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This Yagi was developped 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!
Band
|
Gain
|
F/B
|
Bandwidth
SWR 1,5
|
6m
|
4,49
dBd
|
8,6
dB
|
1,75
MHz
|
4m
|
4,29
dBd
|
10,8
dB
|
1
MHz
|
2m
|
5,43
dBd
|
10,6
dB
|
>
2
MHz
|
Only
a finetuning of the 2-m-open-sleeve radiator was necessary, the other
elements have exact the predicted lengths! |
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
|
|
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. |
|
|
|
|
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
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