US2166674A - Indicating device - Google Patents

Description

Patented July 18, 1939 UNITED STATES PATENT OFFICE INDICATING DEVICE Loy E. Barton, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application December 7, 1932, Serial No. 646,074

9 Claims.

My invention relates to indicating devices and, more particularly, to tuning indicators, dials, etc., adapted for use in radio receivers.

There recently has developed a very decided trend toward the use of automatic gain-control devices in radio receivers for the purpose of maintaining the sound output therefrom substantially constant in amplitude despite fading of the signal-carrier wave. Receivers so equipped, how- 10, ever, are'somewhat diicult to tune accurately to a desired carrier-Wave and recourse, heretofore,

has been had to the use of tuning-meters and the like to indicate resonance.

Tuning meters are relatively expensive. Also, they are of necessity fragile and do not stand up Well in service or during shipment of a receiver from the factory to its ultimate destination.

It is, accordingly, an object of my invention to provide an inexpensive tuning indicator particularly adapted for use in receivers of the automatic gain-control type.

Another object of my invention is to provide a combined tuning indication and dial-lighting system.

Another object of my invention is to provide a system of the type referred to that shall also be capable of giving an indication of the adjustment of a background noise control device.

In practicing my invention, as applied to a radio 30, receiver, I prefer to provide the power-transformer, which supplies energizing potentials to the various thermionic devices, the loudspeaker, etc., with an extra secondary that is connected to one or more pilot lamps, which lamps may or may not be utilized to illuminate the tuning dial, through the primary winding of a small step-up transformer. The secondary of the transformer is connected to the plate and cathode of a control tube, the impedance of which is proportional to the potential applied to the grid thereof. The grid potential is obtained from a point in the receiver circuit, the potential of which varies according to the amplitude, or inversely as the amplitude in some instances, of an incoming signal. Accordingly, the impedance of the control tube and its elfectiveness as a load on the step-up transformer is a function of the signal amplitude, and the pilot lamp uctuates in brilliancy as the impedance changes.

I also so connect another pilot lamp of somewhat higher voltage across the primary of the step-up transformer that its intensity decreases as the intensity of the series lamp increases, and vice versa. A lamp of the same voltage as the seriesconnected lamp may, of course, be used but, in

(Cl. Z-20) such event, it is connected to an intermediate tap on the primary of the transformer. The seesaw variation in intensity of the tWo lamps permits quite accurate tuning of the receiver to the l peak resonance point.

Furthermore, according to my invention, the several lamps may be differently colored, they may both be utilized for dial-illumination, or they may be disposed in any suitable position on the radio-receiver cabinet Where they are visible to the operator. Translucent color filters may be utilized instead of colored lights, as well as various combinations of screens, mirrors, or lenses, without departing from the spirit of the invention.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, Will best be understood from the following description of a spe-v cie embodiment, when read in connection with the accompanying drawing, in which Figure 1 is a diagrammatic view of a radio receiver including a preferred embodiment of my invention,

Fig. 2 is a fragmentary diagrammatic View of an alternative embodiment of my invention,

Fig. 3 is a front elevational view of a tuning dial showing the appearance thereof when the receiver is in the tuned in condition, and

Fig. 4 is a fragmentary sectional View of the receiver dial, taken along a line corresponding to the line 4-4 in Fig. 3.

As hereinbefore pointed out, the primary object of my invention is to provide a tuning indicator Which will enable a receiving system of the automatic gain control type to be accurately brought into syntony with a desired incoming signal without reliance necessarily being placed upon the volume of sound output therefrom.

As is Well known to those skilled in the art, the majority of radio receivers of the automatic gain control type utilize a direct current, proportional to the amplitude of an incoming carrier wave, for the purpose of controlling the bias applied to the input circuits of one or more amplifying tubes. Although my invention may be applied to a radio receiver equipped with a volume control system of substantially any wellknown type, I find it quite expedient to combine it with an improved automatic volume control system Which I also have invented.

Referring to Fig. 1 of the drawing, my improved volume control system is exemplified as applied to a second detector tube I of a radio receiver of the superheterodyne type. Specifically, the second detector includes a thermionic cathode 3, two diode electrodes 5 and 1, a control grid 9, and an output anode II. One of the diode electrodes, 5, is connected back to the cathode through the secondary winding of an intermediate frequency transformer I3 and a resistor I5. From a point on the resistor furthest away from the cathode, a connection extends to the control grid, the connection, preferably, including a resistor I9 which impedes the flow of grid intermediate frequency current.

The cathode is connected to the negative terminal 2| of a source (not shown) of uni-directional potential through a resistor 22, and the output anode II is connected to the positive terminal 23 of the same source through the primary winding of an audio frequency output transformer 25, or through an equivalent transfer network.

In the specific receiver under discussion, a bleeder resistor 21 and the eld winding 29 of a loudspeaker are connected in shunt to the terminals of the high potential source, and a point 3| between the resistor and the winding is provided with a connection 33 to ground.

The resistor 22 in the cathode circuit is of such magnitude that the voltage drop thereacross occasioned by plate current in the detector tube I during the no signal condition is greater than the drop across the loudspeaker field winding 29. The reason for this difference in potentials will be hereinafter apparent.

During the reception of signals, the intermediate frequency is impressed upon the diode plate 5 through the intermediate frequency transformer I3, it is rectified and direct current, varying at audio frequency, due to modulation, flows in the resistor I5 included in the input circuit. The current is in such direction that the control grid 9 is negatively biased with respect to the cathode of the tube and, as a result, the current in the resistor 22 connected to the cathode decreases as a signal is tuned in, and the potential drop thereacross also decreases.

The second diode plate 1, as will be noted from an inspection of the drawing, is connected over a resistor 35 to ground and the said plate is, therefore, at a negative potential, normally, with respect to the cathode 3. However, as the potential drop across the resistor connected to the cathode decreases, the diode plate and the cathode approach the same potential and, eventually, if the signal-carrier is of sufficient amplitude, the cathode will become negative with respect to the diode plate. In such event, current then flows in the resistor 35 connected between the diode plate and ground, which creates a potential drop thereacross. The potential drop developed along the resistor may be utilized to apply bias more negative than normal to an amplifier tube 31, or to a plurality of tubes (not shown) which bias becomes more and more negative as the signal carrier amplitude increases, and vice versa.

The primary function of the automatic volume control network is to correlate the gain in the system to the amplitude of an incoming signal, which varies because of fading and because of the distance Vand strength of the transmitting station. If it is assumed, however, that the signal is relatively constant in amplitude, the diminution of current in the resistor 22, as well as the increase in current in the resistor 35, are indicative of the accuracy of tuning of the receiver, exact tuning being accompanied, as is obvious, by respective minima and maxima.

From a consideration of the foregoing, it will be noted that, in my improved volume control system, there are two potential sources available which vary in response to the amplitude of an incoming signal impressed upon the detector tube, namely, the resistor 22 connected between the cathode of the second detector tube and the negative terminal of the high potential source, and the resistor 35 connected between the diode plate and ground. Either of these sources may be utilized to energize a tuning indicator according to my invention, but I nd it preferable to make use of the cathode resistor rather than the diode circuit resistor for that purpose. Specifically, I nd it expedient to utilize the change in potential across the said resistor to control the impedance of a thermionic tube which, in turn, serves as a load upon a circuit supplying energy, differentially, to a plurality of light sources.

Referring to the drawing, I provide a secondary winding 39 on the main power transformer 4I which supplies energizing potentials to the receiver, and connect the primary winding of a step-up transformer 43 and a plurality of light sources 45 and 41 in series therewith. The primary winding is also tapped at an intermediate point 49, and an additional light source 5I, or light sources, are connected across the tapped portion.

In the specific system chosen for purposes of illustration, the potential developed by the Winding on the power transformer which supplied the light source is 7.5 volts and each of the lamps is rated at 2.5 volts.

The secondary winding of the transformer 43 is connected between the anode 53 and cathode 55 of a therminoic tube 51 of the screen grid pentode type,hereinafter called the control tube, having, in addition to the said anode and cathode, a suppressor grid 6 I, a control grid 63, and a screen grid 65. A connection 61 including a current limiting resistor 69 extends from the control grid to the cathode of the second detector I and a con-- nection 1I extends from the cathode of the control tube to groimd. The screen grid may be connected by a conductor 13 to an appropriate point on the bleeder resistor 21, in order that they said grid may be maintained at the proper positive potential.

A control tube of the screen grid type is preferable if the changes in potential available from the resistor 22 are of small magnitude. It is not to be inferred, however, that my invention is limited to such tubes, since tubes of many other types may be substituted therefor, and, in the specific circuit illustrated, a three-element control tube may be used, if desired.

When no signal is being received, the cathode of the second detector is positive with respect to ground, which results in a slight grid current to the grid of the control tube through the current limiting resistor 69. The resistance of the said resistor is large as compared to the resistance of the resistor 22 in the cathode circuit of the second detector, and also' with respect to the resistance of the grid of the control tube when it is positive. Accordingly, the grid voltage on the control tube is essentially zero when no signal is being received and the plate resistance of the tube is minimum, which resistance is reected to the primary of the transformer.

The low resistance reflected to the primary permits the series-connected lamps, and`41, to be supplied with energy, and to be lighted to approximately their full brilliancy, whereas the voltage across the tapped portion of the primary is suiiiciently low that the tube 5i is substantially deenergized. As a signal is tuned in, thecathode of the second detector tube becomes less and less positive, until it reaches ground potential with practically no chang-e in illumination of the series connected lamps because of the practically constant zero biasing potential still being applied on the control tube.

Further increase in signal amplitude causes the cathode of the second detector to assume a potential negative with respect to ground which results in a negative bias being applied to the control tube, thus causing its impedance to increase,

resulting in high impedance on the secondary of the transformer included in the plate circuit thereof. This increase in impedance in the secondary of the transformer is reflected into the primary winding thereof and causes a diminution in the potential applied to the series connected lamps, while the potential applied to the shuntconnected lamp increases.

As soon as the station is tuned in to a peak resonant condition, the series-connected lamps will have minimum brilliancy while the shunt-- connected lamp will be giving off its maximum light for the particular signal strength and sensitivity setting of the receiver.

As pointed out above, the light sources 45 and 41 remain substantially fully brilliant until the cathode of the detector tube, by reason of decreased current in the resistor 22, becomes slightly negative with respect to the diode electrode l.

Furthermore, th-e diminution of the brilliancy of the light sources 45 and 4l, the application of sufficient potential to the light source 5l to cause it to begin to glow, and the initiation of automatic volume control by the supplying of additional negative potential to the controlled amplifier tubes'in the system can only happen when a signal of proper predetermined amplitude is impressed upon the detector tube. If it is assumed that the tubes in the system preceding the detector tube are normally biased, in the absence of signal, to the point at which the gain therein is maximum, the action of the light sources is indicative of the correctness of tuning.

On the other hand, if manually controllable means, (not shown), or the equivalent, are provided for making more negativev the normal bias on the amplier tubes, independent of the automatic volume control network, whereby background noise between stations is minimized during tuning, the receiver may be made so insensitive as to fail to supply sufficient signal to the detector tube to operate the automatic volume control and to control the light sources.

Under such conditions, the signal from the loudspeaker may be of any value from zero to its value at the threshhold of the automatic volume control system or to the point at which the automatic volume control is delayed. Such being the case, the fading of the signal cannot be compensated, nor will the volume from the loudspeaker be constant. However, it will be noted, as eX- plained, that the tuning lights will not respond, which fact indicates to the operator that the adjustment of the noise suppressor is such that a constant volume of audio signal cannot be received. If the noise control is then adjusted so that the automatic volume control can function, the tuning lights respond, which indicates that the noise suppressor adjustment is such that the signal is substantially unaffected.

It may also be expedient to utilize the rectifier space current in the control tube for either control or indicating purposes through the inclusion of one or more impedance devices in series with the secondary Winding of the transformer 43. Such devices have been indicated in the drawing by a plurality of rectangles designated Z.

In connection with the foregoing description of my improved circuit, it should be noted that a resistor of proper magnitude may be substituted for one of the series-connected lamps, or the lamp may be omitted entirely. However, two lamps in series result in somewhat better operation of the light system because of the large variation in resistance of the two lamps from low brilliancy to high brilliancy.

It will be noted that the shunt-connected lamp may be of a higher voltage type and may be connected directly across the primary winding of the transformer, instead of across only a portion thereof. In the specific case under discussion, if the lamp is connected across the entire primary, its rated voltage should be approximately 6 volts.

It is also possible to secure the see-saw effect `iust described, as shown in Fig. 2, through the use of a saturating reactor l5, the direct current winding of which is included in the plate circuit of one of the radio or intermediate frequency amplifier tubes, or in any other circuit in which the direct current is a function of the amplitude of the receiver signal. In such event, a light source 'l'l maybe connected in series with the secondary winding of the power transformer, While another source 19, requiring higher voltage, may be connected in shunt thereto. The principle of operation of the modified circuit is essentially the same as explained in connection with Fig. l of the drawing, the lamp 'i9 being equivalent to the lamp 5I, while the lamp 11 functions in a manner analogous to the operation of the lamps 45 and 41. However, the saturating reactor 15 will not permit as sharp an indication of the tuning as the system previously described and in general the system is not as iiexible in its application.

Should it be desired to utilize indicating lamps requiring the same voltage, the winding of the saturating reactor 15 may be tapped and a light source 80 be connected thereacross, as indicated by dotted lines in the drawing.

The positions of the tuning indicator lamps are, of course, optional with the manufacturer of a radio receiver. I have found it desirable, however, to so dispose both of the lamps that they serve alternately to illuminate a tuning dial, one of the lamps, through any desired arrangement of color screens, or the like, being utilized to indicate that the set is exactly tuned in, while the other lamp provides light to assist in the tuning operation.

Specifically,referring to Figs. 3 and 4 of the drawing, I prefer to dispose the light 5| behind a translucent dial 8| carrying frequency indicia, or the like, and surround it with a shield 83 which limits the area of the dial illuminated thereby. I prefer, also, to so mount the other light sources 45 and 41 below the shield that they illuminate the dial during the tuning operation. Naturally, the several light sources may be arranged in any other desired manner, they may be colored, or

they may be mounted behind-colored screens in order that attractive lighting effects may be had during the tuning operation, Without departing from the spirit of my invention.

It will, accordingly, be apparent from a consideration of the foregoing description of a receiver comprising my improved tuning indicator that it offers many advantages not heretofore obtainable. For example, it is quite easy to visually tune in any desired station, even though the loudspeaker is not audible, which is desirable in the event that the incoming signal is being reproduced in a situation distant from the point at which the receiver itself is located. The visual tuning indication is also much more exact than the indication of tuning given by the quality and amplitude of the sounds reproduced, since the automatic volume control device tends to maintain the volume constant, even though, by reason of inaccurate tuning, the amplitude of the signal impressed upon the second detector is less than it should be.

Advantages other than those enumerated will be readily apparent to those skilled in the art to which my invention pertains, as will also many modifications thereof. My invention, therefore, is not to be restricted except as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. In a radio receiver, a plurality of light sources, means for supplying alternating potentials thereto and means controllable by an incoming signal for varying the intensity of illumination from one of said light sources in inverse ratio to that from another of said light sources.

2. In a radio receiver, a plurality of light sources, means capable of supplying alternating potentials to said sources, means including a transformer responsive to the condition of sensitivity of said receiver for determining which of said sources receives potential from said energy supply.

3. In a radio receiver, means for correlating the sensitivity thereof to the amplitude of an incoming signal, a plurality of light sources, means for supplying alternating potentials thereto and means including a variable impedance in series with one of said light sources and in shunt with another of said light sources, said means being responsive to the condition of sensitivity of the receiver for determining which of said sources gives off the greater light.

4. In .a radio receiver, a light source, alternating potential supply means for energizing said source when the receiver is in syntony with signals from a desired transmitter, a second light source, and alternating potential supply means for energizing said second source when the receiver is not in syntony with signals from the desired transmitter, whereby, through observation of the condition of illumination of said sources, the exactness of tuning of the receiver may be judged.

5. In an amplifier, a light source, an alternating current supply circuit connected to said source, a step-down transformer, the primary winding of which is included in said circuit, a. thermionic device, the space current path in Which is in series With the secondary Winding of said transformer, and signal-responsive means for varying the impedance of said thermionic device.

6. In a radio receiver, a plurality of light sources, means for supplying alternating potentials thereto, .a turning indication device adapted to be illuminated by said light sources, means for screening certain portions of said tuning indication device from illumination by respectively different ones of said light sources, and means controlled by an incoming signal for varying the intensity of illumination from one of said light sources in inverse ratio to that from another of said light sources.

7. In a radio receiver, a receiving network, a source of automatic volume control potential therefor, a transformer having a primary Winding and a secondary winding, a tube having an anode circuit connected with said secondary winding whereby said tube is a load upon said transformer, a tuning indicator, a source of light associated therewith, an energizing circuit including at least a portion of said primary winding for supplying alternating current to said light source, means for applying the potential from said .automatic volume control source to said tube to control the effectiveness of the load upon said transformer, and means for adjusting the impedance of said tube whereby signal variations cause the load upon said transformer to vary between limits adapted to cause an indicating change in the illumination of said light source.

8. In a radio receiver, a receiving network, a source of .automatic volume control potential therefor, a saturatable reactor, a tube having an anode circuit, said reactor being connected with said anode circuit to receive saturating current therefrom, a tuning indicator, a lamp associated therewith, a lamp energizing circuit including at least a portion of said reactor for supplying a1- ternating current to said lamp, means for applying said potential from said automatic volume control source to said tube to control the flow of saturation current whereby to cause an indicating change in the illumination of said lamp.

9. Radio receiving apparatus comprising, in combination, signal-selecting means tunable to receive any signal of specified frequency in a band of frequencies, signal-amplifying means for amplifying the signals thus received, incandescent indicating means connected to said amplifying means for producing variations in light in accordance with the average current flowing through said amplifying means, .and light-diffusing means for rendering readily perceptible small variations in the light produced by said indicating means, indicative of small variations in the tuning of said selecting means.

LOY E. BARTON.

Images