US2448908A - Television receiver - Google Patents

Description

SCpt. 7, 1948. L, w, PARKER 2,448,908

TELEVISION RECEIVER Filed July 15, 1944 Bremse 2759 i f6 27,3 -P- 5 27g INVENTOR W 27e .502055 Zl/ 1001*??? Patented Sept. 7, 1948 UNITED STATES PATENT OFFICE aussos rmvrsloa' asoman A una w. rarer. wwaslae, N. Y. l prima my 1s, 1944, serai No. 544,126 zc calms. (ci. 17a-5.a)

This invention relates to television receivers. and more particularly to a television receiver embodying an improved way of separating and reproducing the video and audio components of the received television signal.

In the conventional television receiver the sound and picture can'iers must be seperated so that no sound components reach theA video detector, as otherwise the sound modulation will appear on the screen as undesired picture interference.

The present standards for the transmission of black-and-white television images, as prescribed by the Federal Communications Commission, require that the image be transmitted by a carrier that is amplitude modulated by the video signals and that the accompanying sound part of the program be transmitted as a frequency modulation of a sound carrier spaced 4.5 megacycles above the video carrier. If the receiver is of the superheterodyne type, frequency drift of the local oscillator used to beat with the sound and image carriers introduces very serious problems, especially in the soundv intermediate frequency channel, and if the radio frequency used is above 100 megacycles, this trouble is very greatly increased.

In accordance with my invention I am able to produce television pictures of very satisfactory clarity and freedom from interference, particularly from the sound modulation, while at the same time reproducing the sound accompaniment equally well and eliminating a number of the receiver component parts heretofore believed necessary.

In accordance with my invention it is no longer necessary to completely separate video and audio components before detection. On the contrary, I permit both these components to reach the second detector and utilize the interaction between them to produce the audio signal. The conventional sound channel is thus eliminated and a single channel is used for both the video and the audio components of the television signal.

By the application of my invention, I am able to employ an oscillator which may have a frequency inaccuracy of as much as 200 kc. plus or minus without harmful effects on the picture or To produce a-television receiver in which it is not necessary to separate the video and audio components before detection.

To provide such a receiver in which interaction between video and audio components is utilized to produce the audio frequency signal.

' To produce a receiver in which many of the component parts heretofore considered necessary are eliminated, thereby reducing the cost of construction and maintenance of the receiver.

To produce a receiver of the superheterodyne type in which frequency drift of the oscillator is not a serious problem.

To produce a generally improved and simplined television receiver. l

Stili -other objects and advantages of my invention will be apparent from the specification.

The features of novelty which I believe to be characteristic of my invention are set forth with particuiarity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, will best be understood by reference to the specification and accompanying drawing, in which Fig. 1 is the acceptance curve of a television receiver to which my invention is applied,

Fig. 2 is a schematic diagram of a television receiver in accordance with my invention,

Fig. 3 is a series of curves showing the performance of a television receiver in accordance with my invention,

Fig. 4 is an idealized curve of a receiver in accordance with my invention, and

Fig. 5 is a detail of one form of circuit which may be employed in the practice of my invention.

Referring now more particularly to Fig. l, in which the ordinates represent response and the abscissae frequency, the curve X indicates the acceptance of a television receiver according to my invention, before using any of the absorption circuits explained with reference to Figs. 3 and 5.

'I'he picture or image carrier is located at the frequency P and the receiver at this frequency is made to have approximately half its sensitivity. On the lower side band the receiver will accept frequencies down to a frequency approximately one and one-half megacycles below the picture carrier frequency, all frequencies lower than this being rapidly attenuated.

For frequency increase above the carrier, the sensitivity of the receiver increases to a substantially constant value, extending over most of the upper side band, at the upper end of which it begins to decrease', and if the receiver has a broad enough acceptance, both the picture and the sound carriers (which in the present illustration is 4.5 megacycles above the picture carrier) may reach the detector. In asuperheterodyne receiver it is conventional practice to cause the local heterodyne oscillator to operate at a frequency above the image and sound radio frequency carriers. Under such circumstanceathe sound I. F. carrier S would be of a lower frequency than the image I. F. carrier P. The two I. F. carriers would still be displaced by an amount equal to the displacement of the two radio frequency carriers.

If the slope of the receiver acceptance curve over the frequency deviation band of the sound carrier is other than zero, sound frequencies will pass through the detector and result in interferencev with the picture in the conventional receiver, and, accordingly, it has been the practice to provide filters ahead of this detector to separate these two intermediate frequency carriers.

In accordance with my invention, I permit both of these carriers to reach the detector and I utilize the interaction of the two carrier frequencies to produce a beat frequency of 4.5 megacycles, which frequency is passed on to the video amplifier, which may have some amplification at this frequency so that a signal of comparatively large amplitude, l volt or more, is secured from its output.

The beat frequency thus produced will be the frequency difference or displacement between the original image and sound radio frequency carriers as radiated, and this difference according to present black-and-white standards, is 4.5 megacycles. The beat frequency may be produced by the interaction or heterodyning of the two radio frequency carriers (in a TRF receiver), or the two I. F. carriers (in a superheterodyne receiver). In either event, the same beat frequency is produced.

A circuit employing this principle is diagrammatically indicated in Fig. 2, in which I represents the usual doublet antenna, I I a superheterodyne television receiver having a video output channel IIa and an audio output channel IIb,'

the latter of which may comprise coupling coil I2 tuned by variable condenser I3 coupled to discriminator input coils I4 and I5 feeding the discriminator diagrammatically indicated as I6, and the output of which is supplied to audio frequency amplifier I'I and thence to loud speaker I8.

The final stage of the last video frequency amplifier in the receiver I I may be tuned to 4.5 megacycles by a parallel resonant circuit in series with the plate resistor of the video frequency amplifier tube. In this way the video frequency amplifiers work as reflex amplifiers reducing the number of tubes needed in the completed television receiver. Certain precautions must be taken and certain adjustments made, as will be pointed out more in detail.

If the frequency modulated sound carrier falls on a portion of the receiver selectivity curve which have a slope other than zero, some frequency discriminator action would take place over the range of frequency swing of the frequency modulated sound carrier, and some audio frequency signals will be generated which will be present in the video signal. If the frequency acceptance curve of the receiver be made so broad as to include the sound carrier. the slope of this curve may be made approximately zero in the vicinity of the sound carrier: and if this is done, no troublesome audio frequency component will be generated.

However, if the sound carrier is left at the same amplitude as the picture carrier, the video modulation will appear in the audio frequency signal and will be dimcult to remove, and also the gain per stage would be reduced because of the greater band width, requiring a greater number of tubes for the same gain.

In accordance with my invention. I do not make the acceptance curve so wide that the response of the receiver is substantially the same at the sound carrier frequency as over the upper side band of the picture carrier. I prefer to use a somewhat narrower acceptance so that the sound carrier falls, as indicated in Fig. 1, on the lower portion of the upper side of the selectivity curve, where it is approaching zero, so that the amplitude of the sound carrier is about 1,50 of the video carrier. This 1,50 amplitude, however, is not an absolute necessity and may vary within wide limits above or below this value.

Fig. 3 shows this portion of the curve of Fig. l on an enlarged scale, and it will be observed that over the 150 kc. total frequency swing of the sound carrier there is a change in amplitude of curve X. as shown by A, which, in the absence of my invention, would produce audio interference in the picture. I, therefore, alter curve X to give a curve shown in idealized form in Fig. 4, in which the sound carrier S is reduced to about 1,50 of the intensity of picture carrier P. and the slope of the selectivity curve near the sound carrier is also reduced to substantially zero.

Since the idealized curve. as in Figure 4, has zero slope in the region of carrier S, no frequency discrimination takes place, and consequently no demodulated audio frequencies appear in the output of the second detector. Also, since the amplitude of the sound carrier is only 5% of the amplitude of the picture carrier, a 90% modulation of the picture carrier will not alter the amplitude of the 4.5 megacycle beat frequency produced by the interaction of the sound and picture carriers. This is because of the well-known fact that if one of two heterodyning frequencies is more than twice the amplitude of the other, the beat fre-` quency amplitude cannot be altered by further increasing the larger one of the two heterodyning frequencies (assuming that a linear detector, such as a diode, is used to obtain the beat frequency) If the modulation increases above 90 the picture carrier will drop below the necessary two to one ratio at times, and there may be a downward modulation of the 4.5 megacycle carrier, but since the video signal is broken by blanlcing signals 15,750 times a second, the picture carrier can stay low for only a shorter time than 1/is,15o second. One hundred per cent modulation of the picture carrier may, therefore, cause a 15,750 cycle audio tone to reach the audio amplifier, and this may be either filtered out, or in many instances be disregarded, since a conventional audio frequency amplifier and loud speaker ordinarily will not reproduce it to any troublesome extent.

No limiter is necessary to remove any video modulation from the audio frequency. The 60- cycle blanking pulses (with their harmonics within the audio frequency range) are of such phase in the system employed in the United States that they increase the picture carrier and, as previously stated, this has no eilect on the 4.5 megacycle beat frequency. A limiter, however, may be used employed to absorb energy from the intermediate frequency coils over a particular range.

In Fig. 5 the tube 20 may be one of the intermediate frequency amplifier tubes preceding the second detector. and this may be a pentode comprising cathode c, control grid 22cm screen grid 20w, suppressor 20sra, and anode 22a. The cathode may be grounded through resistor 221' shunted by by-pass condenser 20h, and the anode 22a may be connected through inductance 2| shunted by tuning condenser 22 and resistance 22 to the source of B voltage.

Coupled to the inductance 2| I may provide additional inductance 24 shunted by tuning condenser 25 and by resistance 26. one common point of said elements being connected to ground and the other to the control grid Non of tube 27. which may also be a pentode, having cathode 21e, control grid Tico. screen grid 21.10, suppressor 21srg, and anode 21a. The cathode of this tube may be connected to ground through resistance 28 shunted by by-pass condenser 28.

Coupled to the inductances 2| and 24 I may provide an additional inductance 2li shunted by resistance 2|, and by tuning condenser 22, and this may constitute an absorption circuit or wave trap. This absorption circuit is preferably tuned to a frequency spaced 150 kc. l(or any other suitable amount) from the sound carrier in the direction of the video carrier. By control of the parameters of this absorption circuit; that is. by varying the tuning, the damping, and the coupling of this circuit. it is possible to obtain a curve Y which is substantially the mirror image of the curve X over the range of frequency swing of the sound carrier.

The overall acceptance of the receiver with the absorption circuit or wave trap so adjusted is. therefore, the resultant of the two curves X and Y. and is shown by the dot and dash curve. X-l-Y. from which it will be seen that the total change in slope of the acceptance over the 150 kc. swing of the sound carrier, as indicated by B, is a very small proportion of the change which would otherwise be obtained. as indicated at A.

It is possible to reduce the audio frequency interference from the picture without using the absorption circuits shown with reference to Figs. 3 and 5 by reducing the audio frequency carrier amplitude to a value much lower than l/io of the picture carrier amplitude: for example, x/wa This, while it simplifies construction, is not always desirable. since the audio frequency signal becomes very low and makes additional amplification necessary.

While I have described my invention particularly with reference to its incorporation in a receiver of the superheterodyne type. it is to be understood that my invention is not limited thereto and may be employed with tuned radio frequency receivers. In present television receivers of the superheterodyne type the local oscillator must be adjusted within the limits of plus or minus 10 kc., for instance. in order to keep the sound carrier at the proper point on the discriminator curve: but with the employment of my invention this is no longer necessary, and an oscillator change of plus or minus 200 kc. may occur without harmful eil'ects on picture or sound.

In applying my invention to a TRF receiver, the radio frequency amplifier is treated in the same way as the intermediate frequency amplifier in the superheterodyne receiver already described; that is. absorption circuits or wave traps, asshown in Fig. 5, are introduced approximately 6 iokabeiowthesoimdcarrierfrequenc! (i. e.. inthedireetionofthevideocarrier') andthsparamstersofthecircuitaresocontrolledasto obtain an absorption curve which is lsubstantially the mirror image of the selectivity curve of the sound carrier frequency swing.

Inthesuperhetcrodynereceiveritwillgeneraily not be necessary to alter the selectivity of the preselector since this usually will4 not introduce enoughl audio frequency components into the picture to make it worth while to use absorption circuits. However. this may be done if desired.

It may be noted that in applying this invention to a luperheterodyne or TRP receiver the 4.5 megacycle frequency modulated best frequency carrier that is extracted from the output oi' the video amplifier by the discriminator I2, which may be tuned to 4.5 mc. has such high amplitude thatordinarliyonlytwoorthreetubesarenecessary to receive the sound accompaniment instead of the usual five tubes.

While I have shown and described certain preferrrd embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope thereofI as will be clear to those skilled in the art.

In this application I have particularly pointed out and distinctly claimed the part, improvement, or combination which I claim as my invention or discovery. and I have explained the principles thereof and the best mode in which I have contemplated applying those principles so as to distinguish my invention from other inventions.

I claim:

l. In a television receiver for a television system in which a picture signal carrier is amplitude modulated and the complemental sound signal is transmitted as a frequency modulation of a second carrier, in combination, an amplifier, means for supplying said picture and sound carriers of a television signal to said amplifier, a detector supplied by said amplifier, and a selecting circuit connected between said amplifier and `said detector and having a frequency characteristic such that both picture and sound carriers are passed to said detector, the two carriers being heterodyned with each other in the detector, and means in the selecting circuit for modifying the characteristics of that circuit so that it is characterized by substantially zero slope over the range of frequency swing of the sound carrier and has an amplitude level below the minimum modulated amplitude of the amplitude-modulated picture signal carrier, whereby the output from said detector contains both detected video signals and undetected frequency modulated audio signals, and a detectorresponsive to the undetected signals to produce the audio signals.

2. In a television receiver, adapted to receive upon an antenna concomitantly transmitted video and audio signals supplied upon two carriers having substantially constant frequency separation and in which one carrier is frequency modulated by one of the signals and the other carrier is amplitude modulated by the other signal, in combination, a selecting circuit supplied with said received signals, said selecting circuit having a frequency characteristic such that both picture and sound carriers of the same television signal4 as accepted thereby are supplied therefrom in an amplitude ratio which is of the order of 20:1. means for heterodyning said accepted carriers with each other to produce a third car. rier. and a detector for said third can'ier.

3. The method of receiving a television frequency band including video and sound signals on carriers 4.5 megacycles apart, with the video carrier amplitude modulated and the sound carrier frequency modulated which comprises the steps of selectivity amplifying the two carriers to produce video and audio components in a substantially 20:1 amplitude ratio in a common channel, and heterodynlng saidvideo and audio components with each other to provide a frequency modulated oscillation of 4.5 megacycles carrying the sound signal and substantially free from video modulation.

4. In a television receiver for receiving television -signals consisting of an amplitude modulated video signal carrier and a related frequency modulated audio signal carrier,l the two carriers being separated by a substantially fixed frequency difference. in combination, means for receiving incoming signals, including a selecting circuit having an overall selectivity curve providing substantial cut-off 1.5 megacycles on one side of the video frequency, increasing to substantially half amplitude at video carrier frequency and full amplitude over substantially the entire video sideband on the other side of the video carrier, and decreasing to the order of las maximum amplitude in the region of the audio carrier frequency, means operating conjointly with said selecting circuit and having a selectivity curve which is substantially the mirror image of the selectivity curve of said selecting circuit in the region of the audio carrier, said means being effective to establish a resultant selectivity curve in the region of the audio carrier for substantially preventing amplitude modulation of the audio carrier, detecting means energized from the selecting circuit for beating together and amplitude detecting the modulated carriers from said selecting circuit, and means energized from said detecting means for reproducing audio frequency signals from the resulting frequency modulated beat frequency.

5. In a television receiver for receiving television signals consisting of an amplitude modulated video carrier and a related frequency modulated audio carrier. the two carriers being separated by a substantially fixed frequency difference, in combination, means for receiving incoming signals, including a selecting circuit having an overall selectivity curve providing substantial cut-off 1.5 megacycles on one side of the video frequency carrier, increasing to half amplitude at video carrier frequency and full amplitude over substantially the entire video sfdeband on the other side of the video carrier frequency, and decreasing to substantially l/zii maximum amplitude in the region of the audio carrier frequency, means having a selectivity curve which is substantially the mirror image of said selecting circuit in the region of the audio carrier for substantially preventing amplitude modulation of the audio carrier, said last mentioned means modifying the action of said selecting circuit to provide substantially zero frequency selectivity over the swing of the audio frequency carrier, means including detecting means, and energized from the selecting circuit for beating together and for amplitude detecting the modulated carriers from said selecting detecting circuit, and a circuit connected to receive the produced beat frequency output.

6. In a television receiver for receiving television signals consisting of an amplitude modulated video signal carrier and a related frequency duced as a result of audio carrier frequency deviations, and an absorption circuit coupled to said selector circuits, said absorption circuit being tuned to a frequency spaced substantially 150 kc. from the audio carrier in the direction of the video carrier, whereby the frequency characteristics of the selector circuits is modified to establish a resultant or net frequency characteristic that is substantially flat or constant, so that amplitude variations in the audio frequency carrier are substantially prevented, and means energized from the selector circuits for he'terodyning the two carriers to produce a beat frequency carrier, and means for detecting the beat frequency carrier.

7. The method of receiving a television signal frequency band including related video and sound signals on separated carriers, the video carrier being amplitude modulated and the sound carrier being frequency modulated with the carriers separated by a substantially constant frequency difference, which comprises the steps of amplifying the two carriers in a common channel to different average amplitudes such that when the video carrier is to be modulated m percent, the sound carrier may have a maximum amplitude not in excess of (1GO-m) percent of the average amplitude of the video carrier, heterodyning the video and the sound carriers with each other to produce a beat note having a frequency equal to the difference between the original separation of the video and the sound signal carriers, simultaneously detecting the amplitude modulated video carrier to derive a video component, and amplifying the video component together with said beat note, and then separating out the beat note to derive the sound signal therefrom, and passing the video component to a video signal reproduction system and the sound signal to an audio signal reproducer.

8. The method of receiving a television signal frequency band including related video and audio signals on separate carriers, the video carrier being amplitude modulated and the audio carrier being frequency modulated with the carriers separated by a predetermined substantially fixed frequency difference, which comprises the steps of amplifying the two carriers in a common channel to different average amplitudes such that when the video carrier' is to be modulated m percent, the sound carrier may have a maximum amplitude not in excess of (10G-m) percent of the modulated audio signal carrier. the two carriers being separated by a substantially fixed frequency difference, in combination, an amplifier, a detector supplied with both audio and video carriers by said ampiiner, and a selector circuit preceding said detector and including means to cause the frequency characteristic of the selecting circuit to be such that the amplitude of the audio carrier supplied to said detector is substantially constant with frequency change and not in excess of the minimum value of the video carrier at the maximum modulation of said video carrier, whereby said detector output contains both detected. amplitude modulated video signals and undetected frequency modulated audio signals.

10. In a television receiver for receiving a television signal band consisting of an amplitude modulated video signal carrier and a related frequency modulated audio signal carrier, the two carriers being separated by a substantially fixed frequency difference, in combination, a selecting circuit adapted to be supplied with said signal carriers, said selecting circuit including means to cause the circuit characteristic to be such that the picture and the sound carriers of the same television signal band, as accepted, are amplified in an amplitude ratio of the order of 20:1, with substantially zero amplitude change of the audio carrier with frequency change, means for heterodyning and detecting said carriers to produce both a detected video signal and an undetected frequency modulated audio carrier.

l1. The method of receiving a television signal band including video and sound signals on carriers separated by a substantially fixed frequency separation of the order of 4.5 megacycles. with the video carrier amplitude modulated and the sound carrier frequency modulated, said method comprising the steps of conducting the carriers of a received signal band through a common channel and amplifying the carriers, as received, so that the maximum amplitude of the sound carrier will be less than the minimum value of the video carrier 'at the maximum modulation of said video carrier, .heterodyning the video and the sound carriers of the received signal band with each other to produce a beat note of the order of the original frequency separation of 4.5 megacycles, simultaneously detecting the amplitude modulated video carrier to derive a video signal component, amplifying the video component together with the beat note, and then separating out said beat note and detecting the sound signal therefrom.

12. In a television system, in which the picture signal is radiated on an amplitude modulated carrier and the sound signal on a frequency modulated carrier separated from the picture carrier by a substantially constant frequency dierence within an allotted transmission band, the method of receiving and reproducing the picture and the sound signals in proper relationship, which comprises the steps Aof receiving the two radiated carriers of the transmission band, heterodyning the carriers of the transmission band with a locally generated frequency to convert the incoming earriers to I. F. carriers, transmitting the I. F. car riers through a common channel with the amplication of the picture signal I. F. carrier relative to the sound signal I. F. carrier made such that any minimum value of the picture carrier due to its amplitude modulation shall be greater than any maximum value of the sound carrier, heterodyning and amplitude detecting the picture and 10 the sound I. F, carriers to produce the picture video band and a beat frequency carrier of the order of the original frequency difference between the radiated carrier frequencies, amplifying the detected picture video band and the said beat frequency carrier, feeding the picture video band to the video output picture reproducing device while simultaneously separating the frequency modulatedenergy of the beat frequency carrier from the picture video band, detecting said separated carrier to obtain a sound signal corresponding to the sound intelligence as radiated, and feeding the sound signal to a sound reproducing device.

13. The method of operating a receiver of the superheterodyne type for receiving a television signal comprising an amplitude modulated video signal carrier of one frequency and a related frequency modulated audio signal carrier of a second frequency separated from the video carrier by a substantially constant frequency spacing, which comprises the steps of feeding the two carriers to a first detector or converter for conversion to intermediate frequency carriers having a like frequency spacing, selectively amplifying the two I. F. carriers in a common I. F. channel so that the maximum amplitude of the audio signal carrier is less than the minimum value of the video signal carrier, deriving from the I. F. signal channel a beat frequency carrier having a frequency corresponding to the original frequency spacing between the video signal carrier and the audio signal carrier, and also deriving from the I. F, signal channel a detected video signal, feeding the detected video signal to an image reproducing tube, feeding the derived beat frequency carrier to a frequency discriminator to develop the audio signal therefrom, and energizing a sound reproducer with the sound audio signal.

14. The method of operating a superheterodyne television receiver to detect the related sound and video signals of a television broadcast, in which the video carrier is amplitude modulated and the sound carrier is frequency modulated, the two carriers being separated by a predetermined substantially constant frequency difference, which comprises the steps of receiving and converting the two carriers to two corresponding I. F. carriers separated by a similar frequency difference, transmitting both I. F. carriers with their modulating intelligence through a common I, F. amplifying circuit and amplifying the sound carrier to a. level of amplification that is less than the minimum value of the video carrier at maximum modulation of said video carrier, demodulating the amplified amplitude modulated video L F. carrier to derive the video signal, heterodyning both I. F. carriers to provide a resultant output beat frequency carrier that is frequency modulated according to the sound signal intelligence, and thereafter deriving the sound signal from the beat frequency carrier for delivery to a sound reproducing device while the derived video signal is fed to a picture reproducing device.

15. A television receiver for receiving a selected television signal band which includes two separate radio frequency carriers for conveying the video and audio intelligence, one of the carriers being amplitude modulated by the intelligence conveyed thereby and the other carrier being frequency modulated by the intelligence conveyed thereby, the two carriers being displaced from each other by a predetermined relatively ilxed frequency spacing, said receiver comprising amplifying means to selectively amplify the two carrier frequencies so that the maximum amplitude l 1 of the frequency-modulated carrier is less than the minimum amplitude, of the amplitude-modulated carrier. means for heterodyning the amplified carriers to produce a beat'frcquency carrier of a frequency equal to the frequency spacing between the video carrier and the audio carrier, the beat frequency carrier being frequency modulated in accordance with the frequency modulation present on the originally received frequency modulated carrier. means energized by the beat frequency carrier and including a frequency discriminator for demodulating the beat frequency carrier to produce one intelligence,'and means including an amplitude detector energized by and operative to demodulate the amplified amplitude modulated carrier to produce another intelligence.

16. A television 'receiver for receiving a television signal band including an amplitude modulated image carrier and a related frequency modulated sound carrier spaced a substantially fixed frequency from the picture carrier, said receiver comprising means to select and amplify one such band of frequencies so thatthe amplitude of the sound carrier will be less than the amplitude of the image carrier at the maximum modulation of that carrier by the picture or image signal. means for heterodyning said carriers to produce a new carrier having a frequency equal to the frequency spacing of the image and sound carriers and for amplitude detecting the image carrier to produce image-signals, and demodulating means energized in accordance with the new carrier for producing audio signals.

17. A television receiver comprising an incoming selecting circuit for simultaneously receiving two spaced carriers having different types of modulation, one carrier being amplitude-modulated and the other carrier frequency-modulated said receiver including frequency converting means to convert the received carriers to two local similarly spaced I. F. carriers, means constituting a common I. F. amplifying channel connected to be energized from the frequency converting means and having a suflicient band width to transmit both I. F. carriers but having such frequency characteristic as to transmit the frequency-modulated carrier at an amplitude of the order of 5% of the amplitude-modulated carrier. heterodyning and detector means connected to be energized from the I. F. channel in order to detect one of the I. F. carriers and to heterodyne the two l F. carriers to produce a beat frequency carrier, a subsequent detector connected to be energized by the output of the heterodyning means for detecting the produced beat frequency carrier, and reproducing means energized by the two detected outputs.

18. A television receiver for receiving a television signal band including a picture carrier and a sound carrier spaced a substantially fixed fre` quency difference apart within the signal band the picture carrier being amplitude-modulated and the sound carrier being frequency-modulated. said receiver comprising means to select and amplify one such television signa1 band, said means including frequency converting means to convert the two carriers of said band to two corresponding I. F. carriers, means constituting a common transmission channel to amplify the two I. F. carriers, means constituting part of the transmissionchannel for controlling the unequal amplification of the two carriers according to a predetermined ratio such that when the picture carrier is to be modulated m percent, so that its minimum modulated value will be (D-m) percent of the average amplitude of the picture carrier, then the sound carrier may be given an arnplitude whose maximum shall not be in excess of said (1D0-m) percent, means energized from the transmission channel to heterodyne and to detect the two I. F. carriers to produce the demodulated intelligence of the greater of the two I. F. carriers and to also produce a beat frequency carrier having a frequency equal to the frequency difference between the two carriers, and an additional detector tuned to said beat frequency for extracting therefrom the intelligence of the lesser I. F. carrier.

-19. A television receiver tfor receiving and reproducing intelligence from a distance, which is modulated onto and transmitted by an amplitude modulated video signa1 carrier and a frequency modulated audio signal carrier spaced a predetermined relatively fixed frequency distance apart within an allotted television signal frequency band, said receiver comprising an incoming selecting circuit including frequency Aconverting means to select a desired television band and to convert the incoming carriers to two corresponding video and audio I. F. carriers similarly spaced and carrying the intelligence modulated onto the corresponding incoming carriers, an I. F. amplifying circuit of sufficient band width to accommodate the two spaced video and audio I. F. carrlers, means to apply both the I. F. carriers to the common I. F. amplifying circuit for amplification thereby so the audio carrier will be of the order of 5% of the video carrier, means including a detect-or and energized from the I. F. amplifying circuit to detect the video I. F. carrier to obtain therefrom the modulated intelligence carried thereon. and to heterodyne the video and audio I. F. carriers to produce a beat frequency carrier of a frequency equal to the frequency spacing between the two I. F. carriers, the beat frequency carrier including the intelligence carried by the audio I. F. carrier, means including a subsequent detector energized by the beat frequency carrier to detect the beat frequency carrier to obtain therefrom themodulated intelligence transferred thereto from the audio I. F. carrier, and means energized by the intelligence obtained from both detectors for reproducing the original television intelligence as modulated onto the original carriers of the television signal band.

20. In -a television receiver for receiving a television signa1 band consisting of an amplitude modulated video signal carrier and a related frequency modulated audio signal carrier, the two carriers being separated by a substantially fixed frequency difference, the combination comprising a selecting circuit adapted to be supplied with said signal carriers, means energized from the selecting circuit for detecting the video carrier to derive the video signal therefrom, means for substantially preventing sound interference with the video signal, means energized from the selecting circuit to use the video carrier as a source of fixed oscillator frequency and to beat it with the audio signal carrier to establish a new beat frequency carrier for the audio signal, said beat frequency carrier having a frequency equal to the frequency difference between the original video and audio carriersl and means for frequency detecting the beat frequency carrier to obtain the audio signal therefrom.

21. In a television receiver for receiving a television signal band consisting of an amplitude modulated video signal carrier and a related frequency modulatedaudio signal carrier, the two 13 carriers being separated by a substantially fixed frequency difference, the combination comprising a selecting circuit adapted to be supplied with said signal carrie means energized from the selecting circuit icy' detecting the video carrier to derive the video vsignal therefrom, means for substantially preventing sound interference with the video signal. means energized from the selecting circuit to use the-video carrier as a source of fixed oscillator frequency and to beat it with the audio signal carrier to establish a new beat frequency carrier for the frequency-modulated audio signal, said beat frequency carrier having a frequency equal to the frequency difference between the original video and audio carriers, an output circuit to receive the beat frequency carrier and including elements forming a parallel resonant circuit tuned to said beat frequency, and a frequency discriminator energized from said tuned circuit to frequency detect the beat frequency to derive the frequency-modulated audio signal therefrom.

22. A television receiver for receiving and reproducing a television signal band including an amplitude modulated video carrier of fixed frequency and a frequency modulated audio carrier spaced a constant frequency difference from the video carrier; said receiver comprising a selecting circuit with means for converting the carriers of a selected television signal band to I. F. carriers spaced an equal constant frequency distance apart; an I. F. amplifier circuit for the I. F. carriers; amplitude detecting means energized from the I. F. amplifier circuit for detecting the video signal from the video I. F. carrier; means for substantially preventing sound-interference with the video'signal a frequency discriminator for detecting the frequency modulated audio signal, said discriminator being tuned to a frequency corresponding to the frequency difference between the video carrier and the audio carrier;

and means connected to the I F. circuit to re-l ceive and beat the video and the audio I. F. carriers to derive a beat frequency carrier therefrom and to supply the beat carrier to the discriminator with a predetermined limited amplitude.

23. A television receiver for receiving and reproducing intelligence from a distance, which is modulated onto and transmitted by an amplitude modulated video signal carrier and a frequency modulated audio signal carrier spaced a predetermined relatively fixed frequency distance apart within an allotted television signal frequency band, said receiver comprising an incoming selecting circuit including frequency converting means to select a desired television band and to convert the incoming carriers to two corresponding video and audio I. F. carriers similarly spaced and carrying the intelligence modulated onto the corresponding incoming carriers, an I. F. amplifying circuit of sufficient band width to accommodate the two spaced video and audio I. F. carriers, means to apply both the I. F. carriers to the common I. F, amplifying circuit for amplification thereby, means energized from the I. F. circuit to detect the video I. F. carrier to derive the video signal therefrom. means for substantially preventing sound interference with the video signal means energized from the I. F. circuit and using the video I. F. carrier as a source of fixed oscillator frequency to beat with the frequency modulated I. F. audio signal carrier to establish a new beatfrequency carrier for the audio signal band with said new beat frequency carrier having a frequency equal to the frequency difference between the original video and audio carriers, an

output circuit for receiving said beat frequency carrier and including elements forming a parallel resonant circuit tuned to said beat frequency, and a frequency discriminator energized from said tuned circuit to detect the beat frequency carrier to obtain the audio signal therefrom.

24. A television receiver for receiving and reproducing intelligence from a distance, which is modulated onto and transmitted by an amplitude modulated video signal carrier anda frequency modulated audio signal carrier spaced a predetermined relatively fixed frequency-distance apart within an allotted television signal frequency band, said receiver comprising an incoming selecting circuit including frequency converting means to select a desired television band and to convert the incoming carriers to two correspond ing video and audio I. F. carriers similarly spaced and carrying the intelligence modulated onto the corresponding incoming carriers, an I. F. amplifying circuit of sumcient band width to accommodate the two spaced video and audio I. F. carriers, means to apply both the I. F. carriers to the common I. F. amplifying circuit for amplification thereby, means energized from the I. F. circuit to detect the video I. F. carrier to derive the video signal therefrom, means for substantially preventing sound interference with the video signal means energized from the I. F. circuit and using the video I. F. carrier as a source of fixed oscillator frequency to beat with the frequency modulated I. F. audio signal carrier to establish a new beat frequency carrier for the audio signal and having a frequency equal to the frequency difference between the original video and audio carriers, an output circuit for receiving said beat frequency carrier and tuned to said beat frequency. a frequency discriminator energized from said output circuit to detect the beat frequency carrier, and means for limiting the amplitude of the beat frequency carrier to be supplied to the discriminator.

25. A television receiver for receiving a television signal band including an amplitude modulated image carrier and a related frequency modulated sound carrier spaced a substantially fixed frequency from the picture carrier, said receiver comprising means to select and amplify one such band of frequencies; means to heterodyne the carriers to produce a new beat carrier having a frequency equal to the frequency spacing of the two carriers; means for substantially preventing sound interference with the video signal an output circuit for receiving the beat frequency carrier and including a parallel resonant circuit in series with a plate resistor; the parallel resonant circuit being tuned to the resultant heterodyned beat frequency; and a frequency discriminator tuned to said heterodyned frequency and energzed in accordance with the voltage across said tuned circuit for deriving a sound signal therefrom; and a reproducing device energized from the discriminator.

26. A television receiver for receiving a television signal frequency band including related video and audio signals on separate carriers separated by a substantially fixed frequency difference, the video carrier being amplitude modulated and the audio carrier being frequency modulated, said re` ceiver comprising means for selecting the tele-.

vision band to bring in the two related carriers, means for substantially preventing sound interference with the video signal means for heterodyning the two carriers with each other to produce a'y beat frequency carrier having a frequency ergized by the beat frequency carrier to frequencydetect that carrier and obtain the audio signal therefrom.

' LOUIS W. PARKER.

REFERENCES CITED The following references are of record in the 1 111e of this patent:

UNITED STATES PATENTS Number Name Date 1,495,470 Farrington May 27, 1924 1,681,564 Wright Aus. 21, 1928 1,735,134 Schroter Nov. 12, 1929 Number Name Dato Brand Mar. 24, 1931 Clements May 26, 1931 Adams June 23, 1931 Braden Jan. 16, 1934 Holmes Oct. 6, 1936 Koch May 24, 1938 Kentner July 4, 1939 Tubbs Mar. 11, 1941 Branson Sept. 30, 1941 Mailing Jan. 20, 1942 -Hewe1 June 9, 1942 OTHER REFERENCES 15 Duplex 'Transmission of FM Sound and Facsimile, by Artzt, RCA Rev. 6:88-101, July 1941, Only page 96 cited.

Images