied from any suitable source such as a self bias resistor 42 in the cathode return lead, indicated at 43. The self biasing resistor 42 is provided with a suitable radio frequency and audio frequency bypass condenser 44 also connected with the ground lead I4. A suitable high frequency bypass. for the circuit 31, directly to the cathode lead 43, is provided by a condenser 45.

The input circuit 31 is tuned to the frequency of the incoming signal, such as the selected intermediate frequency, and through it, the incoming sesame signal, usually an audio frequency modulated radio frequency carrier wave, is applied to the control electrode 32. p

Intermediate frequency signals delivered to the control grid 32 from the input circuit 3.1 are amplified and transmitted from the pentode output anode circuit indicated at 46, through a coupling device 41 located therein and a supply lead 48 to at least one, and preferably both, of the diode plates 30 and 3| in parallel as shown.

In the present example, the coupling device 41 is a high or intermediate frequency transformer having a primary 49 in the amplifier output circuit 38 and a secondary 5|] connected to the lead 48 in the diode rectifier circuit. The low potential side of the primary is connected, to ground through a suitable high frequency bypass condenser 59, and also, to the input circuit 22, through which it is connected to the positive anode supply lead 25, as indicated in the drawings. The last named lead is connected with a main high potential supply lead 52 which is connected with a suitable current supply source,

The current supply unit 53 is energized from a a suitable power source such as a battery 54, in an automobile installation, although any other suitable power source may be utilized with the proper supply means in the unit 53. The battery and the power supply unit 53 connected therewith are grounded as indicated. While the present receiving system shown in Fig. 1 relates particularly to automobile radio receivers, the supply source and battery circuit do not form part of the invention and, therefore, are not believed to require further description.

The low potential side of the secondary 50 of the coupling device 4? is connected, through a resistor 5'! having arelatively high resistance value, to the movable contact 58 of a potentiometer device or resistor 59. The potentiometer device is connected between a lead 69 in turn connected with the cathode lead 43 and the cathode, and a lead SI and a coupling condenser 62. The latter is connected with the lead 49 and the low potential side of the input or grid circuit 31, between the latter and the coupling resistor ll. The leads 65 and ii are preferably electrically shielded, with the shield connected to ground as indicated by the dotted lines 55' and 6!, for the reason that they are usually extended, in use, to a suitable control point for the device 59, in an automobile installation.

From an inspection of the circuit diagram, it will be seen that modulated high frequency signals appearing in the output circuit 46 are amplified because of the high frequency impedance means ll in circuit therewith and are, through said device, transferred to the rectifier circuit which includes the lead 58 and the diode plates 30 and 3|. tified in conjunctionwith the cathode 29 through the rectifier circuit which may be traced through the cathode lead 43, thence to the lead 60, through the resistor element 59 of the potentiometer device to the movable contact 58 and the lead',

63, and through the high resistance element 5'! The modulated signals are then rec-' back to the low potential side of the. secondary 5B of the high frequency coupling device 41.

'The diode rectified signal current flowing in the circuit above outlined comprises both an audio frequency'signal component and a direct current component and is applied to the .resistance elements in series to set up controlling potentials across the element 51 and any portion of element 59 which may be in circuit there-, with. The direct potential is applied to the automatic volume control circuit ll through a supply lead 64 connected to the resistance element 5! at a suitable point such as its negative end or terrninal adjacentgto the low potential side of the secondary 50. g

Because of the diode rectification, it will be seen that the resulting rectified current will flow in'the resistor 5'! in the direction of the arrow, whereby a negative potential is applied to the control circuit l'l' for the amplifier'ii in response to an applied carrier wave, an increase in the intensity of the latter causing an increased negative control potential to be applied tothe preceding amplifiers and a corresponding reduction in the gain therein. The potential drop caused by the flow of rectified signal current through the resistor 5! is thus applied to the amplifier for automaticv volume control use and varies in.

response to changes in the carrier wave intensity.

Because of the nature of the amplifier devices used in modern radio apparatus, a' Wide range of control potentials is required, and therefore, the voltage available across the rectifier circuit, including the, resistor 51, or between the supply lead 64 and the groundlead 14, may be'relatively high. For the above reason, the resistor 5'6 may have a relatively high value,'preferably several hundred thousand ohms, with. the type of tubes and circuit shown.

This resistor 5'! also serves the purpose of stepping down the corresponding audio frequency signal potential to be applied at the contact 58 in order not to overload the grid 32, with an adjustment of the contact 58 for maximum volume.

It will be seen that as the contact 58 is moved to the lower end of the resistor 59, as viewed in the drawings, the contact will be at cathode potential, while as the contact is movedto positions approaching the extreme opposite position, the contact will be decoupled increasingly from the cathode through the introduction of the resistor59 and will correspondingly increasingly be coupled to the control grid 32.

1 Audio or low frequency potentials set up across the resistor 59 are conveyed from said resistor through the lead 6!, the coupling condenser 62 and the lead 58, to the grid 32 through the circuit 3? which is of low impedance, to audio frequency signals. The impedance of the coupling resistor 45 is of such a value that it offers a relatively high impedance to the audio frequency signal potentials.

Viewed in another aspect, operation of the audio frequency volume control potentiometer,

gridof the pentode amplifier. The greater ,re-

sir ta nce causes a greater potential ,dropand,

therefore, a higher audio frequency potential on the control grid 32.

A suitable bypass condenser 65 is provided for the high frequency circuit to ground from a point between the resistor 51 and the low potential end of the secondary 50. The screen grid 34 is also supplied with potentials through a supply resistor 66 in connection with the supply lead 52, and the resistor is provided with a suitable bypass capacitor 6'! for filtering purposes.

Audio frequency signals placed upon the control grid 32 are amplified and applied to the output anode circuit 45 and find a low impedance path through the high frequency coupling device 4'! to the input circuit 22 for the audio frequency amplifier 6. The high frequency bypass condenser 5! is of a value which does not offer any appreciable shunt effect for audio frequencies upon the circuit. However, for tone control purposes it may be desirable to provide a bypass capacitor such as that indicated at 68, and a controlling switch 69 in the anode output circuit 46 between ground and the junction of the high and low frequency circuit impedance elements, represented by the coupling elements 41 and 24 in the present example, as indicated. Upon closure of the switch 69 certain higher audio frequency signals may then be bypassed to ground and interference from noise sources eliminated, prior to amplification in the audio frequency amplifier.

The rectified signal current flows through fixed and variable voltage divider resistors 53 and 59, respectively, in the rectifier output circuit, the first of which is utilized as an impedance for supplying automatic volume control potentials to preceding amplifier devices, at a relatively high value for the suppression of strong signals. The rectified audio frequency signal component is reduced through the resistor 51 to such a value that with a maximum incoming signal wave and with the potentiometer volume control contact 58 at the maximum volume position at the upper end of the resistor 59, as viewed in the drawings, the control grid 32 may not then be overloaded appreciably by the audio frequency signal, whereby noticeable distortion may be introduced.

In the present example, and as a preferred arrangement of the circuits, the high frequency signal input circuit 3? is connected with the innermost or first grid of the amplifier device, which is the grid 32 indicated in the drawings. While both of the anodes 3i) and 3! 'of the diode rectifier are connected together and utilized in parallel in the common rectifier circuit, they may, in certain applications, be connected to a common signal input circuit and to separate output circuits for controlling difierent functions in the receiving system, as will hereinafter be described.

The resistor 4! between the low potential side of the circuit and ground may be relatively high, for example, such as one half megohm, as an audio frequency coupling impedance, while the radio frequency bypass condenser 45 may have a value of substantially 300 micro-micro-farads, being in shunt tothe grid circuit and therefore being of relatively hi h impedance to audio frequency signals as is desirable in order not to affect appreciably the audio frequency characteristic of the signal transmission. The resistor 42 is of suflicient value to provide the desired bias potential on the grid 32, for example, 3 to 6 volts in a preferred device of the type shown, and the bypass capacitor or condenser 44 may have a value of 5 microfarads.-

It should be noted that the devices 9 and I0 in the input signal circuit of the receiver receive a normal biasing potential from the fixed source provided by the self bias resistor l6 and an additional signal controlled bias potential from the rectifier circuit through the supply lead 64, with the resistor 57 as the source.

With the diode rectifier circuit connected to the cathode and with a self bias resistor 42 in circuit with the cathode 29 of the combined detector amplifier device 28, it will be seen that the potential existing in the self bias resistor 42 is applied to the biasing circuits of the devices 9 and H] in opposition to the bias potential provided by the source it. Accordingly, in the circuit shown, the source 16 is arranged to provide an additional potential equal to that provided by the source 42, whereby a normal bias is obtained on the devices 9 and I0.

This may more readily be seen by tracing the bias circuit for the device 9- from the input grid circuit thereof, through the circuit Ii, resistor I8, circuit lead l1, through the second filter resistor I8 to the lead E4, thence through the impedance or resistor 5'1, lead 63, the contact 58, a portion of the volume control resistor 59, through the lead 69 to the cathode lead 43. From this point, the circuit may further be traced through the self bias resistor 42 to the ground lead (4,

thence through the resistor I 6, to the cathodes of the devices 9 and Ill. The polarity of the potential existing in the various resistors mentioned'is indicated by suitable polarity marks adjacent to the terminals thereof, and in tracing the circuit outlined, it will be seen that a potential existing in the resistor I6 is, in the circuit outlined, in opposition to that existing in the resistor 42.

.ttention is now directed to Fig. 2 wherein an electric discharge amplifier and rectifier device 70, of the tetrode or screen grid type is provided with an inner grid H connected with a high frequency signal input circuit E2, the low potential side of which is represented by the grid return lead 13.

The main anode is indicated at 8B and is connected with a high frequency anode output circuit M, which is connected through a high frequency coupling device '85 and a high frequency supply lead 16 with an anode ll associated with the cathode 78 to provide a diode rectifier. A screen grid 19 is provided between the main anode 89 and the control grid ll.

High or intermediate frequency signals, amplified in the tetrode portion of the device 18, are supplied through the output circuit 14 and the coupling device to the input circuit 16 for the anode Tl. The signals are rectified through the diode rectifier provided by the anode Ti and the cathode l8, and pass through an audio frequency and direct current impedance element 8! in the form of a tapped resistor providing a potentiometer, the movable contact of which is indicated The rectifier circuit is completed from the resistor 8| to the low potential side 33 of the rectifier circuit, which includes the coupling device 15. This may be a suitable tuned high frequency input transformer as indicated. Any other suit-- able coupling device, however, may be used in the output anode circuit M for coupling the latter to the diode rectifier circuit.

It will be noted that the rectifier or diode circuit returns directly to the cathode 7S, whereby the only potentials existing in the rectifier circuit are those caused by the rectification of signals, the signal potentials being available across the impedance element BI. These potentials are variably applied to the inner or control grid 'iI through a connection with the variable tap 92 which may be traced through a coupling con- 1 denser 86 and a combined coupling and high frequency filter impedance represented by a resistor element Bl between the coupling condenser 89 and the ground lead indicated at 89.

The connection for the grid lead 73 is made at a suitable lower potential tap point 83 on the resistor 8'! whereby overloading of the grid ii with audio frequency signals is prevented, when the tap 82 is moved to the extreme audio frequency volume position at the right hand end of the resistor 8!, as viewed in the drawings. A bypass condenser 84 from the lead T9 to ground and cathode provides, with the resistor 8'5, a suitable high frequency filter for the audio frequency or diode rectifier circuit.

Suitable normal operating or biasing potential for the grid II is supplied through a portion of the resistor 81 from a self bias resistor 99 in the cathode return lead 99.

This circuit is similar to that shown in Fig. 1, except that the audio frequency potentials applied to the inner or control grid '7! are prevented from reaching excessively high values by a fixed ratio established by the tap 98 on the'impedance device 87. The audio frequency volume control device is directly connected to the impedance element iii in the rectifier circuit, and suitable audio frequency potentials for the desired volume are then selected directly therefrom, subject, however, to a fixed reduction ratio in the impedance 81. High frequency or intermediate frequency signals are supplied to the input circuit 12 through a suitable input coupling device 9!, and the audio frequency output signals are transferred to the output circuit through an audio frequency output device 92 in connection with the output anode circuit M for the tetrcde, in the same manner as described in connection with the preceding figure. Therefore, further description is not believed to be necessary in connection with these features.

In this circuit modification, the supply of potentials for automatic volume control purposes is obtained from a separate impedance element in a separate diode rectifier circuit provided in connection with the second rectifier anode 93 which, like the anode TI, is directly associated with the cathode I8 outside the electron stream of the tetrode.

High frequency or intermediate frequency signals are supplied to the anode 93 fromthe same circuit I6 as the anode I! through a coupling condenser 99. The second diode rectifier circuit may be traced through a lead 95 directly connected with the anode 93 and connected to the ground lead 89 through an impedance element or resistor 96, and a control potential supply resistor 9'! provided with a shunt radio frequency bypass condenser 98. The diode rectifier circuit is completed through the self bias resistor 99 and a cathode return lead 99 in which this resistor is located. It should be noted that it is desirable to provide a lower impedance at 99 than at 9'! in order that the major portion of the potential drop may occur in the resistor 91, and, therefore, be available-for control purposes.

It will be seen that with this arrangement. the potential existing across the self bias resistor 99 is applied to the anode 93 in opposition to signal potentials impressed thereon by the circuit it,

whereby a delayed rectifier action is provided. This is for the reason that a positive potential is applied to the cathode 18 because of the potential drop in the resistor 99, and a positive potential is also applied to the anode 99 when rectification occurs on each positive half cycle. Un til the positive signal potential on the anode 93 is greater than the positive potential existing on the cathode '58, no rectification can take place.

Therefore, the delayed action on the rectifier anode 93 and a delayed automatic volume control of the gain in the preceding amplifier devices is obtained and, as is well known, is desirable in radio receiving systems to permit a certain signal level to be reached before suppression of the gain is initiated.

Automatic volume control leads indicated at I90 are connected through suitable filter resistors indicated at I9I to the direct current impedance element 9'! for supplying controlling potentials to preceding amplifier devices, in the manner disclosed in Fig. 1. This connection may be made at any suitable point on the element 971 to provide the desired potential for automatic volume control purposes, resulting from rectification of the signal currents. Because 91 is of higher resistance than 96, more D. C. voltage is developed across 91 for automatic volumecontrol purposes, which is desirable in this case.-

It will be seen that in the embodiment of'the I fier circuit is provided with an impedance elef- U ment in series with the diode-rectifier therein to set up potentials whichin the audio frequency circuit may variably be applied to the control grid of the amplifier portion of the device I9, while in the case of the automatic volume control circuit, the impedance is utilized as a source of variable direct potentials which are responsive to the variations in intensity of the carrier wave to control the gain of preceding amplifier devices.

Referring now to Fig. 3, a similar circuit to that shown in Fig. 2 is illustrated, inwhich a pentode type electric discharge device I92, like the device 28 of Fig. 1, is utilized in place of a tetrode. The cathode is indicated at I49 and. the main anode at MI. The diode plate or anode electrodes associated with the cathode are shown at I42 and I43 and the screen grid at I44. The cathode or suppressor grid is shown .at I45. A fixed tap connection I03 is provided on the-diode rectifier circuit impedance 92a for applying to, the control grid indicated at I94, variable audio frequency potentials for further amplification- The impedance 82, with a condenser85, providesa suitable high frequency filter for the rectifier circuit.

The tap connection acoupling condenser I95 to one end of avolume control potentiometer resistor I96, theotherend of which is connected directly-to the ground lead 89. The variable volume control tap I9! is connected with a gridjleadIiIB which, in turn,

is connected with the low potential sideof the,

high frequency input circuit 12 and thence to, the

control grid I94. The lead I99 is provided with,

I93 is connected through an audio frequency coupling condenser I I which may be utilized instead of a transformer connection in certain receiving apparatus. Also, the coupling device I is untuned on the primary side as is desirable in certain receiving circuits.

The operation of the system shown in Fig. 3 is similar to that shown in Figs. 1 and 2. However, the arrangement has the advantage that the audio frequency signals are applied to a potentiometer device lii6iil'|' which is connected directly to ground at one end, whereby as the volume is reduced, the grid approaches or is finally connected to ground, thereby providing a more stable operating circuit.

As the volume is increased, the maximum audio frequency signal potentials are applied to the grid I04 when the tap I0! is at the upper end of the resistor I06, as viewed in the drawings. The potentials available at that point are determined by the fixed tap I03 on the signal ratio determining impedance element 82 in the rectifier circuit, the tap being placed at an intermediate point thereon for the purpose of preventing overload of the pentode-grid from audio frequency signals when the volume control device is at a maximum position.

It will be seen that the condenser I09 operates as a compensating tone control, for the reason that the relative impedance between it and the impedance of the potentiometer element I06 varies as the tap I0! is moved along the latter, so that for very low volume adjustments of the tap I01, the shunt impedance of the condenser I09 is relatively high with respect to the portion of the resistance I06" than in circuit between the tap and ground. Accordingly, the signal potentials in the higher audio frequency range are less attenuated as the volume is reduced, which is desirable, as the human ear is less responsive to high frequency sounds at low volume and the high frequency sounds are less attenuated for low volume adjustment than at higher volume adjustments of the volume control device, whereby to the listening ear, the high frequency sounds are maintained at substantially uniform relation to the remainder of the audio frequency range as the volume is reduced. A desired compensated volume control and high frequency bypass arrangement is, therefore, provided in the circuit shown.

In order that the sensitivity of the preceding radio input circuit may be controlled through a variation of the biasing potential applied to the preceding amplifier devices in a receiving circuit such as that shown in Fig. 1, the tap 81 on the automatic volume cohtrol supply impedance or resistor 88 may be made variable as indicated. Furthermore, this variable tap may be connected to or ganged with the volume control potentiometer I06 as indicated by the dotted connection I46 and may be provided with a common operating 'means indicated at I41 whereby the sensitivity of the receiver may be reduced simultaneously with a reduction in volume.

In the present example, movement of the potentiometer contact of the device I06 in a downward direction, as viewed in the drawings, causes a reduction of the amplitude of audio frequency potentials applied to the input grid J04. When ganged with the potentiometer orimpedance 83, simultaneous movement of the. contact 81 in the same direction is arranged as shown to cause an increase in the negative biasing potentials supplied to the leads I00, thereby more effectively to bias the preceding amplifier devices, such as those in Fig. 1, in a direction to reduce the gain therethrough.

With an arrangement as above described, an audio frequency volume control potentiometer in the audio frequency rectifier circuit is ganged or connected with a sensitivity control potentiometer in the automatic volume control potential supply circuit and arranged to be operated by a common means simultaneously to control both the audio frequency signal gain through the audio frequency portion of the receiver and the high frequency amplifier gain in the input portion of the receiver.

It Willbe noted that the automatic volume control diode lead I3 is returned, in the circuit of Fig. 3, directly to the cathode lead 99, whereby no delayed automatic volume control action is provided. This may, however, be provided as in Fig.

2, by connection to the ground side of the self bias resistor 91.

A simplified and eflicient circuit for combined high frequency amplification, diode signal and diode automatic volume control rectification, audio frequency amplification and automatic volume control operation is shown in Fig. 4, to which attention is now directed.

This circuit may utilize any suitable amplifierrectifier device. A screen grid tube or tetrode type as shown at I II is preferred, however, for a simplified circuit, and is provided with a high frequency input circuit I I2 connected with the control grid I I 3, a high frequency output circuit H4 connected with the output anode H5 and with a coupling system IIG, to the high frequency lead I H of the diode input circuit to which both diodes IIB-I I9 are connected in parallel, as in Fig. 1.

The diode circuit coupling device comprises a tuned high frequency choke coil I 20' connected in the anode output circuit H4 in series with an audio frequency output coupling resistor I2I provided with an audio frequency output coupling condenser I22, thereby providing a similar output circuit to that shown in Fig. 3.

The high frequency choke coil I20 is connected through a high frequency coupling condenser I 23, to a coupling impedance or choke coil I24, in the diode rectifier circuit I I1, providing an input device therefor. The two choke coils I24 and I20 are electrically separated by a grounded shield I25, whereby electrostatic coupling only is provided between them through the condenser I23. The condenser preferably should have a relatively high impedance to audio frequency signals. This circuit arrangement provides a relatively high selection just preceding the diode rectifier or detector which is desirable for preventing interference in certain radio receiving systems.

The diode rectifier circuit is completed from the cathode, indicated at I21, through a cathode lead i28 directly to the ground lead I29, and from the ground lead I29 through the rectifier circuit impedance I30 which, in itself, provides the volume control potentiometer means, and from the opposite end of the potentiometer resistor I30 directly to the low side I3I of the input device I24.

Audio frequency signals existing in the diode rectifier circuit and available across the impedance element I30 are controlled in amplitude and applied to the inner or control grid II3 through a grid lead I32 and thehigh frequency input circuit II 2 by the variable tap I33 of the potentiometer device. Movement of the tap I33 serves to control the audio frequency volume as in the preceding embodiments of the invention.

R tential taken through the same contact.

Control potentials for automatic volume control purposes are also derived from the direct potential drop in the impedance element I30 through a suitable connection thereon. In the present example this connection is made normally at the high potential point indicated at I34, and the potentials therefrom are conducted through a lead I to automatic volume control leads I36, in which are located suitable filter resistors I31, and across which is connected a suitable bypass capacitor 33, forming with the resistors I 3?, a filtei for the automatic volume control leads.

In the embodiment of the invention shown in Fig. 3, the audio frequency volume control means and a sensitivity control means for a receiving system are shown in ganged relation. In the present embodiment of the invention, the single potentiometer device H30 may be arranged in circuit to control both the audio frequency gain and the bias potential supply for preceding amplifier devices through the medium of a connection with both the input lead I32 for the control grid H3 and the automatic volume control bias supply leads I 36.

To this end, a suitable switch, such as a twoway switch I45, is arranged to connect the input ends of the circuit leads I36 alternatively with the potential supply lead I35 or with the lead I32.

In the present arrangement, the switch ,arm I539 is connected through a lead I5!) with the input terminal ends of the filter resistors I31 and is arranged to connect with either of two contacts I5! or 52. The contacts are connected respectively with the leads I35 and I32, whereby the D. C. component of the signal potential available across the resistor I 30 may be taken in full through the lead I35 or in part as supplied by the contact I33 through the lead I32.

The connection is normally made as indicated, to the lead I35. It will be seen, however, that when connected to contact I52, the biasing potential supplied to leads I36 may simultaneously be varied by operation of the contact I32 along with the audio frequency component of the signal po- With this arrangement, combined audio frequency and sensitivity control is provided through a single instrumentality in the form of a simple potentiometer resistor.

It will be noted in connection with the circuit shown and described herein, that the operating bias potential for the control grid II3 is derived wholly from the resistor or impedance element its and such bias potentials result only from the reception of a signal and from rectification thereof, so that the control grid is diode biased or signal biased and the bias potential automatically increases with increasing signal, and with increased output volume resulting therefrom' the adjustment of the volume control tap I33. This arrangement has the advantage that the bias potential applied to the control grid automatically increases with increased signal strength and with an increase in the volume adjustment.

Thus, the system shown in Fig. 4 differs from that shown in the preceding figures, wherein the biasing potentials are derived from a fixed source such as a self bias resistor in the cathode return lead of the amplifier device.

From the foregoing description of the circuit shown in Fig. 4 it will be seen that through the medium of a single variable potentiometer device inserted as an impedance element in a rectifier circuit between a high frequency amplifier input circuit and a low frequency output circuit, in conjunction with a combined amplifier and rectifier device having a common cathode, combined high frequency amplification, rectified signal and automatic volume control potentials, audio frequency amplification, and simultaneous control of audio frequency and sensitivity control may be obtained, the one potentiometer device serving as a source of both variable and fixed signal and direct current components of the rectified current.

This circuit has the further advantage that the bias potential supplied to all amplifiers, including theaudio frequency amplifier, is increased automatically with increase in the signal strength along with the signal potential applied to the audio frequency amplifier, and that'no fixed additional source of bias potential is required, thereby simplifying the problem of supplying biasing potentials for the amplifier devices.

This circuit arrangement results in a simplificaticn of the receiving system, a reduction in the number of circuit elements required, and consequently a reduction in the'cost of manufacture of apparatus embodying this circuit.

The use of a single electric discharge device for four major functions, including the control of biasing and signal potentials by a single means in a receiving circuit, is of considerable importance in apparatus such as automobile and other battery operated portable receivers where the size of the complete apparatus, the current consumption and cost of said apparatus must necessarily be kept at a minimum.

I claim as my invention:

. 1. In a radio signal receiving system, the com-' bination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of a signal input circuit connected with said control grid, a rectifier circuit for said rectifier connected with said main output anode to receive the signal output therefrom, an impedance network providing coupling means between the rectifier-circuit and said input circuit, said network including a fixed and a variable impedance element providing a fixed and a variable potential drop determining means in said etwork, said variable potential drop determining means comprising a potentiometerhaving a resistor element and a movable tap thereon, one end of said resistor being connected with the cathode and said movable tap being connected with the fixed impedance element, and means. connected between the other end of the resistor element and the control grid for applying signal potentials to said grid.

2-. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrodeassociated therewith to provide a rectifier, a control grid and a main outputanode, of a signal input circuit con-s nected with saidcontrol grid, a signal output circuit connected with the main output anode, a rectifier circuit for said rectifier connected with said main output anode, and an impedance net work providing a coupling means between the rectifier circuit and said input circuit, said network including a fixed and a variable impedance element providing fixed and variable potential. drop determining means in said network, said variable impedance element being connected between the cathode and said control grid and havin a movable tap connection with said fixed impedance element.

3. In a signal receiving system, the combination of an electric discharge device comprising amplifier and rectifier elements having a common cathode in a single envelope, a signal input circuit and a signal output circuit for said amplifier element, a variable volume control impedance device in circuit with said rectifier element connected with said input circuit to variably apply rectified signals thereto, a second variable impedance device, circuit means for supplying rectified current therethrough from said rectifier element, an amplifier control circuit connected with said second variable impedance device to receive controlling potentials therefrom, means for simultaneously controlling said variable impedance elements, means for coupling said output circuit to said rectifier element, and means for receiving signals from said output circuit.

i, In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of a signal input circuit connected with the rectifier anode and with the cathode, an impedance element in the last-named connection, means for variably connecting the control grid with said impedance element to supply rectified signal and biasing potentials to said grid from said impedance element, said potentials being thereby simultaneously variable, and an amplifier circuit connected with said impedance element to receive gain controlling potentials therefrom simultaneously variable with said first named potentials.

5. In a signal receiving system, the combination of an electric discharge device comprising amplifier and rectifier elements having a common cathode in a single envelope, signal input and output circuits for said amplifier element, a circuit for controlling the sensitivity of said system, and means for simultaneously varying the control potentials applied to said last named circuit and signal potentials applied to said amplifier element, said means including a variable potentiometer device in circuit with the rectifier element and connected with the signal output circuit.

6. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of a signal input circuit connected with said rectifier, an impedance network including a variable impedance element, connected in part in circuit with said rectifier and in part between said rectifier circuit and the control grid, whereby said control grid is coupled to said rectifier to receive signals therefrom, the connection with the control grid being direct with said impedance element whereby direct biasing potentials may be received therefrom, a sensitivity control circuit for said system, and means for connecting said circuit with said variable impedance element, whereby control potentials simultaneously variable with said biasing potentials may be applied to said control circuit.

'7. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of an impedance network including a variable impedance element, connected between the control grid and the rectifier, and a fixed voltage ratio determining impedance element in circuit with said variable impedance element.

8. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of an impedance network including a variable impedance element, connected between the control grid and the rectifier, a fixed voltage ratio determining impedance element in circuit with said variable impedance ele-- ment, and means associated therewith in circuit to provide a filter.

9. In a radio signal receiving system, the combination with an electric discharge device having a cathode, a pair of anode electrodes associated therewith, a control g 'id and a main output anode, of an impedance network including a variable impedance element connected between the control grid and the cathode, a rectifier circuit connected between one rectifier anode element and the cathode through said impedance element, a second rectifier circuit, a second impedance element in said second rectifier circuit with the other rectifier anode electrode, and a control circuit connected with said last-named impedance element to receive a direct current controlling potential therefrom.

10. In a signaling system, an electric discharge amplifier device having a cathode and at least one rectifier plate associated therewith to providea rectifier, of a signal input circuit for said device, a signal output circuit for said device, high and low frequency impedance means in said output circuit, a signal circuit connected with the low frequency impedance means, a rectifier circuit, including the cathode and one rectifier plat-e, connected with said high frequency impedance means, impedance means connected in circuit between the cathode and the signal input circuit, a second impedance means connected in said rectifier circuit, means for deriving a potential from said second impedance means, and for applying a derived potential variably to said first impedance means.

11. In a radio signal transmission circuit, a diode rectifier and an electrical impedance device connected in series therewith, means for supplying high frequency signal potentials to said rectifier, an electronic tube amplifier having a cathode providing one electrode of said rectifier and a control grid connected with said impedance device, a variable impedance network providing said connection, means providing a low frequency separate output circuit for said amplifier, a second diode rectifier having an anode electrode associated with said cathode, circuit means for applying signals to said anode, a low impedance device in circuit adjacent to said anode, and a high impedance device in circuit adjacent to said cathode in series in circuit with said second rectifier circuit, and a control circuit connected with said last-named impedance device to receive direct-current controlling potentials therefrom.

12. In a radio receiving system, the combination with an electric discharge amplifier device having in a common envelope, a cathode, a conan impedance element, means providing a connection between said impedance element and. the

ico'ntr'ol grid, and a low frequency output circuit connected with said first-named anode.

tion with an electric discharge amplifier and rectifier device comprising a cathode, a control electrode, an anode, and at least one auxiliary anode associated with the cathode, of a signal input circuit for said control electrode including a high frequency impedance element, a low frequency impedance element, an output circuit for the first-named anode including a second high frequency impedance element and a second low frequency impedance element, a rectified circuit including said auxiliary anode and the cathode connected with the output circuit through the second named high frequency impedance element, and potentiometer means providing a variable connection between said rectifier circuit and the signal input circuit between the high frequency impedance element and the low frequency impedance element therein.

14. In a radio receiving system, the combination with an electric discharge amplifier and rectifier device comprising a cathode, a control grid, an anode, and at least one auxiliary anode associated with the cathode, a signal input circuit for said control grid including a high frequency a rectifier circuit including the auxiliary anode and the cathode connected with the output anode circuit through the second high frequency impedance element, means providing potential drop producing resistance and a variable potentiometer connection between said rectifier circuit and the input circuit, a high frequency amplifier connected with the first named input circuit, said amplifier having an automatic gain control circuit, and means providing a connection for the last-named circuit with said potential drop producing means for receiving automatic gain controlling potentials therefrom established by a direct current component of the signal current in said rectifier circuit.

15. In a radio receiving system, the combination with an electric discharge amplifier and rectifier device comprising a cathode, a control grid, an anode, and at least one auxiliary anode associated with the cathode, of a signal input circuit for said control grid including a high frequency impedance element, a low frequency impedance element and a source of biasing potential, an output circuit for the anode including a second high frequency impedance element and a second low frequency impedance element, a rectifier circuit including the auxiliary anode and the cathode connected with the output anode circuit through the second high frequency impedance element, and means providing potential drop producing resistance in the rectifier circuit and a variable potentiometer connection between said rectifier circuit and a point on said input circuit between the high frequency impedance element and the low frequency impedance element therein, and said rectifier circuit further including said source of biasing potential so poled that a predetermined fixed positive potential is applied to the cathode with respect to the auxiliary anode in the rectifier circuit, whereby a delayed rectifier action is provided.

16. In a radio receiving system, the combination with an electric discharge amplifier and rectifier device comprising a cathode, a control grid, an anode, and at least one auxiliary anode associated with the cathode, a signal input circuit for said control grid including a high frequency impedance element, an output circuit for the anode, a rectifier circuit includingthe auxiliary anode and the cathode connected with said outi put anode circuit, potential drop producing impedance means in said rectifier circuit, a common circuit lead connecting the input and'output circuits with the cathode, and a potentiometer resistor connected between a point on said potential drop producing impedance and said common circuit lead, and havingia variable contact connected with the control grid.

17. In a radio receiving system, the combina-' tion with an electric discharge amplifier and rectifier device comprising a cathode, a control grid, an anode, and at least one auxiliary anode associated with-the cathode, a signal input circuit for said control grid including a high frequency impedance element, an output circuit for the anode, a rectifier circuit including the auxiliary anode and the cathode connection with said output anode circuit, potential drop producing impedance means in said rectifier circuit, a common circuit lead connecting the input and output circuits with the cathode, apotentiometer resister connected between a point on said potential drop producing impedance and said common circuit lead, and having a variable contact connected with the control grid, and high frequency by-pass means connected between the movable contact of said potentiometer and said common circuit lead.

18. In a radio receiving system, the combination with an electric discharge device having a cathode, a control grid, an anode, and two auxiliary anodes associated with the cathode, of a high frequency signal-input circuit having one terminal connected to the control grid and having one terminal connected to the cathode through a potentiometer resistor, a rectifier circuit including said auxiliary anodes and the cathode and said potentiometer resistor, means for supplying amplified high frequency signals to said rectifier circuit whereby said control grid receives direct current potentials for biasing purposes and rectified signal potentials, from said potentiometer resistor, an audio frequency output circuit connected with said anode, and a gain control circuit connected with said potentiometer device to receive direct-current controlling potentials therefrom.

19. In a superheterodyne radio receiver for cult, means for variably applying a controlling potential from said impedance means to said amplifier device through said input circuit, an automatic volume control circuit, and means for deriving a second controlling potential from said impedance means for said automatic volume control circuit.

20. In a signalling system, the combination with an electric discharge amplifier and rectifier device having a control electrode, a cathode, an output anode, and at least one diode rectifier anode associated with the cathode, of a rectifier circuit connected between said rectifier anode and the cathode and including a resistor provided with a movable tap, a high frequency signal input circuit connected between said control electrode and the movable tap on said resistor, high frequency coupling means connected between said output anode and the rectifier circuit, an

automatic volume control circuit connected with said resistor to receive controlling potentials therefrom, and a separate low frequency output circuit connected with said output anode in series with said high frequency coupling means.

21. In a radio receiving system, a multi-electrode space current device and circuit connections whereby said device functions simultaneously to provide volume control potentials, as a demodulator of incoming signals and as an amplifier of the incoming signals as well as the demodulated signals, said device having electronic amplifier elements and electronic rectifier elements provided with a common cathode, and said circuit connections including signal input and output circuits for said amplifier elements, means for coupling said output circuit to said rectifier elements, an impedance device in circuit with said rectifier elements for producing a potential drop corresponding to the amplitude of received signals and the modulation component thereof, and automatic volume control circuit variably connected with said impedance element, and means for selecting from said impedance element and applying to said amplifier elements a demodulated signal.

22. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of a signal input circuit connected with said control grid, a rectifier circuit for said rectifier connected with said main output anode to receive the signal output therefrom, and an impedance network providing coupling means between the rectifier circuit and said input circuit, said network including a fixed tapped voltage divider resistor providing a tap connection for said input circuit, means for applying signal potentials across the terminals of said voltage divider resistor and a potentiometer resistor in circuit with said voltage divider resistor for varying the potentials derived therefrom for said input circuit.

23. In a radio signal receiving system, the combination with an electric discharge device having a cathode, an anode electrode associated therewith to provide a rectifier, a control grid and a main output anode, of a signal input circuit connected with said control grid, a rectifier circuit for said rectifier connected with said main output anode to receive the signal output therefrom, an impedance network providing coupling means between the rectifier circuit and said input circuit, said network including a fixed and a variable impedance element providing a fixed and a Variable potential drop determining means in said network, a self bias resistor in circuit With the cathode, means for utilizing the potential drop in said resistor to provide a delay potential for said rectifier, and means for utilizing potentials derived from said rectifier above a predetermined delay potential for automatic volume control of said system.

ROGERS M. SMITH.