US2227001A - Regulation of television receivers - Google Patents

Description

Dec. 31, 1940. SCHLESINGER 2,227,001 7 REGULATION 0F TELEVISION RECEIVERS Filed DEC. 9, 1935 Jarew/ar? Patented Dec. 31, 1940 UNITED STATES ArENr OFFICE REGULATION or'rsmvrsron RECEIVERS Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments; to Loewe Radio, Inc., a corporation of New York Application December 9, 1935, Serial No. 53,534 In Germany December 10; 1934 Claims. (c1. 178---7.5)

I The reception of television transmissions provides a special problem in the question of regulation .of the sensitivity of reception, which'problem differs from those usual in the radio art and accordingly calls for novel methods of solution.

W -In a high-class television receiving system the light intensity of the television tube should be in direct proportion to the strength of'the field at the place of reception, independently of the frequency with whichthis strength of field is modulated. -If, therefore, the transmitter provides a constant strength of field, and if, as is necessary in the case of present-day receiving apparatuatheD. C. component is transmitted to the television tube, the lightv intensity of the image would fluctuate up and down upon varying the receiving amplification by means of a control knob, because the high frequency reaching the rectifier would be large or small dependent on the amplification, and it is a condition that the light intensity of the television tube be proportional to the excitation.

other hand the light intensity value in the case of unmodulated carrier Wave should correspond with the black value of the images, a dependency-of this kind is not permissible. The mean value of the lightintensity would be displaced more and more towardswhite if the amplification factor were increased, say, for the purpose of obtaining greater image potentials. A second control knob would then-be necessary for adjusting the mean light-intensity of the television tube, which kn ob would. require to be actuated in reverse direction dependent on the adjustment of the receiving amplifier. A complicated and positive adjustment of this kind in reception is not to be expected of the unskilled user. The problem accordingly arises of regulating the amplification factor of the receiving amplifier automatically, and raising the same to that level, or maintaining it constant at that level, at which the image contents potential picked up upon full modulation of the transmitter fully ,modulates correctly the television ltube. In similar cases in the radio art there is employed a special rectifier which rectifies the carrier Wavaand therectified potential of which receiver.

Since on the the output transformer 4.

biasses the emplifier. This method is fundamentally incapable of use for television purposes. If for example there is considered a television transmitter, which radiates powerfully upon white and weakly upon black, and if "there is imagined a scene taking place continuously in black, i. e., with poor lighting,'a regulating rectifier coupled with the carrier wave amplification would supply to the amplifier during the scene too small acontrolling potential and would accordingly cause the amplifier to perform a higher amplification. In view of the previous remarks this would result in turn in the fact that the medium light intensity of the image would be increased, and the correct mean value, Vin, black, would be displaced towards white. versa, very white images, for example upon the transmission of snow scenes, regulated according rive the amplifier regulating potential not from the carrier frequency, but from the synchronisation signals occurring'after the rectifier of the The second idea in the invention consists in not rectifying these synchronisation signals by the'amplitude filter which is present in any case, but to employ this amplitude filter solely for the synchronisation and to use a special regulating'rectifier, which converts the synchronisation peaks" into direct potential independently of the amplitude filter. The third idea in the invention consists in not transmitting the synchronisation peaks to this regulating rectifier "dir'ectly,;as would be necessary and convenient in the case'of the amplitude filter, but capacitatively or inductively, as in this way it is accomplished that the excitation of the regulating rectifier rises and falls together with the strength of signal frequency. t

The conditions will be explained in conjunction with the single figure of the drawing. An aerial l is coupled with the carrier wave amplifier 2, which is also coupled with the local oscillator 3, so that an amplified carrier frequency occurs at This frequency is rectified in the grid current rectifier arrangement 5 for ultra-short waves described in previous specificationsand converted without any traces of carrier frequency into a video frequency,

Vice I which occurs at the resistance 6 and is passed direct to the television tube 8 by way of a lead 1. The only factor which in the case of each transmission remains constant independently of the contents of the image is the fact that the carrier wave is caused to disappear during the synchronisation impulses. The absolute height of this impulse represents, therefore, independently of the contents of'the image, an exact measure as regards the strength of the receiving field with a given amplification factor in 2. As well known, the transmitter is adjusted to a certain average aerial feed current,for example to 30% of its maximum aerial current. The amplitude filter 9 is connected directly by its cathode with the lead I through the medium of the line 10. In this way, as explained earlier, it is accomplished that at the transformer ll there is obtained a positive impulse potential, which may be conducted to the relaxation apparatus of the receiver, andthe" amount of which may be regulated once and for all by the counter-potential I2. When the amplification of the receiving amplifier 2 is increased, or the strength of field becomes greater,

the impulse potential allowed to pass through the filtertube 9 in no way varies, because the potential I2 is so adjusted that a current is able to,.traverse 9 only when the carrier wave ceases.

As the strength of signal increases the cathode potential l9 recedes more and more from the break-down potential of the tube 9, and all signalling amplitudes increasing in this direction serve to block the tube better. In consequence the filter tube 9 serves onlythe highest peaks .fromthe impulses, and is not affected in its outi for the regulating function a new and second rectifier l3.

This in accordance with the invention is coupled with the output lead I, i. e., with the rectified received potential, only by way of alternating current circuit, and not directly, for example by means of a condenser I4. As regulating rectifier l3 there is shown in the drawing a crystal detector, the direction of the arrow indicating its transmission. The use of simple rectifiers .of this nature, which are desirable for economic reasons and in viewof the simple function of I3, is only rendered possible if, by means of a series resistance It of approximately ten times the size of 6, the capacitative shunts represented by the capacities of the rectifier [3 are prevented from affecting the image lead I. By

means of a resistance l6, which in turn requires to be large in relation to IE, a manually adjustable bias I! is supplied to the cathode of I3. There is thus'produced a delayed initiation of the regulation, and in this way-the maximum amplification which may be maintained automatically by the receiver is determined once and for all. The bias H is preferably adjusted once at-the back of the apparatus and then not fur- .theral-tered; The condenser I8 is so selected as regards its capacity that it is capable of followi potential variations at the desired rate of several images.- The regulating potential resuiting at the same is then supplied to the amplifying valves of the intermediate-frequency amplifier 2. In practice the orders of magnitude in the case of ISO-line images are as follows:

Audion resistance 6:5000 ohms. Protective resistance [5:50000 ohms. Leakage resistance it=0.5 megohm. Leakage resistance l9=0.5 megohm. Blocking condenser l8=approx. 0.5 mi.

The leakage resistance l'9has the object of providing for a sinking of the bias with which thecondenser I8 is charged when the reception decreases. The time constant of the circuit [8/19 is selected in the manner known per se dependent on the requirements placed on the rate of regulation.

As regards the practical embodiment, it may be remarked that the contact rectifier l3 may also 'be replaced by other valves. The use of contact rectifiers merely offers economical advantages and no disadvantages of any kind. In the case of hot-cathode rectifiers of small dimensions It may possibly be omitted. The amplitude filter 9 is. united in practice with the detector valve 5 in one glass bulb, as described in the application Ser. No. 45,729/ 35.

I claim: 1. A television system for receiving a carrier ,w-ave modulated with picture signals and synchronizing impulses, comprising a receiver having an input, a plurality of amplifying tubes and an output, a demodulating device for producing detected picture signals and synchronizing impulses, an amplitude filtering device for separating the synchronizing impulses from the picture signals, a rectifier including a cathode and an anode, means including a condenser for applying the detected picture signals and synchronizing impulses between thecathode of said rectifier and a point of fixed potential, a source of potential and an impedance for normally maintaining therectifier and the point of fixed potential, and

means for altering the eifectiveness of at leastv one of theamplifying tubes in accordance with the potential present at the anode of the recti- 2. A television system for receiving a carrier wave modulatedwith ;.picture signals and synchronizing impulses and wherein the synchronizing impulses have a greater amplitude than the picture signals, comprising a receiver having an input, a plurality of amplifying tubes each havinga control electrode, and an output, a demodulating device for producing detected picture signals and synchronizing impulses, an asymmetric unit including a cathode and an anode, means including a condenser for applying the detected picture signals and synchronizing impulses'between-the cathode of said asymmetric unit and a point of fixed'potential, a source of potential and a high. resistance for normally maintaining the cathode at a predetermined substantially constantpotential relative to the point of fixed potential, a time constant circuit including a parallel connected resistance and condenser connected between the anode of the asymmetric unit and the point of fixed potential, and means for connecting the control electrode of at least one of the amplifying tubes to the anode of the asymmertic unit to alter the effectiveness of the amplifying tube in accordance with changes in the potential at the anode of the asymmetric unit.

3. A television system for receiving a carrier wave amplitude modulated with picture signals and synchronizing impulses and wherein the synchronizing impulses have a greater amplitude in a predetermined direction than the picture signals, comprising a receiver having a plurality of amplifying tubes each including a control electrode, a demodulating device for producing detected picture signals and synchronizing impulses, an amplitude filtering device for separating the synchronizing impulses from the picture signals, a diode rectifier including a cathode and an anode, means including a condenser and a series resistance for applying the detected picture signals and synchronizing impulses between the cathode of said diode and a point of fixed potential, a source of potential and a resistance for normally maintaining the cathode at a potential difference relative to the point of fixed potential, a time constant circuit including a parallel connected resistance and condenser connected between the anode of the diode and the point of fixed potential, and means for connecting the control electrode of at least one of the amplifying tubes to the anode of the diode to alter the effectiveness of the amplifying tube in accordance with changes in the charge on the condenser of the time constant circuit associated with the anode of the diode.

4. In a television system in which the, synchronizing impulses have a higher amplitude than the video signals means for fading regulation of a television receiver by varying the bias of at least one of its high frequency amplifiers, said means consisting of a biased rectifier coupled inductively to the control electrode of the cathode ray tube of said receiver so as to charge a storage condenser being provided with a leakage resistance and being connected to a grid of said amplifier, said inductive coupling being tuned to the synchronizing frequencies.

5. In a television system in which the synchronizing impulses have a higher amplitude than the video signals means for fading regulation of a television receiver by varying the bias of at least one of its high frequency amplifiers, said 20 means consisting of a biased rectifier coupled to the control electrode of the cathode ray tube of said receiver so as to charge a storage condenser being provided with a leakage resistance and being connected to a grid of said amplifier, 25

said rectifier consisting of a crystal detector of very low capacity.

KURT SCHLESINGER.

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