2-Element-Portable-Yagi with 25 Ohm, dismantable, for 10 m-20 m (by DK7ZB) - Антенны КВ - Антенны - Каталог статей - Radio
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Приветствую Вас, Гость · RSS 16.01.2017, 15:46
Главная » Статьи » Антенны » Антенны КВ

2-Element-Portable-Yagi with 25 Ohm, dismantable, for 10 m-20 m (by DK7ZB)

This Yagi has a constant element-distance of 1,50 m. You must only correct the lengths of the elements for QSY, see table down. For the bands 10 m and 12 m the Yagi is working as a reflector-radiator-Yagi, for 15 m and 17 m as a beam with radiator and director. All parts are not longer than 1,55 m and fit in a fishing bag for the transportation. The Yagis are a high-gain beams with small bandwidth. The dipole must be mounted insulated with two halfs, spacing 20 mm.

For tuning you can shift the end pieces of the radiator, the other element should not be changed.

Short data for the 4 bands (free space)

 

10m

12m

15m

17m

Gain

4,8dBd

4,6dBd

4,6dBd

4,5dBd

F/B

6dB

9dB

12dB

16dB

Needed aluminium parts for the beam

Dimension

Use

1 piece 30x30x2mm-square-Alu, 155cm

Boom

2 pieces round tube 25x2mm, 150cm

inner pieces rad + ref/dir

4 pieces round tube 20x1,5mm, 150cm 

middle pieces for the elements

4 pieces round tube 16x1,5mm, 150cm 

middle pieces for the elements

2 pieces round tube 12x1,0mm, 85cm+60cm

outer pieces for the elements

The schematic picture of the beam (one element half)

The Balun

The impedance for all bands is 25Ohm, so we use a homemade balun 1:2 for the matching 25Ohm balanced to 50Ohm unbalanced. The balun has two sections on the same core and the principle is shown in the picture right.

The first part is a trifilar Ruthtroff-Un-Un 50 Ohm to 28 Ohm with the windings 1-6 (1,0 mm isolated copper-wire).

The second Guanella-transformer is a 25-Ohm-Balun Un-Bal, made with two parallel coax-cables RG174U. A-B is the outer braid of the two cables, C-D are the inner conductors. The mismatch 25/28 Ohm does not cause any problems.

Both parts are wound on the same core, an Amidon FT240-77. 

With RG174 the max. power is 200 Watts, with Teflon-coax RG188 about 500 Watts.

The table shows that the balun has an inductive part +j  which can be compensated by shortening the radiator halves.

Band

6m

10m

12m

15m

17m

20m

30m

Impedance

38+j15W

51+j20W

58+j19W

66+j13W

68+j9W

67+j3W

64+j5W

SWR 50W

1,5

1,4

1,4

1,4

1,4

1,3

1,

The director/reflector is mounted with two 5-mm-screws and nuts (Inox steel)

The middle part of the radiator

The box with the balun

Table 1: Lengths for the 10-m-Band (Radiator-Reflector), one half

Tubes

25x2mm

20x1,5mm

16x1,5mm (CW)

16x1,5mm (SSB)

Reflector

75cm

135cm

51cm

47cm

Radiator

75cm

135cm

40cm

37,5cm

Table 2: Lengths for the 12-m-Band (Radiator-Reflector), one half  

Tubes

25x2 mm

20x1,5 mm

16x1,5 mm

Reflector

75 cm

135 cm

92 cm

Radiator

75 cm

135 cm

73,5 cm

Table 3: Lengths for the 15-m-Band (Radiator-Director), one half  

Tubes

25x2 mm

20x1,5 mm

16x1,5 mm

12x1 mm

Radiator

75 cm

135 cm

135 cm

9 cm

Director

75 cm

135 cm

123,5 cm

-

Table 4: Lengths for the 17-m-Band (Radiator-Director), one half  

Tubes

25x2 mm

20x1,5mm

16x1,5 mm

12x1 mm

Radiator

75 cm

135 cm

135 cm

74 cm

Director

75 cm

135 cm

135 cm

50 cm

It is possible to use the Yagi for 20m with reduced gain of 3,6 dBd. We must decide if we use the CW- or the SSB-Band. Try it with the following tubes:

Table 5: Lengths for the 20-m-Band (Radiator-Director), one half

Rohre

25x2 mm

20x1,5 mm

16x1,5 mm

12x1 mm

10x1 mm (CW)

10x1mm (SSB)

Radiator

75 cm

135 cm

135 cm

135 cm

73 cm

65 cm

Director

75 cm

135 cm

135 cm

135 cm

34 cm

29 cm
Категория: Антенны КВ | Добавил: URC (11.01.2011)
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