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Приветствую Вас, Гость · RSS 23.08.2017, 05:11
Главная » Статьи » Антенны » Антенны КВ

2-Element-Portable-Yagi with 28/12.5 Ohm Dismantable, for 10 m-20 m (by DK7ZB)

2-Element-Portable-Yagi with 28/12.5 Ohm

Dismantable, for 10 m-20 m (by DK7ZB)

Because the 25-Ohm-Yagi is sometimes difficult to tune (you need an antenna-analyzer) I constructed another type with a radiaton resistance of 28/12,5 Ohm. For the balun we use an impedance choke. 

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 with a simple SWR-meter you can shift the end pieces of the radiator, the other element should not be changed. Each band has an own choke.

Band/Impedance

Principle

Bandwidth for SWR < 1,5

Gain

F/B

  10 m, 28 Ohm 

Radiator-Reflector

500 KHz

4,77 dBd

7,5 dB

12 m, 28 Ohm 

Radiator-Reflector

430 KHz

4,4 dBd

10,5 dB

15 m, 28 Ohm 

Radiator-Director

330 KHz

4,62 dBd

12 dB

17 m, 28 Ohm 

Radiator-Director

330 KHz

4,32 dB

17 dB

17 m, 12,5 Ohm 

Radiator-Director

100 KHz

5,1 dBd

6 dB

12 m, 28 Ohm 

Radiator-Director

240 KHz

3,45 dBd

12 dB

10 m and 12 m

15 m, 17 m and 20 m

For the impedance matching 28/50 Ohm we need two quarterwave pieces of 75-Ohm-coax parallel, for the 12.5-Ohm-type we use 2x50 Ohm parallel (DK7ZB-match).

Lengths for full-PE-cables (V = 0,667):

Band

Length

10 m

2x 1,76 m

12 m

2x 2,00 m

15 m

2x 2,36 m

17 m

2x 2,76 m

20 m

2x 3,54 m

With PL-connectors for RG213 it is possible to solder two cables RG59 (black) into one connector.

Better is 5,6-mm-CATV-cable (white).

Both cables handle 500 Wtts RF without any problems.

If you use cable with foam-PE, you must know the velocity of propagation (VF), in most cases it is 0,8-0,85.

Each band needs an individual choke!

The construction of the radiator middle part:

Needed tubes, fitting in a snowboard bag:

Tubes

Pieces

Length

Use

30x30x2 mm 1 155 cm Square boom

25x2 mm

2

74 cm

Middle pieces Radiator

25x2 mm

1

150 cm

Middle pieces parasitic elements

20x 1,5 mm

4

150 cm

Intermediate parts Radiator and parasitic elements

16x 1,5 mm

4

150 cm

Intermediate parts Radiator and parasitic elements

12x 1 mm

4

85 cm

End pieces Radiator and parasitic elements 10-17 m

The lengths of the tubes (for one element half!):

 

Effective tube lengths (add a part for pushing in)

25 mm

20 mm

16 mm

12 mm

10 mm

Length

10 m

CW

Rad

75 cm

135 cm

40,5 cm

-

-

250,5 cm

Ref

75 cm

135 cm

55 cm

-

-

265 cm

10 m

SSB

Rad

75 cm

135 cm

36,5 cm

-

-

246,5 cm

Ref

75 cm

135 cm

50 cm

-

-

260 cm

12 m

Rad

75 cm

135 cm

72,5 cm

-

-

282,5 cm

Ref

75 cm

135 cm

95 cm

-

-

305 cm

15 m

 

Rad

75 cm

135 cm

135 cm

8 cm

-

353 cm

Dir

75 cm

135 cm

122 cm

-

-

332 cm

17 m

12,5 Ohm

Rad

75 cm

135 cm

135 cm

68,5 cm

-

413,5 cm

Dir

75 cm

135 cm

135 cm

57,5 cm

-

402,5 cm

17 m

28 Ohm

Rad

75 cm

135 cm

135 cm

74,5 cm

-

419,5 cm

Dir

75 cm

135 cm

135 cm

48 cm

-

393 cm

20 m

CW

Rad

75 cm

135 cm

135 cm

135 cm

75 cm

555 cm

Dir

75 cm

135 cm

135 cm

135 cm

32 cm

512 cm

20 m

SSB

Rad

75 cm

135 cm

135 cm

135 cm

66 cm

546 cm

Dir

75 cm

135 cm

135 cm

135 cm

23,5 cm

503,5 cm

Категория: Антенны КВ | Добавил: URC (11.01.2011)
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