Universal matching device. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal matching device. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The device is designed to match the transmitter with various types of antennas, both with a coaxial feeder and with an open input (such as "long beam", etc.). The use of the device allows you to achieve optimal matching of the transmitter on all amateur bands, even when working with an antenna of random length. The built-in SWR meter can be used when tuning and adjusting antenna-feeder systems, as well as an indicator of the power delivered to the antenna.

The matching device operates in the range of 3-30 MHz and is designed for power up to 50 watts. With a corresponding increase in the electrical strength of the parts, the permissible power level can be increased.

Schematic diagram of the matching device is shown in fig. 1. It includes two functional units: the matching device itself (coils L1 and L2, capacitors C6-C9, switches B2 and BXNUMX) and an SWR meter assembled according to the balanced RF bridge circuit.

Universal matching device

The device is mounted on a chassis. All the tuning controls are displayed on the front panel, and the dial indicator of the SWR meter is also installed on it. On the rear wall of the chassis, there are two high-frequency connectors for connecting the output of the transmitter and antennas with a coaxial feeder, as well as a bushing with a clamp for antennas of the "long beam" type, etc. The SWR meter is mounted on a printed circuit board (see Fig. 2) .

Universal matching device

Capacitors C1 and C2 - air or ceramic with an initial capacity of 0,5-1,5 pF. The RF transformer Tr1 is wound on a ferrite ring M30VCh2 with dimensions 12X6X X4,5 mm. The secondary winding contains 41 turns of PELSHO 0,35 wire, the winding is evenly spaced around the ring. The primary winding consists of two turns of PEV-1 0,51 wire. The inductor Dr1 is wound on a ring of ferrite 600NN with dimensions 10X6X X4 mm and contains 150 turns of PELSHO 0,18 wire, evenly spaced around the ring. Coil L1 is wound on an M30VCh2 ring with dimensions of 32X15x8 mm and contains 23 turns of PEV-2 0,81 wire. Taps are made from 1, 2, 4, 6, 8, 10, 12, 14, 16 and 19 turns. The winding is insulated with two layers of PTFE tape. Coil L2 is wound on an M30VCh2 ring 12X X6X4.5 mm and contains 30 turns of PELSHO 0,41 wire. Blocks of variable capacitors - self-made, from air-tuned capacitors of the KPV type. The design of their articulation into blocks can be any, it is only important to ensure the isolation of the rotors and stators from the chassis.

The matching device itself does not require any adjustment. The SWR meter is set up as follows. A wire is soldered from the printed circuit board to the capacitors C6, C7. A resistor with a resistance of 75 ohms and a power of 5-10 W is connected to it (you can use several MLT-2 resistors connected in parallel). The meter input is connected to the transmitter. Switch B1 is set to the "Direct" position. Such an RF voltage (with a frequency of 21 or 28 MHz) is applied so that the indicator needle deviates to the full scale. Then set the switch to the "Reflected" position and adjust the capacitor C2 to achieve zero readings of the indicator. If this fails, select a resistor R2 or a diode D2.

Swap the load and the output of the transmitter and repeat the setting of the capacitor C1, as well as the selection of the resistor R1 and the diode D1.

The ratios of the direct and reflected waves, corresponding to SWR == 1, in a properly tuned meter must be maintained over the entire frequency range.

For a general check of the matching device, the transmitter is connected to the input of the device, and an active load with a resistance of 75-200 Ohms is connected to its output. Capacitors C6 and C7 are set to the maximum capacitance position, the switches are set to the positions shown in the diagram. The transmitter is turned on and resistor R3 achieves the deviation of the indicator arrow on the full scale. Move switch B1 to the "Reflected" position and switch B2 to achieve the minimum reading of the indicator. Then, by adjusting the variable capacitors C6 and C7, zero readings of the indicator are achieved, which corresponds to the SWR value = 1 and indicates full matching of the transmitter output with the equivalent load. On high frequency bands, it may be necessary to connect the L2 coil in parallel with L1.

A similar setup procedure is performed when connecting real types of antennas. The SWR is calculated according to the formula

KCB=(A+B)/(A-B),

where A is the reading on the indicator scale for a direct wave. B-for reflected. The scale can be calibrated directly in SWR units.

The described device is used by the author with an "oblique beam" antenna 80 m long. On all amateur bands, it is possible to obtain complete antenna matching with the transmitter. Television interference is completely absent. This device was tested on the UA4IF radio station when working with a piece of wire of random length (15-17 m). On all amateur bands, an agreement was obtained with an SWR of no worse than 1,2 - 1,5.

Author: Ing. V. Kobzev (UW4HZ); Publication: cxem.net

See other articles Section Civil radio communications.

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