US2199273A - Short wave television transmitter - Google Patents

Description

April 30, 1940.

y K. SCHLESINGER SHORT WAVE TELEVISION TRANSMITTER.

Filed April 20, 1936 2 Sheets-Sheet 1 April 30, 1940- K. SCHLESINGER 2,199.273

SHORT WAVE TELEVISION TRANSMITTER Filed April 20, 1936 2 Sheets-Sheet 2 Jule/2101.

Patented Apr. 30, 1940 r 2,199,273 snon'r WAVE TELEVISION TRANSMITTER Kurt Schlesinger, Berlin, Germany, assignorriby mesne assignments, to Loewe Radio. Inc., a corporation of New York.

Application April 20, 1936, Serial No., 75,403 In Germany April 30, 1935 3 Claims. (o1.ira+v .1

- In the construction of short wave andultrashort wave transmitters, which require to be modulated with very high modulating frequenciesgthere occurs again and again'the problem i of dynamically ear-thing in reliable fashion certain points of. the connection system for the ultra-short carrier'wave, and at the same timeof impressing on the same points the high modulating frequency without the occurrence, by reason of the earthing elements in respect of the ultrashort wave, of an inadmissible load on the modulating circuits, and accordingly adrop in the maximum modulating frequencies. This problem can merely be solvedincompletely with the usual blocking condensers, since in the first place the size of these condensers is limited in an upward direction by the fact that the same shortcircuit the high modulating frequencies more and more and a large modulation output is required for generating the reactan'ce currents by' way of these condensers. On the other hand it is found in the short-wave art that merely a certain critical size of condensers,- whichis dependent on the self-inductions of the circuit to be earthed, really solves the-problem of dynamic 'earthing, whilst both smaller as well as greater capacity values are completely ineffective" dynamically, and by the formation of flywheel circuits may even lead to an oscillation of the particular potential point, i. e., may produce exactly the opposite to thedesired'efiect. 1 Y v The object of the following measures according to the invention is to solve in satisfactory manner the earthing problem. and the combined problem of high-frequency earthing and lowfrequency coupling with the modulator by the use of suitable series-resonance connectionaauxiliary chokes and tuning condensers.

The novel features which I believe to be'characteristic for my invention are set forthwith particularities in the appended claims. My invention, however, both as to itsorganization 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, which show two exemplary embodiments of my invention.

Fig. 1 shows a practical example as applied to simultaneous modulation and earthing. This refers to a three-grid modulation connection making use of a -electrode valve I, which has already been explained in principle in the earlier specification Ser. No. 717,309. In this valve the cathode 2 is linked up with a counterpoise, for

of the anode circuit 1.

example with the metallic mass of the casing 3. The innermost grid 4 is connected through the medium of; a coil 5 with an exciting circuit .6. This circuit oscillates with half the frequency 6 is preferably a quartz oscillator, for example on the 14-metre wave. A detrimental coupling by way of the inner capacities of grid and anode and the assembly capacities is already reduced in the first order by the tuning of Ito the 'T-metre wave. The two remaining grids of the ti-pole tube l, viz., the screening grid 8 and the 'so-called' intercepting grid, or better, reflecting grid 9, belong to two other modulating circuits. The screening grid 8; is connected with the image-current amplifier I 0; whilst the reflecting grid 9 is coupledwith an impulse apparatus H, which for the purpose of synchronisation produces sharp, negatively directed synchronisation impulses at the end'of each line and? image. Thedifliculty in the operation of this connection resides in practice in the fact that even in the case of valves, in which galvanometricdimensions have resulted in faultlessoperation of'the grid control, a dynamicseparation of the anode oscillation cannot be successfully accomplished even with the strongest negative impulses of In or II; To the contrary, even in the case of complete electronic blocking of the modulating valve I, there always remains a considerable proportion of residual high-frequency potential in the .anode circuit 1, which is conveyed byway of the coupling condenser, l2 to the later output amplifying stages of the transmitter. This condition is also not affected by screening partitions l3 which may be introduced between the grid and anode circuits of the modulator l. An inner capacitative coupling of the 5-ele'ctrode valve must accordingly be involved.

As a matter of fact experiments have shown that it is impossible to obtain neutralization with the aid of simple blocking condensers, which are shown in Fig. 1 in theform M or I5 for screening 'gridand' reflecting grid; The short-circuit re- Til lected at less than 50 cm. The self-induction coils l6 and I! are so dimensioned that they acquire series resonance at a medium capacity value of 14 and 15. In this connection, if the coils and condensers are built up without loss, a very low series resistance is produced which, as experiments have shown, solvesthe problem better than wouldbe at all possible with a capacity alone. The capacitative load on the generators H and I is nevertheless smaller than,

when not using the resonance coils l6 and IT, as the capacities l4 and I merely require to "be of approximately 20 cm. in capacity. .There is conveniently provided a graduated scale on the condensers l4 and I5, as a readjustment thereof is.

required when altering the operating wave. In order to avoid a high-frequency reaction of the generators l0 and II on the short-circuits, it is necessary to connect a choke I 8 or [9- in the leads to these generators. In place of the chokes there may also be used a resistance of not more than 500 ohms, so long as there is no inadmissible'weakening of the high modulating frequency by reason of the potential distribution of the resistance then occurring against the capacities l4 and I5.

The feeding of the grids with bias takes place by way of series resistances 20/2 I, likewise behind the chokes l8 and I9. In this connection it may be remarked as follows: In the case of a 5-electrode valve accordingto Fig. 1 the screen ing grid 8 will be entirely without current when the reflecting grid 9 is traversed by a higher positive potential than the screening grid '8. In Fig. 1 this occurs by a tapping of the battery 22. By this measure it is accomplished thatthe control of the screening gridcircuit 8 is successful without taking over current, i. e., without output. Certainly the bias of the intercepting grid 9' renders necessary a powerful negative amplitude of the impulse generator II. To avoid this drawback it is also possible in accordance with the invention to apply the control circuit l9 to a special grid, which is provided between the reflecting grid 9 and the'anode I and in turn possesses the potential of the cathode. The control of this grid then also occurs in wattless fashion. The reflecting grid 8 is then no longer modulated, but serves merely for suctional action on the electronic current, which otherwise would flow to the screening grid 8 and then load the image amplifying circuit Ill/l8.

In Fig. 2 there is shown such an embodiment of the invention, wherein 9'. is the additional fourth grid lying between. the reflecting grid 9 and the anode I. The elements 23 and 24 represent the series connection of this additional grid for earthing the carrier oscillations. The element 25 performs the D.-C. connection to the cathode and earth respectively.

I claim:

1. In an ultra-short wave transmitter for television purposes amodulator comprising a multielectrode modulator valve having at least an earthed cathode, an anode, and three grids, an oscillation generator, a synchronizing impulse generator, and an image contents current generator, an oscillatory circuit in the anode circuit of said valve, each of said generators being connected to one ofsaid grids two series connections comprising each at least one condenser and one inductance so dimensioned as'to be in .series resonance with respect to the frequency of the oscillations of said oscillation generator, the

two grids, which are next ones to the anode, being connected to the synchronising impulse generator circuit and the image contents impulse generator circuit respectively and connected to earth by means of said series connections.

' 2.'In an ultra-short wave transmitter for television purposes a modulator comprising a multieIectrode modulator valve having at least an earthed cathode, an anode, and four grids, an oscillation generator, a synchronising impulse generator, and an image contents current gens erator, an oscillatory circuit in the anode' clrcuit of said valve, each of said generators being connected to one of three of said four grids, two series connections comprising each at least one condenser and one inductance so dimensioned as tobe in series resonance with respect to the frequency of the oscillations of saidoscillation generator, three of said grids which are the next ones to said anode being-connected to earth by means of said series connectionsythe firstand the third of said grids numbered from the anode being connected to the synchronising impulse generator circuit and the image contentsimpulse generator circuit respectively, the second grid numbered from the anode being supplied with a suitable positive bias potential higher than that of said third grid numbered from the anode, the first of said "grids numbered from the anode having the same bias potential as the cathode and the fourth of said grids, numbered from the anode being connected with said oscillation enerator.

3..In a short-wave or ultra-short-wave transmitter preferably for television purposs'a-modulator comprising a multi-electrode modulator tube having an anode, a cathode and several interposed electrodes, a plurality of energizing circuits for supplying said interposed electrodes with short or ultra-short oscillations and modulation currents having frequency values up to very high frequencies to be modulatedon'said short or ultra-short oscillations, said electrodes supplied with modulation currents being connected to earth as regards said short or ultra short 0scillations by means of an inductance and a capacity connected in series as to form a seriesresonant circuit resonating at said short or ultrashort oscillation, and being simultaneously connected to the modulation and bias sources respectively by means of chokes and resistances.

KURT 'SCHLESINGER.

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