Antenna range 2 meters. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / VHF antennas

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To conduct local communications on VHF (including through repeaters), an antenna is needed that has a circular radiation pattern and a noticeable gain. In amateur radio practice, this problem is usually solved by using elongated vertical antennas, consisting of several radiators, which are fed through phasing two-wire lines. Very similar models of antennas are produced by many foreign companies, and almost identical models are sometimes produced under different names. A typical antenna of this class (for example, model ARX-2B from CUSHCRAFT) has a gain of 7 dB and an SWR at a resonant frequency of no more than 1,2 (typical value). The bandwidth is about 3 MHz. In the horizontal plane, the antenna has a circular radiation pattern; in the vertical plane, the maximum radiation angle is 7 degrees. Typically, antennas have a certain margin for adjustments, therefore, during installation, their operating frequency can be varied over a wide range (for example, for the model mentioned above, in the band from 135 to 160 MHz). Similar antennas can be made in amateur conditions.

The design of this type of antenna is shown in Fig.1. It is made of aluminum thin-walled tubes and installed through an insulator on a grounded metal mast (the total height of the antenna is 4,3 m). Antenna dimensions are for the 2 meter amateur band, with a center frequency of 145 MHz.

(click to enlarge)

Element 1 - a tube 890 long and 9 mm in diameter. A plug is installed in the upper part of element 1, which prevents moisture from getting inside the antenna. Element 3 - a tube 700 long, 13 mm in diameter. Element 6 - a tube 530 long, 13 mm in diameter. Element 7 - a tube 380 long, 16 mm in diameter. Element 8 - a tube 1000 long, 19 mm in diameter.

At the upper ends of the tubes 3, 7, 8, vertical cuts 30 mm long are made, providing a tighter fit of the internal fixed elements. Tubular elements are fixed with the help of expanding clamps 2, the sketch of which is shown in Fig. 2. The design uses three collars with inner diameters D=13, 16 and 19 mm.

Elements 3 and 6 are electrically connected to each other through a phasing element 5. For this, an insulator is installed between elements 3 and 6, Fig.3. The phasing element is a U-shaped bracket made of aluminum wire with a diameter of 6 mm. At the ends of tubes 3 and 6, inserted into the insulator at a distance of 10 mm from the edge, holes 6 mm in diameter were drilled. Using M5 screws, elements 3, 5 and 6 are fastened together through threaded holes in the insulator. The length of the phasing element 5 is set according to the dimensions shown in fig. 1.

The antenna through the insulator 11 (Fig. 4) is mounted on a metal mast 17 with a diameter of 32 mm. At the upper end of the mast is fixed (welding or any other mechanical connection) a metal cup 16 with an inner diameter of 32 mm. An insulator 11 is placed in this cup. The depth of the cup 16 is chosen so that the insulator 11 protrudes from it by 30 mm.

To elements 8 and 16, as seen in Fig. 1, metal corners 13 are attached with screws. At the ends of the corners, remote from the antenna, one hole 127 mm in diameter was drilled from copper wire 5 mm in diameter.

On the corner attached to part 16, closer to the antenna, a 50-ohm socket is installed so that its threaded or bayonet part is facing down to the base of the antenna. A piece of copper wire 12 with a diameter of 5 and a length of 130 mm is soldered to the central terminal of the connector (Fig. 5).

At one end, the wire is flattened, and a hole is drilled in it, equal to the diameter of the central terminal of the connector. The wire is bent in such a way that, without touching the antenna, it lies with its opposite end on element 9. Using a metal bracket (item 10, Fig. 6) and an M5 screw located on the bracket, the end of wire 12 is fixed on element 9. In At the same time, this contact is movable and is used when tuning the antenna. By moving the bracket 10 within certain limits along the circumference of the ring 9, its position is chosen in which the SWR of the antenna is minimal.

Before installing the antenna mast, put on a metal ring 18, made according to fig. 7. Three aluminum counterweights 19 521 long and 6 mm in diameter are screwed into this ring. At one end of the counterweights, an M6 thread 20 mm long is cut. Before installing the counterweights in their places, lock nuts are screwed onto the threads.

A corner 18 is attached to part 13 with a screw, by analogy with part 16. Only the connector is installed here through. Separately, a cable with connectors at the ends and a total length of 1272 mm is made.

Ring 18 is installed on the length of the stretched connected cable and, having screwed in the counterweights until it stops, it is rigidly fixed on the antenna mast. Then tighten the locknuts.

The lengths of the tubes given in this article correspond to the antenna version, which allows you to tune its operating frequency over a wide range. For an antenna for a range of 2 meters, the radiators can be non-composite, which will significantly simplify the design of the antenna.

Author: Alexander Krasnoperov (UA3IAP)

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