US2203521A - Modulated-carrier wave-signaltranslating system - Google Patents

Description

M. CAWEIN June 4, 1940.

MODULATED-CARRIER WAVE-SIGNAL-TRANSLATING SYSTEM Filed Nov. l2, 1938 ATTORNEY Patented 'June 4, 19.40

UNITED STATES,

PATENT OFFICE MODULATEDFCARRIEB WAVE-SIGNAL- TRANSLATING SYSTEM Madison Cawein, t, N. Y., asslznor to Hazeltlne Corporation, a corporation of Dela- Application November 12, 1938, Serial'No. 239,981

4 Claims.

" This invention relates to modulated-carrier tems, itis necessary or desirable to use a carrier Wave. which is modulated by the signal, comp'onents in a particular polarity. Frequently, however, the only available signali comprises a carrier wave modulated by the signal components in a. pomnty opposite to that desired. 1n this case, if the available signal is to be utilized, some means must'be provided whereby a carrier wave modulated in the desired polarity may be" derived therefrom. Entirely 'satisfactory systems 90 for accomplishing this purpose have heretofore not been available.

For example, in television receivers of the cathode-ray tube. type. the reproducing tubes themselves are sometimes arranged to effect the required detection of the signal from the carrier wave avoiding the requirement of a separatedetector. For such receivers, it is essential that the carrier wave applied to the reproducing tube lbe of the positively-modulated type; that is, that 3 the signal components be so impressed upon the carrier wave that increases in carrier amplitude correspond to increases in iight intensity. However, certain television broadcast systems now proposed develop and transmit negatively-modulated carrier waves in which the signal components are so impressed upon the carrier wavethat decreases in its amplitude correspond to increases in light intensity.

- Heretofore, in order to derive a carrier'wave 40 modulated in one polarity from a carrier wave modulated in an opposite polarity, it has been necessary, first, to detect the available carrier wave, thereby to derive its modulation compacnents, and then to modulate an independently developed unmodulated-carrier wave in the desired polarity with the detected signal components. For various reasons, including its requirement of relatively complicated apparatus. this method has not proved entirely satisfactory.

Itis an object, therefore. of the present invention to provide an improved system whereby a carrier wave modulated by signal components in a desired polarity may be derived from another carrier wave modulated by the signal components' .55 inanopposite polarity. l

(Cl. IHS-7.5)

A further object of the invention is to provide an improved television receiver of the cathoderay tube grid-detection type which is adapted to receive and reproduce either a positivelyor negatively-modulated carrier wave.

In accordance with the present invention, there is provided a signal-translating system which comprises means for translating a iirst carrier wave of a predetermined frequency and modulated in one polarity by signal components. 10 Means are further provided for generating` a second unmodulated-carrier wave of said predetermined frequency but substantially 180 degrees out of phase with respect to the rst wave. The system includes means responsive to variations 15 in the amplitude of the first carrier wave and independent of its signal modulationfor controlling the generating means to maintain the ratio of the peak amplitudes of the rst and second waves substantially constant. Means are further pro- 20 vided for combining the first and second waves to derive a third carrier wave of the aforementioned predetermined frequency modulated by the signal components in a polarity opposite to that of the modulation oi the first wave. 25

- Further in accordance with the present invention, a television signal-reproducing system is provided which is adapted for the reception of a television carrier wave negatively-modulated by modulation signalv components. This system vcomprises a cathode-ray signal-reproducing tube of the self-detection type. Means are arranged to derive from a received negatively-modulated carrier wave a carrier'wave of the same frequency.

`but modulated positively by the signal components of the received wave. The positivelymodulated Wave is applied by suitable means to the input circuit of the self-detecting reproducing tube.

vIibr a better understanding of the invention, o together with other and further objects thereof. reference is had to the following description taken in connection with the accompanying drawing andits scope will be pointed out in the appended claims.

In the acompanying drawing, F13. 1 is a circuit diagram. partially schematic. of a complete television signal-receiving system including an arrangement for deriving a positively-modulated carrier wave from a received negatively-modu- 50 lated carrier wave in accordance with the present invention, whileFig. 2 is a group of wave forms illustrating the operation oLthe invention.

Referring now more particularly to Fig. l. the

illustrated comprises a television receiver 6B of the superheterodyne type including an antenna system lli, ll, connected to a radio-frequency amplifier l2 to which are connected in cascade, in the order named, an oscillator-modulator it, an intermediate -ampliiier It, a v further intermediate amplifier l5, which comprises a part of the system of the present invention as is hereinafter described in more detail, and a cathode-ray signal-reproducing tube l.

The cathode-ray tube it comprises the usual envelope il containing, in the order named, a cathode i9 having a heater 20, a signal input electrode orcontrol grid 2i, a screen 22, a first anode 23, a second anode 2d, and the usual fluorescent Yscreen 25 at the end of the tube. Line-frequency and field-frequency scanning coils ita and it?) are disposed about the neck of the tube for defiecting the beam in two directions normal to each other. The output circuit of the amplifier tube ita is connected to the control grid 2l by way of a series condenser 2t and leak resistor 2l, providing a time-constant input circuit whereby grid detection of a modulated carrier applied thereto is effected in the well-known manner. Operating potentials are supplied to the electrodes of the cathode-ray tube from a suitable source, such as battery 2d. A line-frequency generator 29 and a field-frequency generator d@ are coupled to an output circuit of the intermediate-frequency amplifier ifi by way of a synchronizing signal separator 3l, which serves in a conventional manner to. separate the synchronizv ing pulses from the carrier wave, from the other modulation components, and from each other, in the usual manner.

The stages of units just described may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are unnecessary herein. Referring briefly to the operation of the system described above as al Whole, television signals intercepted by the antenna circuit lil, il are selected and amplified in the radio-frequency amplifier l2 and supplied tothe oscillator-modulator i3, wherein they are converted into intermediate-frequency signals, which, in turn, are first selectively amplied in the intermediate-frequency ampliers lil and i@ and then impressed upon input circuit 2d, 2li of the cathode-ray signal-reproducing tube lit. With proper operating potentials supplied from the battery 28 to the electrodes of the tube ift, the electron beam is emitted from the cathode and accelerated and focused into a beam by the electrodes 2& 265 to strike the target 25. The input circuit 2d, 2i cooperates with thecontrol grid l to eect grid detection of the carrier wave so that the cathode raydeveloped by the tube is modulated; that is, its intensity is controlled in accordance with thevideo-frequency signal components.4 If desired, the cathode-ray tube may be arranged for target detection, in which case the time-constant input circuit is omitted and the control grid is simply connected by a coupling condenser to the amplifier i5, the target of the cathode-ray tube itself eecting the signal detection in the well-known manner.

and lb to lproduce electric scanning fields, thereby to deflect the ray in two directions normal to each other so as to trace a rectilinear scanning pattern on the screen of the target to' -reconstruct the transmitted picture.

intermediate-frequency carrier wave developed by the oscillator-modulator i3. The generator 32 is so vcontrolled that this second carrier wave,

while being of the same frequency as the first carrier wave, is 180 degrees out of phase with respect thereto. A synchronizing connection 32a, is provided betweerrsuitable points in the amplifier lf3 and the generator 32 to maintain the operation of the generator 32 at the desired frequency and phase with respect to the first intermediate-frequency carrier wave. The repeater or amplifier tubes ia and 33 may be o identical design, preferably of the pentode type, and together comprise a combining amplifier. The input circuits of tubes ida. and 33 are connected to the amplifier it and generator 32 by 'way of transformers tl and 35, respectively, each tuned to the intermediate frequency. A common load circuit or paralleloutput circuitis provided for these tubes comprising a resistor tit and an inductance 3l, by wayof which operating voltage is supplied to the anodes of the tubes from a suitable source indicated at +B. The suppressor grids of the tubes are connected directly to their cathodes and screen potential is supplied from a suitable source indicated at -l-Sc. l

` For thel purpose of maintaining substantially constant the ratio of the peak amplitudes of the modulatedand unmodulated-carrier waves as applied to the input circuits of the tubes ita and 33, therevis provided'a rectifier @d energized by means of a winding t@ forming a part of the transformer 3d. l parallel-connected resistor it and condenser il and having a suitable time constant is provided for the rectifier, as shown. The positive end oi the load resistor d@ is connected by way o a filter, including a series resistor d2 and a shunt condenser @3, and by way of the secondary winding of the transformer 35, to the control grid or the tube 33. The rectifier @d operates in conven- A load circuit comprising a.

tional manner to peak-rectify the intermediatei frequency carrier wave derived from the received signal, thereby to develop a unidirectional-bias vvoltage proportional tc the peak value and, hence, the average intensity or this carrier wave independent of light modulation components. This bias voltage is applied positively to the control grid of the tube 33 Athereby to control the ampiitude'of the unmodulated-carrier-wave output of this tube directly in accordance with variations in the average amplitude or the rst or received carrier wave soas to maintain the ratio of the peak amplitudes of the two waves substantially constant.

Switches S1 and S2 are preferably included in the lead 32a to the generator 32 and in the connection between the anode ofthe tube 33 id and the load circuit V36, 31, respectively, and are adapted for operation by a unicontrol member U so that this part of the system maybe disconnected when its use is not desired, as when a positively-modulated-carrier wave is being re- 'Ihe general operation of the system of the increasing light lntensity. The signal levels corresponding to black and white are indicated at B and W, respectively. The unmodulated-carrier wave developed by the generator 32 is, of course,v

of substantially uniform amplitude and is not shown. The first carrier wave, modulated as just described, is applied to the input circuit of the tube i5. The unmodulated-carrier wave developed' by the generator 32 with the' same frequency as, but 180 degrees out of phase with respect to, the rst carrier wave is applied to the input circuit of the tube 33, the ratio of the peak amplitudes of two carrier waves being maintained substantially constant, as ydescribed above. The two carrier waves are combined, or algebraically added, in the common output circuit 36, 3l of the tubes i5, 33, and a third carrier wave is thereby first carrier Wave.

When the system is adjusted so that the unmodulated-carrier wave has the same amplitude as the peak amplitude of the main modulatedcarrier wave, there is developed a 100 per cent ter, for the purpose vof having modulation in one polarity from another positively-modulated-carrier wave having a wave form such as illustrated by curve B. That is, .in this wave, increases in carrier amplitude represent increases in light intensity so that it is suitable for direct application to the input circuit of the cathode-ray tube i6, to which itis applied by Way of the condenser 2t, as shown. Being 100 per cent modulated, the amplitude oi the carrier wave is reduced to zero for peak values of the modulation voltages in the black direction. y

In case a wave less than per cent modulated is desired, it may be developed by simply adjusting the generator 32 so that the unmodulatedcarrier has an amplitude greater than the peak amplitude of the main carrier wave. A Wave similar to that represented by curve B but having` less than 100 per cent modulation is indicated by curve C of Fig. 2. The signal components and shade levels are indicated on the curves B and C by the same reference letters as used in connection withv the curve A.

While the present invention has been described in connection with a particular type of television receiver, it will be appreciated that it is of general application and may be utilized in any signaltranslating system, whether receiver or transmitderiving a carrier wave carrier wave having modulation of an opposite polarity. d

While there has been .described what is at present considered to be the preferred embodiment of this 'lnvention, it will be obvious to those skilled in the art that various changesand modifications may be made therein without departing fromthe invention, and it is, therefore, aimed in the appended. claims to cover all such `changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is: f

- 1. A signal-translating system comprising, means for translating a rst carrier wave of a predetermined frequency and modulated in one polarity by signal components, means for generating a second unmodulated-carrier wave of .said predetermined frequency but substantially degrees out of phase with respect to said first wave, means responsive to variations in the amplitude of said first carrier wave and indepndent of. its signal modulation for controlling said generating means to maintain the ratio of the peak amplitudes of said rst and second waves substantially constant, and means for combining said first and second waves to derive a-fthird carrier wave of said predetermined frequency modulated by said signal components in a polarity opposite to that of the modulation of said first wave.

2. A signal-translating system comprising a vacuum-tube repeater having an input circuit,V

means for applying to said input circuit a rst carrier wave of a predetermined frequency modulated by said frequency components in one polarity, a -second vacuum-tube repeater having an input circuit, means for generating a second unmodulated-carrier wave of said predetermined frequency but y180 degrees out of phase with respect to said first wave and having a peak amplitude at least as great as thatof said first wave, means for applying said second wave to said input circuit of said second repeater, means for controlling said generating means to maintain the ratio of the peak amplitudes of said rst and second waves substantially constant, and a common output circuit for said two repeaters for deriving a third carrier wave of said predetermined frequency modulated by said signal components in a polarity opposite to that of the modulation of said first wave.

3. A signal-translating. system comprising a vacuum-tube repeater having an input circuit,` means for applying to said input circuit a first carrier wave of a predetermined frequency modulated by said signal components in one polarity, a second vacuum-tube repeater having'an input circuit, means for generating a second unmodulated-carrler wave of said predetermined frequency but 180 degrees out of phase with respect to said rst wave and having a peak amplitude at least as great as that of said first wave, means for applying said second wave to said input circuit of said second repeater, means for developing a control-bias voltage proportional to variations in the amplitude of said first carrier wave carrier waves of any of a plurality of. predetenmined frequencies and modulated either negatively or positively by signal components, comprising a cathode-ray reproducing tube of the self-detecting type and including a control 'electrode,` means for applying received carrier waves of the .positively-modulated type directly to said control electrode, separate means for developing from received carrier4 waves of the negativelymoduiated type a second television carrier wave of. the same predetermined frequency positively modulated by they signal components and for applying'said developed'carrier wave to said con-i trol electrode, and means for selectively connecting said separate means in circuit in said system only f or the reception of negativelymodulated carrier waves.' v

-, MADISON CAWEIN.

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