DE628944C - Adjustable wave filter with constant absolute bandwidth - Google Patents

Description

GERMAN EMPIRE

ISSUED ON
APRIL 20, 1936

REICH PATENT OFFICE

PATENT LETTERING

JVi 628944 CLASS 21a ⁴ GROUP 29o4

Siemens & Halske Akt.-Ges. in Berlin-Siemensstadt *) Adjustable wave filter with constant absolute bandwidth

Patented in the German Empire on March 19, 1931

For many purposes of AC technology, e.g. B. radio reception, power cleaner, reception in the case of multiple traffic along power lines with portable stations and the like it is desirable to use wave filters (band filters) which can be set in a simple manner are that, similar to a radio receiver, tuning to a desired frequency band is easy,

z. B. by operating a rotary knob, can be done without resulting in the edge frequencies the oblique slope of the resonance curve can be distorted. When receiving the radio the need for such a wave screen grows with the number of transmitters, because the frequency range available for a program increases with Development is becoming more and more restricted. But not just keeping away from foreign transmitters, but also the elimination of atmospheric interference leaves the Reception on a sharply delimited frequency range appear desirable. There are Filters have already been proposed, with the help of which such a reception is possible. These consist of several oscillation circles of equal coordination, loosely with one another are coupled. According to a suggestion, the capacitor settings should of the individual circles are mechanically coupled in such a way that the coordination of these Band filter can be made with a single movement. Filters of this type however, they have the disadvantage that their impedance depends on the vote. Also, only the relative hole width remains constant in the event of detuning, while the absolute one Hole width must be brought to the desired value by changing the coupling. Wave filters with an almost constant bandwidth have also become known; However In these, the wave resistance changes when the permeability range is shifted.

The invention relates to a wave screen with constant absolute bandwidth, in which according to the invention the magnitude of the wave resistance when the permeability range is shifted obtained in the pass band for the entire frequency range that can be swept remain. The wave screen according to the invention is composed of two branches, which on. on one side directly, on the other side via an induction coil. A The pair of clamps (input) of the wave screen is formed by the common point of the branches and the center of the coil, while the second pair of terminals (output) on the coil on both sides of the Middle is tapped. Instead of the induction

*) The patent seeker stated as the inventor:

Dipl.-Ing. Dr. Andreas Laumann in Berlin-Charlottenburg.

tion coil (autotransformer) can also connect a winding of a transformer, the second winding of the transformer serving as the output. Filters of this type were made already proposed, but without mechanical coupling of the tuning elements.

_{As FIG. 1} illustrates, the wave screen is formed from two impedances Z 1 and Z ₂ , each of which consists of at least one series circuit of coil and capacitor. However, Z ₁ or Z ₂ or both can also be constructed from several parallel branches of this type. In each resonance branch, an element (coil or capacitor) is arranged to be adjustable in such a way that the setting of one element of one resonance branch is coupled with the setting of the element of the other branch. Are the branches Z ₁ and Z ₂ by parallel connection of several series circuits of coil and. Capacitor formed, a variable impedance must be provided for each of the parallel resonance branches. .

The coupled setting for the two capacitors from Z ₁ and Z _{2 is} shown in FIG. Since the capacitors of the series circuits have an occupancy at a common potential, they can be brought to a common axis in a simple manner, as illustrated in FIG. 2. The rotating plates of the capacitors are used. . moderately given a shape, as indicated in Fig. 3, such that the capacitance is inversely proportional to the square of the angle of rotation. The frequency of a connected oscillating circuit is proportional to the angle of rotation when such capacitors, which are already known _{per se, are used. If Z 1} and Z ₂ in FIG. as in the following exemplary embodiment

'C ₁ = C ₂ - -'

_{Since the capacitor values C 1} and C ₂ differ only slightly from each other in the case of a "small relative hole width - this is practically the most important part - _{(] / ag 0} ΑΩ C ₂ <g τ), two identical capacitors C _{2 are expediently used} and the deviation of the capacitances due to a small additional capacitor that is firmly coupled to one of the capacitors

reach.

will be shown. In this, for the sake of simplicity, it is assumed that the coils of the two branches Z ₁ and Z _{2 are the} same and the relative hole width is small (& = o, i). With a given average wave resistance (in the permeability range) g ₀ , which must be adapted to the 'impedance of the connected line or the receiver or the antenna, with an absolute hole width ΔQ = Co ₁ - ω ₂ and one

relative hole width & =

ΑΩ Ω

Elements of

the size

L -

C ₁ =

ΔΩ

■ b)

τ _ ² 3ο r - ^ΔΩ - ~ ΔΩ ' ² ~ «« «*

ΔΩ

ζ S ₀ eof ΔΩ

2 S ₀ ω- (ι - δ)

when Co ₁ and ω _{2 are} the resonance circuit frequencies of the branches.

From these equations it can be seen that when using constant inductances im If the absolute bandwidth 8g of the filter remains the same, also the magnitude of the wave resistance So the sieve chain is retained in the permeability area.

The condition of constant absolute hole width coincides with the requirement that the distance between the resonance frequencies of the two oscillation circles always remain constant target.

AQ / __ J- J-_

ve; .Yc ₁

ΔΩ

ΔΩ = ω. ₂ - Co ₁ =

Vc ₂ Vc ₁

If the capacitance of the second circuit is designed as a rotary capacitor of any plate shape (C ₂ = / (α), <x = angle of rotation), the above condition gives the plate shape of the first capacitor: * os

■ C ₂ +

> ΔΩ

■ he.

The condition no constant hole width can be fulfilled even more easily if one specially used capacitors whose capacitance is equal to the reciprocal square of the angle of rotation increases:

k Ti ¹¹ S

^{C. c}

In this case one obtains according to the above ΔΩ = ^I '

So you can do the same in both branches

Claims (9)

Use capacitors of the prescribed plate shape which, twisted by a constant small angle, are tightly coupled (cf. Fig. 3). In this embodiment, moreover, the absolute hole width of the filter can be varied in a simple manner for the entire frequency range that can be covered by changing the adjustment angle of the coupling; In the process, however, the wave resistance of the sieve chain also inevitably changes for the entire frequency range. If several resonance branches are connected in parallel in the impedances Z1 and Z2, the capacitors contained in the resonance branches must be subjected to the same conditions. In this case, as indicated in FIG. 4 for one branch Z1, a small additional capacitor, which is best designed as an adjustable additional occupancy, can ensure that the F1UtCr maintains the hole width and the characteristic impedance in a large approximation, but the steepness of the increase in attenuation at the hole boundaries can be adjusted in order to make favorable conditions for the elimination of external disturbances still selectable at will. The small additional capacitance Cx shown in FIG. 4 results in the possibility of shifting two resonance frequencies of the wave screen, which are within the permeability range, more or less close to the hole boundaries. It has already been proposed to influence the steepness of the increase in attenuation in this way in filters constructed in this way. Branch s2 must then be taken with the same structure and the additional capacitor must be mechanically coupled to the additional capacitor of branch 2x in such a way that the internal resonance frequencies can be shifted symmetrically from the center of the hole towards the edge frequencies. The number of resonance branches need not be the same in Z1 and Z2. Furthermore, a further series branch within ^ 1 or S2 can serve to keep the wave resistance not only constant when the permeability range of constant magnitude is shifted, but also leveled in the respective permeability range. The capacitors for the branches added for this purpose must then also be subjected to the mechanical coupling conditions of the other capacitors. The coordination of the resonance branches added to level the wave resistance must match the cut-off frequencies of the permeability range, i.e. H. with the coordination of these determining resonance branches. The same. However, correct resonance branches are in different branches Z1 and Z2. Instead of giving the capacitors a suitable plate shape and coupling them through a common axis, the same capacitors with any plate shape can also be used in the corresponding branches in pairs, although care must be taken to ensure that there is a mechanical transmission when the individual capacitors are rotated realizes the previously stated laws of capacity change. The connection of the branches zt or Z2 (see FIG. 1) or the output does not have to be made at the ends of the transformer, and the individual resonance branches within Si or 22 do not need to be tapped from the same point of the transformer. By choosing the tapping points, a means for varying the wave resistance is still available. The reciprocal resistance networks of the sieve chains described also allow the construction of adjustable sieve chains with constant absolute bandwidth and constant wave resistance. With these forms, however, it is advisable to choose fixed capacitances and variable inductances (variometer). go patent claims: 1. Adjustable wave filter with constant, absolute bandwidth, characterized in, that for the adjustment of the filter held variable elements in such a way are selected and connected that the size of the wave impedance im Passband for the entire frequency range covered by the adjustment preserved. 2. wave filter according to claim 1, characterized characterized in that it is composed of two branches which are electrically connected on one side,. on the other Side are connected to the winding of a transformer, the output of which is a pair of terminals of the filter, while the other pair of terminals through the center tap of the transformer winding and the common point of the two branches is given, and that the two branches are separated by at least one each Series connection of a capacitor and a coil formed and similar elements, preferably the capacitors are mechanically coupled in their setting. 3. wave filter according to claim 2, characterized characterized in that when using the same adjustable variable capacitors in the appropriate branches the desired Vote by a small NEN, with one of the capacitors firmly coupled additional capacitor of the corresponding PJattenform will receive. 4. wave screen according to claim 2, characterized by the use of Capacitors whose capacitance values are opposite, increase proportionally to the square of the angle of rotation. 5. wave screen according to claim 4, characterized in that one occupancy each of the capacitors mounted on a common axis, the assignments of different capacitors against each other, however are shifted against each other by a constant angle of rotation, which at the common setting of the capacitors remains constant. 6. Wave screen according to claim 2, characterized in that the branches of the wave screen (Z ₁ and Z ₂ ) consist of a parallel connection of several resonance branches, the capacitors of which are mechanically coupled to one another in de'r adjustment. 7. wave screen, characterized by a ^{reciprocal resistance formation to a wave screen according to claim 2, preferably in front of J} with adjustable inductances. 8. wave filter according to claim 1, characterized in that the elements (Coils or capacitors) of the wave filter arranged in two branches or circles are connected to each other so that the input voltages or currents of the wave filter in two in the different branches or circles effective partial voltages or partial currents are broken down are, the difference of which forms the output voltage or the output current of the wave filter, and that the electrical Values of the two branches or circles of the wave filter in constant relationship are made mutable to each other. 9. wave filter according to claim 2, characterized in that the two different Branches or circles from one or more oscillation circles stand whose similar elements are mechanically coupled in their setting are. 1 sheet of drawings