A simple ultra-wideband TV antenna. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television antennas

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Significant difficulties in providing high-quality television reception usually arise where a large number of television stations operate nearby, and at different frequencies and from different directions. It can be difficult for the average user to use a separate directional antenna for each channel. Therefore, the best way out is to use ultra-wideband antennas, which allow you to simultaneously receive television stations in both the meter and decimeter wave bands.

Various variants of such antennas, though long ago, were described, for example, in [1 - 3].

Now on sale there are Polish-made antennas that have unidirectionality in the decimeter range and almost bidirectionality in the meter range. Each of them is equipped with an antenna amplifier. However, if the gain is chosen incorrectly, it is overloaded by the signal of a powerful station and interference due to crosstalk distortions.

For repetition by radio amateurs, a simpler TV antenna with a very large bandwidth is offered. It (see sketch drawing) is the result of a serial connection of two zigzag vibrators. And from above they are closed by a half-wave connector, from below the feeder is connected through a quarter-wave transformer. The distance between the feeder connection points is 1 ... 3 cm. These connection and matching elements are made in the form of a single design with the elements of the antenna itself, which, at the same time, turns out to be extremely simple and technologically advanced.

In the decimeter wavelength range (the antenna was made to receive the 38th channel with a X / 2 size of 24 cm), the maximum antenna sensitivity is obtained for the calculated wavelength. However, zigzag antennas are very broadband, and with a high level of signals, they receive them in the entire decimeter wavelength range.

In the meter range, the antenna can be viewed as one large loop or deformed diamond with a resonant frequency that is approximately in the middle of the range. This makes it possible to use it for receiving television stations in this frequency range as well.

In such a wide frequency range, it is impossible to offer a reflector with acceptable geometric dimensions that ensures the antenna is unidirectional. Therefore, it is used without a reflector. The radiation pattern of such an antenna has the form of a figure eight and. of course, when installing it, you need to find the optimal orientation.

Even without the use of additional balancing and matching devices, that is, with a direct connection of a 75-ohm television cable to an antenna, good results can be obtained. For example, in the conditions of Rostov-on-Don, when the antenna is located on the loggia of the 9th floor, the author successfully receives transmissions from television stations operating on channels 1. 7, 9. 12. 22. 32, 35, 38. 49 and 51. Moreover, the signals Channel 49 was received from neighboring Azov. to which, with a direct line of sight, about 30 km.

For the manufacture of the antenna, any suitable material can be used: aluminum or brass tubes, profile or strip material. A bimetallic (inside - steel, outside - aluminum) electrical wire with a diameter of 5 mm is very convenient. You can use aluminum conductors from power cables. In extreme cases, such an antenna can be made from a television cable (connecting the braid to the central conductor at the connection points), stretched over a wooden cross of the appropriate shape, using it for the drop feeder.

Literature

1. Kharchenko K. Zigzag antenna. - Radio. 1961. No. 3.
2. Kharchenko K. Rhomboid antenna. - Radio. 1971. No. 8.
3. Boriychuk G., Bulych V., Shelonin V. Dual band antenna. - Radio. 1980. No. 3.

Author: G. Petin, Rostov-on-Don

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