Spiral antenna for portable radios. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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The spiral antenna is intended for installation on personal radio stations in a portable version. Compared to a whip telescopic antenna, a spiral antenna has a smaller length, which creates undeniable advantages when using a radio station in a city. Despite its small dimensions, this antenna has great flexibility without breaking the electrical contact, which cannot be said about the telescopic antenna, which often loses inter-knee contact and requires more careful handling. But, most importantly, the efficiency of the "spiral" type antenna in terms of field strength is 1,2 - 1,5 times higher than the whip antenna with a typical size of 525 mm.
The results of experimental data for two communication options - with whip and helical antennas - show clear advantages of the latter. So, with a transmitter output power of 0,2 W and a receiver sensitivity of 1,5 - 2,0 μV, the range of reliable communication between radio stations of the same type in a city with spiral antennas was 1,4 km, which is 0,5 km more than with whip antennas. .
The material of the antenna blank is polyethylene or any other used for the production of high-frequency cables. On fig. 1 shows the dimensions and design of such a workpiece.
The molding of a threaded connection in the simplest case is carried out by heating the workpiece in the connector body of the SR-50-74FV type.
The placement of the windings on the workpiece is shown in fig. 2. Winding I contains 80 turns of wire wound turn to turn over a section 34 mm long. Winding II contains 29 turns of wire, spaced evenly along the winding length of 150 mm. Both windings are made with PEV-2 wire 0,4 mm. The end of the winding is fixed by fusing the wire into polyethylene.
Tuning the antenna into resonance is carried out by winding or winding one or two turns of wire from the side of the connector. Resonance is achieved at maximum transmitter power output, which is recorded by a field strength device or any spectrum analyzer at a distance of at least 2 meters. After tuning, the antenna must be placed in a flexible waterproof casing.
The general view of the assembled antenna is shown in fig. 3.
Author: S. Sushko, Tyumen; Publication: cxem.net
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