loop antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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Telescopic antenna of radio receivers "VEF", "Ocean", etc. in field conditions it often breaks down, and in urban conditions such an antenna is ineffective due to susceptibility to industrial interference Traditional connection of a loop antenna to the input of such a radio receiver requires a complex matching system in each frequency range. However, the advantages of a loop antenna are obvious due to its spatial selectivity and less susceptibility to industrial interference.
Consider turning on the loop antenna using the example of the Ocean radio with a drum range switch. A fragment of his circuit is shown in Fig. 1 [1]. In all sectors of the switch, contact 18 (K18) must be released. The circuits disconnected from it must be connected to contact 6. The fixed lamella of contact 18 must also be disconnected from the body and a loop antenna, which is a single coil of wire of arbitrary shape, laid along the perimeter of the chassis, must be connected to the break point so as to obtain the maximum area of the coil. You can use any copper wire with a diameter of 0,3 ... 0,5 mm.
Ris.1
In the ranges of 50, 31 m, the frame is switched on in series with the loop coil, for which it is necessary to disconnect the output of the loop coil from Kb and connect it to K18 (Fig. 2). After that, the input circuit must be adjusted in the long-wavelength section of each range to the maximum signal by unscrewing the core of the contour coil.
Ris.2
In the range of 25 m and above, this inclusion of the loop leads to such an increase in the inductance of the circuit, which cannot be compensated by the ferrite core. In these ranges, the frame is included in the circuit through the range stretching capacitors. To do this, capacitor C14 with a capacity of 300 pF of a range of 25 m is disconnected from K6 and switched to K18 (Fig. 3). The adjustment of the input circuit is carried out as usual.
Ris.3
The described inclusion of a loop antenna ensures its maximum efficiency, since on any range it is an integral part of the resonant circuit in the input circuit. In the same way, the frame can be included in any radio receiver, taking into account its circuitry. The efficiency of the loop antenna with this method of inclusion is no worse than the telescopic one, and the noise immunity of the radio receiver is noticeably improved.
Literature
- Belov I. F., Dryzgo E. V. Handbook of transistor radios, radio tubes and electrophones - M, 1975
Radio amateur 12/2000, p.3
Publication: N. Bolshakov, rf.atnn.ru
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