Bobtail Antenna Rolf Merrettig (DL7ME). Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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The article describes the developed modifications of the so-called Bobtail antenna, found in the American amateur radio literature, for the 2 m and 70 cm bands. The construction principle of the Bobtail is shown in Fig. 1.
Ris.1
The antenna consists of a quarter-wave radiator and two external elements of the same length as the radiator, lying in the same plane. External elements are powered by antiphase half-wave lines and therefore the horizontal component of their radiation is suppressed. The antenna diagram is bidirectional (Fig. 2), with radiation maxima in directions perpendicular to the plane of the quarter-wave elements. The gain in gain, compared to GP, is about 5 dB.
Ris.2
The modification of the antenna proposed by the author is, as it were, an "inverted" version of the Bobtail (Fig. 3) with a direct connection of a 50-ohm power cable. The exact position of the phase of the external elements in the "inverted" version is achieved by connecting the conductors of the half-wave lines to the screen of the coaxial cable at the feed point.
Ris.3
On the 70 cm band, the antenna works like 3/4l, and the extreme elements are fed by 1,5l lines. Figure 4 shows a "wire" version of the design, where ab + ab = 3,04 m of stranded copper wire (a = 1 m, b = 52 cm); c - emitter 52 cm long; d - three supporting PVC pipes with a diameter of 15 mm and a length of 54 cm; e - 8 self-tapping screws; f - extensions from a synthetic cable.
Ris.4
In Fig. 5 - a "hard" version of an aluminum profile and tubes, where a is the middle bar of a 15x15 mm profile 1 m long; b - side strips (profile 11x11 mm, length 60 cm); c - three vertical radiators from a tube with a diameter of 6 mm and a length of 56 cm; d - bayonet 50-ohm connector; e - screw cable clamp PG7; f - steel screws 3,5x13 mm for fixing external emitters.
Ris.5
In the next modification, Rolf suggested using half of the Bobtail antenna (Fig. 6). In this case, however, the gain becomes 2 dB less, and the diagram is 25 ° wider (in the level of -3 dB), but a very compact design is obtained.
Ris.6
By adding a reflector, similar in design to the emitter, - increasing only the length of the vertical elements by 5%, the author received a unidirectional antenna (Fig. 7) with a gain of 6 dB (Fig. 8).
Ris.7
Ris.8
Figure 9 shows the design of a 2-element antenna, where a is a 50-ohm bayonet connector with a ground lobe; b - phasing line of copper insulated wire 1 m long with a diameter of 0,8-1 mm; c - two telescopic antennas from broadcasting receivers with threaded holes in the ends, pulled out to the required length; d - PVC pipe with a diameter of 25 mm and a length of 1 m; e - wooden plank 220x35x5 mm with two holders for PVC pipes; f - supporting PVC pipe with a diameter of 25 mm and a length of 22 cm; e - a suitable end fastening unit.
Ris.9
In Fig. 10 - the design of a unidirectional antenna, where a, b, c, d, e, f, g - similar to Fig. 79, and cg - the same telescopic antennas as c, but 5% longer, h - PVC pipe with a diameter 25 mm long 26 cm.
Ris.10
Literature
- "Funk" N 12/2000, p. 38,39; No. 1/2001, p. 42, 43
Publication: N. Bolshakov, rf.atnn.ru
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