Contours for KB antenna. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Antennas. Measurements, setup and matching

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Among Soviet and foreign shortwaves, the W3DZZ dipole antenna is quite widespread, which works well for reception and transmission, is quite simple to manufacture and is in good agreement with the widespread 75-ohm cables RK-1 and RK-3.

On the bands (14,21 and 28 MHz}, the antenna has a complex radiation pattern, which allows you to work in any direction with almost the same success.

A diagram of such an antenna with an indication of the dimensions is shown in fig. one.

Fig. 1

Many shortwavers are frightened off by the apparent complexity of manufacturing circuits built into the antenna sheet, which are subject to rather high requirements for moisture resistance, mechanical and electrical strength.

The present article is devoted to the production of such contours. Capacitors of 62 pF and inductances of 8,2 μH are attached to the lids of two identical plastic boxes (sandwich boxes can be used). Under the capacitors, an additional sheet of mica is placed.

The outputs from the circuits are made through ceramic bushings (the authors used bushings from the antenna shield of the RSB radio station), and the circuits used permanent air capacitors from the same station, assembled on a ceramic base with a plate area of ​​50x30 mm. Capacitors of another type can also be used, but their capacitance should be 62 pF, and the breakdown strength should be at least 2,5-3 sq.

The coils are wound with PEL 2,0 wire and mounted on getinax plates for greater rigidity. Each coil contains 27 turns, winding diameter - 30 mm, winding length - 75 mm.

More precisely, the inductance and capacitance of the circuit can be adjusted using an LC bridge, but good results are obtained without such fine tuning; it is enough to tune each circuit with the help of a GIR to a frequency of 7,05 MHz, changing the length of the coil winding within a small range.

To increase the mechanical tensile strength of the box, a textolite plate 1,5-2 mm thick is superimposed on its upper plane. Tubular bolts of ceramic bushings pass through it and the box cover.

Brass plates are laid under the heads of the through-bolts, to which, after preliminary twisting, sections of the antenna cord of the required length are soldered. Under the nuts of these bolts, double petals are laid, to which the contour details are soldered.

To protect the ceramics of the bushings from contamination and precipitation, they (each separately) are covered with textolite circles with a diameter of 90 mm.

In the bottom cover, to prevent the accumulation of condensed moisture, six holes with a diameter of 2-3 mm are drilled along its edges.

The halves of the box are fastened with a strapping of insulating tape or nylon cord. All parts of the bolts and soldering that go out are painted over with nitro enamel or BF-2 glue.

An antenna with a feeder made of cable RK-1 and RK-3 has been successfully used by the authors for a long time. With poor transmission, a large number of communications were made both by telegraph and by telephone with all continents using transmitters of no more than 100 watts,

SWR measurements showed that on the 7, 14, 21 and 28 MHz bands it does not exceed two, and on the 3,5 MHz band - no more than three.

The disadvantage of the antenna is its large length (about 34 m), which, with a significant weight of the feeder cable, forces it to be placed on three supports.

Authors: A. Ilyin (UB5PB), N. Soprun (UB5YE), Cherkasy; Publication: N. Bolshakov, rf.atnn.ru

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