shortwave antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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The description of the shortwave antenna "IIIDX Antenna" operating on the bands 80, 40, 20 and 15m is published by the American shortwave W3JHR. The antenna is a vertical rod with a height of about 15 m without guys, the base of the mast is grounded.
On fig. Figure 1 shows the directivity patterns in the vertical plane and the current distribution curves in the antenna on the ranges of 40 (Fig. 1, a), 80 m (Fig. 1, b) and 20 m (Fig. 1, c).
Ris.1
The given values of the standing wave ratio (SWR) on the 40 m and 20 m bands are close to unity, on the 80 m band the SWR varies from 1-3,9 MHz to 1,7-3,8 and 4 MHz.
Structurally, the antenna is made of four aluminum pipes of different diameters, inserted one into the other and fastened with four bolts at the joints (see Fig. 2).
Ris.2
Antenna dimensions in fig. 2 are in meters and millimeters. The attachment points of the gamma-matching device to the mast for each range are shown in Fig.3.
The design of the coaxial glass, a (Fig. 2 and Fig. 3) consists of six aluminum wires tightly stretched over four aluminum rings. The top and bottom rings are made from aluminum strips 6 mm thick and 25 mm wide. The two middle rings measure 3x18 mm. The inner diameter of the rings is 230 mm. The upper ring of the cup is electrically connected to the mast, the other rings are insulated. Two cords are attached to the lower ring, holding the glass taut.
Ris.3
The antenna is powered by a 50-ohm feeder. The matching is done in the form of a "gamma". Tubes of "gamma" aluminum, with a diameter of 25 mm. The lower ends of the tubes are fixed on insulators at a distance of 500 mm from the ground (Fig. 4, b). The upper ends are attached to the mast with aluminum brackets (Fig. 4, a).
Ris.4
Adjustment of "gamma" is made by condensers on each range separately. The setup block diagram is shown in Fig.5.
Ris.5
Capacitors C1, C2, C4 110 pF each; C3-750 pf, C5-150 pf, C6 and C7 1000 pf each for an operating voltage of 5 kV. The relay is powered from the AC mains. To improve the grounding of the antenna, 4 wires are buried in the ground, two of them are 1800 cm long, and the other two are from 1050 to 1500 cm. These four wires are mounted on an aluminum bracket fixed at the base of the antenna mast.
Literature
- Radio No. 7 1963, p.59-60
Publication: N. Bolshakov, rf.atnn.ru
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