Small-sized transceiver antenna in the range of 27 MHz. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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The problem of antennas with reduced dimensions remains relevant, especially for radio amateurs living in large cities.
As a result of experiments with various types of shortened antennas, a design has been developed that is a good compromise between the smallest possible dimensions and antenna efficiency.
The antenna (Fig. 1) is extremely easy to manufacture and configure, takes up very little space (the height of the dipole is slightly more than 1,5 m), can be installed on a balcony, mounted on a house wall, etc.
The antenna can be used, in addition to conventional communications, in signaling systems, for communication with a summer house, etc.
The author's antenna is located on the 4th floor inside a panel 9-storey building and is essentially a room. Structurally, it is suspended at its highest point through an insulator to the cornice above the window.
The antenna is a vertical dipole with capacitive loads at the ends. The dipole arms and capacitive loads are made of copper wire or rod with a diameter of 2,5 ... 5,0 mm. The dipole arms and capacitive loads are connected by soldering.
The connection between coils L1 and L2 is inductive. Structurally, the L2 coil is located in the middle part of the L1 coil. The turns of the coil L2 are located between the turns of L1. L1 and L2 are wound on a ceramic frame with a diameter of 8 mm. L1 contains 15 turns of PEL-0,8 wire. Coil winding pitch L1 - 1mm. L2 contains 3 turns of PEL-0,8 wire. As C1, KPI with a capacity of 12 ... 150pf was used.
As a matching device between the feeder and the proposed antenna, you can also use the tuned symmetrical circuit described in [4], choosing the optimal inclusion of the feeder in the circuit and leaving the data of the coil L1 and capacitor C1 unchanged.
Coaxial cable can have a characteristic impedance of 50 or 75 ohms.
Since the dipole is vertical, it is desirable that the length of cable perpendicular to the radiator be as long as possible. The antenna is tuned to the required frequency by capacitor C1 according to the maximum reading of the field strength indicator or the minimum reading of the SWR meter. The dimensions of the arms 11 and 12 of the dipole were chosen so that the entire antenna would fit in the window opening. If the radio amateur has the opportunity to increase the length of the arms 11 and 12, the efficiency of the antenna can be increased.
When working with an antenna, you need to remember that, like any shortened antenna, it is subject to the influence of closely spaced objects, wires, etc., and is also quite narrow-band.
The test results of the antenna with portable and car radios are presented in table. one.
| Range of reliable communication in the conditions of Kharkov |
| 1. Portable r/s "Informtechnika" Receiver sensitivity 1 mkV. P out = 0.5 W |
5 - |
6 km |
| 2. R/C -COBRA 19 PLUS- Receiver sensitivity 0,5 µV, Pout=4W |
15 - |
20 km |
Literature
- Dual band vertical antenna. Radio, - 1970, N9, p.28.
- Antenna "shortened dipole". Radio. 1987, N5, p.17.
- Benkovsky 3., Lipinsky E. Amateur antennas of short and ultrashort waves. Moscow: Radio and communication, 1983.
- Bunins., Yaylenkol. Handbook of a radio amateur-shortwave. - Kyiv: Technique, 1984.
Author: S. Zaugolny (LA-00299); Publication: cxem.net
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