Tri-band dipole. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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Among shortwave radio amateurs, the W3DZZ multi-band antenna (Fig. 1a) is widely used, the principle of operation of which is based on the use of stopper filters tuned to the middle frequency of the 7 MHz band; The capacitances and inductances of these plug filters must be carefully selected, as in the rest of the ranges. They shorten or lengthen the antenna to the desired number of half-waves. Nevertheless, you can achieve good W0DZZ performance on a maximum of three of the five amateur bands.
Ris.1
The proposed antenna uses, instead of plug filters, shorted segments of a two-wire line having an electrical length L/7 in the 4 MHz range (Fig. 1b). It is easy to see that the current propagation in the 7 MHz range along the shorted line segments corresponds to the current distribution along the antenna itself, i.e., the shorted segments can be bent in the direction of the arrows in Fig. 1b. Then the antenna will take the form shown in Fig. in. This version of the antenna has been successfully used on the UP2NV radio for several years. The dimensions in Fig. 1c are given in centimeters. In addition to the 3,5 and 7 MHz bands, the antenna should also work well in the 21 MHz band.
The antenna fabric is made of stranded wire with a diameter of 2 mm. In the case of using a thicker wire, it is necessary to slightly increase the distance between the wires in a two-wire line. The required distance between these wires is maintained by means of dielectric spacers. When installing the antenna, care must be taken to ensure that the two-wire part of the antenna does not overlap.
A coaxial cable is used as a feeder. If the antenna is suspended horizontally at a high height, then the cable should have a wave impedance of 75 ohms, and when installing the antenna in the form of an "Inverted Vee" it is desirable to use a 50 ohm cable. Sometimes when placing the antenna between the Houses, the feeder is located at an acute angle to the antenna. In this case, it is advisable to put rings on the feeder every 2-3 meters from high-frequency ferrite grades with a permeability of 50-150.
Author: V.Zalnerauskas (UP2NV); Publication: N. Bolshakov, rf.atnn.ru
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