Like w3dzz antenna tri-Band dipole
Among radio Amateurs, Amateurs widespread multi-band antenna like w3dzz (Fig. 1A), the principle of which is based on the application of the filter-plugs configured to average the frequency range 7 MHz; Values of capacitance and inductance of these filter-plugs must be carefully selected, as in other ranges. Ni shorten or lengthen the antenna to the desired number of half wavelengths. And nevertheless to achieve a good work like w3dzz up on three of the five Amateur bands.
The proposed antenna uses instead of filter tubes is short-circuited two-wire line segments having in the range of 7 MHz electrical length L/4 (Fig.1B). It is easy to see that the spread of current in the range of 7 MHz along shorted line segments corresponds to the current distribution along the antenna, i.e. shorted segments can be bent in the direction of arrow in Fig.1B. Then the antenna will look as shown in Fig. V. This antenna option - for several years successfully applied to radio stations UP2NV. The dimensions in Fig.1B are given in centimetres. In addition to the ranges of 3.5 and 7 MHz, the antenna has to work well in the 21 MHz band.
The leaf antenna is made of stranded wires with a diameter of 2 mm In the case of thicker wire is necessary to slightly increase the distance between the wires in a two-wire line. The necessary distance between these wires is maintained due to the dielectric spacers. When installing the antenna, you must take steps to make the two-wire portion of the antenna is not perechityvali.
As the feeder coaxial cable is used. If the antenna is suspended horizontally at high altitude, the cable should have a characteristic impedance of 75 Ohms, and when you install the antenna in the form "Inverted Vee" is desirable to use a 50 Ohm cable. Sometimes when placing the antenna between the Houses feeder is at an acute angle to the antenna. In this case it is advisable to wear at the feeder every 2-3 meter ring brands of high frequency ferrite permeability 50-150.
Author: V. Galneryus (UP2NV); Publication: www.cxem.net