Range filters. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Range filters. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Filters and matching devices

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Band filters

SIGNIFICANCE OF THE ELEMENTS

In the table: capacitances - in pF, inductances - in μH, SV - the so-called civilian range of 27 MHz.

Table 1
Range C1-C3 L1-L3 С2 L2
160m 3900 1.9 390 19.2
80m 2000 0.95 200 9.5
40m 1000 0,51 100 5.1
20m 470 0.27 47 2.7
15m 330 0,17 33 1.7
NE 270 0,13 27 1.3
10m 240 0.13 24 1.3

DESIGN OF INDUCTIVE COILS

They are wound on Amidion T-80-6 ring cores with enameled wire with a diameter of at least 1 mm for ranges from 20 to 10 meters and 0,8 mm for the rest. Winding occupies about 3/4 of the surface of the torus. The circuit is adjusted by two extreme turns with the help of a GIR to the middle of the range in which it will work.

The table shows the number of turns.

Table 2
Range 160 80 40 20 15 NE 10
L1-L3 23 16 11 8 7 6 6
L2 70 50 35 25 20 18 18

SELECTION OF CAPACITORS

It is best to use mica capacitors. Their data are given in the table.

CONTROL ADJUSTMENT

You need to turn on the GIR in the generation mode and place it near the frequency meter in order to accurately measure the frequency. The ring core has a closed magnetic field. And for communication with the GIR, an aperiodic communication line with low resistance is used. It is necessary to make a turn on the filter coil and a turn around the GIR coil. The wires of the communication line are bundled together (Fig. 2).

Band filters

The adjustment is carried out by unwinding and rewinding the coil and finally by moving and expanding the coils. At the end of the tuning, the turns on the torus are fixed.

FILTER INSTALLATION

The filter is mounted on a board with foil on one side. The details are located on the "clean" side, where only three contact surfaces and a mass conductor are left (Fig. 3).

Band filters

To eliminate parasitic phenomena, these surfaces should not be under the annular coils. The input and output of the filter (it is reversible) can be easily switched using a relay, which must be of good quality with contacts for a current of 1,5 A (at 100V) and 2 ... 3 A (at 250 V). The board is fixed vertically in the structure.

THREE-BAND BUTTERWORTH FILTER

It has the shape of the letter P and contains parallel oscillatory circuits at the input and output, and between them a series oscillatory circuit. It is known that at their resonant frequency Fo is parallel, the circuit presents more resistance to Fo than to other frequencies. In contrast, the series circuit acts as a short circuit. Thus, L1/C1 and L3/C3 filter out frequencies other than Fo, and L2/C2 presents a large impedance to them.

Author: Pierre Villemagne (F9HJ); Publication: N. Bolshakov, rf.atnn.ru

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