Multi-element vertical antenna for 144 MHz
Readers are invited to describe the construction of multi-element antenna range 144...146 MHz. It will feature original performance and light weight. The antenna is placed inside telescopic fishing rods and convenient to take with you, for example, in a rustic trip to the country, etc. the manufacture of the antenna requires only a few hours of free time. Of course it can be performed in a stationary mode.
As can be seen from Fig.1, the antenna consists of four half-wave vibrator 1, vertically, powering from the end through the short-circuit quarter-wave matching line transformer 4. Photodiode elements 2 provide common-mode enable vibrators. The antenna has a vertical polarization and circular radiation pattern.
The antenna design shown in Fig. 2. The author has placed her in the part of the rod from plastic with a length of 4.5 m In the figure for easier reading individual elements (knee) rods are shown as separate tubes. In fact, they naturally, firmly fitted into one another without requiring sealing.
The transformer is made of copper wire of diameter 2 mm. To increase rigidity of the wire is soldered to the three plates-spacers 3 made of one-sided foil fiberglass. The foil in the middle of plates removed, leaving only the ends, soldering to the wire. You can apply spacers of a different design from a different insulating material. For matching a-line fit and a thicker wire. However, it should be remembered that the ratio of the distance between the conductors of the transformer to their diameter must be 8:1.
Each phase-shifting element antenna is a cage quarter-wave segment of a two-wire line - plume. To reduce the size, they are rolled in the form of coils. To manufacture each loop take cut of PEV-2 in diameter of 1.4 and a length of 1040 mm, the mandrel is of a dielectric material (Teflon, Plexiglas) with a diameter of 9 to 10 and a length of 75 mm. Wire fold in half and, starting from the middle of the mandrel, wound in different directions turn to turn. The ends of the wires of the windings are passed through the through holes, pre-drilled at the edges of the mandrels, sanded and hocus.
Material for vibrators serves as the antenna cord with a diameter of 2...3 mm (for the fixed antenna used copper wire of the same diameter).
The individual elements of the antenna are joined to each other by soldering in accordance with Fig.1.
The fishing rod, it is desirable to choose the most hard and with such internal diameter that all the elements of the antenna could be placed inside. In the slim knee antenna cord is attached with fishing line with a diameter of 0.7 mm or a suitable elastic cord (Fig. 2).
At the base of the rod is mounted RF connector. Connector is connected to a matching transformer short segment of coaxial cable (50 or 75 Ohms). The center conductor of the cable is soldered to the other side of the transformer to which mounted antenna cloth. The braided cable is soldered, respectively, to opposite. Point connect the power cord to the transformer selected by the minimum readings on the SWR meter. Measurement is performed at the most remote from antennas of all foreign objects.
Setting the fixed antenna is preferably carried out at the place of its permanent install. In addition, the antenna should be grounded at the base jumper matching transformer, and its fabric have to wear a foam cubes to exclude the effect of "rattles" (Fig.2). In case of insufficient stiffness of the rod you should use additional stretching of nylon cord, pinning them in the area of the second (third) of the knee.
The antenna, made by the author, has a gain of about 5 dB and VSWR more than 1.2 on the Amateur band edges.
Author: G. Bonev (RA3WQV)