Multi-band vertical antenna 1. Scheme, description

Multiband vertical antenna. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / HF antennas

The proposed vertical antenna (Fig. 1) was developed as a compromise that provides satisfactory performance on all major amateur HF bands.

Multiband vertical antenna
Ris.1

The vibrator of the universal antenna is made of aluminum pipes with a diameter of 40...50 mm. In its upper part there is a stopper filter tuned to the middle frequency of the 40 MHz range (7,05 MHz). In the range of 80 m, the filter has an inductive reactance and "extends" the vibrator to an electrical length of L/4. In the range of 40 m, the plug filter "turns off" the upper part of the vibrator, as a result of which the electrical length of the antenna is also equal to its L/4. In the range of 20 m, the filter resistance has a capacitive character and its length becomes equal to 3L/4.

In the ranges of 21 and 28 MHz, the filter plug electrically shortens the vibrator to a length of 5L/4 and 7L/4, respectively.

The system of counterweights consists of 20 pieces of copper wire with a diameter of 1...3 mm, connected at one point, located under the vibrator. On each of the five ranges, four counterweights are used, for a range of 80 m - 20,8 m long, 40 m - 10,4 m, 20 m - 5,2 m, 15 m - 3,49 m, 10 m - 2,62 .2 m. XNUMX shows the location of counterweights in one quadrant.

Multiband vertical antenna
Ris.2

The antenna is fed through a 50- or 75-ohm coaxial cable with a length equal to half the wavelength in the 80 m band. This simplifies the matching of the antenna with the feeder, since the active resistance of the antenna changes markedly when moving from one range to another.

The described antenna is installed on the roof of a four-story reinforced concrete panel house. The best results were achieved in the bands 80, 40 and 20 m. The SWR did not exceed 2 on any of the bands.

If the antenna will be placed on or near the ground, the point of connection of the counterweights should be grounded (their length in this case should be about 0,4L), and the counterweights themselves should be buried in the ground to a depth of 40...70 cm.

Author: M. Chirkov (UL7GCC), Alma-Ata; Publication: N. Bolshakov, rf.atnn.ru

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