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Приветствую Вас, Гость · RSS |
26.04.2024, 07:50 |
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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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