US2227038A - Coupling circuit arrangement for television arrangements - Google Patents

Description

1940- K. SCHLESINGER ETAL 2,227,038

COUPLING CIRCUIT ARRANGEMENT FOR TELEVISION ARRANGEMENTS Filed Oct. '7, 1938 3 Sheets-Sheet 1 i i Hum Fig.2

Jn-venfop M Ma, P wwwv Dec. 31 1940. K. SCHLESINGER ETAL 2,227,038

COUPLING CIRCUIT ARRANGEMENT FOR TELEVISION ARRANGEMENTS Filed Oct. 7, 1958 3 Sheets-Sheet 2 Fig.4

' megacycles Dec. 31, 1940. K. SCHLESINGER ETAL 2,227,038

COUPLING CIRCUIT ARRANGEMENT FOR TELEVISION ARRANGEMENTS Filed Oct. -'7, 1958 s Sheets-Sheet s 23 l oscillator vdll e 22 i i w 5 1| 23 systems arranged be'fweefl fhe sf'ages of a .superlre erodyne Fl 5 receiver WWW Wad ma U Patented Dec. 31, 1940 PATENT OFFICE COUPLING CIRCUIT ARRANGEMENT FOR TELEVISION ARRANGEMENTS Kurt Schlesinger andFriedrich Woerner, Berlin, Germany, assignors, by= mesne assignments,.to Loewe Radio, Inc., a corporation of New York Application October 7, 1938, Serial No. 233,817 In Germany December 18, 1937 3 Claims.

The present invention relates to circuits for wide-band amplifiers especially for short, or ultra-short waves and more particularly to the development of the coupling circuits between the 3- single stages of amplifiers of this kind. The systems for amplifiers as set forth hereinafter can be employed for straight reception or also as preliminary amplifiers for heterodyne receivers.

In the present invention systems for amplifier I arrangements with which there can be obtained an optimum amplification with a given width of band, and with which it is possible to embrace an extremely wide tuning range with constant amplification, are set forth.

i In the first place there will again be dealt with in a general way the conditions for obtaining the greatest possible amplification per stage for a given width of band. In this connection it is to be observed fundamentally that the tuning of l the grid and anode circuits requires to be performed solely by a variable self-induction, with the smallest possible earthand tube-capacities.

The frequency curve for the amplification of the different frequencies of the total width of band is unfavourable for the single circuit. If, however, there is employed a coupling arrangement such asdescribed in the present case and comprising two band filter circuits, the frequency curve, which corresponds normally to a so-called bell curve, can be converted into a rectangular curve, whereby there is ensured a constant amplification over the entire range.

As already described in Schlesinger application Serial No. 220,876, filed on July 23, 1938, the tuning of the coupling arrangement between the circuits to be coupled takes place by pairs of coils, into which, for tuning purposes, there is introduced a cylinder consisting of good-conductormaterial (for example a copper tube). In addition to the tuning coils there are also employed in the coupling arrangement special coupling coils for coupling the tube stages.

The circuit system according to the present invention no longer makes use of these additional coupling coils, and the coupling and the tuning take place simultaneously by means of one pair of coils which are located in'each case in one of the two circuits to be coupled, and into which, for tuning purposes, there is introduced a member consisting of a good conductive material.

Further, according to an additional feature of the invention, the two coupling circuits are completely screened off or shielded with respect to one another, and in addition they are also, capacitatively coupled. together in direct fashion more particularly by a small rotating plate condenser. The capacitative coupling takes place by means of the already existing stray capacity.

In Figs. 1 to 6 there are shown embodiments of the circuit system according to the invention.

Fig. 1 shows the fundamental circuit system according to the invention.

Fig. 2 shows a particular embodiment of the coupling arrangement according to the invention, in which the tuning takes place by means of an endless belt, to which there are secured the members for tuning the coils.

Fig. 3 shows a further embodiment of the circuit system according to the invention, and more particularity the development of the requisite screening or shielding measures.

.Fig. 4 shows diagrammatically the embodiment for a group arrangement.

'Fig. 5 is a curve which shows the dependency of the frequency on the depth of introduction of the coil cores for the tuning, and

Fig. 6 shows the circuit system of a heterodyne receiver,.which is employed with particular advantage in conjunction with the coupling arrangement according to the invention.

In Fig. 1 the fundamental embodiment with respect to the circuit system according to the invention is illustrated in the form of an example. The tube stages R1 and R2 are coupled by the two coils l and 2, the tuning of these coupling coils taking place by the members 5 and 6 consisting of a highly conductive material (for example copper tube). These tuning means 5 and 6 are coupled together mechanically and can be pushed into the coils as desired. Each coil in itself forms in the anode circuit of the tube R1 or in the grid circuit of R2 a tuned circuit, which is damped by the parallel resistances 3 and 4. The diameter of the members 5, 6 should be as near as possible to the diameter of the coils l, 2' as already set forth in the prior application. The windings of these coils I and 2 must accordingly be located on a very thin spool, and the plungers 5 and 6 should be insulated, so that their capacity to the winding does not take effect.

The tuning range which is capable of being obtained with an arrangement of this kind is limited towards the short waves by two causes 1. By the not entirely perfect short-circuiting effect of the plungers 5 and 6, 5O

2. By the inherent self-inductance of the circuit which is represented by the leads to the tube. It is advisable, therefore, to arrange these leads to be bifilar, i. e., the leads from the coupling coil to the tube are arranged to lie adjacent one another so that the currents in the adjacent leads flow in opposite directions. With the most favourable guiding of the leads there can then be obtained a tuning range of practically one octave.

The coupling between grid and anode circuits can take place in itself by the stray inductance of coils I and 2. The connection of special self-inductances for coupling purposes in series with these coils I and 2, as shown in the prior application, Ser. No. 220,876 filed July 23, 1938, is not advisable, as these self-inductances reduce the tuning range in the manner as just described in conjunction with the tube lead inductances. The best adjustable coupling possibility is represented by a small condenser 1, which connects the circuits to be coupled, which are completely screened off one from the other by screening casings 8 and 9. The larger this condenser 'I is made, the greater will be the width of band obtained, with reduction in the amplification, in which connection the law V.b=const. is very well fulfilled (V being the power amplification ratio and b the width of band).

A grid circuit and anode circuit coil unit of this kind with intermediately disposed sheet metal screen to is shown in Fig. 2. The tubes are indicated schematically. The leads which are connected via the blocking condensers II] and II to the cathodes of the tubes are as short as'p'ossible. The two coils I and 2 of the anode and grid circuits are electrically separated by the sheet metal screen 8a. The two plungers 5 and 6 are operated simultaneously, in the most simple form by an endless belt I2 on which they are mounted on opposite sides, thus effecting'detuning of the coils in the same sense. The smaller tube capacity, unusually that of the anode, is raised to the value of the greater tube capacity by means of a parallel condenser I3. The coils, and accord- Y ingly also the tuning curves, are equal to one another. The damping resistances 3 and 4, in order to preclude the effect of loops, are disposed directly parallel to the coils.

A plurality of coupling units of this kind can accordingly be operated together in synchronism by the one shaft I4, on condition that the same type of tube is used at all points.

The selection of the tubes is governed to a large extent by the desired tuning range. A decisive factor as regards the type of tube is its inner capacity Ci. An increase of the tuning range does not occur if the tube capacity Ci becomes smaller 'than the stray capacity Ca, as the stray capacity C9. of the coupling circuit then restricts the tuning range itself. No useful purpose is accordingly served in employing the modern acorn tubes, inasmuch as with the frequencies of the meter waves effects arising from the time of passage of the electrons play no important part. On the other hand theuse of a tube with greater slope S is also usually without object, as in the tubes hitherto known the Ci increases in the same proportion as the slope S. In the first place, therefore, there is a loss of tuning range, and greater amplification is not obtained, as greater damping is required. The considerations accordingly lead to the use of tubes, the value for Ci of which is of the order of the stray capacity Ca. Since the latter amounts to approximately 8 mm, normal radio pentodes are arrived at, which with equal grid and anode capacities have a slope of approximately 3 mA. per volt. In tubes of this kind there is obtained with a width of band of two times 2.5 mega-cycles an amplification of approximately 6, per stage, whereas in the case of "acorn tubes, owing to the much smaller slope, only approximately one-third to one-half of this value would be obtained.

In connecting together a plurality of these cascades the screening of capacitative fields plays a more important part than in the normal radio art. In view of the high frequencies to be coupled even the smallest stray capacities cause good conductibility between the tubes. It has been necessary, therefore, to develop a special screening art, which is illustrated in Fig. 3.

According to Fig. 3, I6, II, II, I8 and I8 are special screening means. The coils I, 2 are selected in size to be approximately equal in length to the height of the tubes I5 to be coupled. The coil Z'pertaining to the grid circuit of the next tube must be completely screened, together with the appertaining connection 2', from the anode circuit of the preceding tube comprising the coil I and the anode circuit connection I. This is performed by the fact that an intermediate sheet I6 divides both the tube as well as the band filter at the centre, and at the same time screening covers II, II and I8, I8 are placed over the appertaining tube and band filter parts, which moreover are moved as near to each other as possible in order to reduce the initial inductance. After the grid and anode circuits of the stages to be coupled have been completely balanced in this manner in relation to one another, a very small adjustable coupling capacity I9 (corresponding to the capacity 1 in Fig. 1 and 2) is produced. preferably by the fact that two condenser plates I9a., l9b are arranged over an opening 20 in the intermediate sheet I6. The opening 20 is then more or less closed by an earthed plate, which is arranged to be shiftable over the opening 20 between the electrodes I90. and I9?) and is preferably earthed or conductively connected with the earthed sheet metal screen. By displacement of the plate 2| the desired width of band of the vario-coupler can be adjusted in direct fashion. This remains substantially constant for all waves.

In Fig. 4 thereis shown in plan an arrangement comprising three stages of this kind.

As already disclosed in the prior application, Ser. No. 220,876 filed July 23, 1938, attention must be paid in the arrangements set forth to synchronism between the coupled circuits. A state of synchronism of several cascades of this nature can beobtained comparatively simply so long as similarly constructed coupling arrangements are employed. Difficulties do not occur until it is desired to synchronise a heterodyne oscillator with these stages. The tuning curve of a vario-coupler according to Figs. 1 and 2 is of a peculiar form, as shown by Fig. 5. The frequency dependency on the depth of introduction h of the tuning plungers into the coils exhibits roundedportions at the points of maximum and minimum introduction, whereas in the middle zone it is approximately linear. None of the known types of rotating plate condensers has a frequency curve similar to that disclosed above. A special marginal curve section according to Fig. 5 according ly requires to be ascertained, preferably by measurement, the capacity of the heterodyne being measured which pertains to each depth of introduction h, and the marginal curve of the condenser being determined therefrom by methods known per se. If the requirement for accuracy is not so great, it is also possible to arrive at the desired result by the method illustrated in Fig. 6., There is shown a heterodyne in three-point connection with the tuning condensers 2!, which are coupled together and earthed at the centre. They would result alone in an excessively large tuning range. They are bridged by a parallel condenser 22, so that their minimum capacity approaches an extreme value. This point corresponds to the maximum frequency received and accordingly simulates the upper curvature a in Fig. 5. The lower bend b of the frequency curve of the variocoupler is simulated. by the series condensers 23. In the case of low demands on accuracy this circuit system is suflicient when using circular plates for the condensers 2| to obtain synchronism between. the heterodyne and the high-frequency amplifiers.

We claim:

1. In a coupling circuit arrangement for short or ultra-short waves for television purposes the use of a single pair of coils arranged between the circuits to be coupled namely in the input and output circuit of the two succeeding stages, one coil of said pair being arranged in said input and the other in said output circuit, the inductancevalue of each coil beingvariable by tuning means, said tuning means consisting of metal members which are good conductors and pushed simultaneously into both said coils, said input and output circuits being screened off from one another and connected together by means of a small variable condenser, said metal members being secured to an endless belt on opposite sides for varying at the same time the self-inductance of said coils, said input and output circuit with the associated circuits each one containing one of said coils, being furnished with a screening case for avoiding stray capacities between the circuits to be coupled, said screening case having an opening on. both sides of which the electrodes of said small variable condenser are arranged, the magnitude of said opening being adjustable by a shiftable metal plate.

2. In a coupling circuit arrangement for short or ultra-short waves for television purposes the use ci a single pair of coils arranged between the circuits to be coupled namely in the input and output circuit of the two succeeding stages,

one coil of said pair being arranged in said input 5 and the other in said output circuit, the inductance-value of each coil being variable by tuning means, said tuning means consistingof metal members which are good conductors and pushed simultaneously into both said coils, said 1 input and output circuits being each one supplied with a screening case and connected together by means of a small variable condenser, said screening case having an opening on both sides of which the electrodes of said small variable con- 1 denser are arranged, the magnitude of said opening being adjustable by a shiftable metal plate.

3. An amplifier circuit for high frequency television purposes comprising a pair of amplifying tubes each having an input and an output electrode, a first coil connected to the output electrode of one of the tubes, a second coil connected to the input electrode of the other tube, means including an electrically conducting core associated with each coil foraltering the inductance of the coils, means for simultaneously moving the cores in the coils to simultaneously and substantially similarly alter the inductance and tuning of the coils, an electrical shield member positioned between the coils, said shield member having an opening therein, means for coupling the output electrode of the said one tube to the input electrode, of the said other tube comprising a condenser having a pair of plates, the condenser plates beingpositioned on opposite sides of the shield member and opposite the opening in the member, and means for altering the size of the opening to vary the capacity of the condenser and accordingly the coupling between the amplifying tubes.

KURT SCI-ILESINGER. FRIEDR. WOERNER.

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