Antenna for field day. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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Often, shortwavers complain about the lack of the necessary materials for the manufacture of antennas. How do radio amateurs of the city of Kolomna (RK3DZD) solve the problem? For example, in the manufacture of multi-element VHF antennas, they use materials bought in a store or literally lying under their feet.
For the antenna traverse in a sporting goods store, metal hoops (“hulahoops”) are purchased, the same ones that girls (and not only them) love to twist so much. Aluminum conductors of the power cable are used as active and passive elements (cuttings can always be found at any construction site, landfill ...).
"Hula hoop" is cut with a hacksaw, the opened inner cavity of the pipe is filled with sand and, heated on fire, straightened. The power cable is cut into pieces a little over a meter long, the outer insulation is cut off and the conductors are removed. The insulation is also cut off from them, but not completely - leaving small sections 30 ... 40 mm long in the center (Fig. 1).
From such blanks we made nine- and sixteen-element antennas of the F9FT design. They were provided to the participants at the "Field Day" competitions.
The antenna traverse was assembled from pipe sections obtained after cut hula hoops, using inserts (If the antenna is designed to work in specific competitions and only a few days, then the inserts can be made of wood). After assembling the traverse, the attachment points of the elements are marked on it. To do this, a sheet of metal measuring tape is fixed to the traverse using rings of electrical tape. The canvas is fixed along the entire length in increments of 30 cm. Next, the points of future holes are punched in accordance with the calculations of this antenna scheme. The diameter of the drill is chosen so (taking into account the diameter of the insulation of the conductors) that the antenna elements are inserted into the prepared holes (Fig. 1) with considerable force.
On fig. 2 shows a diagram of a variant of a nine-element 144 MHz antenna.
The active element is a vibrator made of copper tubes. Its design is shown in Fig. 3.
Connect the feeder that feeds the antenna to the vibrator through a coaxial connector soldered directly to the elements of the vibrator.
Antennas intended for transport should be easy to disassemble. Nine-element antennas made according to the described technology are disassembled into two parts, and sixteen-element antennas into three.
It is quite possible to use dry pine as a mast in the field, and if one is not nearby, the mast will have to be built from a pre-sawn water pipe taken with you.
If FM operation is planned and the antenna polarization is vertical, then it is better not to mount it directly to the metal mast, but to move it sideways with the help of an "arm" with a length of at least λ / 2.
Author: I.Grigoriev
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