US2094073A

US2094073A - Tone control system

Info

Publication number: US2094073A
Application number: US8711A
Authority: US
Inventors: Vernon D Landon
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1935-02-28
Filing date: 1935-02-28
Publication date: 1937-09-28
Anticipated expiration: 1954-09-28

Description

Sept. 28,' 1937. v. D. LANDON TONE CONTROL SYSTEM Filed Feb. 28, 1935 aow cum. cem. @wm acm e2 o3 om. o H n Y M 0 @Nl n .MN .quoo H N 1M M.. ow.. n. m .-m w a M d. Qomwm. T .m a.. 1 d D bl I n W n HESSEN w m 0 n .me arb a1 owm \.\1 i. V n u @nimm 3 B um. l um Hm. www mm. hm.

ETT

NNN @NN "Ill LQ HNJ .mi Balsam 0 Si L LNH N Mm blrbbnw .UR-u dei.- DN

k. HN

b QN Patented Sept. 28, 193i UNITED STATES PATENT OFFICE TONE CONTROL SYSTEM tion of Delaware Application February 28, 1935, Serial No. 8,711

10 Claims.

The present invention relates to tone control systems for radio receiving apparatus and the like, and has for its primary object to provide an improved automatic tone control system for 5 apparatus of the character above referred to, for` v-arying the audio frequency response range thereof with variations in signal strength and/ or variations in percentage modulation, without introducing harmonic distortion.

It is a further object of the present invention, to provide a tone control system for radio receiving apparatus and the like which operates automatically in response to variations in signal strength and/or percentage modulation to control the audio frequency response characteristic thereof in a manner to decrease the reproduction of electrical and other disturbances causing noise. More specifically, a system of this character may operate automatically to reduce the audio frequency output in the higher audio frequency range in response to weak signals or low percentage modulation.

It is a still further object of the present invention, to provide an improved tone control system which is responsive to both modulation and carrier wave variations in a received modulated high frequency signal.

It is also an object of the present invention, to provide an improved tone control system for radio receiving apparatus and the like providing a variable audio frequency band width which is a function of percentage modulation as well as carrier wave length.

It is also an object of the invention, to provide an improved tone control network, including an electric discharge amplifier device as a control element therein, and means for deriving rectified controlling potentials therefor from high frequency and low or audio frequency signals, together with means for varying the degree of control from each of said sources. The invention, will, however, be better understood from the following description when considered in connection r with the accompanying drawing and its scope will be pointed out in the appended claims. In

the drawing Figure 1 is a schematic circuit diagram of a portion of a radio receiving system embodying the invention, and

50 Fig. 2 is a curve diagram illustrating further operating characteristics thereof.

Referring to Fig. 1, 5 is a high frequency rectiiier or detector for modulated high frequency signals, and is preferably of the diode rectifier 55 type having a 4cathode 'I and a rectifier anode (Cl. Z50-20) 9. The rectifier is supplied with modulated high frequency signals through a tuned input circuit I0, the high side of which is connected with the anode and the low side of which is connected with the cathode through a rectifier output im- 5 pedance or resistor II. One terminal I3, of the resistor is connected to the cathode and the opposite terminal I5, is connected with the input circuit Ill through suitable high frequency filter means comprising a series resistor I1 and bypass condensers I3 to cathode.

Modulated high frequency signals are applied to the input circuit I0 through a coupling device such as a tuned transformer 2i, having input terminals 23. In the present example, this may be the intermediate frequency amplifier output transformer and the device 5 may represent the second detector of a superheterodyne receiver.

The high frequency rectifier device or detector 5 is also provided with a triode lcontrol grid 25 and output anode 2'I associated with the cathode I for amplifying the rectified signal or modulation component and, for this purpose, the grid 25 is directly connected through a lead 29 with the rectifier output impedance II from which it also receives a biasing potential in response to signals. The connection for the lead 29 with the impedance I I is adjustable through a contact 3I, whereby the -amount of biasing potential and the amplitude of the modulation or audio frequency signals to be amplified may be varied.

A modulation or audio frequency transmission circuit for connecting the detector device 5 with a succeeding utilization device such as a second stage amplifier device 33 is indicated at 35. This circuit is connected with the output anode 2l of the amplifier portion of the device 5, and includes an anode coupling resistor 31 through which anode potential is supplied to the anode 2l, a coupling condenser 3S for the anode resistor 3l, a volume control potentiometer resistor 4I having grounded

return connections

43 and 45 with the cathode T through a return lead 4'I for the cathode. The grid of the amplifier device 33 is connected to a variable tap 49 on the volume control resistor 4I and the cathode thereof is grounded as indicated at 5I. The volume control potentiometer 4l is preferably provided with a tone compensatingnetwork indicated at 53 for 50 the purpose of reducing the amplitude of signals in the intermediate portions of the audio frequency range simultaneously with a reduction in the volume control adjustment. The audio frequency output circuit for the device 33 is indi- 55 cated at 55 and 51 and is provided with output terminals 59.

A tone control network is connected across the audio frequency transmission circuit betweeny the lead and ground and, in the present example, includes a high frequency tone control condenser 6| connected on one side with the lead 35 and on the opposite side with the anode 63 of a pentode type electric discharge ampliiier device 55, the cathode of which is connected to ground through the lead 41. The device 65 is provided with a control grid 69, a screen grid il and a suppressor grid 13. rI'he anode 63 is connected with an anode circuit impedance or resistor 15 which is provided with an anode return circuit connection through an anode potential supply lead 11, a tap connection 19 on a potential supply source such as a resistor 8|, a grounded tap connection 83 thereon, the ground connection 45 and the cathode return lead 41. An impedance device or choke coil 85 is preferably connected in shunt with the resistor 15 in the anode circuit, as indicated, as an impedance limiting means.

The potential supply resistor 8| is supplied with direct current through terminals 81 having a f'. polarity as indicated. It will be noted that the ground connection 83 is located at a tap point 89 between the terminals 81 to provide a negative bias potential supply section between the negative terminal and the tap point 89. The anode lead 1;'11 receives an operating potential from a tap point 9|, and the anode circuit 51 for the device 33 is also connected to the positive terminal, the anode potentials being provided between the tap point 89 and the positive terminal. The

voltage divider resistor 8| represents any suitable grounded source for supplying positive operating potentials and negative biasing potentials for an electric discharge amplifier system.

From the foregoing description it will be seen @that the tone control network for the audio frequency transmission circuit 35 is controlled by the plate impedance of the electric discharge amplier device 65. In the present network, variation of the anode impedance of the device 65 1 causes the condenser 6| to become more or less effective as a shunt tone control means for reducing the amplitude of signals in the high frequency end of the audio frequency range as the anode impedance of the device 65 is decreased.

In accordance with the invention, the device 65 is of the pentode type and further, is preferably ofthe multi-mu or gradual cut-olf type. For example, it may preferably be provided by a tube known commercially as an RCA-58 tube. For a condition of no signal and maximum sensitivity, the anode impedance of the device 65 is initially adjusted to a relatively low value. In the present example this serves to reduce the high frequency response to a point where the noise transmission is sufficiently low to render it unobjectionable. The anode impedance is lowered by placing a. negative biasing potential on the suppressor grid 13 y through a connection lead 93 having a variable tap connection with the neg- `ative bias supply section of the source 8|. For

flthrough a supply lead 91 and tap 99 of substantially volts positive with respect tothe cathode.

The. plate impedance of the device 65, ordi- 75Mnarily relatively high, is adjusted by the above titl 4 under such conditions of operation.

In order that the audio frequency response characteristic of the system may be varied automatically in response to changes in the amplitude of a received carrier wave, that is in response to variations in received signal strength, the control grid 69 of the amplifier or control device 65 is connected to the output impedance through suitable control elements comprising, in the present example, a potentiometer device |0| to which the control grid 69 is connected through a lead |93 and a variable tap connection |05. One end of the resistor IBI is connected with the cathode 61 and the opposite end is connected through a lead |01, a terminal |09, a variable series resistor and a supply lead ||3 with the resistor preferably at the point of maximum negative potential or terminal |5 as indicated.

Since the

cathodes

61 and 1 are connected together, the biasing potential developed across the output impedance is applied to the grid 69 in response to signals, and the full amount of such potential is applied to the grid 69 when the potentiometer IUI-|05 is adjusted to its maximum position with the contact |05 at the terminal to which the lead |91 is connected. A suitable bypass condenser ||5 is connected between the lead 53 and the cathode 61 for filtering purposes in conjunction with the resistor which is also adjustable in value as indicated.

It will be seen that the output circuit of the high frequency rectifier not only supplies signal and biasing potentials to the amplifier included therein, but also supplies a controlling or biasing potential to the tone control device 65. Furthermore, automatic volume control biasing potentials at terminals indicated at ||1 are likewise derived from the output impedance connection therewith including a lter impedance H9.

Further control of the tone control network for variations in modulation percentage is provided by a second rectifier device responsive to the variations in the amplitude of the audio frequency signals delivered to the circuit 35. In order that the audio frequency circuit may not be loaded thereby suliiciently to cause distortion of audio frequency signals, the rectifier is coupled therewith by means of a buffer amplifier.

To provide this rectifier arrangement, an'electric discharge amplier device |2| is provided, and may be of substantially the same construction as the device 5 including rectiiier and amplifier portions. The control grid |23 is connected to the audio frequency transmission cirlead |35 having a tap connection |31 with the potential supply source 8|.

Audio frequency signals in the circuit 35 are applied to the grid |23 and are amplified in the device |2i, are applied to the anode |39 of the diode rectifier through a coupling condenser |4| and appear across the rectifier output impedance or resistor indicated at |43. One end of the resistor is connected to the anode |39 and the o-pposite end is connected to the cathode either directly or as shown, through a ground connection |45, whereby a delay potential equal to the drop in the self bias resistor |29 is provided for the anode |39.

It will be noted that one end |3, of the output impedance l of the high frequency rectifier, and the positive end of the output impedance |43, of the audio frequency rectifier are connected to ground. Since the cathode 61 of the tone control device |2| is likewise so connected, the negative potential from the negative terminal |5 of the impedance and the negative potential at the terminal |41 of the output impedance |43 may be applied to the control grid 69 in predetermined relation to each other by the addition of a connection lead |43 from the terminal |131 to the terminal |39 through a suitable series variable resistor indicated at |5|.

With this circuit arrangement, it will be seen that the tone control network may jointly be controlled by the two rectiers. The plate impedance of the control tube is normally reduced to a relatively low value by means of a bias potential on the suppressor grid, while the control grid is jointly controlled by potentials derived from rectier devices in the signal circuit and the audio or modulation frequency circuit, whereby the tone control means is placed jointly under control of variations in both signal strength and percentage modulation.

When the rectified signal or high frequency and audio frequency currents are Weak, providing a relatively low biasing potential on the control grid 69, the plate impedance is low and the tone control means causes the predetermined portion of the audio frequency signal to be attenuated.

The control range of the tube 55 may effectively be increased by the addition of external capacity coupling between the anode 63 and the suppressor grid 13, as by means of a condenser |53 between them, together with a resistor |55 in circuit between the suppressor grid and the bias impedance to be further lowered by increasing the change of anode current resulting from a given change in anode potential.

Vxfhen compensated volume control means is provided in the audio frequency transmission circuit, the source of rectified modulation or audio frequency is taken preferably at a point preceding such volume control means as at the point |51 in the present example, whereby the effect of the automatic tone control may be independent of manual volume control and may depend only on the strength of the high frequency signal and/or the percentage modulation. The automatic tone control means comprising the tube 65 is thereby actuated partly by rectified high frequency currents and partly by rectified audio frequency currents. 'Ihe ratio of control by the two differing currents is determined primarily by adjustment of the variable control elements and |5|.

In operation, during a lapse in modulation, for example, when a radio program is interrupted or is in process of change, the automatic tone control means is effective to reduce the audio frequency band Width to prevent the transmission of noise signals through the audio frequency circuit. When the modulation is resumed, the band width is automatically increased again. Likewise, with a relatively weak high frequency signal, the audio frequency band width will also be reduced automatically, and, further, the compensated volume control device 4| may further modify the fidelity in a desired manner according to its construction and adjustment. The volume may also be adjusted by the contact 3|. However, the ratio of audio frequency to high frequency control of the tone control means is changed thereby, as is obvious, because of the fact that the audio frequency control is derived from the audio frequency transmission circuit following the device 5. Accordingly, the adjustment at 3| preferably is xed and volume adjustments are then made at 49.

The effective control characteristic of the pentode device 65 is further illustrated by the curves shown in Fig. 2, to which attention is now directed.

In Fig. 2 the curves are plotted between plate current and plate voltage with various negative biasing potentials on the control grid 69. The anode impedance for the various curves, with a fixed plate potential, for example, of 250 volts, is indicated on each curve. tion experienced with certain types of tone control devices near the cut-off point of the control tube is prevented by the pentode device, operated as herein described and as shown in the drawing, and it will be seen from a consideration of the curves that regardless of grid bias supplied by the high frequency and low frequency rectiers, the control tube of the type shown may be operated at substantially zero anode current in the center of the anode voltage anode current curve.

The combined high frequency and low frequency control voltages delivered to the point |09 in the control circuit may both be controlled jointly by operation of the potentiometer and together With the devices and |5| serve to completely adjust the relation of the two control voltages and the amplitude of the combined control voltage resulting therefrom as applied to the automatic tone control tube 65.

I claim as my invention:

1. In a radio signalling system, a detector, an audio frequency output circuit connected with said detector, a tone control network for said output circuit including an electric discharge device as a control element therein, a rectifier connected with said audio frequency output circuit, electric discharge amplier means in said connection, means for deriving a controlling potential for said control device from said rectifier, means for deriving a second controlling potential for said control device from the detector, variable means for jointly applying said potentials to said control device, said first named electric discharge device as a control element being of the pentode type having a suppresser grid and having a control grid for receiving said controlling potentials, and means connected with said suppresser grid for applying thereto a negative potential.

2. In a radio signalling system, the combination with a signal transmission circuit, of a tone control network therefor comprising a reactance device and a variable impedance means in series across said circuit, said variable impedance means The harmonic distorf' ing potential comprising an electric discharge device havingacathode connected to one side of said circuit, an anode connected to the opposite side of the circuit through said reactance device, a control grid adjacent to the cathode, a suppressor grid adjacent to the anode, means for applying a [controlling potential to said control grid, means for deriving said potential jointly from a modulated high frequency signal and from the modulation component thereof, means for applying a negative potential to the suppressor grid including a series resistor in circuit with said suppressor grid, an anode circuit impedance for said anode in circuit therewith and a condenser providing coupling means between said anode and the suppressor grid.

3. In a radio receiver, the combination with an audio frequency signal circuit, of a tone control circuit, of a tone control network therefor including ari electric discharge device providing a control element therein and including a cathode, a control grid, a suppressor grid and an output anode, an impedance device and a reactance device in said network connected with said anode, a signal rectifier having an output impedance, an audio frequency signal rectifier having an output impedance, electric discharge amplifier means providing coupling means between said last named rectifier and the audio frequency signal circuit, means providing a variable connection .between each of said output impedances and said control grid whereby variable biasing potential is applied to said grid in response to variations in signal strength and in the amplitude of the audio frequency signals in said circuit, and means for applying a negative potential to said suppressor grid thereby to reduce the anode impedance of said device in the absence of signals and audio frequency modulation.

4. A tone control system for radio receiving .apparatus and the like, comprising in combination a rectifier each for modulated and demodulated signals, a variable impedance tone control device responsive to a variable direct current biasfor controlling the impedance thereof, means for jointly applying controlling potentials to said tone control device from said rectiers, and means for varying the relative values of said controlling potentials.

5. A tone control system for radio receiving apparatus and the like as deiined in claim 4, further characterized by the fact that one of said rectiers is provided with a signal amplifier for applying thereto said modulated and demodulated signals.

6. In a radio receiving system, the combination with a signal detector comprising a diode rectiiier, of an audio frequency ampliiier for receiving the rectied signal output from said detector having volume control means, and tone control means including an electric discharge control device, said control device comprising an anode, a cathode, a control grid adjacent to the cathode;l a vsuppressor grid adjacent to the anode and a screen grid between said control and suppressor grids, means for applying rectied audio frequency signals to said control grid, means for applying rectified signals to said control grid from said detector, and means for operating said suppressor grid at a negative potential thereby initially to reduce the anode impedance of said device.

'7. A tone control system for radio receiving apparatus and the like as defined in claim 4 further characterized by the fact said variable impedance tone control device includes a pentode electric discharge amplifier tube having a control grid for receiving said controlling potentials and that means are provided for applying a negative p0- tential to the suppressor grid thereof, thereby to provide an initial predetermined anode impedance.

8. In a tone control system, a diode triode electric discharge device connected in circuit for detecting and amplifying a modulated Signal, a second diode triode connected with the output of said iirst named device for amplifying and then rectifying an audio frequency signal, a pentode electric discharge control device for said system, means for deriving negative controlling potentials from the rectiiied output of each of said devices, means for independently applying said potentials to the control grid of said pentode devices to vary the anode impedance thereof, and means for applying a negative biasing potential to the suppressor grid of said pentode device to provide an initial relatively low anode impedance.

9. In a radio receiving system, the combination with a signal detector, and an output circuit therefor, of a rectifier connected with said output circuit, coupling tube means in said connection whereby said rectifier is prevented from loading said output circuit, a tone control network for said system, a pentode tube in said network as a controlling impedance element therein, and means for deriving controlling potentials for said pentode tube from said detector and rectifier to vary the anode impedance thereof, and means for reducing said anode impedance to an initial low value.

10. A tone control system for radio receiving apparatus and the like, comprising receiving means for modulated signals, demodulating means for said signals, a rectifier each for said modulated and demodulated signals, said rectifiers each having an output circuit providing controlling potentials derived from said signals, a variable impedance tone control device in said receiving system responsive to controlling potentials, and means for jointly applying controlling potentials thereto from said rectiiiers, comprising a potentiometer resistor conductively connected with said output circuits and said tone control device.

VERNON D. LANDON.

CERTLFCATE OF CORRECTION Patent No. 2,09L\O75 September' 28, 195T VERNON D. LANDON.

It is hereby certified that error appears in the printed of the above numbered patent requiring correction as fol] ows: Page l., first column, line 55, for the word. ulength read strength; and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the oase inthe Patent Office.

Signed and sealed this 16th da'y of November, A. D. 1957 Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

specification