2-El.-6-17m-V. Mk Vl |
2-El.-10-17m-28 Ohm |
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. |
The 2-El.-28-Ohm Yagi built by Oli, CT1JGA He has tested the difference between the 7-m-high Yagi and a HF9V-Vertical with 20 radials and optimal radiating conditions (see picture left). He reports 1-3 S-units plus for the Yagi in all situations. |
Band/Impedance |
Principle |
Bandwidth
for SWR
< 1,5 |
Gain |
F/B |
|
Radiator-Reflector |
500 KHz |
4,77
dBd |
7,5 dB |
12 m, |
Radiator-Reflector |
430 KHz |
4,4 dBd |
10,5 dB |
|
Radiator-Director |
330 KHz |
4,62
dBd |
12 dB |
17 m, |
Radiator-Director |
330 KHz |
4,32 dB |
17 dB |
17 m, |
Radiator-Director |
100 KHz |
5,1 dBd |
6 dB |
20 m, |
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 Lengths for full-PE-cables (V = 0,667):
|
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 |