Another version of the antenna for a cell phone. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Mobile telephony
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I decided to get a mobile phone to establish a connection with the summer cottage. It turned out that the connection was unstable, there were disconnections, missing words. The likely reason for this phenomenon is the long distance to the base station. Indeed, if you climb a tree, the connection quality is good, but from home - not so much.
The way out of this situation is to install an external antenna. Of course, such antennas are sold in companies specializing in cellular accessories, but the price of such antennas is usually high. The idea arose to make a simple antenna on my own. I decided to start by trying what I had already tried for receiving television in the UHF range - a double triangular antenna. It is described in some detail in Mikhailov's article "UHF antenna - per hour of work"(See "Radio" No. 6 for 1998).
A drawing of an antenna designed for the 900 MHz band is shown in the figure.
Material - foil fiberglass or getinaks (the latter is better - the foil is more easily torn off from it). Having marked the sheet, cut the foil with a knife or cutter, then remove unnecessary sections. The cable is 75 ohm, its braid is soldered to the bottom half of the antenna, and the center conductor is soldered to the top. Then lay the cable as shown in the figure. A and B are zero potential points, a mast is attached to them, which can be metal. Since the polarization of electromagnetic waves in cellular communications is vertical, the antenna is installed so that point A is at the top and B is at the bottom.
You can also add a reflector, but this is not necessary. Reflector dimensions - 170x150 mm. It is mounted at a distance of 65 mm from the antenna web. Metal fasteners can be used if screwed at zero potential points.
The antenna sheet (more precisely, foil) must be coated with some kind of varnish or glue to protect it from corrosion. The length of the cable should be minimal - at such frequencies it has an attenuation of the order of 1 dB / m, and the gain of such an antenna is only 5 ... 6 dB.
The best way to connect the antenna to the phone is through a special cord (antenna adapter). If there is no such cord, and the phone is equipped with a whip antenna, you can make a communication coil and connect an external antenna through it. The end of the cable is cleaned of external insulation and braid for a length of 25 ... 30 cm. The central conductor in the insulation is wound on a metal rod (for example, a drill), the diameter of which corresponds to the phone's whip antenna, fixed with threads and slightly heated (for example, by applying the rod to a hot soldering iron). After cooling, a good spring is obtained, which is put on a standard telephone antenna. The number of turns is 5-7. The terminals of the coupling coil are soldered to the cable. The results of using the antenna exceeded all expectations.
Author: M.Nikolastnikov, Moscow
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