SU1417178A1 - Adjustable band filter - Google Patents

Abstract

FIELD OF THE INVENTION The invention relates to radio engineering and makes it possible to increase the constancy of the coefficients. transmission in the frequency tuning range. The tunable bandpass filter consists of two LC circuits 1, 2 and a coupling element between them, which is made in the form of a capacitor 9. The LC circuits 1, 2 consist of a voltage divider made on two capacitors, one of which is adjustable, and inductors. Voltage dividers in LC-circuits 1, 2 are selected so that, when restructuring, the increase in the coefficients. the transfer of one of them corresponds to the same decrease in the coefficient. transfer of another. Moreover, their multiplication at any point of the tuning range gives a constant number with constant input and output impedances of the load. When changing the input and output impedances of the load in the tuning range, the compensation of the arising non-uniformity of the coefficients. range transmission is accomplished by varying the communication between the LC circuits 1.2. I il. (L

Description

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The invention relates to radio engineering and can be used in radio and television, receiving and transmitting devices.

The purpose of the invention is to increase the constant of the transmission coefficient in the frequency tuning range.

The drawing shows an electrical schematic diagram of a tunable bandpass filter.

The tunable bandpass filter contains the first 1 and second 2 LC circuits. The first LC circuit 1 consists of a (voltage divider made on adjustable capacitor 3 and capacitor 4 and inductance coil 5. Second LC circuit 2 consists of a voltage divider made in adjustable capacitor 6 and capacitor 7j and inductance coil 8. The tunable bandpass filter also contains a communication element made on an additional capacitor 9.

Tunable bandpass filter works as follows.

With an increase in tuning frequency, a decrease in capacitance of adjustable capacitors 3 and 6 causes a decrease in the voltage ratio of the voltage divider of the first LC circuit 1 and an increase in the voltage ratio of the voltage divider of the second LC circuit 2, and as the frequency decreases, the transmission ratio of the voltage divider of the first LC increases circuit 1 and the voltage ratio of the voltage divider of the second LC circuit 2 is reduced. The voltage dividers of the first 1 and second 2 LC circuits are chosen so that the increase in the coefficient before Such one corresponds to the same reduction in the transmission coefficient of the other, that by multiplying one by another, a constant number is obtained at any point of the tuning range with constant input and output impedances of the load.

The capacitor capacitance values are selected in the following ratios: the capacitor 4 capacitance is about 3 times the average capacitance of the regulated capacitor 3, 10 times the capacitance of the capacitor 9, and is approximately equal to the average capacitance of the first LC circuit 1 taking into account the mounting capacity. In this capacity adjustable capacitors 3 and 6 are equal between

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7178 2

the capacitor capacitors 4 and 7 are also equal.

With a significant change in the input and output impedances of the load in the tuning range, compensation for the resulting non-uniformity of the transmission coefficient over the range is performed by changing the ratio 10 of the switching element of the communication element from the first 1 and second 2 LC circuits.

The proposed tunable bandpass filter provides high

15 the constant transmission coefficient in the tuning range, not exceeding 0.4 dB (4.7%) with the maximum allowable variation of the ratings of radio elements, excludes the possibility

20 of the appearance of parasitic resonances, does not contain additional elements that degrade the parameters of the electrical path.

Claims (1)

Formula iso p and e and Tunable bandpass filter containing two LC circuits, while each LC circuit contains parallel-connected inductors and a voltage divider, made in the form of a series-connected adjustable capacitor and a capacitor, between the taps of the voltage dividers of the first and second LC circuits, a communication element is included, the junction point of the first output coil of the inductance and the output of the adjustable the capacitor of the voltage divider of the first LC circuit is the input of a tunable bandpass filter, and the connection point of the second output of the capacitor of the voltage divider of the first LC circuit is connected to the common bus, the connection point of the first output of the voltage divider and the first output of the inductance of the second LC circuit is the output of a tunable bandpass filter, and the connection point of the second terminals of the voltage divider and inductors of the second LC circuit is connected to a common bus, characterized in that, in order to an increase in the constant of the transfer coefficient in the frequency tuning range, the first input of the voltage divider of the second LC circuit is the output of the condensation 3117178 torus, and the second output - the output of the regulator - the communication element is made in the form of a condensable condenser, with a scator.