US2173496A - Television transmitter - Google Patents

Description

Sepi- 1939- K. SCHLESINGER TELEVISION TRANSMITTER Filed March 23, 1936 2 Sheets-Sheet l Far 7i a- Jnren/ar":

Sept. 19, I939.

TELEVI S IO N TRANSMITTER K. SCHLESINGER I 2,173,496

Filed March 23, 1936 I 2 Sheets-Sheet 2- v AM 28 WWW Patented Sept-i 19, 1939 Kurt Schlesinger,

Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application March 23, 1936, Serial No. 70,424

In Germany March 28, 1935 10 Claims.

Upon the modulation'of a radio transmitter with television transmission it is necessary. in addition to the image current modulation, to apply also the synchronisation. In the amplitude method usually employed the synchronisation,

as well known, tinguished by a constant peak level independent of the contents of the image. In practice difflculties arise in maintaining this independence in these, amplitudes. By way of solution there have beenset forth in part heretofore rectifying connections in which the synchronisation signals are only able to modulate the transmitter downwards and the image signals are only able to modulate it upwards, and in part there has been proposed an arrangement similar to the Heising connection, which by means of a special impulse feeler tube enforces brief potential peaks on the modulating line leading from the image amplifier to the transmitter. Whilst the rectifying methods are accompanied by difliculties as regards the linearity of the rectiflers and other disadvantages the last-mentioned Heising system is hindered in practice by mutual reaction of the image and signal currents.

If in the case of a television transmitter the modulation of the radio-frequent carrier wave is performed at one single terminal of the modulating device, for example at the control grid of 80 the modulating tube, it is necessary to mix the potentials of the image contents and the synchronisation impulses before entry into the modulator. In this heterodyning of image and synchronisation signals careful consideration must '86 be paid to the law relating to difference in amplitude. It has been found in practice that in the case of a "single-channel modulation of this kind interferences frequently occur in the synchronisation. Even if the amplitude diagram of 40 the heterodyned image and synchronisation oscillations' reveals the correct relative difference in amplitude, that is to say. if the synchronisation signals are always more powerful than the strongest image signals of the same sign, failures occasionally occur in the synchronisation immediately the medium absolute potential of the diagram fluctuates for any reason in relation to earth. It may, therefore, very easily occur that either the peaks of the synchronisation impulses no longer reach the potential value which is required for the complete range of the aerial current, or it may also occur that the medium potentials sink to such extent that also the strongest image signals are able to suppress the aerial current, whereby in the first case there occurs consists of impulses which are disa breakdown in the synchronisation and in the second case a faulty synchronisation by reason of the contents of the image. Another error which frequently occurs and renders the operation unreliable already resides in the heterodyn- 5 ing of image and synchronisation signals on to the sameline. According-to an earlier application Ser. No; 14,846 there is employed for this purpose a peak-potential device, the object of which is accurately to insure that the highest peak 10 values of the image current are not sufliciently high for synchronisation purposes, so that the difference in amplitude is always maintained in relation to the synchronisation signals. This device, termed level-maintaining means, natural-' 15 ly also possesses a certain inertia, as the same upon its function requires to charge condensers, and it is, therefore, diflicult to avoid that an occasional potential peak of the image amplifier exceeds the maximum permissible value and passes into the synchronisation range. In this manner also there is caused: an error in synchronisation even when due care is taken to maintain the absolute values of the impulse peaks in relation to earth.

It is the fundamental object of the present invention to simplify and to facilitate the operation of a television transmitter of this kind, which performs synchronisation by differences in amplitude. The method according to the invention departs fundamentally from the single-channel method, and-makes use of transmission means having more than one modulation input. There is employed a two-channel method, that is to say, the image and synchronisation potentials are conducted over separate lines to two separate control elements of the modulating device.

The novel features which I believe to be characteristic for my invention are set forth with particularity in the appended claims. My invention, however, both as to its organization and method of operation together with further objects and advantages thereof may be best understood by reference to :the following description taken in connection with the accompanying drawings, in which Figs. 1, 3 and 4 show exemplary embodiments, while Fig. 2 illustrates diagrammatically the method of modulation.

Fig. 5 is a diagrammatic ciple arrangement according to the present invention.

The transmitter accordingly possesses two modulators,. which in accordance with the invention are connected in series. Fig. 1 discloses s5 showing of the min- 50 exactly the properties of these modulators. The first channel is the image potential channel. The same comprises the output line of the image-current amplifier l, which is employed, for examplenot essentially-for scanning the film 2 by means of the photo-cell 3. Its output line 4 enters a level-maintaining means 5. This has the property of ensuring that the maximum peak values in a certain direction of sign, for example the most negative peaks corresponding with bis-ck" in the image, are unable to drop below a certain absolute value in relation to earth. This value, which is represented in broken lines by a battery 6, amounts for example to -5 volts, assuming the radio transmitter is fully controlled down to zero with approximately -l volts. The level-maintaining means may ensure that on the whole negative peaks of more than 5 volts do not occur during the entire transmission. Whereas in the case of the single-channel methods it has been necessary to rely solely on the proper functioning of 5, it is accomplished according to the present invention that in the case grid bias.

of the two-channel method according to the invention an occasional failure on the part of 5 does also not endanger'the transmission. The line 1 conducts the image potentials thus regulated to the first modulator 8 of the transmitter. This is shown in its most simple form as a threepole tube 9 with grid modulation. The grid is adjusted by the negative bias 6, which prevails in the case of black, to the range of the lower bend, but at no time in such negative fashion that the high-frequency anode current flowing by reason of the foreign excitation at the radio' transmitter l0 disappears entirely. It is assumed that the point of disappearance is located at 10 volt 6 is then adjusted, for example, to -5 volts, and fluctuates during the transmission, for example, between 5 and +20. Occasional depreciations below the value 5 occur merely by way of exception, and in accordance with the invention are rendered harmless. For this purpose, according to the invention, the'electronic path between grid and anode is bridged by means of 'a shunt impedance I I-in its most simple form a small condenser. In-the present connection system this condenser must be applied to a potential point which has a phase shift of in relation to the grid bias, which is unimportant, however, for comprehension of the method. In a later form of embodiment (Fig. 3) a phase shift of this kind is, for example, unnecessary. The shunt condenser H, by-passing the tube 9, transmits oscillations of radio frequency to the anode in the same phase in which they would also reach the anode through the medium of the electronic current. If the condenser II were missing, the aerial oscillations would cease entirely at ---10 volts and still more negative biases. By reason of the shunt II a cessation at all of the aerial oscillations is rendered impossible. They are at no time able to drop below a minimum value which is adjustable by means of l l.

In Fig. 2 there is shown anaerial current diagram which would occur in the case of a television transmission if the image channel .I and the modulator 9 were employed alone. The minimum height I! ofthe aerial current amplitudes is set by adjustment of the condenser Ii. If the amplitude filter of the receiver is likewise located with its threshold of .response at l2, the image transmission can fundamentally at no time synchronize the reception. Forthis purpose there is necessary at the transmission end a second synchronization modulator, which in accordance with Fig. 1 is constituted as follows:

A synchronization generator, which is composed, for example, of a perforated disc is and photo-amplifier ll, supplies to the edge of the image through the medium of a condenser impulses of negative sign and constant intensity. During the intervals the synchronization channel I! possesses earth, potential. The line I excites a second modulator I8. This modulator has the property of being able'to perform a complete suppression of the anode current if its control grid is sufilciently negatively biassed. This requirement is merely capable of being performed by the use of a screening grid tube II, the screening grid of which is earthed as faras possible without resistance by earthing condensers, or still better by means of a short circuit "I", which is tuned to resonance with the carrier wave. The synchronization modulator It must accordingly represent a pure electronic coupling and be free from shunts pertaining to connections of any kind (in contradlstinction to the image modulator I). There is shown in the drawing a modulator which is excited by a foreign source and to which the radio excitation is conducted by means of a control transmitter l9, which oscillates in the known manner, for example in crystal-controlled fashion, with constant amplitude and frequency.

The function of the arrangement is now clearly recognizable from Fig. 1. Owing to the shunted image modulator 9 in accordance with the invention the image currents are unable to suppress the aerial current. On the other hand the synchronization signals cover their synchronization modulator l6, which has no shunts, completely down to zero. Since the two modulators l6 and I are so connected with respect to a common aerial that they act onthe same carrier, the aerial oscillation ceases entirely only during the synchronization, but does not cease upon oscillation of the synchronization potential even if, owing to failure on the part of the level-maintenance in the image passage, inadmissibly powerful negative image oscillations sometimes prevail. Owing, therefore, to the use of two separate modulation channels the apparatus provides an automatic differentiation between image-black and ultra-black.

In Fig. 2 there is indicated at 20 a synchronization signal which performs complete suppression of the aerial current because at this point the image modulator 9 has been deprived of the highfrequency excitation by the synchronization modulator. In Fig. 1 there have been shown for the purpose of better comprehension two separate modulating valves. It is possible, however, to utilize the idea according to the invention in more simple form, making use of merely one single penwde. An embodiment of this kind, which has been found to be very good in practice, is illustrated in Figs. 3 and 4.

According to these exemplary embodiments the modulating stage of the transmitter possesses two control electrodes, which are independent of each other but are situated in the common path of discharge, and one each of which is modulated with the image current and with the synchronization current respectively. A mixing of the-two passage-ways accordingly takes place only within the modulating tube. According to the invention, the modulating tube is of such kind that upon blocking the synchronization electrode it is impossible to pass electronic current through the tube even if the image-way should be open. An operation of this kind is readily obtained for monic of the example withinterengaging cylindrical control grids, such as usual in the case of hexodes.

In Fig. 3 there is applied to the first grid.2| of a pentode 22 the foreign excitation by means of the quartz transmitter l9 and at the same time there are applied thenegative synchronization impulses by means of the impulse generator- IS. The screening grid 23 is completely earthed dynamically as far as is technically possible, preferably by means of a series resonance cirthat between the control grid 2| and the electrodes, which follow the screening grid 23, there is merely a pure electronic cou pling. The image modulation is conducted to the reflector grid 24. This grid is closed oil for high frequency in highly'ohmic fashion by means of a choke 25, and is accordingly able to perform the oscillations of the high frequency. By. means of a variable earthing condenser 26 of small capacity, adjustable between and 50 cm, the grid 24 may be more or less short-circuited for high frequency, and by means of a very small neutrode 21, which certainly is frequently rendered unnecessary by reason of the inner capacity between reflector grid and anode, a coupling of both electrodes may be adjusted. Preferably, the anode circuit is tuned to a hargrid circuit 2|, whereby the conditions in respect of the electronic coupling are still more simplified.

The operation of this connection system is briefly as follows: So long as the control. grid 2| is not blocked in extremely negative fashion by the impulse generator I 3 an oscillating space charge cloud passes through the screening grid 22. If the reflector grid 24 were well earthed by the earthing condenser 26, the electrons would be unable to reach the anode if the image current amplifier l were to cause a sufliciently negative oscillation of thereflector grid, with which it is connected. In this case, therefore, an error in synchronization would take place. By reason, however, of the differential condenser 26/21 according to the invention the reflector grid 2| is made to be capable of oscillation, and it participates 1n the pulsations of the electronic cloud. By reason of the part capacity 21 to the anode oscillations are transmitted to the anode by influence independently of the condition of charge of the reflector 24. This small and adjustable residual oscillation protects the system against a synchronization, i. e., against a control of the aerial current down to zero by the image signal I. It'is only when sufliciently powerful negative synchronization signals impinge on the inner grid 2|, which cause the electronic current to disappear, that the electronic cloud in the space between the screening gridand the anode completely ceases, and the aerial current is then actually reduced to zero. This, 1. e., the synchronization, is accordingly merely capable of being performed by the control grid circuit, 1. e., by the impulse generator N, which is the desired condition.

Fig. 4 shows a particular form of embodiment of the idea according to the invention having the special feature that the high-frequency carrier wave is conducted to the modulating tube at a third, separate electrode '(control circuit), and that the anode circuit of the modulating tube is tuned to a higher harmonic of this control frequency. By is accomplished that also in case of the very short waves employed for television purposes an aerial excitation is, in the blocked condition, un-

-by means of a battery -the ordinary pentode.

reason of this detuning it l 3 able to take place through the medium of a residual grid-anode capacity. By reason of the separation of the control circuit traversed by the high' frequency from the modulating circuits there is also avoided a penetration of the control frequency into the modulating circuits and accordingly interfering reactionon the amplifiers.

In Fig. 4, I is the multi-grid modulating tube according to the invention. The control frequency is applied to the innermost grid 2 of the same. This, for example, is one-half. of the operating frequency to be radiated by the aerial. It is supplied through. the medium of a coupling '3 by a preferably quartz-controlledcontrol transmitter l. This transmitter accordingly operates on the l-metre wave if the transmission is to be radiated on a7-metre wave. By means of a bias 5 the control grid 2 is blocked in such fashion that merely the most extreme positive peak values of the control frequency 4 are able to produce an electronic current in I. For the modulation with image currents there is employed for example the next grid 6. This at the sametime is the first suctional or screening grid of the hexode To the same there are conducted at a working resistance 'l by way of the line 8 the image-content potentials which proceed from the photo-amplifier 9. The screening grid 6 is adjustably biased I B. An essential feature as regards this modulating circuit, the image current circuit, is the provision of a level-maintaining means |||4, which ensures that the extreme negative peak values .never drop below a certain minimum value. This extreme lower limit is not suficient to cause the aerial current to disappear entirely. The same is controlled and maintained constant by a special connection of the diode l2.

The synchronisation modulation takes place in accordance. with the invention at a special control grid I5. For this purpose there may conveniently be employed the intercepting grid of The synchronisation modulation consists of short and long impulses,

which are derived from a known impulse generator l6 and areinitiated in the manner known per se by the decomposing means of the transmitter. The impulse signals are of such intensity .that the anode current is completely suppressed by the same or withheld by the intercepting grid l5 respectively. In this way it is accomplished, dependent on the particular potential condition of the screeninggrid circuit, that the aerial current essentially disappears in each case upon the transmission of the synchronisation signals.

The 14-metre oscillation excited by the-control circuit 2/3, after traversing the two separate modulating grids of the pentode The same meets here with an operating circuit l8, l9, which in accordance with the invention is tuned to a higher harmonic 4, for example a 7-metre circuit, and from this point, after a power amplifier 20 has been employed, may be conducted to an aerial 2| and transmitted. 1

Naturally the modulating circuits 6 and I5 require to be blocked against thecontrol frequency. s takes place by means of small condensers 22, 23 of approximately 50 to 100 cm. and shortwave chocks 24, 25, which prevent the ultra-high frequency from penetrating into the modulating circuits 9 or I6.

6 and'l5, reaches the anode I1 I different grids on the same anode current, and 7 also the fact that the synchronisation grid is capable, independently of all other potential conditions, of completely blocking the anode current or of raising the same to a definite peak value.

5 In Fig. 5 the idea accordin to the invention is illustrated once more in pur y diagrammatical form, and it is obvious that this idea may be performed by means of a large number of equivalent connection systems. A modulator Ms is a pure 1 electronic coupling; the high-frequencyv excitation is shown as electromotive force I! and passes its current through the synchronisation modulator Ms and the image modulator Ms. Whilst the modulator Ms may be made completely nonconductive by the synchronisation generator ii,

the image modulator Me is maintained permanently in a weakly conductive condition by the small shunt condenser i I. Even if the image current amplifier I makes it itself non-conducgo tive an exciter current from the E. M. F. I! is still able to reach the aerial transformer 28 so long as Ms performs conduction. In Fig. 5, therefore, the essential matter, viz., the series connection of a fully controllable and a bridged modulator and their connection with two channels, image current and synchronisation current, is shown in its most general form.

It may be specifically remarked that in the above there have been described particular forms 30 of embodiment of the general idea according to the invention, and that the measures set forth may be employed and claimed both in combination as well as singly.

I claim: as 1. In a television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, an output circuit connected to an aerial circuit said synchronizing impulse fredl quency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is 0 dependent on the operation of said first modulator system, the use of special means within said second modulator system for preventing said image-contents signal frequency generating circuit from reducing to zero said carrier said special means comprising an impedance arranged between said image-contents signal'clrcuit and said output circuit. H

2. In a television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, an output circuit connected to an aerial circuit said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of said first modulator system,

is within said second modulator system for prevent:

and to the anode the use of special means amasseing said image-contents signal frequency generating circuit from reducing to zero said carrier, s

first modulator system including a screening grid valve. the control grid of which is connected to said synchronizing impulse frequency generating g circuit and said carrier frequency generator, said second modulator system including a modulator valve having at least cathode, control grid and anode, the control grid of which is connected to said image-contents frequency generator circuit 10 of said screening grid valve said special means comprising an impedance arranged between said image-contents signal circuit and said output circui 3. In a television circuit system for modulat- 1 ing a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency generating circuit connected to said first modua lator system, an image contents signal frequency generating circuit connected to said second modulator system, an output circuit connected to an aerial circuit said synchronizing impulse frequency generating circuit being adapted to re- 55 ducing to zero said carrier, the first' modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of said first modugo lator system the use of'special means within said second modulator system for preventing said image-contents signal frequency generating circuit from reducing to zero said carrier, said first modulator system including a screening grid 3 valve, the control grid of which is connected to said synchronizing impulse frequency generating circuit and said carrier'frequency generator, the screening-grid being short-circuited by means of a resonance circuit tuned to said carrier, said 4 second modulator system including a modulator valve having at least cathode, control grid and anode, the control grid of which is connected to said image-contents frequency generator circuit and to the anode of said screening grid valve said 4, special means comprising an impedance arranged between said image-contents signal circuit and said output circuit.

4. In a television circuit system for modulating a carrier wave with image-contents signals and 5 synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency 5 generating circuit connected to said second modulator system, said synchronizing impulse frequency generating circuit being 'adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of said first modulator system, the use of special means within said second modulator system'for preventing said image-contents signalfrequency generating circuit from reducing to zero said carrier, said first modulator system including ascreening grid valve, the control grid of which is connected to said synchronizing impulse frequency generating circuit and said carrier frequency generator, said second modulator system including a modulator valve having at least cathode, control grid and anode, the control grid of which is connected to said image contents frequency generator circuit second modulator system, a carrier frequency generator, a synchronizing impulse' frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current fiowing through said second modulator system is dependent on the operation of said first modulator system, the use of special means within said second modulator system for preventing said image-contents signal frequency generating circuit from reducing to zero said carrier, said first modulator system including a screening grid valve, the control grid of which is connected to said synchronizing impulse frequency generating circuit and said carrier frequency generator, said second modulator system including a modulator valve having at least cathode, control grid and anode, the control grid of which is connected to said image contents frequency generator circuit and to the anode of said screening grid valve, said special means within said second modulator system consisting of a variable impedance connected between the control grid and the anode of said second modulator valve, and of a peak p tential levelling arrangement within said imagecontents frequency generating circuit.

6. In a television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of said first modulator system, the use of special means within said second modulator system for preventing said imagecontents signal frequency generating circuit from reducing to zero said carrier, said first and second modulator system being combined within a -electrode valve having cathode, anode] and three grids, the first grid numbered from the cathodebeing connected to said synchronizingimpulse frequency generating circuit and said carrier frequency generator, the second grid being the screening grid and connected to ground via a resonance circuit tuned to said carrier, the third grid being connected to said image-contents frequency generating circuit, said special means consisting of a variable impedance connected between said third grid and said anode.

'7. In a television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, a synchronizing impulse frequency bined within a 5-electrode valve generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator. system is dependent on the modulator system, the use of special means within said second modulator system for preventing said image-contents signal frequency generating circuit from reducing to zero said carrier, said first and second vmodulator system being combined within a 5-electrode valve having cathode, anode and three grids, the first grid numbered from the cathode being connected to said synchronizing impulse frequency generating circuit and said carrier frequency generator, the second grid being the screening grid and connected to ground via a resonance circuit tuned to said carried, the third grid being connected to said image-contents frequency generating circuit, and via a variable condenser to ground, said special means consisting of a variable condenser connected between said third grid and said anode.

8. In a television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a a carrier frequency second modulator system, generator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to saidsccond modulator system, said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of saidfirst modulator system, the use of special means within said second modulator system for preventing said image-contents signal frequency generating circuit from reducing to zero said carrier, said first and second modulator system being comhaving cathode, anode and three grids, the first grid numbered from the cathode being connected to said synchronizing impulse frequency generating circuit and said carrier frequency generator, the second grid being the screening grid and connected to ground via a resonance circuit tuned to saidgenerator, a synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signal frequency generating circuit connected to said second modulator system, said synchronizing impulse frequency generating circuit being adapted to reducing to zero said carrier, the first modulator system being so connected with respect to said second modulator system that the carrier current flowing through said second modulator sysoperation of said first,

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6 tem, is dependent on the operation of said first modulator system. said-first and second modu-.- lator system being combined within a 5-electrode valve having cathode, anode and three grids, the first grid numbered from the cathode being connected to said carrier frequency generator, the second grid being connected to 'said image-contents irequenoy generating circuit via a peak potential levelling arrangement. the third grid being connected to said synchronizing impulse generating circuit.

10. A television circuit system for modulating a carrier wave with image-contents signals and synchronizing impulses comprising a first and a second modulator system, a carrier frequency generator, 9. synchronizing impulse frequency generating circuit connected to said first modulator system, an image-contents signals frequency generating circuit connected to said second modulator system, said synchronizing impulse irequency generating circuit being adapted to rcducing to zero said carrier, the first modulator system being so'connected with respect to said second modulator system that the carrier current flowing through said second modulator system is dependent on the operation of said first modulator system, said first and second modulator system being combined withina li-electrode valve having cathode, anode and three grids, the first grid numbered irom the cathode being connected to said carrier frequency generator, the second grid being connected to said image-contents frequency generating circuit via a peak potential levelling arrangement, the third grid being connected to said synchronizing impulse generating circuit, the anode being connected to an output circuit tuned to the double frequency value of said carrier frequency. t

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