US2206096A - Band-pass filter arrangement - Google Patents

Description

July 2, 1940. E. KLOTZ BAND PASS FILTER ARRANGEMENT Filed Jan. 13, .1937

LOOSE (OZ/PIE [0W DAMP/N6 1005f COUPLE ll/Gl/ DAMP/N6 DAMP/1V6 RES/STANCE lNVENTOR ERNST KLOTZ 62 ATTORNEY Patented July 2, 1940 PATENT OFFlCE BAND-PASS FILTER ARRANGEMENT Ernst Klotz, Berlin, Germany, assignmfnnken Gcscllechaft fiir m. b. H., Berlin, Germany to Tele- Drahtlose Telegraphic Germany, a corporation of Application January 13, 1937, Serial No. 120,342 In Germany January 25, 1936 2 Claims.

Modern receiver sets are provided with an operating knob designed to adjust the receiver set so that it will either operate at will for optimum reproduction (quality) or high selectance. In order that not too much selection may be lost in the attempt to secure high quality reproduction, it is preferable that not only the damping be changed, but at the same time also the coupling. An increase in the damping is advantageous when the coupling is close, because in this manner an undue crevass of the resonance curve is prevented. In the prior art it has been customary to occasion a change in the damping by cutting in or changing a resistance, or else by the shifting of a supplemental damping winding.

In an arrangement designed to change the band width of a band-pass filter according to the invention, a damping winding or turn being fixed for a definte frequency is disposed in such a manner that the coupling relation between the rotatable or pivotal coil and the said winding or turn is rendered closer or stronger when the coupling with the other coil becomes closer.

The present invention will be explained more fully by reference to the accompanying drawing wherein,

Fig. 1 illustrates in schematic form a pair of coils in uncoupled condition;

Fig. 2 illustrates the same arrangement but with the coils in coupled condition;

Fig. 3 is a schematic side view of the arrangement shown in Fig. 2;

Fig. 4 illustrates diagrammatically a unit made up in accordance with the present invention; and,

Fig. 5 illustrates in diagrammatic form a use for the unit shown in Fig. 4.

Referring now to Fig. 1 it will be seen that the two coils both of which are provided with cores are arranged so that their axes are at right angles to one another. A short-circuited turn R in conjunction with a resistor W are shown alongside of the lower coil structure. In Fig. 2 it will be seen that the lower coil has been rotated so that its axis is now parallel with the axis of the upper coil. These coils are now shown in close coupled condition.

In the arrangement illustrated in Fig. 4, the band-pass filter is built into a shielding cylinder. The damping turn or ring R is attached. to the insulation plate Pl by the aid of two rods St, the said insulation plate serving also as a support for the top coil and the rotatable lower coil.

The coils are disposed dissymmetrically inside the cylinder. This scheme has been adopted for be possible to use a a definite object. Before plained in more detail, understoodzi The looser the coupling between the damping turn and the revoluble coil (in Fig. 1), the lower must be the resistance W which is cut in the circuit, if the desired damping is to be secured. Inasmuch as the ratio between the inductance and ohmic resistance of the damping turn becomes then increasingly greater, there occurs more detuning of the rotatable coil. In other words, it is most favorable to make the coupling of the damping turn close and to choose the damping resistance high. However, in practice this is possible only to a certain extent inasmuch as the rotatable coil requires a certain amount of space for which reason the damping turn and the rotatable coil must be mounted a certain distance apart. For this reason, a certain detuning will arise, that is, the inductance declines with closer coupling.

In this connection, there arises another action which has a favorable effect. In the arrangement Fig. 4, without a damping turn, provided the coils are disposed in the middle of the shielding cylinder, the inductance of the rotatable coil decreases as the coupling becomes stronger seeing that the short-circuit currents in the shield are made to flow over a longer path. Now, in order that such an increase in the inductance may be prevented the rotatable coil according to the invention is so mounted that, as the coupling with the other coil is strengthened, also the coupling with the shield becomes stronger, with this consequence that the inductance is stabilized and preserved.

If a damping ring or turn R is provided th is no need for disposing the rotatable coil equally dissymmetrically seeing that, with closer coupling with the damping ring, the inductance will in part be balanced again as a result of the longer path in the shield.

Fig. 5 illustrates a Way in which the unit shown in Fig. 4 may be connected in a band pass filter circuit. The input terminals 4 and 5 of the band pass circuit are connected to a suitable source of signal energy and the output terminals 6 and 1 to a utilizing device. It will be noted that the coils I and 2 are variably coupled and that the short-circuited turn 3 is variably coupled to the coil 2. Variations of one coupling also vary the other as shown by the uni-control 8.

In lieu of a short-circuiting ring it would also circuit presenting the requisite amount of damping and being tuned to the the latter is to be exthe following must be frequency of the oscillation circuits of the bandpass filter. What happens in this case is no detuning, but merely a damping.

The present invention is useful not only in connection with band-pass filters with fixed tuning, but also with band-pass filters designed for adjustable tuning, for instance, input band-pass filters in receiver apparatus. In order that for different frequencies the proper amonut of damping may be secured, the damping ring may ice moved as a function of the tuning. It is also feasible to vary the damping resistance W as a function of the tuning. What may also be mentioned is that the invention is not confined to an arrangement of the coil as shown in the accompanying drawing, in fact, that it is also useful in cases where the axial positions are different.

What I claim is:

1. In radio signalling apparatus, a band pass circuit including a first coil fixedly mounted within a shielding container, a second coil movably mounted within the shielding container between a position where the axes of the coils are parallel and a position where the axes thereof are perpendicular to each other, a closed circuit including resistance and an auxiliary coil fixedly mounted within said container said auxiliary coil being in coupling relationship with said movable coil whereby adjustments of the movable coil simultaneously varies the coupling between it and the first coil and the damping.

2. In radio signalling apparatus, a band. pass circuit including a pair of coils mounted in coupling relationship within a shielding container, damping means mounted adjacent one of said coils and comprising a closed circuit including resistance and a coil, means for adjusting the position of one of said coils with respect to the other and to said closed circuit to thereby simultaneously vary the coupling between the two coils and between the last named one of said coils and the closed circuit whereby the amount of damping of said band pass circuit is varied simultaneously with variations in coupling between said pair of coils.

ERNST KLOTZl

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