Vertical multiband antenna. Scheme, description

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Vertical multiband antenna. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / HF antennas

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So, I put up for general review a version of a multi-band antenna designed to operate on the HF bands of 20-17-15-12-10 meters, as well as on any intermediate range, which, for example, will be of interest to SiBists. In addition, the antenna also operates at higher frequencies than 28-29 MHz, only the lower bar is limited - a range of 20m. The antenna can be recalculated for lower ranges - for example, starting from 40 meters, and again only the lower range will limit the antenna's broadband.

Vertical multiband antenna

If you take the CushCraft or HihgGain vertical, remember how much it costs. This antenna will cost you only the time spent searching for the wire and measuring its length. In general - a gift. The antenna is easily placed on any of our roofs, you just need to think about where to fix the radials.

For each range, 3-4 radials are needed for the required resonant frequency. If there are 2 radials of different lengths per band (beginning and middle of the band, for example), then the broadband of the antenna increases within the range. The length of the radial is equal to 1/4 of the wavelength. Calculate like the canvas of a half-wave dipole using a simple formula: radial length L (m) \u1d 2/142500 * (XNUMX / f (kHz)). The frequency f is chosen based on what range you are counting on.

For example:

Calculation for 20 m range:

L=1/2* (142500/14200) = 5.017 m

L=1/2*(142500/14010) = 5.085 m

Got two lengths, based on the fact that you need to work in both the CW and SSB section, do 2 radials for each frequency.

The more radials, the greater the efficiency of the antenna, but this common truth is known from theory, in this case, the more different radials per band, the less dips in SWR. Do not place radials on different ranges close to each other. The inclination of the radials with respect to the horizontal does not need to be done more than 15-20 degrees. But also parallel to the ground, too, in this case, the angle of the main lobe of the antenna is very small.

A 150 ohm matching line can be made as follows: take a wire a little over 2,65 m, put a thick vinyl chloride tube on it and wrap it around the emitter (highlighted in blue in the figure). Approximately 20 turns are obtained for the entire length of the line. A power core is attached to the central lower point of the emitter, and a braid is attached to the wire wound over it; radials are attached to the connection point with the braid.

The mast and crossbar on top are best made of insulating material. One feature: there may be no crossbar, then the ends of the antenna are reduced to one point at the top, but do not short-circuit. The length of the crossbar determines the bandwidth on the 10 m range, since it occupies the widest frequency range. The closer the ends are brought together, the wider the antenna is. I advise you to choose an average length - 1,2 - 1,5 m. But you can expand the range with different radials (see above). Testing the antenna on the 10 m band with manufactured radials only for a frequency of 28400 kHz showed the following results:
Frequency SWR
28000 2,2
28100 1,8
28150 1,6
28200 1,4
28300 1,2
28390 1,1
28450 1,2
28500 1,4
28600 1,6

Other ranges occupy a relatively small frequency band, and the results are as follows:
Frequency SWR
14010 1,2
14050 1,2
14100 1,1
14150 1,05
14200 1,1
14250 1,2
14300 1,25
21010 1,5
21100 1,4
21150 1,3
21200 1,4
21250 1,5

On the 18 and 24 MHz bands, I have not yet installed radials, despite this, in the entire section of these bands, the SWR turned out to be no higher than 1,5.

The radiation pattern is along the lower power line of the main lobes due to the phasing of the two vertical arms of the antenna.

The antenna has a gain of about 5-6 dB with respect to the dipole in the calculated range, i.e. at 20 meters. Ball is something! On other ranges, the antenna parameters depend on the quality of the matching line. You can prepare a wire with a diameter of 2-3 mm and start manufacturing.

Developers and testers: RW4NA and UA4NBH

Author: Andrey Korsakov (RA4NF), ra4nf@vti.vyatka.ru; Publication: vti.vyatka.ru/~ham

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