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 you can shift the end pieces of the radiator, the
other element should not be changed.
Short data for the 4 bands (free space)
|
10m
|
12m
|
15m
|
17m
|
Gain
|
4,8dBd
|
4,6dBd
|
4,6dBd
|
4,5dBd
|
F/B
|
6dB
|
9dB
|
12dB
|
16dB
|
Needed aluminium parts for
the beam
Dimension
|
Use
|
1 piece 30x30x2mm-square-Alu, 155cm
|
Boom
|
2 pieces
round tube 25x2mm, 150cm
|
inner
pieces rad + ref/dir
|
4 pieces round tube 20x1,5mm, 150cm |
middle pieces for the elements |
4 pieces round tube 16x1,5mm, 150cm |
middle pieces for the elements
|
2 pieces round tube 12x1,0mm, 85cm+60cm |
outer
pieces for the elements
|
The schematic
picture of the beam (one element half)
The
Balun
The impedance for all bands is 25Ohm, so we use a homemade balun 1:2 for the matching 25Ohm balanced to 50Ohm
unbalanced. The
balun has two
sections on the same core and the principle is shown in the picture right.
|
|
|
The first part is a trifilar
Ruthtroff-Un-Un 50 Ohm to 28 Ohm with the windings 1-6 (1,0 mm isolated
copper-wire).
The second Guanella-transformer is a
25-Ohm-Balun Un-Bal, made with two parallel coax-cables RG174U. A-B is
the outer braid of the two cables, C-D are the inner conductors. The
mismatch 25/28 Ohm does not cause any problems.
Both parts are wound on the same core, an
Amidon FT240-77.
With RG174 the max. power is 200
Watts,
with Teflon-coax RG188 about 500 Watts. |
The table shows that the balun has an inductive part
+j which can be compensated by shortening the radiator halves.
Band
|
6m
|
10m
|
12m
|
15m
|
17m
|
20m
|
30m
|
Impedance
|
38+j15W
|
51+j20W
|
58+j19W
|
66+j13W
|
68+j9W
|
67+j3W
|
64+j5W
|
SWR
50W
|
1,5
|
1,4
|
1,4
|
1,4
|
1,4
|
1,3
|
1,
|
The director/reflector is mounted with two 5-mm-screws and nuts
(Inox steel)
The middle part of the radiator
The box with the balun
Table 1: Lengths for the
10-m-Band (Radiator-Reflector), one
half
Tubes
|
25x2mm
|
20x1,5mm
|
16x1,5mm
(CW)
|
16x1,5mm
(SSB)
|
Reflector
|
75cm
|
135cm
|
51cm
|
47cm
|
Radiator
|
75cm
|
135cm
|
40cm
|
37,5cm
|
Table 2: Lengths for the
12-m-Band (Radiator-Reflector), one
half
Tubes
|
25x2
mm
|
20x1,5
mm
|
16x1,5
mm
|
Reflector
|
75
cm
|
135
cm
|
92
cm
|
Radiator
|
75
cm
|
135
cm
|
73,5
cm
|
Table 3: Lengths for the
15-m-Band (Radiator-Director), one
half
Tubes
|
25x2
mm
|
20x1,5
mm
|
16x1,5
mm
|
12x1
mm
|
Radiator
|
75
cm
|
135
cm
|
135
cm
|
9
cm
|
Director
|
75
cm
|
135
cm
|
123,5
cm
|
-
|
Table 4: Lengths for the
17-m-Band (Radiator-Director), one
half
Tubes
|
25x2
mm
|
20x1,5mm
|
16x1,5
mm
|
12x1
mm
|
Radiator
|
75
cm
|
135
cm
|
135
cm
|
74
cm
|
Director
|
75
cm
|
135
cm
|
135
cm
|
50
cm
|
It is possible to use the Yagi for 20m
with reduced gain of 3,6 dBd. We must decide if we use the CW- or the SSB-Band.
Try it with the following tubes:
Table 5: Lengths for the
20-m-Band (Radiator-Director), one
half
Rohre
|
25x2
mm
|
20x1,5
mm
|
16x1,5
mm
|
12x1
mm
|
10x1
mm
(CW)
|
10x1mm
(SSB) |
Radiator
|
75
cm
|
135
cm
|
135
cm
|
135
cm
|
73
cm
|
65
cm |
Director
|
75
cm
|
135
cm
|
135
cm
|
135
cm
|
34
cm
|
29
cm | |