In most cases a dipole has better
radiation angles and gain than a simple vertical antenna. Exception is
operating on the low bands, where dipoles close to the ground have no DX
performance.
For portable operation a height of 10
m can be possible for a dipole for the 10-m-band, built with tapered
aluminium tubes. For the following examples we use a 14-MHz-antenna.
 |
The normal Dipole
Impedance is 72 Ohm |
| Because it is difficult to find to 10 m high places for
mounting the two legs of the dipole, it is much easier to use only one
mast and an Inverted-V mounting of the dipole. The advantage is that we
need only one support, but the disadvantage is the higher elevation
angle in comparison with the normal dipole. That means, the
DX-performance of the Inverted-V is not so good as we need. The
impedance is lower and is influenced by the angle of the wires and the
height above ground (35-55 Ohm). |
 |
| For constructing the Inverted-V the table left has the
lengths for a mounting of the antenne top in a heigth of 10 m. The angle
between the two legs is 90°. The data are for 2-mm-not insulated wires.
With insulated wires the lengths are 1-2% less.
Of cause the angle can be greaiter than 90°, then the impedance
is raising.
The different impedances are caused by the effective heights above
ground. |
|
Band
|
Lengths
|
Impedance
|
|
10
m
|
2
x 2,62 m
|
48
W
|
|
12
m
|
2
x 2,96 m
|
45
W
|
|
15
m
|
2
x 3,50 m
|
35
W
|
|
17
m
|
2
x 4,12 m
|
37
W
|
|
20
m
|
2
x 5,26 m
|
55
W
|
|
30
m
|
2
x 7,24 m
|
56
W
|
|
40
m
|
2x
10,29 m
|
38
W
|
|
 |
The central part is a tapered dipole for the 10-m-band.
On each side 25% of the dipole is bent down. So we come to the
Inverted-U with better performance than the Inverted-V.
For the support we need a entral mast, made of glassfibre or
aluminium. |
For the construction of the
Inverted-U see down!
For a comparison of the three antennas I have plotted the
azimuth and elevation patterns:
|
Type
|
Elevation
Main Lobe
|
Gain
|
|
Dipole
|
29°
|
4,79
dBd
|
|
Inverted-V
|
34°
|
3,16
dBd
|
|
Inverted-U
|
29°
|
4,16
dBd
|
|
The table shows the advantage of the Inverted-U against
the Inverted-V. All antennas 14,15 MHz, top of the mounting 10 m above
ground. |
The central part of the Inverted-U-Dipole with a glassfibre
tube for reinforcing
The construction of the mast holder and the connection box
 |
The W1JR-current Balun for feeding.
For 3,5-50 MHz the FT140-43 is a good choice. For
higher power up to 1 KW a FT240-43 is recommended.
The core is not critical! |
|
I have used PTFE-coax, but RG58 is possible, too.
2x3 turns on an Amidon FT140-66 core.
|
 |
 |
The construction of the center part. With the given
lengths this is a normal dipole for 10 m. For the other bands additional
2-mm-wires are added at each side like the picture down shows.
With the given tapering the dipole has 2x 2,57 m length.
|
|
Band
|
Lengh
L
|
|
10
m
|
-
|
|
12
m
|
44
cm
|
|
15
m
|
105
cm
|
|
17
m
|
178
cm
|
|
20
m
|
307
cm
|
|
 |
 |
For 30 m and 40 m the additional wires are mounted
with an angle of 45°.
| Band |
Length
L |
|
30
m
|
510
cm
|
|
40
m
|
790
cm
|
|
| 
Меню сайта