US2056607A - Sound and television receiver - Google Patents

Description

Oct. 6, 1936. R, s, HOLMES 2,056,607

SOUND AND TELEVISION RECEIVER Filed June 28, 1934 5 sheets-sheet 1 .STAT/@N 1. .STAT/0N Z.

Ralph Holmes T'T'RNEY 11000 ff. c. .9500 lf. c.

(LE) (LE) v Oct. 6, 1936. R. s.`HoLMEs 2,056,607

SOUND AND TELEVISION RECEIVER Filed June 28, 1954 5 Sheets-Sheet 2 INVENTOR E I Ralph lHolme ATTORNEY 5 Sheets-Shea?I 3 Filed June 28, 1934 INvLwron Ralph 5.1170111126 AT TOHNEX 5N DZsom.

#Allinll BY Oct. 6, 1936.

SOUND SIGNAL l.r S. HOLMES SOUND ANDl TELEVISION RECEIVER File'd June 28, 1934 5 Sheets-Sheet 4 R. s. HOLMES SOUND AND TELEVISION RECEIVER Filed June 28, 1954 5 Sheets-Sheet 5 HLN NNN MKN QWNl

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ATTORNEY l Patented Oct. 6, 1936 PATENT OFFICE SOUND AND TELEVISION RECEIVER Ralph S. Holmes, Haddonfield, N. J., assigner to' Radio Corporation of America. a corporation oi' Delaware Application .lune 28. 1934, Serial No. 732,759

14 Claims.

My invention relates to radio receivers and particularly to receivers adapted to receive picture signals and sound signals simultaneously.

In Carlson Patent 1,975,059, issued September 25, 1934, there is described a radio system in which picture signals and sound signals are transmitted simultaneouslyfrom a transmitter in order that a picture accompanied by speech or music may be received. The picture signals and sound signals are transmitted on separate carrier waves which are spaced apart a denite fixed amount in the frequency spectrum. All the transmitters in this system radiate two carrier waves, for the purpose mentioned, which are spaced apart the same definite fixed amount. The different transmitters transmit at different wave lengths, in accordance with usual practice, to permit selection at a receiver of the desired transmitting station.

In a radio system of the above-described type, the receiver includes a picture translating device such as a cathode-ray tube and a sound translating device such as a loud speaker. It has been found that, in tuning one of these receivers from one station to another, some very unpleasant effects are encountered. One results from the sound channel of the receiver being tuned for an instant to the incoming picture signal so as to produce a noise in the loud speaker. Another results from the picture channel of the receiverbeingtuned to the lncoming sound signal for an instant so as to produce flashes of light on the fluorescent screen of the cathode-ray tube. Not only are these eects displeasing to a person operating the receiver, but they may result in injury to the apparatus, especially the cathode-ray tube.

An object of my invention is to provide an improved receiver for receiving picture and sound signals simultaneously.

More specifically, an object of my invention is to provide a receiver for use in a system of the above-mentioned type in which the aforesaid undesirable effects are avoided.

A further object of my invention is to pro vide a picture and sound receiver which will make a signal visible or audible only when the receiver is tuned to two carrier waves.

In a preferred embodiment of my invention ll employ a superheterodyne receiver having an intermediate frequency channel through which picture signals are supplied to a cathode-ray tube and having another intermediate frequency channel through which sound signals are sup-- plied to a loud speaker. A noise suppressor circuit is provided which normally prevents signals from being impressed upon either the cathode-ray tube or the loud speaker. The noise suppressor circuit is so connected to the intermediate frequency channels that, when signals of the proper amplitude appear in both channels, the suppressor is released.

In one embodiment of my invention I take vadvantage of the fact'that the frequency spacing between the carriers of the intermediate frequency signals is the same as the frequency spacing of the sound and picture carrier waves sent out from a transmitter. The two intermediate frequency carriers are heterodyned in a detector or mixer tube and the resulting beat frequency current is utilized to release the noise suppressor. A

In another embodiment of my invention, instead of utilizing a beat frequency, use is made of an automatic volume control or A. V. C. circuit in each intermediate frequency channel. Each A. V. C. circuit is so connected to a noise suppressor circuit that the suppressor will be released only when signals of sufiicient volume are being received in both channels. I

Other objects, features and advantages of my invention will appear from the following description taken in connection with the accompanying drawings in which Figure l is a diagram showing the frequency spacing of signals transmitted in a system of the above-described type and also showing certain selectivity characteristics of my improved receiver.

Fig. 2 is a diagram, similar to Fig. l, showing the frequency spacing of a modified transmitting system,

Fig. 3 is a circuit diagram of an embodiment of my invention utilizing beat frequency control,

Fig. Il is a circuit diagram of a modified form of the receiver shown in Fig. 3,

Figs. 5 and 6 are circuit diagrams of embodiments of my invention utilizing automatic volurne control circuits for actuating the noise suppressor.

Referring to Fig. 1, two transmitter stations are indicated which are operating on adjacent channels and which are widely spaced apart geographically. Station No. 1 is represented as transmitting a picture signal on a 50,000 k. c. carrier, the picture signal side bands having a width of 1000 lr. c. This same station transmits sound signals on a 51,500 k. o. carrier which may have a side band width of 10 k. c.

' Station No. 2, on an adjacent channel transmits a picture signal on a 53,000 k. c. carrier and a sound'signal on a 54,500 k. c. carrier.

The curve I shows the selectivity characteristie of the picture channel in a receiver of the type described in the above-mentioned Carlson patent*'while the curve 3 shows the selectivity characteristic of the intermediate frequency sound channel in the same receiver. These curves are positioned with respect to the diagram for station No. l to indicate that the receiver is properly tuned to this station.

Consider now the operation of a receiver similar to the one shown in the Carlson patent, assuming the condition before the receiver was tuned-to station No. 1: As the receiver is tuned towards stations No. 1 and No. 2, the intermediate frequency sound channel will first receive the signal from the picture carrier of 50,000 k. c. Under these conditions no energy is being received by the intermediate frequency picture channel, while the picture signal is appearing in the loud speaker as a disagreeable noise. Further tuning of the receiver tunes it accurately to station No. 1, as shown vin the diagram.

Assume now that the receiver is tuned towards station No. 2: It will be apparent that before the receiver is properly tuned, the sound channel will receive the signal from the picture carrier of station No. 2 while the picture channel will be tuned to the sound carrier of station No. 1. As the signal from station No. 2 on the adjacent channel will be weak because of its geographic location, the picture signal noise in the loud speaker may not be very disturbing. The sound signal from station No. 1, however, will be a strong signal and will appear on the fiuorescent screen of the cathode-ray tube as flashes of light which are annoying to an observer and which may injure the tube.

With respect to the system indicated in Fig. 2, there is the same condition of operation except that, because of the single side band transmis- `sion of the picture signals and the correspondlngly closer frequency spacing of adjacent channels, the two intermediate frequency channels of the receiver may supply signals to the loud speaker and cathode-ray tube only when the receiver is properly tuned to the picture and sound signals from a single transmitting station.

Referring to the embodiment of my invention showing in Fig. 3, it comprises a superheterodyne receiver having a radio frequency selecting circuit 5, a first detector 1 and a tunable oscillator 9. As described in the above-mentioned Carlson patent, the selecting circuit has a pass range wide enough to permit the passage of both the picture and sound signals from a single transmitting station. At the same time the selectivity is sufficient to separate the signals from one transmitting station from those from a different station. Preferably, the variable condensers or other tuning elements of the selecting circuit and of the oscillator are connected to a Icommon control knob II to permit simultanelplate current is flowing therethrough.

'intermediate frequency sound amplifier I 5 is tuned to 9,500 k. c. The selecting circuits in both amplifiers are of the band-pass type, as indicated by the curves I and 3 in Figs. l and 2.

The output of the picture amplifier I3 is impressed upon an amplifier tube I1 which may be of the four-electrode type comprising a cathode I9, a control grid 2|, screen grid 23 and an anode 25. The signal appearing in the plate circuit of the tube |1 is impressed upon a second detector 21 which may be of the diode type whereby the picture signal appears across a resistor 29 in the diode circuit.

It will be understood that the picture signal appearing across resistor 29 includes the synchronizing impulses or signals. The picture signal is impressed upon an amplifier 3| which includes circuits for separating the picture signal proper from the synchronizing signals. The output of the amplifier 3| is applied to the control grid 33 and to the deflecting devices 34 and 35 of a cathode-ray receiver tube 36. The tube illustrated is of the type having a first anode 31, a second anode 39 and a fluorescent screen 4| at the end of the tube. y

The output of the sound amplifier I5 is im'- pressed upon an amplifier tube 43 which may be of the screen grid type comprising a cathode 45, a control grid 41, a screen grid 49 and an anode 5|. The sound signal appearing in the plate circuit of the amplifier tube 43 is impressed upon a second detector 53 which may be of the diode type whereby the sound signal appears across a resistor 55 in the diode circuit. The sound signal is amplified by an amplifier 51 and supplied to a loud speaker 59.

In accordance with my invention, the amplifier tubes 43 and I1 are normally so biased that they will not amplify a signal. The circuit which maintains this high negative bias on the amplifier tubes comprises a vacuum tube 6| having a cathode 63, a control grid 65, an anode 61 and a rectifier electrode 69. A tuned circuit 1|, which will be more fully described hereinafter and which comprises an inductance coil 13 shunted by a condenser 15, is connected at its upper terminal to the rectifier electrode 69 while it is connected at its lower terminal through a resistor 11 to the cathode 63. The control grid 65 is connected to the end of the resistor 11 which is connected to the lower terminal of the tuned circuit 1|.

The cathode 63 of the tube 6| is connected through a resistor 19 to ground while the anode 61 is connected to a suitable source of positive potential whereby there is a flow of plate current through the resistor 19 so long as the control grid 65 is not too negative with respect to the cathode 63.

The cathodes of the amplifier tubes 43 and I1 are connected through conductors 8| and 83 to the cathode end of the resistor 19 whereby they are held positive with respect to ground when It will be seen, therefore,.that when no signal is being impressed upon the tuned circuit 1I there is no ow of current through the diode circuit resistor 11, the control grid 65 is at cathode potential and the flow of plate current through the resistor 19 holds the cathodes 45 and I9 at a positive potential with respect to ground.

By making the cathodes 45 and I9 of the amplifier tubes 43 and |1'positive with respect toA ground, the control grids 41 and 2| of these tubes are put at a negative potential with respect to their cathodes since they are connected to ground through their tuned input circuits. The circuit is so adjusted that when the grid 06 of the noise suppressor tube- 0| is at cathode potential, the flow of plate current through the resistor 19 makes the control grids of the amplifier tubes 43 and I1 so negative that these tubes are ineective to amplify either picture or sound signals. .l

The release of the suppressor is effected in response to signals appearing in both the sound amplifier I5 and picture amplifier I3 by means of a mixer or detector tube 85 which comprises a cathode 81, a control grid 99, a second control grid 9|, a screen grid 93 and an anode 95. The cathode 81 is connected to ground through a source of biasing potential such as a. battery 91 whereby the control grids 89 and 9| are biased to a suitable negative potential through the rey sistors 99 and |01, respectively;

' The control grid 89 is connected through a coupling condenser |03 and a conductor |05 to the output circuit of the sound amplifier I5 while the control grid 9| is connected through a coupling condenser |01 and a conductor |09 to the output circuit of the picture amplifier I3. The anode 95 of the mixer tube is supplied with positive potential from a suitable source through a tuned circuit I I which is coupled to the tuned input circuit 1I of the noise suppressor tube 6|. The two coupled tuned circuits III and 1| form a circuit which is sharply tuned to 1500 k. c.,

which is the beat frequency between the intermediate frequency picture signal and the intermediate frequency sound signal.

When the receiver is so tuned to a station that signals appear in the output circuits of the sound and picture intermediate frequency ampliers, a beat frequency is produced in the tuned output circuit of the mixer tube 85 which frequency is selected by the tuned circuit and impressed across the rectifier electrode 99 and the cathode 63. As a. result, current flows through the rectifier resistor 11 in such a direction as to make the control grid B5 negative with respect to the cathode 63. This flow of current through the resistor 11 is caused to have a substantial steady value by shunting a filter condenser II3 thereacross. If the picture and sound signals have a sufficient amplitude, the grid 65 of the suppressor tube is made so negative that the current flow through the plate resistor 19 is greatly reduced whereby the high negative bias is removed from the control grids 2| and 41 of the amplifier tubes I1 and 43 and these tubes function to amplify the picture and sound signals so that they appear at the cathoderay tube 36 and loud speaker 59, respectively.

From the foregoing description, it will be understood that if the picture channel of the receiver is tuned to the sound signal or if the sound channel of the receiver is tuned to the picture signal, no signal will be impressed upon either the cathode-ray tube or the loud speaker. With the transmitting system indicated in Fig. 1 there is a. possible exception to this statement which would seldom occur in practice. If a receiver happens to be so located that it receives signals of approximately equal strength from two stations, such as stations No. 1 and No. 2, which are on adjacent channels,' it is possible to get signals on the cathode-ray tube and in the loud speaker by receiving a sound signal from one station and a picture signal from the other station.

With the transmitting system indicated in Fig. 2, there is no condition under which signals will appear at the cathode-ray tube and loud speaker unless the receiver is properly tuned, since it must be tuned accurately to a station in order to obtain the 1500 k. c. beat note.

Under certain conditions either the sound signal or the picture signal arriving at a receiver from a transmitter may be weak or of poor quality while the other signal from that transmitter is of good quality. Or, a station may transmit a picture signal unaccompanied by a sound signal or vice versa. Therefore, in order that a single signal may be received from a transmitter it is desirable that means be provided for making the suppressor circuit of the receiver inoperative at will.

Referring to Fig. 3, this may be accomplished by `providing a switch 92 in the plate circuit of the suppressor tube 8|. The receiver will normally be operated with the switch 92 closed. If it is known that a certain station should be transmitting a program which may be either a picture or sound alone, the receiver will be tuned to that station while the switch 92 is closed. Then the switch 92 will be opened to permit reception of the single signal.

In a similar manner, the suppressor for the receiver shown in Fig. 6 may be rendered ineffective by opening a switch 288 in the plate circuit of the suppressor tube 219.

In Fig. 4 there is shown a modification of the circuit shown in Fig. 3. In the two figures, like parts are indicated by the same reference numerals. The difference between the two circuits is the manner in which the control or biasing voltageis supplied from the noise suppressor tube 6I to the amplifier tubes 49 and I1.

In the modification shown in Fig. 4 the cathodes 45 and I9 of the amplifier tubes 43 and I1 are connected to ground while the control grids 41 and 2| are connected through conductors III and I|9 and through a filter resistor I2I to a biasing resistor |23 in thenoise suppressor circuit. The bias resistor |23 is included in the plate circuit of the noise suppressor tube 6| in series with the secondary |25 of a transformer |21 which supplies voltage to the plate 61. It will be understood that a battery may be substituted in the plate circuit for the alternating current supply if desired. It will be seen that when plate current iows through the biasing resistor |23, the control grids 41 and 2| of the amplifier tubes 43 and I1 are biased negatively with respect to their cathodes. When the plate of the noise suppressor tube 6I is supplied from an alternating current source as shown, it is preferred to connect a lter condenser |29 be# tween one end of the filter resistor |23 and ground in order to supply a substantially constant bias voltage to the amplifier tubes 43 and I1.

The operation of the circuit is substantially the same as that of the circuit shown in Fig. 3. If one of the intermediate frequency amplifier channels is not receiving signal energy, no beat note appears in the output circuit of the mixer tube 85 and the flow of current through the biasing resistor |23 maintains the amplifier tubes 43 and I1 biased so negatively that neither one of them will amplify a signal impressed upon it. n the other hand, when both intermediate frequency channels are receiving energy, a. 1500 k. c. beat note appears in the output circuit of the mixer tube and the flow of current 'amplifier tubes through the biasing resistor I 23 is reducedto a value which permits the two amplifier tubes 43 and |1 to amplify the signals impressed upon them.

Referring to Fig. 5, there is shown an embodiment of my invention in which a noise suppressor circuit is controlled by means of automatic volume control circuits. The radio frequency amplifier or selecting circuit, the first detector, and the oscillator superheterodyne receiver are indicated at |3|. The output circuit of the first detector is coupled to the input circuit of an intermediate frequency sound ampliner 33 through a secondary winding |35 of a transformer |31 and to the intermediate frequency picture amplifier |39 through another secondary Winding |4| of the transformer |31.

In order to simplify the drawings, only the circuit of the first tubein each intermediate frequency amplifier is shown. The input circuit of the first tube |43 of the sound amplifier |33 includes the secondary winding |35 which is tuned to the sound intermediate frequency by a condenser |45. The cathode |41 of the tube |43 is maintained at a positive potential with respect to ground by means of a self biasing resistor |49 which is shunted by the usual bypass condenser |5I.

The gain of the amplifier tube |43, as well as the gain of other intermediate frequency amplifier tubes (not shown), is controlled automatlcally by varying the bias on its control grid |53 through a conductor |54 to the output circuit of an automatic volume control tube |55.

The output circuit of the sound amplifier |33 is coupled through a tuned intermediate frequency transformer |51 to an amplifier tube |59, which in turn has its output circuit coupled to a second detector |6|. The amplifier tube |59 may be of the screen grid type having its cathode |63 maintained at a positive potential with respect to ground by means of a self-bias resistor |65 and having its control grid |61 connected through vthe secondary of the transformer |51 and through a conductor |59 to the noise suppressor circuit which will be described later. In the particular embodiment illustrated, the second detector ISI is of the diode type and includes in its circuit a resistor |1| across which the sound signals appear.

The picture amplifier |39 is similar to the sound amplifier and includes a first amplifier tube |13 which has its cathode |15 maintained at a positive potential with respect to ground by means of a self-bias resistor |11. The control grid |19 of this amplifiertube, as well as the control grids of other intermediate frequency (not shown), is connected through a conductor |8| to the output circuit of an automatic volume control tube |83.

The output circuit of the picture amplifier |39 is coupled through a tuned intermediate frequency transformer |85 to an amplifier tube |81 which has its output circuit coupled to a second detector |89. As in the sound channel, the second detector |89 may be of the diode type having a resistor |9| in its circuit across which the picture signals appear.

Referring now to the automatic volume control circuit for the sound channel, it comprises the amplifier tube |55 which may be of the screen grid type having a cathode |93, a control grid |95, a screen grid |91 and an anode |99. The tube |55 also includes a rectifier electrode 20| which is positioned adjacent to a small section of the cathode |93. The cathode |93 is held positive with respect to ground by means of a self-biasing resistor 203 which is shunted by a suitable by-pass condenser 205.

The control grid |95 is connected through a resistor 201 to a point on the self-biasing resistor 203 for maintaining the tube |55 biased at such a value that it will function efliciently as an amplifier. The upper portion of the selfbiasing resistor 203 is preferably shunted by another by-pass condenser 209. The plate |99 and the screen grid |91 are supplied with positive potentials from any suitable source.

The input circuit of the tube |55 is coupled through a coupling condenser 2|| to the` output circuit of the sound amplifier |33. Therefore, when an incoming signal is received, an amplified high frequency current appears in the plate circuit of the amplifier tube |55. This current is impressed upon the rectifier section of the tube |55 through a sharply tuned transformer 2|3. The rectifier circuit, which includes a resistor 2|5, may be traced from the rectifier plate 20| through the secondary 2|1 of the transformer 2|3 and the resistor 2|5 to ground and through ground and the self-biasing resistor 203 to the cathode |93. v

It will be seen that as soon as a sound signal appears in the output of the sound amplifier |33,

current is caused to fiow through the rectifier circuit in such a direction as to make the upper end of the resistor 2|5 negative with respect to ground. It is to this end of the resistor 2|5 that the conductor |54 from the control electrodes of the intermediate frequency amplifier tubes is connected. The connection is made through a filter resistor 2|9 which has filter condenser 22| connected between one end and ground. A filter condenser 223 is also connected across the resistor 2|5. It will be understood that as the strength of the signal increases the upper end of the resistor becomes more negative, whereby a more negative bias is applied to the amplifier tube |43 to reduce the gain.

The A. V. C. circuit for the picture channel is the same as the A. V. C. circuit described above and includes the amplifier tube |83 which has its input circuit coupled to the output'circuit of the picture amplifier |39 through a coupling condenser 225 and its output circuit coupled through a sharply tuned transformer 221 to a rectifier section of. the tube. The circuit of the rectifier section includes a resistor 229 which is so connected that its upper end becomes increasingly negative as the strength of the picture signal increases. The conductor |8| from the control grids of the intermediate frequency amplifier tubes is connected through a filter resistor 23| to the upper end of the resistor 229.

In accordance with my invention, the sound channel is provided with a noise suppressor tube 233 while the picture channel is provided with a noise suppressor tube 235. 'I'he noise suppressor tubes may be of the screen grid type. The tube 233 comprises a cathode 231, a control grid 239, a screen grid 24|, and a plate 243. The control grid 239 is connected through a filter resistor 245 to the upper end of the volume control resistor 2|5. The cathode 231 may be connected to ground through a battery 241 or another source of biasing potential for maintaining the cathode negative with respect to ground for providing the desired delay in the noise suppressor action. A filter condenser 249 is connected between the grid end of the filter resistor 245 and ground.

Since the bias voltage supplied by the battery 241 opposes the voltage drop across the volume control resi'stor 2|5, the control grid 239 will not become negative until the amplitude of the incoming signal reaches a predetermined value. Until the control grid 239 reaches a certain negative value, current flows through a resistor 250 in the plate circuit of the tube 233, the plate potential being supplied through a transformer 25| or a battery (not shown). So long as plate current flows through the resistor 250, its upper end is negative with respect to ground.

The control grid |61 of the amplifier tube |59 is connected through the conductor |69 and through a filter resistor 253 to the upper end of the plate resistor 259 whereby the amplifier tube |59 is biased substantially to cut-oir until the amplitude of an incoming signal reaches a value sufficient to put a high negative bias on the control grid of the noise suppressor tube 293. 'I'he usual filter condenser 255 is connected between the grid end of the filter resistor 253 and ground.

In the picture channel, the noise suppressor circuit is the same as .that in the sound channel. The input circuit of the tube 235 is connected across the volumel control resistor 229 whereby the tube 235 is biased approximately to cut-a when an incoming signal reaches a predetermined amplitude. Until the signal reaches this amplitude, current flows in the plate circuit of the tube 235 through the plate resistor 250 which is common to the plate circuits of both suppressor tubes. Likewise, both plate circuits are supplied with plate voltage from the same alternating current source.

The control grid of the amplifier tube |81 is connected through the secondary of transformer |85 and through a conductor 251 to the grid end of the filter resistor 253, whereby the tube |81 is rendered ineffective to amplify a signal while there is a flow oi plate current through the resistor 259.

The suppressor circuit is so adjusted that if the resistor 259 has plate current flowing therethrough from either the suppressor tube 233 or the suppressor tube 235, both amplier tube |59 and amplifier tube |81 will be biased so negatively that they are ineffective to amplify a signal. Therefore, if only one of the signal channels is receiving a signal, the noise suppressor of the other channel is preventing a signal from being applied to either the loud speaker or to the cathode-ray tube. For example, if the sound channel is tuned to the picture signal the picture signal will not appear as noise in the loud speaker because the noise suppressor circuit in the picture channel will be holding the amplifier tube in the sound channel negatively biased to a high value.

The suppressor tubes 233 and 235 should hav their voltages adjusted to give quicker cut-or than the intermediate frequency amplifier 'tubes which are controlled directly from the A. V. C. circuit. It has been found that RCA-57 type tubes are satisfactory as suppressor tubes when RCA-58 type tubes are being used as the intermediate frequency amplier tubes.

In order to insure that the receiver will be tuned exactly to a desired station before the noise suppressor releases, the transformers 213 and 221 may be tuned to have an over-al1 selectivity (together with .the preceding tuned transformers) shown by the curves 259 and 258, respectively, in Figs. 1 and 2. In some cases it may be preferred to tune the transformers 2|3 and 221 no more sharply than each of the preceding intermediate frequency transformers. It will be seen, however, that in any case the selec- .tivity of the sound channel insures that the picture channels will be tuned with reasonable accuracy to the picture signal .before the noise suppressor releases.

In Fig. 6, I have shown a simplified form of noisesuppressor circuit in which the A. V. C. action is utilized. In Figs. 5 and 6 like parts are indicated by the same reference numerals. In this modification, the second detectors |6| and |89 are coupled directly to the output circuits of the amplifiers |33 and |39, respectively, and the A. VT. C. bias for the intermediate frequency amplifier tubes is obtained from the resistor in the diode circuit.

Sound signals appearing across the resistor 1| in the circuit of the diode i6| are supplied through a coupling condenser 259 to the input circuit of an audio frequency amplifier tube 26|. The tube may be of the three electrode type comprising a cathode 263, a control grid 265, and a plate 261.

In the picture channel, the picture signals appearing across the resistor |9| in the second detector circuit are supplied through a coupling condenser 289 to a picture amplifier tube 21| which may be of the three electrode type comprising a cathode 213, a control grid 215, and a plate 211. f

Signals are prevented from appearing at the loud speaker and cathode-ray tube by biasing the 4grids of the sound amplifier tube 26| and the picture ampller tube 21| to a high negative value. This is accomplished by means of a circuit comprising a suppressor tube 219 which functions as two separate amplifier tubes. It includes one set of electrodes consisting of a cathode 28|, a control grid 283, and a plate 285, and a second set of electrodes consisting of a cathode 291, a control grid 289 and a plate 29|. The cathodes 281 and 291 are connected to ground while the anodes 285 and 29| are connected together and supplied through a. transformer 293 with potential from an alternating current source or from a direct current source (not shown). The plate circuit of the tube 219 includes a resistor 295 for supplying the control bias to the audio amplifier tube 26E and picture amplier tube 21i.

The control electrode 289 of the tube 219 is connected through a lter resistor 291 tothat end of the second detector resistor |1| which supplies the A. V. C. bias for the tubes in arnplifier 999. The other control grid. 283 of the tube 219 is connected through a filter resistor 299 to that end of the second detector resistor 191 lwhich supplies A. V. C. bias for the tubes in amplifier 139. It will be seen that if there is no signal in one of the signal channels, one of the control grids of the suppressor tube 219 will be substantially at ground potential whereby there will be a flow of plate current through the plate resistor 295 to so bias the amplifier tubes 251 and 2li that they are ineffective to amplify a signal. On the other hand, if the receiver is properly tuned to a station, the sound signal will cause a high negative bias to be put on the control grid 299 of the noise suppressory tube 219 while the picture signal will cause a high negative bias to be put on the other control grid 283 of the noise suppressor tube 219 and the'iiow of current through the plate resistor vso 295 will be so reduced in value that the amplifier tubes 28| and 21| will be properly biased for amplifying the sound and picture signals.

From the foregoing description it will be un.- derstocd that by applying my invention to a combined television and sound receiver, the receiver is made inoperative when either the television carrier wave or the sound carrier wave is not being received or when either one of them is so reduced in value that the reception would not be satisfactory. The receiver is operative to render a signal visible or audible only when the receiver is properly tuned to two carrier waves having a predetermined frequency spac- Various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1. In a radio receiver for the simultaneous reception of two carrier waves, each of which is modulated by a different signal, two translating devices, and means responsive only to the reception of both of said carrier waves for impressing one of said signals upon one of said translating devices.

2. A receiver according to claim 1 characterized in that one of said translating devices is a loud speaker and the other translating device a cathode-ray tube.

3. In a radio receiver for receiving simultaneously two modulated carrier waves having a predetermined frequency spacing, a tunable selecting circuit, two translating devices, means for demodulating said carrier waves whereby two signals are produced, circuit connections between said demodulating devices and said translating devices whereby one of said signals mayA be impressed upon one of said translating devices and the other of said signals may be impressed upon the other of said translating devices, and means responsive only to the reception of both of said carrier waves for impressing one of said` signals upon one of said translating devices.

4. In a receiver for receiving simultaneously one carrier wave modulated by a picture signal and another carrier wave modulated by a sound signal, a tunable selecting circuit,`a.cathoderay tube, a loud speaker, means for demodulating said carrier waves to produce a picture signal and a sound signal, means whereby said picture signal and said sound signal may be impressed upon said cathode-ray tube and loud speaker, respectively and means responsive only to the reception of both of said carrier waves for impressing one of said signals upon said loud speaker.

5. A radio receiver comprising a radio frequency selecting circuit adapted to select a. plurality of modulated carrier waves, means for heterodyning said carrier waves to a plurality of intermediate frequency signals, means for demodulating one of said intermediate frequency signals to produce a certain signal, means for impressing said certain signal upon a translating device, means for demodulating another of said intermediate frequency signals to produce a different signal, means for impressing said diiIerent signal upon a second translating device, and means for preventing either saidcertain signal or said different signal from being impressed upon said translating devices so long as said selecting circuit is not tuned to a plurality of said carrier waves.

6. A receiver according to claim 5 characterized in that means is provided for making said last means ineffective at the will of the operator.

7. In a receiver for the simultaneous reception of two carrier waves, each of which is modulated by a signal, a plurality of translating devices. means for heterodyning one of said carrier waves with the other of said carrier waves to produce a beat frequency, and means responsive to the production of said beat frequency I for impressing said signals upon said translating devic.

8. A receiver according to claim 7 characterized in that one of said translating devices is a cathode-ray tube for the reception of picture signals.

9. In a receiver for the simultaneous reception of two carrier waves, at least one of which is modulated by a signal, means for heterodyning said carrier waves to two intermediate frequency signals. means for heterodyning one of said intermediate frequency signals by the other of said intermediate frequency signals to produce a beat frequency, a translating device, and means for impressing said signal upon said translating device in response to the production of said beat frequency.

10. A receiver according to claim 9 characterized 'in that said signal is supplied to said translating device through an amplifier, and further characterized in that said last means includes means for maintaining said amplifier substantially ineffective to amplify so long as said beat frequency is not being produced.

11. In a receiver for the reception of at least two carrier waves, each modulated by a signal, means for selecting said carrier waves, means for converting said modulatedvcarrier waves to intermediate frequency signals, an amplifier tuned to one of said intermediate frequency signals, an amplifier tuned to another of said intermediate frequency signals, a plurality of translating devices, means for transferring signal energy from one of said amplifiers to one of said translating devices, means for transferring signal energy from said second amplifier to another of said translating devices, and means for making said two last-named means ineffective in response to the signal strength in either, of'said amplifiers falling below a predetermined value.

l2. A receiver according to claim 11 characterized in that one of said amplifiers is tuned comparatively sharply to receive sound signals while the second of said amplifiers is tuned comparatively broadly to receive picture signals, and further characterized in that said one translating device is a loud speaker while said. second translating device is a cathode-ray tube.

13. A receiver comprising a broadly tuned radio frequency selecting circuit, a heterodyne oscillator and detector, a sharply tuned intermediate frequency amplifier, a broadly tuned intermediate frequency ampliiier, an automatic volume control operating in conjunction with each intermediate amplifier in such a manner that the output of each amplifier remains substantially constant under proper receiving conditions, and means controlled by both automatic volume controls for rendering a subsequent amplifier tube in each channel inoperative when a signal of insufiicient strength to operate the automatic monaco? volume controls is impressed upon either intermediate amplifier.

14. A receiver comprising a broadly tuned radio frequency selecting circuit, a heterodyne oscillator and detector, a sharply tuned intermediate frequency amplifier, an automatic volume control operating in conjunction with said intermediate frequency amplier to maintain its output substantially constant when a'signal of sutilcient intensity is being received, a second intermediate frequency amplier having a relatively broad selectivity characteristic tuned to a slightly dfferent frequency than the first intermediate amplier, an automatic volume control operating in conjunction with the second' intermediate frequency amplifier to maintain its output substantially constant when a signal o! sumcient intensity is being received, said second automatic volume control having a selectivity characteristic such that it will operate over only a substantially small band of the frequenciesv passed by the second intermediate amplifier, a demodulating device following each intermediate amplifier, an amplifier following each demodulator, a utilization device folowing each of the last mentioned apliers, and means responsive to the outputs of both automatic volume controls for preventing any signal voltage from reaching either utilization device when a signal of insufficient strength or of improper frequency to operate the automatic volume controls is impressed upon either intermediate frequency amplifier.

RALPH S. HOLMES.

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