The dipole antenna
On the construction of the attention of the reader antenna was told on the radio 10-15 years ago ham V. Volia beach (UA6DL), for which the author is very grateful to him. The antenna still works and in the absence of necessary switching and adjustment during the transition from one band quite often used as a review or backup. Measured SWR at the frequency of 1.9 MHz And 1.9; 3,6 MHz To 1.3; 7,05 MHz To 1.2; A 14.1 MHz-1,4; 21,2 MHz to 1.7; 28,6-1,6.
Structurally, the antenna is a simple dipole (see Fig.) with a beam length of 20.5 m, which is supplied via a coaxial cable with a characteristic impedance of 50 or 75 Ohms.
As matching device applies a two-wire line with a characteristic impedance of 300 (cable CATV) length of 17.7 m and broadband balun transformer 1:4 (T).
The transformer is wound on a ferrite ring permeability 30-50 HF with an outer diameter of 24 - 32 mm depending on the input to the antenna power (the ring with the cross-section of the core 1 square centimeter able to pass without damage to about 500 watts). If one ring is not enough, then take two, three rings stacked together. Before winding ring (ring) pre-wrapped with a heat-resistant insulating tape, such as Teflon, because at maximum power ring may be heated to 70 °C. Both windings of the transformer contain 9...10 turns are wound simultaneously by two folded together pigtails sew 0,8...1,0 or similar cross-section Litz wire in Teflon insulation (not afraid heating). The windings have uniformly around the circumference of the ring, and the soldering is carried out according to the scheme in the figure, where the dots mark the beginning of the respective windings. The transformer is protected from moisture, winding insulation material and coating varnish.
The point of connection of the transformer to the two-wire line are at a distance of 5.9 m from the junction line of the canvas of the antenna. The antenna blade made of galvanized wire 02 mm and only thanks to that described multiband dipole stood for such a long time in difficult conditions environmental conditions of Donbass.
Publication: N. Bolshakov, rf.atnn.ru