Antenna with switchable radiation pattern. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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The switchable antenna is a type of two-element active powered linear antennas and is designed to operate in the 7 MHz band. The gain is about 6 dB, the front-to-back ratio is 18 dB, the side-to-side ratio is 22-25 dB. The width of the DN at the level of half power is about 60 deg.
Fig.1 For 20 m range L1=L2= 20,57 m: L3 = 8,56 m
Bimetal or ant. cord 1,6 ... 3 mm.
I1 =I2= 14m cable 75 ohm
I3= 5,64m cable 75 ohm
I4 =7,08m 50 ohm cable
I5 = free length cable 75 ohm
K1.1 - RF relay REV-15
As can be seen from Fig. 1, two active vibrators L1 and L2 are located at a distance L3 (phase shift 72 degrees) from each other. The elements are powered in antiphase, the total phase shift is 252 degrees. K1 provides switching of the direction of radiation by 180 degrees. I3 - phase-shifting loop I4 - quarter-wave matching segment. Antenna tuning consists in adjusting the dimensions of each element in turn according to the minimum SWR with the second element short-circuited through a half-wave repeater 1-1 (1.2). SWR in the middle of the range does not exceed 1,2, at the edges of the range -1.4. The dimensions of the vibrators are given for a suspension height of 20 m. From a practical point of view, especially when working in competitions, a system consisting of two similar antennas located perpendicular to each other and separated in space has proven itself well. In this case, a switch is placed on the roof, instantaneous switching of DN in one of four directions is achieved.
One of the options for the location of antennas among typical urban buildings is proposed in Fig.2.
Ris.2
This antenna has been used since 1981, it has been repeatedly repeated on different QTHs, with its help tens of thousands of QSOs have been made with more than 300 countries of the world.
Author: D. Kolenchuk, RW1ZZ; Publication: N. Bolshakov, rf.atnn.ru
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