2El.617mV. Mk Vl 
2El.1017m25 Ohm 
2ElementPortableYagi with 25 Ohm,
dismantable, for 10 m20 m (by DK7ZB)
This Yagi has a constant elementdistance 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 reflectorradiatorYagi, 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 highgain 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 30x30x2mmsquareAlu, 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 

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 RuthtroffUnUn 50 Ohm to 28 Ohm with the windings 16 (1,0 mm isolated copperwire). The second Guanellatransformer is a 25OhmBalun UnBal, made with two parallel coaxcables RG174U. AB is the outer braid of the two cables, CD are the inner conductors. The mismatch 25/28 Ohm does not cause any problems. Both parts are wound on the same core, an Amidon FT24077. With RG174 the max. power is 200 Watts, with Tefloncoax RG188 about 500 Watts. Peter, HB9PJT, has tested the FT24061 as a better choice. He found that 3 trifilar windings for the balun 2:1 gave the best results of nearly 1:1 with this core. Look for the pictures of HB9PJT below! 
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+j15 Ohm 
51+j20 Ohm 
58+j19
Ohm 
66+j13
Ohm 
68+j9
Ohm 
67+j3
Ohm 
64+j5
Ohm 
SWR
50 Ohm 
1,5 
1,4 
1,4 
1,4 
1,4 
1,3 
1,2 
The director/reflector is mounted with two 5mmscrews and nuts (Inox steel)
The middle part of the radiator
The box with the balun
The Beam, built by Peter, HB9PJT. Click on the thumbnails for greater pictures!
Table 1: Lengths for the
10mBand (RadiatorReflector), 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
12mBand (RadiatorReflector), 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
15mBand (RadiatorDirector), 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
17mBand (RadiatorDirector), 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 SSBBand. Try it with the following tubes:
Table 5: Lengths for the
20mBand (RadiatorDirector), 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 