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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Zigzag antenna. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Television antennas

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The antenna is designed to work in the first five television channels (50 ... 100 MHz). It has a high directivity (8-10 dB) and is well matched with a 75-ohm cable (standing wave ratio 1,25...2). Such an antenna can be used outside the reliable reception area at a distance of 10 ... 15 km. Important advantages of the antenna are the simplicity of its design, the ability to assemble from widely available materials.

Wooden block 1 with a section of 60x60 mm (Fig. 1) serves both as a central antenna post and a mast. Two rails 90 with a section of 2x40 mm are attached to the bar at an angle of 40 °. The top rail is fixed at a distance of at least 1100 mm from the top of the rack. It is advisable to cut the rails into the central rack, and then fasten it with a nail or bolt. Two metal strips 3 are attached directly to the rack from below and above the rails, the same strips 4, but through dielectric spacers 5 (for example, made of organic glass) are installed at the ends of the rails.

Board 7 with power points is placed in the middle between the rails; it consists of two rounded metal plates assembled on a dielectric spacer. After installing the plates 3, 4 and the board 7, the antenna web is pulled, which consists of three zigzag wires 6 with a diameter of 2 ... 3 mm (or an antenna cord). Zigzag wires are parallel to each other. In places of bending, they are soldered to the strips and plates of the power board. The antenna feeder 8 from the feed points is laid parallel to the inner wire of the canvas, as shown in fig. 1.

Zigzag Antenna

Dual zigzag antennas

It is possible to increase the efficiency of a zigzag antenna with a reflector by building an in-phase array on its base. In this case, naturally, the antenna system becomes more complex and cumbersome. The simplest in-phase array is best built using two zigzag antennas.

The antennas forming the array can be positioned relative to each other in the planes of the electric E or magnetic H vector of the field strength. The antenna system of the first type is schematically shown in Fig. 2, the second - in Fig. 3. Various materials can be used to make the antenna and reflector web - a thick mounting wire, tubes, strips (preferably copper and brass). Pay special attention to the laying and connection of distribution cables to the feed points of the antennas.

Zigzag Antenna

Antenna dimensions according to fig. 2

Channels IV VI-XII
I, mm 1200 343
dE, mm 4980 1420
dH, mm 3500 1000
S, mm 600 170
dC, mm 1920 550

Zigzag Antenna

Antenna dimensions according to fig. 3

Channels IV VI-XII
I, mm 1200 343
dE, mm 3000 860
dH, mm 7000 2000
S, mm 600 170

To maintain the correct phasing of the antennas, the screens of both distribution cables must be connected to the right (or left) halves of the antenna sheet, and their central conductors, respectively, to the left (or right). There should be no connection errors, otherwise the design will not work. Distribution cable lengths from the tee to the antenna feed points must be the same.

Antenna arrays of both the first and second types are broadband and cover the frequency range from I to V or VI-XII channels inclusive.

For work in the range of all twelve television channels, two antennas are required. Their sizes are shown in the table.

In order to fully use the range properties of antenna arrays for reception on several television channels and from different directions, it is necessary to provide for the possibility of turning the antenna system in the direction of one or another television center. If television centers operate both in the range of IV and VI-XII channels, it is better to make a combined antenna system, using a reflector twice for this purpose. In this case, for the first group of television channels, an antenna array of type H should be made, and for the second - type E, of increased size. Such a combined system is shown in Fig. 4, which shows the placement of antennas relative to each other and the structural dimensions for a small array (range VI-XII channels).

The reflector web of the combined antenna should be placed on the side of the small grid, and the reflector wires should be laid more often against it. They should only be located horizontally, parallel to the vector of the electric field strength of the signal. The power cables of the small and large antenna arrays are laid separately (Fig. 2 and 3).

In order to save material and reduce the weight of the antenna web, it can be made not in three wires, but in two, as shown in Fig. 4. In this case, the SWR in the feeder will increase almost insignificantly.

Zigzag Antenna

For the manufacture of the antenna, the following materials are needed: wooden slats (or bars), antenna cord (or wire), dielectric (organic glass, ebonite, getinax, glass insulators), sheet brass (or tinned tin), RK-1 (RK-3) cables ) and RK-50 (RK-150). Frames are made of wood for tensioning the antenna web and reflector wires, as well as supporting racks. Antenna fabric is pulled from the cord. At its corners, dielectric plates should be laid between the conductor and the tree. The upper and lower corners of the canvas are attached directly to the frame. The conductors of the antenna web at the corner vertices should be shorted to each other. In the center of the antenna web, the conductors at the points of their intersection are soldered to each other.

At the feed points of the antennas, semicircular brass (or tin-plated) plates are attached to the frame on dielectric boards. The antenna feeder is tied to the mast and laid to the central support post, on which the tee is fixed.

Distribution cables are laid through the center of the web of the antenna system, tied to its inner conductor and led to the feed points of the antennas, where they are terminated in the usual way. On the other side of the canvas, a small lattice is attached, which has a similar design.

The wooden parts of the antenna system are covered with oil paint to protect against moisture, since there is more high-frequency energy loss in a raw tree.

It must also be remembered that the center wire in the PK-50 (or PK-150) cables is not fixed inside, so they must be handled with care.

After the array is made, the power circuits of both antennas forming the array are carefully checked. If one of the distribution cables breaks, reception will still be possible, but the performance of the antenna system will be worse than the normal single case.

At the heart of various variants of zigzag antennas is, as already mentioned, the antenna sheet. The reflector only enhances its directivity, not letting high-frequency energy into the rear half-space. The thicker the conductors from which the reflector is made, and the closer they are located to each other, the less part of the incident energy it passes.

However, for design reasons, the reflector should not be made too dense. It is practically sufficient that the distance between the conductors (with a diameter of 2-3 mm) does not exceed 0,05 ... 0,1 of the minimum wave of the operating range.

When manufacturing a zigzag web, you need to pay attention to its symmetry in order to comply with the condition for compensating the current components on the conductors of the antenna web. Violation of this condition will lead to a decrease in the efficiency of the antenna system.

Author: K. Kharchenko, Mytishchi, Moscow Region

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