ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Calculation of the elements of a J-shaped antenna. Encyclopedia of radio electronics and electrical engineering Encyclopedia of radio electronics and electrical engineering / Antennas. Theory A particularly simple way to feed a half-wave vertical antenna is to connect a closed quarter-wave line to the high-impedance lower end of the radiator "B" and along its length, the resistance corresponding to the characteristic impedance of the power cable is searched. Since the resistance changes along the length L / 4 of the line from tens of thousands of ohms at the point of the lower end of the radiator (voltage maximum) to zero at the closing point of the matching line (voltage minimum), it is thus possible to match the coaxial cable and VHF ribbon cable with the antenna with any wave impedance, as well as a two-wire air-insulated power line with a wave impedance of 600 Ohm. The advantage of this method of feeding the antenna is that the lower closed end of the L / 4 matching line "B" can be grounded and, in addition, the antenna can simultaneously serve as a good lightning rod. Optimal matching of the power line with the antenna (size "WITH") is searched as follows: a neon lamp is connected to the emitter (near the upper point of the matching cable), and the power cable connection point is moved until the brightest glow of the lamp occurs. A quarter-wave matching line is recommended "B" make slightly longer than the estimated length and use a movable closing bridge. The antenna is then excited with a nearby auxiliary antenna connected to the transmitter. At the same time, power lines are not connected to the quarter-wave line and, by changing the location of the closing jumper, the maximum glow of the neon bulb is achieved, which is turned on at the connection point of the lower end of the emitter with the quarter-wave matching line. Thus, the emitter and the matching line are tuned to resonance with the operating frequency. Then the auxiliary antenna is disconnected from the transmitter and the vertical radiator is connected to the power line, the coordination of which is carried out in the manner described above. A radiator configured in this way is an excellent antenna for establishing long-distance communications. The antenna is omnidirectional provided that it is mounted at a high enough height. Literature:
Author: Nikolay Bolshakov, Nizhny Novgorod, rf.atnn.ru See other articles Section Antennas. Theory. Read and write useful comments on this article. Latest news of science and technology, new electronics: Artificial leather for touch emulation
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