TV antenna for cell phone. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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TV antenna for cell phone. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Mobile telephony

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As you know, areas covered by reliable cellular communication are adjacent to areas in which communication is not guaranteed. This usually happens because, due to the terrain, the direct wave is sharply weakened and the electromagnetic field in the resulting radio shadow is formed by reflected rays. Passing different paths and shifting in phase, they create a very complex interference pattern in this space. The field strength in the radio shadow changes very sharply, and local maxima can reach a level at which communication is quite possible.

Under real conditions, it is impossible to predict either the location of local maxima or the field strength in them. However, they can be detected experimentally: it is at these points that the largest number of "cubes" appear on the cell phone display. Such a maximum can also be found inside the building, but it will most likely be small. It is better to look for a field strength peak sufficient for communication outdoors, near the wall facing the nearest base station. Experience shows that such a peak is often located very close to the wall, some 10–20 cm.

By placing the mobile device at the maximum point, you can establish a connection. But it will not be possible to accept the call of a correspondent whose time of appearance is not known. Unless, of course, you do not keep the phone at this point all the time. Essentially, the relationship becomes one-way, as it were.

If you place an antenna with gain, i.e., a directional antenna, at the found point, and connect it to the mobile device with a coaxial cable, the losses in which will be less than the gain of the antenna, then the connection will become more stable and it will be possible not only to make outgoing calls, but also receive calls. In this case, you will have to put up with inconvenience, since the device will be "tied" to the antenna by a cable.

Let us estimate the required gain of the antenna operating in conjunction with a thin coaxial cable PK-50-3-13 3 m long. This cable has an attenuation at a frequency of 1000 MHz 0,65 dB / m, at a frequency of 1800 MHz - 0,87 dB / m. Obviously, 3-0,87 - 2,6 dB would be enough. In other words, to compensate for losses in the cable, there is no need to purchase an expensive antenna with a gain of 10 ... 15 dB (a significant part of these decibels is "consumed" in its own 10-meter cable).

A well-known desktop television log-periodic antenna of the decimeter range can serve as a suitable antenna for these purposes, if all its elements are shortened by half (the inter-element distances remain the same). If there is a choice, then the antenna of the previous design should be preferred - with solid-cast vibrator cloths.

The antenna is set in a vertically polarized signal orientation (in the vertical plane) at the point found by the phone, but the final position needs to be clarified. An adapter (adapter) is included in the telephone's antenna jack, to which, in turn, an antenna cable is connected through the necessary high-frequency connectors. By gradually moving the antenna, they find its position, which corresponds to the maximum number of "cubes" on the indicator of the received phone signal. This should be done slowly, since the information on the indicator is updated with some delay.

When installing the antenna outdoors, it can be completely enclosed in a plastic bag to protect it from moisture. The small size of the antenna allows this to be done.

Author: Yu.Vinogradov, Moscow

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