Triband-DK7ZB-VHF-Yagi for 6 m, 4 m and 2 m with one Feedpoint
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This Yagi was developed with EZNEC +5 and has only one
feeding point of 50 Ω
and a boomlength of 1,25 m. With this length a log-periodic would not
give satisfying results on 50 MHz.
It has 2 elements on 6 m and 4 m and 3 elements on 2 m. The boom is made from 20x20x1,5 mm Aluminium, the elements are all made with 10x1 mm-Aluminium tubes. No other diameters allowed for this design, do not scale for other tubes without a NEC-program!
Only a finetuning of the 2-m-open-sleeve radiator was necessary, the other elements have exact the predicted lengths! |
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The Triband-Yagi built by Jaap, PA0O |
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Element |
Function |
Position |
Length |
|
1 |
Reflector
6 m |
0 mm |
2914 mm |
|
2 |
Reflector
4 m |
300 mm |
2080 mm |
|
3 |
Reflector
2 m |
600 mm |
1044 mm |
|
4 |
Open-sleeve-Radiator
2 m |
1000 mm |
981 mm |
|
5 |
Radiator
6 m, fed |
1065 mm |
2764 mm |
|
6 |
Open-sleeve-Radiator
4 m |
1148 mm |
2006 mm |
|
7 |
Director
2 m |
1200 mm |
970 mm |
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Measured data with a Vector-Analyzer: The SWR between 40 MHz and 150 MHz shows SWR <1,1 in the bands with 6 m low-loss-cable Ecoflex-10. |
| The antenna is fed with a choke-balun. I used 11 turns
of Aircell-5 on a PVC-tube with 25 mm diameter. The length of the cable
is about 1,00 m.
The coax socket is mounted on the bottom of the radiator-box ang grounded to the boom. For better mechanical stability the box has an epoxy-plate. The 2-m-open-sleeve-radiator is not yet fixed with a screw for finetuning. In practise the choke has an influence on the 2-m-element which leads to a length correction. In this case element 4 was cut 3 mm and was shifted + 10 mm away from the 6-m-radiator. In the table are the corrected length and position of element 4. |
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The complex currents in the coupled system when fed with 144,3 MHz |
The measured SWR between 50 and 51 MHz
The measured SWR between 70 and 70,5 MHz
The measured SWR between 144 and 146 MHz
