Small-sized two-element antenna for a range of 20 meters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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One English shortwave developed a small-sized two-element antenna, which received the name. "Zygi-beam". Each element of the antenna (see Fig. 1) is made in the form of a rectangle, the sum of the lengths of the sides of which is approximately equal to L / 2, and the ratio of the large side to the small one is two. The midpoints of the large sides are open. The antenna elements are located in the same plane and are actively powered. The elements are made from pieces of aluminum tubes with outer diameters of 13 and 6 mm. Segments of thin tubes are bent in the form of the letter P and their ends, about 160 mm long, are inserted inside the thick tubes.
The antenna elements are fixed on plates 305x63 mm in size. made of steel and plexiglass (see Fig. 2). The ends of the tubes to which the power is connected are attached to the steel plates, and the free ends of the tubes under high voltage are attached to the Plexiglas plates.
The segment of the transmission line connecting the elements is made of a ribbon cable 2185 mm long with a wave impedance of 300 ohms.
The tuning of the antenna elements to the resonant frequencies indicated in Fig. 1 is carried out with the ribbon cable disconnected by moving thin tubes inside thick ones. Moving the tubes by 2,5 mm results in a resonant frequency change of approximately 100 kHz. The adjustment of each element should be done on both sides in order to maintain the symmetry of the structure. The SWR of a properly tuned antenna at 14,2 MHz should not exceed 1,1. A decrease in SWR can be achieved by adjusting element A. The ratio of the powers radiated in the forward and reverse directions depends mainly on the setting of element B.
The input impedance of the antenna is 42 ohms, which makes it possible to use a cable with a characteristic impedance of 50 ohms to power it. When using a 75-ohm cable, a transformer was used to match the antenna to the feeder, installed near the antenna input terminals. with resistance transformation ratio 1.6.
The half power beamwidth is about -70° with a forward to reverse power ratio of about 8-10 dB. The antenna gain, according to the author's estimates, exceeds 4 dB. The antenna radiates energy mainly at small angles to the horizon, the height of its installation has little effect on performance.
Literature
- "Old man" (Switzerland), 1975. N 2
Publication: N. Bolshakov, rf.atnn.ru
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