Direction finder antenna UB5UG. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / VHF antennas

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Perhaps no part of the fox's equipment remains as unchanged as the antenna. New transistors and smaller components make it possible to build ever more sensitive, economical and lightweight receivers, and the antennas remain the same, although their weight and dimensions are always a hindrance to the athlete.

The ring cores made of high-frequency ferrite that have appeared in recent years make it possible to build antenna arrays with active power supply of all elements by simple means. In this case, the same effect can be achieved as in passive antennas, the phase shift in which is selected by the distance between the elements, by changing the polarity of the transformers.

The following describes an active-powered antenna for the 28 and 144 MHz bands, built on the principle of in-phase anti-phase power of the elements. The basis of the antenna is a combination of an anti-phase pair of emitters and a dipole. The radiation pattern of the antiphase pair is figure eight. Her emf changes sign depending on the direction of signal arrival. Dipole diagram (in plane H) - circle. Polarity e. d.s. dipole is independent of direction. If we add emf an antiphase pair and a dipole combined in space, the total radiation pattern will be single-lobe (in particular, a cardioid if the amplitudes of the two emfs are equal).

The antenna circuit is shown in fig. 1. Antenna elements I - IV and transformers Tr1 - Tp4 are connected in such a way that they form two systems of anti-phase pairs and dipoles. emf each anti-phase pair is removed from the windings of transformers connected in series, and emf. dipoles - between the middle points of the windings. With such power supply of the elements, in-phase and anti-phase currents are separated, which, summed up in the total load (transformer Tp5, and capacitor C1), give a unidirectional diagram. Communication with the antenna is selected by turns of the secondary winding of the transformer Tr5.

Fig. 1

The radiation pattern has two multipliers: a cardioid (a combination of an anti-phase pair and a dipole) and a figure-of-eight (anti-phase pair). The result is a single lobe 60° and 90° wide in the principal planes.

Structurally, the antenna is a sheet of polystyrene or fiberglass, foiled on both sides. The antenna elements I-IV and the connecting lines are printed in the form of foil strips. Strips of antenna elements located on different sides of the sheet are connected to each other at the beginning and end by conductors or rivets. Connecting lines are located on one side of the sheet; on its other side, a wide strip of foil is left, which is used as a common tire. Transformers are glued with BF glue directly at the connection point.

Transformer data for the 28 MHz range: Tr1-Tp4 4 and 2X4 turns PELSHO 0,25-0,3 on a ring made of ferrite 30VCh-2 k7X 4x2. Transformer Tp5, - 12 and 2 turns (for 70 ohm output) PELSHO 0,25-0,3.

Data for the 144 MHz band:
Tp1 - Tp4 1 and 2X1 turns, Tr5-3 and 1 turn.

The dimensions of the antenna are given in fig. 2. Transformer attachment points are shown by dotted lines. Antenna dimensions can be varied within wide limits depending on design requirements and possibilities, however, it is desirable to comply with the indicated proportions. Transformer data are not critical if the length of the antenna elements remains less than 0,1-0,15 lambda.

Fig. 2

Tuning the antenna is reduced to tuning the resonance of the Tr5S1 circuit. To "deepen the zeros", you can introduce an additional capacitor by connecting it between the midpoints of the windings of the transformers Tr3, Tr4 or into the break of one of the wires connecting the midpoints of the windings. If the selected dimensions differ from those shown in the drawing, then you can try to improve the antenna tuning by turning on the capacitor between the midpoints of the windings Tp1, Tr2.

Author: Y. Medinets (UB5UG) Kyiv; Publication: cxem.net

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