Nine-band KB antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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This antenna is a variation of the well-known multi-band antenna "WINDOM" - a dipole, in which the feed point is off-center. At the same time, the input impedance of the antenna in several amateur KB bands is approximately 300 Ohm, which makes it possible to use both a single wire and a two-wire line with the corresponding wave impedance as a feeder, and, finally, a coaxial cable connected through a matching transformer.
In order for the antenna to work in all nine amateur HF bands (1.8; 3,5; 7; 10; 14; 18; 21; 24 and 28 MHz), essentially two "WINDOM" antennas are connected in parallel (see Fig. a ): one with a total length of about 78 m (l/2 for the 1,8 MHz band) and the other with a total length of about 14 m (l/2 for the 10 MHz band and l for the 21 MHz band). Both radiators are powered by a single coaxial cable with a wave impedance of 50 ohms. The matching transformer T1 has a resistance transformation ratio of 1:6.
The approximate location of the antenna emitters in the plan is shown in Fig.b. When the antenna was installed at a height of 8 m above a well-conducting "ground", the standing wave ratio in the 1.8 MHz band did not exceed 1,3, in the 3,5, 14. 21, 24 and 28 MHz bands - 1.5, in the 7. 10 and 18 bands MHz - 1,2.
In the ranges of 1,8, 3,5 MHz, and to some extent in the range of 7 MHz with a suspension height of 8 m, the dipole, as is known, radiates mainly at large angles to the horizon. Therefore, in this case, the antenna will be effective only for short-range communications (up to 1500 km).
The connection diagram of the windings of the matching transformer to obtain a transformation ratio of 1: 6 is shown in fig.c. Windings I and II have the same number of turns (as in a conventional transformer with a transformation ratio of 1:4). If the total number of turns of these windings (and it depends primarily on the dimensions of the magnetic circuit and its initial magnetic permeability) is n1, then the number of turns n2 from the connection point of windings I and II to the tap is calculated by the formula n2=0.82n1.
Authors: Scholle It., Sieins R., Scholle It., Sieins R; Publication: N. Bolshakov, rf.atnn.ru
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