US2137355A - Ultra short wave connection system - Google Patents

Description

Nov. 22, 1938. K. SCHLESINGER ULTRA SHORT WAVE CONNECTION SYSTEM Filed Nov. 20, 1935 Patented Nov. 22, 1938 K l rt schlesinger, Berlin, Germany, assignor to v Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application November .20, 1935, Serial No. 50,137 I 'In Germany November24, 1934 Claims. (01. 250-47) lit is usual the radio art to block the direct potential leads to the tube connections against earth or the cathode by means of blocking conderisers, whereby these condensers together with 5 any resistances or chokes in the lead circuit have the object of filtering the direct potentials in respect-of hum and other ripples. In this connectioni tiis always taken :for granted that the points of the lead thus blocked are earthed also in lo respect of the radio frequencies. This assumption is also correctin radio apparatus of the usual kin'd i-n its application to radio waves of ten meters or more. When employing wavelengths of less than metres, however, new difficulties 1 5 arise owing to the fact that the blocking con densers usual in the art, which are of the order of approximately :1 mt, are in no way capable of effectively short-circuiting the lead for high-frequency currents. Even leads of not more than 5 20. cm. in length eifect interferences in the reception, because the electrodes of the tube connected to the ends of theseshort wires are no longer to be regarded "as being earthed, and that these leads form with the appendant capacities and their own 25. self in'du'ction welldefinite oscillatory circuits which may become resonant in the middle of the reception range. These interferences have been particularly noticeable in the ultra-short wave superhet'erodyne receivers for television reception. 3.0 The present invention relates to the use of means to keep-off high-frequency interferences from the grid circuits of the single valves in ultrashort wave circuit arrangements and in accordance with the invention said means consisting in 35 a condenser and a resistance are arranged in close proximity to the grid to be short-circuited, said condenser connecting the grid in the shortest way to the'cathode of the tube in question and said resistance connecting the grid. in question to the it) hum-preventing device used in said circuit arrangement. i The invention will be clearly understood by way of exemplary embodimentsshown in the accompanying drawingwherein I 45 Fig. 1 shows a special circuit arrangement in accordance with the present invention using a mixing tube with eight electrodes.

wFig. 2showsa special embodiment 'of the condenser and 'the resistance unit.

Fig.1 thereis shown a circuit arrangement using a mixingrstage tube with eight electrodes, in which the receiving circuit I is connected with the inner grid 2 of the mixing system, and should be completely "decoupled from the occurrences in 55; the oscillatory system 4,, 5 bya screening grid 3.

The earthing or blocking of the screening grid 3, i

as usual in the radio art for longer waves, is performed by means of a blocking condenser E. of 1 m'f., which is dimensioned together with asteady ing resistance 8 for filtering against hum in the mains. It has been found in practice that, when using. ultra-short waves, at quite definite frequencies, the apparent inductance 9 of the lead to the screening grid formedtogether with the apparent earth capacity 10 of the screening grid a rejective circuit, and at this .frequency the grids3 is no longer to be considered as being earthed. In consequence at this frequency the oscillation of the mixing grid'll, which is connected with 4 and -has the frequency of the oscillatory circuit I,

passes through'the medium of'the grid 3, which is no longer a screening grid, to the input circuit, and causes there the above cited disturbances.

That which has been stated hereinafter regarding the lead to a screening grid also applies, however, as experiments of the applicant with ultrashort wave 'superhets have shown, quite generally to other earth leads which are required to carry any oscillatory-potential. Forexample, every grid bias" lead situated within the range of a .shortwave oscillator, for example the line 12, is able to form-in conjunction with the inavoidable apparent capacity IS a resonance circuit, even if it is only a fewucentimetres 'in length and is closed off or dehummed at its battery end by a blocking condenser 14, "which from the point of view of the normal long-wave art is generously dimensioned, and a series resistance [5. All of these defective earth connections make themselves apparent in practice by the occurrence of selective defects in reception.

- The-objector the invention consists in the fact that the means for earthing a certain terminal of the ultra-short wave connection system is separated fundamentally from the means for eliminating hum and the filteringof the direct current. For the ultra-high frequency earthing there is employed a special earthing means, the connection of which is described in the following. It should establish a connection of such anature between the points to be precluded from oscillation that its inner resistance remains 'sufliciently small in respect to the operating frequency to render reaction couplings by way of its resistance practically wholly impossible.

It is not required of the earthing means that the same plays any part in the low frequency filtering, for example for eliminating hum. The earthing means is, in accordance with the invention, provided at all points ,whichareintended to be earthed in respect of high frequency, and in which, in the case of very short waves, there is a suspicion of insufllcient earthing owing to excessive impedance of the leads. As experience gained by the applicant has shown, a suspicion of this kind with waves of less than 10 metres in length is well founded when the leads are more than 5 cm. in length, particularly if these leads are disposed over earthed metallic plates, in which case an appreciable self-induction may be assumed, and particularly in the case of two-pole connections with double conductors. r

In Fig. 1 an earthing means l6, I! in accordance with the invention is provided in the screening grid lead 20. The earthing condenser I1 is connected in direct fashion with the tube connection system, by means of such short leads, and is itself -so dimensioned, that the circuit formed by the leads and the by-pass condenser has a higher natural frequency than the ultra-high frequencies occurring. Particularly .when using centimetre waves it may, for example, be necessary to fitthe blocking condenser in the tube itself in order that the lead circuit will have a sufliciently short wave. The sizeof l1 requires to be merely approximately 100 to 500 cm.

There isassociated with the earthing means I! the series resistance l6, which is intended toprevent reaction couplings, which act on the connected lead 9 and are represented symbolically by acounter-inductance l8 or a part-capacity l9, from being able toact 'on the screening grid 3. The series resistance 16 accordingly renders harmless any errors in assembly which have been made in the feed line 9, 8 and which, if l6 were missing, wculdbe able to lead to the stated interferences in operation despite the earthing condenser. I'L' The resistance [6, therefore, requires to be large merely in relation to the alternating resistance of IT. Since it may also be ignored as regards the D. C. circuit its resulting size may be 1000 to 500 ohms. The use of a choke is also possible, but is not equivalent to the aperiodic connection, since the same, as well known, has resonance points. The effectiveness of i6 is rendered'doubtful if the lead 20 has a detrimental impedance between l6 and condenser l1. l6 and H are accordingly disposed in close proximity to each other and to the point to be earthed. The arrangement ofthe earthing means according to the invention for eliminating interference in the circuitof grid 2 is represented in Fig. 1 by the condenser 2| and the series resistance 22.

An arrangementwhich is known per se, but

offers particular advantage in the present connec-' tion, is obtained according to Fig. 2 when the rod resistance 16, which may be formed itself in known fashion by a helical coating, has wound about it the condenser II, the inner armature I'Ia of the condenser being directly connected with the point'to be protected and the outer armature l'lb with the earthing point, for example the cathode of the tube, and the point 30 connected with a resistance of approximately 30-50 ohms, which may already be obtained with technically available resistance wires with a length of line amounting to 5 am, will be sufficient to deprive a circuit of its oscillatory character. It would accordingly be possible, for example, to make the line 9 or l2 of a resistance wire of approximately 250 ohms per metre or more, and then dispense with the resistance IE or 22.

The improved system of earthing as applied here to a mixing hexode may naturally also be employed in conjunction with connection and coupling elements. It is of advantage in those cases in which ultra-short wave potentials seek to penetrate via the feed lines into the coupling element. For example, ultra-high frequency from the anode line may penetrate via a choke coupling 23 to the grid of the next tube 24. When using the earthing element 26, 21 it is then merely necessary to consider the selection of the earthing point 28. It is desirable in every case to connect the earthing condenser 21 by the shortest way with the cathode of the tube to be protected. The connection of the high-frequency earthing means differs also, in this respect from the connection of the steadying condenser. The steadying condensers may be connected to the frame work of the set whilst the high-frequency earthing means requires to be connected in every case to the cathodes of the single amplifying tubes, the coupling circuit or screening grid of which it protects, even if these cathodes belong to other circuits and do not require to be directly connected, eitherstatically or dynamically, with the earth ing mass, for example the chassis of the receiver.

I claim:

1. In an ultra-short wave apparatus comprising a vacuum tube having at least one grid and a cathode and a hum preventing device means to keep-off high-frequency interferences from the grid of said tube, said means consisting in a' condenser and a resistance arranged in close proximity to said grid, said condenser connecting the grid in the shortest way to the cathode of said tube and said resistance connecting said grid to said hum preventing device.

2. In an ultra-short wave apparatus comprising a vacuum tube having at least one grid and a cathode and a hum preventing device, means to keep-off high-frequency interferences from the grid of said tube, said means consisting in a condenser and a resistance arranged in close proximity to said grid, said condenser connecting the grid in the shortest Way to the cathode of said tube and said resistance connecting said grid to said hum preventing device, said condenser circuit between grid and cathode being tuned to a frequency not lower than that of said apparatus.

3. In an ultra-short wave apparatus comprising a vacuum tube having at least one grid and a cathode and a hum preventing device, means to keep-off high-frequency interferences from the grid of said tube, said means consisting in a condenser and a resistance arranged in close proximity to said grid, said condenser connectingthe grid in the shortest way to the cathode of said tube and said resistance connecting said grid to said hum preventing device, said condenser and said resistance being combined in a unit, said condenser being wound upon said resistance, said resistance being in the form of a rod. I

4. In an ultra-short wave apparatus comprising a vacuum tube having at least one grid and a cathode and a hum preventing device'means to keep-off high-frequency interferences from the grid of said tube, said means consisting in a condenser and a resistance arranged in close proximity to said grid, said condenser connecting the grid in the shortest way to the cathode of said tube and said resistance connecting said grid to said hum preventing device, said condenser and said resistance being combined in a unit, said condenser being wound upon said resistance, said resistance being in the form of a rod, said condenser circuit being tuned to a frequency not lower than that of said apparatus.

5. In an ultrashort wave apparatus comprising a vacuum tube having at least one grid and a frequency not lower than that of said apparatus, 10

and arranged inside said tube.

KURT SCHLESINGER,

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