Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Going to the country or on a camping trip, radio amateurs often take a transceiver with them - usually a QRP. In this case, naturally, the question of the antenna device arises. It must be sufficiently effective and at the same time easy to deploy and adjust in the field or close to them. The author of this article proposes his own solution to this problem.

In most cases, they operate at low power on the 14-28 MHz bands. It is on these ranges that work is interesting now - in the year of maximum solar activity. The multi-band antenna shown in fig. 1 has a maximum length of 11,4 m, which corresponds (taking into account a velocity factor of 0,95) to a wavelength X for the 24 MHz band. It is made of copper stranded wire with a diameter of 1,5 ... 2 mm. At certain points corresponding to the length l for the 27 MHz, 28 MHz and λ / 2 bands for the 14 MHz, 18 MHz, 21 MHz bands, mounting petals are soldered to the antenna sheet.

When changing the range, the antenna is connected to the matching device with the corresponding lobe. The resulting excess wire is attached with a clothespin to the antenna web, as shown in Fig. 2.

The matching device (Fig. 3) also operates in the frequency band 14...30 MHz.

It is assembled in a case measuring 80x60x60 mm. made of foil fiberglass (Fig. 4).

The connecting contact X1, fixed on the housing, is an M4 screw 30 mm long. An antenna sheet is attached to it by means of a petal and a nut. The foil on the housing around contact X1 is removed within a radius of 15 mm.

The pin at the bottom of the case serves to provide grounding and to mount the matching device on the ground. It is made of a stainless steel bar with a diameter of 5 mm and a length of 200 mm. Coil L1 frameless. It contains 11 turns of bare copper wire with a diameter of 2 mm (preferably silver plated). Winding length - 60 mm. diameter - 22 mm. The tap is made from the third turn, counting from the "cold" end of the coil. In this case, a good agreement is obtained as with a 50-ohm one. and 75 ohm coaxial cable. Coil 1-2 - one turn of wire PEV-2 1 mm LED HL1 serves as an indicator of tuning the circuit of the matching device to resonance. Its maximum glow corresponds to the maximum power output to the antenna. The brightness of the LED is determined by the value of the resistor R1 and the distance of the coupling coil L2 relative to the coil L1.

A transceiver is connected to connector XW2 (Fig. 5).

If the soil is sandy and the place of work is located far from water bodies, then it is advisable to connect several counterweights to the body of the matching device. In this situation, there is another solution (however, it somewhat reduces the radiated power). A piece of coaxial cable is connected to connector XW1, loaded with a resistor, the resistance of which is equal to its characteristic impedance. It will play the role of radio engineering "earth". The same should be done during the initial setup of the antenna in order to avoid the appearance of high RF voltages on the body of the radio station, which can damage it.

Turning on the transceiver for transmission on the range corresponding to the connected antenna, the capacitor C1 tunes the antenna system to resonance to the maximum glow of the LED.

When making the antenna web and matching device coils exactly as described, no additional tuning of the antenna length is required. The upper edge of the antenna must be raised to a height of at least 4 m, which is quite realistic both in the summer cottage and on a hike.

Author: I. Grigorov (RK3ZK)

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