Automatic switching and matching device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / HF antennas

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The remote matching device proposed by the author of this article allows you to place the antenna in the form of a long wire (beam) in a space free from surrounding objects. It is quite universal and can be applied, with some modifications, to various types of antennas.

The shortwave dream is to have a separate antenna for each amateur band. But it is not always feasible, especially in a big city. More often you have to choose one of the compromise options for multi-band wire antennas. At the same time, an antenna with a length of about 41 m, fed from one end, is suitable for working on the air. It is possible to match such an antenna with a low transmitter output impedance using simple matching devices, but they have one drawback. Agree that the matching device located on the loggia (balcony) and even on the windowsill is not very convenient to manage if the radio amateur's workplace is not located next to the window into which the antenna power wire is connected.

Suggested in Fig. 1 scheme of the automatic switching-matching device (AKSU) allows you to place the antenna in free space, getting rid of the listed disadvantages. The antenna is powered and the AKSU is controlled via a coaxial cable (50 Ohm). The device consists of control units (BU) and switching units (BC). The CU is located next to the transceiver. It contains a switching relay K1 and a reset button SB1. BC is located directly near the antenna. It contains matching circuits for each amateur band and a circuit to automatically select the required matching circuit.

The switching device works as follows. When the +12 V supply voltage is applied to the CU, it is fed to the CU through the L1C3 filter, normally closed contacts of the K1 relay (CU), a coaxial cable and the L2C2 filter. Since in the initial state the normally closed contacts K3.2 of all relays K3 of the selection cells A1 - A10 are connected in series, relay K2 is activated. With its contacts, it connects the equivalent load R1 to the cable. This is necessary so that the output stage of the transceiver for the period of determining the desired range of the AKSU is switched on to the matched load. In parallel with the equivalent, signal selection cells A1 - A10 are included, which are the simplest detector receivers that control transistor switches VT1 and VT1'

When the transceiver is turned on, the transmission is triggered by one of the cells, the tuning frequency of which matches the selected transceiver range, for example, A1. Relay K3 through contacts K3.1 is self-blocking, remaining in the on state even after the transmitter signal is removed. At the same time, contacts K3.2 open, making it impossible to turn on another cell and turning off the equivalent load. The third group of contacts K3.3 includes an appropriate matching device (Fig. 2), for example SU1, in the antenna circuit. The scheme in fig. 2,a was used in the ranges of 160, 80 and 30 meters, in fig. 2b - in the ranges of 40, 20, 17 m; in fig. 2, c - in the ranges of 15, 12, 11 and 10 m. The design data of the matching circuits for each range are given in Table. 1.

When changing the range of the transceiver, AKSU should be returned to its original state by pressing the SB1 button on the control unit. In this case, the supply voltage is removed from the BC unit for a short time. To improve the reliability of the entire system, the matching device should be turned on at a reduced power of the transceiver - 5 ... 10 W.

Table 1

Note. All coils are wound with PEV-2 wire 2,0 mm.

In table. 2 shows the data of the contours L3C4 - L3C4 of the selection cells A1 - A10. When making coils exactly as described, the contours will be tuned to the appropriate range. However, the closely spaced 12, 11 and 10m bands will require more careful tuning. It is produced by trimmer capacitors with a capacity of up to 30 pF, included in the total capacitance C4. Capacitor C3 must not exceed 5,1 pF. If the selection cell does not work with such a capacitance, then the L3C4 circuit is tuned more accurately or the resistance of the base resistor R2 is reduced (but not less than 100 ohms).

Table 2

The adjustment of matching circuits (Fig. 2) should also be carried out at a reduced power of the transceiver (5...10 W). In this case, it is very convenient to use the field strength indicator. By selecting the capacitances of the P-circuits, stretching or compressing the turns of the coils, the maximum readings of the device should be achieved. Only after that it is possible to apply full power to the matching device and measure the SWR of the system. If the SWR on any of the ranges exceeds 2, an additional adjustment of the matching circuits should be made using an SWR meter or a measuring bridge.

In BU and BC, relays K1, K2, K3 - K3' of the RES-22 type (passport RF4.500.131) are used. To switch the matching circuits, relays of the RSM-1 type (passport 10.171.81.50) connected in series are used. The load R1 is made up of ten MLT-2 620 Ohm resistors connected in parallel. Coils L1 in BU and L2 in BC are standard chokes rated for a current of 1 A. They can also be made independently by winding 60 turns of PEV-2 wire 0,8 mm turn to turn on a round ferrite rod with a diameter of 8 and a length of 80 mm from the antenna transistor receiver.

The switching unit is made on two boards made of foil fiberglass. Installation was carried out at the place of installation of parts, on patches. On one board, the matching devices are assembled together with their switching relays, on the other, the range selection cells are assembled. After the final adjustment, the block is hermetically sealed.

AKSU was operated with a transceiver with an output power of 100 watts. With the use of high current relays and the appropriate installation of the device, the power supplied to it can be increased.

The principle laid down in the AKSU can be used with other types of antennas, using only the appropriate matching circuits.

It is advisable to use a counterweight 41 m long or ground the body of the matching device to radio ground at the antenna installation site.

Author: Igor Grigoriev (RK3ZK)

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