Devyatietazhnoe antenna KB
This antenna is a variation of a known multi-band antenna "WINDOM" - dipole, in which the feed point is shifted from the center. In this case the input impedance of the antenna in several Amateur LW bands is approximately 300 Ohms, allowing you to use as a feeder and single wire and two-wire line with a corresponding characteristic impedance, and, finally, coaxial cable, is connected through a matching transformer.
In order for the antenna worked in all nine Amateur LW bands(1.8; 3,5; 7; 10; 14; 18; 21; 24 and 28 MHz), connected in parallel are essentially two antennas "WINDOM" (see Fig. (a): one with a total length of about 78 m (l/2 for the range of 1.8 MHz) and the other with a total length of approximately 14 m (l/2 for the range 10 MHz and l to 21 MHz band). Both emitter powered by a single coaxial cable with a characteristic impedance of 50 Ohms. Matching transformer T1 has a transformation ratio of the resistance 1:6.
The approximate location of the radiators of the antenna shown in plan in Fig.b. When you install the antenna at a height of 8 m above a well conducting ground standing wave ratio in the range of 1.8 MHz is not exceeded 1.3, in the range of 3.5-inch, 14. 21, 24 and 28 MHz - 1.5, in the range of 7. 10 and 18 MHz to 1.2.
In the range of 1.8, 3.5 MHz, and to some extent in the range of 7 MHz at a height of suspension 8 m dipole, as you know, emits mainly at large angles to the horizon. Therefore, in this case, the antenna can only be effective if the conduct of others links (up to 1500 km).
The scheme of connection of the windings of the matching transformer to obtain the transformation ratio 1:6 is shown in Fig.in. The windings I and II have the same number of turns (as in conventional transformer with a transformation ratio of 1:4). If the total number of turns of these windings (and it depends primarily on the size of the magnetic circuit and the initial magnetic permeability) is equal to n1, the number of turns of n2 from the point of connection of the windings I and II before the allocation is calculated by the formula n2=0.82n1.
Authors: Scholle It., Sieins R., Scholle It., Sieins R; Publication: N. Bolshakov, rf.atnn.ru