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Construction Details |
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2-Element parasitic Yagis by DK7ZB for the Shortwave-Bands 10m-30m
Details of a dismantable Yagi built by DL2RMC for portable use see down
Details of a 20m-Yagi by F4EKQ: http://enduro.civaux.free.fr/antenne.htm
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No other antenna has a better relation between gain and expense than the 2-Element-Yagi. One element additional to the dipole will give you 4dB gain. Each further element will give much more mechanical problems and the increase in gain is only 1-2dB for the same bandwidth. What says the ARRL-Antenna-Book about this antenna? "The must bang for the buck". Right! Because the 10m, 15m and 20m-Bands need a greater bandwidth, the radiation resistance must be higher than for the smaller WARC-Bands. Therefore we take the Yagis with radiator-reflector and 50Ohms for 10m (greatest bandwidth), 28Ohms for 15 and 20m and the Yagis with radiator-director and 28Ohms for the WARC-Bands. If you have a height above ground of 10m or higher for a 12m-Yagi, you can try a 12,5Ohm-type for that band. The antenna needs a very clear surrounding! With a very short boom and small bandwidth you get very high F/B. |
Gain, F/B, Boomlength and Elements
of the 50-Ohm-Yagi with Reflector
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Band |
Impedance |
Gain |
F/B |
Boom |
Radiator |
Reflector |
|
10m |
50Ohm |
4,0dBd |
10,5dB |
1,76m |
4,93m |
5,36m |
Gain, F/B, Boomlength and Elements
of the 28-Ohm-Yagis with Reflector
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Band |
Impedance |
Gain |
F/B |
Boom |
Radiator |
Reflector |
|
15m |
28Ohm |
4,2dBd |
10dB |
1,61m |
6,87m |
7,22m |
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20m |
28Ohm |
4,0dBd |
10dB |
2,30m |
10,26m |
11,08m |
Gain, F/B, Boomlength and Elements
of the 28-Ohm-Yagis with Director
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Band |
Gain |
|
Boom |
Radiator |
Director |
|
12m |
4,3dBd |
14,5dB |
1,18m |
6,05m |
5,60m |
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17m |
4,5dBd |
13,5dB |
1,70m |
8,32m |
7,80m |
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30m |
4,4dBd |
14dB |
3,00m |
14,92m |
14,04m |
Gain, F/B, Boomlength and
Elements of the 12,5-Ohm-Yagi for 12m with Director
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Band |
Gain |
|
Boom |
Radiator |
Director |
|
12m |
4,4dBd |
>25dB |
0,67m |
6,09m |
5,78m |
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The antennas are fed with the DK7ZB-match . A quarter-wave choke of coax is grounded at the socket. 50Ohm: Single Lambda/4*V-coax 50Ohm 28 Ohm: 2xLambda/4*V-coax 75Ohm parallel 12,5 Ohm: 2xLambda/4*V-coax 50Ohm parallel
Length of the cables see table below |
Lengths of the Lambda/4-coax for the choke:
| Band | Lambda | Full-PE V=0,667 | Foam-PE V=0,82 (CATV) |
| 10 m | 10,60 m | 1,77 m | 2,17 m |
| 12 m | 12,03 m | 2,00 m | 2,47 m |
| 15 m | 14,18 m | 2,36 m | 2,90 m |
| 17 m | 17,53 m | 2,76 m | 3,60 m |
| 20 m | 21,18 m | 3,53 m | 4,34 m |
| 30 m | 29,62 m | 4,94 m | 6,07 m |
The dismantable Yagi by DL2RMC for portable use
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The Yagi of Tom, DL2RMC during his expedition to Corsica island (TK/DL2RMC) He has a cheap and simple construction similiar to my 3-Ele-portable Yagi with aluminium tubes as a leightweight antenna. Details see in the pictures below. For each band he has an own 2x75-Ohm-quarterwave matching cable. |
Insulated middle part of the radiator:
The middle part of the director:
All parts ready for assembling:
