2-Element-portable-shortwave beam by DK7ZB

2-Element-Portable-Yagi with 28/12.5 Ohm

Dismantable, for 10 m-20 m (by DK7ZB)

Because the 25-Ohm-Yagi is sometimes difficult to tune (you need an antenna-analyzer) I constructed another type with a radiaton resistance of 28/12,5 Ohm. For the balun we use an impedance choke.

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 with a simple SWR-meter you can shift the end pieces of the radiator, the other element should not be changed. Each band has an own choke.

The 2-El.-28-Ohm Yagi built by Oli, CT1JGA

He has tested the difference between the 7-m-high Yagi and a HF9V-Vertical with 20 radials and optimal radiating conditions (see picture left). He reports 1-3 S-units plus for the Yagi in all situations.

Band/Impedance	Principle	Bandwidth for SWR < 1,5	Gain	F/B
10 m, 28 Ohm	Radiator-Reflector	500 KHz	4,77 dBd	7,5 dB
12 m, 28 Ohm	Radiator-Reflector	430 KHz	4,4 dBd	10,5 dB
15 m, 28 Ohm	Radiator-Director	330 KHz	4,62 dBd	12 dB
17 m, 28 Ohm	Radiator-Director	330 KHz	4,32 dB	17 dB
17 m, 12,5 Ohm	Radiator-Director	100 KHz	5,1 dBd	6 dB
20 m, 28 Ohm	Radiator-Director	240 KHz	3,45 dBd	12 dB


10 m and 12 m	15 m, 17 m and 20 m

For the impedance matching 28/50 Ohm we need two quarterwave pieces of 75-Ohm-coax parallel, for the 12.5-Ohm-type we use 2x50 Ohm parallel (DK7ZB-match).

Lengths for full-PE-cables (V = 0,667):

Band	Length
10 m	2x 1,76 m
12 m	2x 2,00 m
15 m	2x 2,36 m
17 m	2x 2,76 m
20 m	2x 3,54 m

With PL-connectors for RG213 it is possible to solder two cables RG59 (black) into one connector.

Better is 5,6-mm-CATV-cable (white).

Both cables handle 500 Wtts RF without any problems.

If you use cable with foam-PE, you must know the velocity of propagation (VF), in most cases it is 0,8-0,85.

Each band needs an individual choke!

Tubes	Pieces	Length	Use
30x30x2 mm	1	155 cm	Square boom
25x2 mm	2	74 cm	Middle pieces Radiator
25x2 mm	1	150 cm	Middle pieces parasitic elements
20x 1,5 mm	4	150 cm	Intermediate parts Radiator and parasitic elements
16x 1,5 mm	4	150 cm	Intermediate parts Radiator and parasitic elements
12x 1 mm	4	85 cm	End pieces Radiator and parasitic elements 10-17 m

		Effective tube lengths (add a part for pushing in)
		25 mm	20 mm	16 mm	12 mm	10 mm	Length
10 m CW	Rad	75 cm	135 cm	40,5 cm	-	-	250,5 cm
10 m CW	Ref	75 cm	135 cm	55 cm	-	-	265 cm
10 m SSB	Rad	75 cm	135 cm	36,5 cm	-	-	246,5 cm
10 m SSB	Ref	75 cm	135 cm	50 cm	-	-	260 cm
12 m	Rad	75 cm	135 cm	72,5 cm	-	-	282,5 cm
12 m	Ref	75 cm	135 cm	95 cm	-	-	305 cm
15 m	Rad	75 cm	135 cm	135 cm	8 cm	-	353 cm
15 m	Dir	75 cm	135 cm	122 cm	-	-	332 cm
17 m 12,5 Ohm	Rad	75 cm	135 cm	135 cm	68,5 cm	-	413,5 cm
17 m 12,5 Ohm	Dir	75 cm	135 cm	135 cm	57,5 cm	-	402,5 cm
17 m 28 Ohm	Rad	75 cm	135 cm	135 cm	74,5 cm	-	419,5 cm
17 m 28 Ohm	Dir	75 cm	135 cm	135 cm	48 cm	-	393 cm
20 m CW	Rad	75 cm	135 cm	135 cm	135 cm	75 cm	555 cm
20 m CW	Dir	75 cm	135 cm	135 cm	135 cm	32 cm	512 cm
20 m SSB	Rad	75 cm	135 cm	135 cm	135 cm	66 cm	546 cm
20 m SSB	Dir	75 cm	135 cm	135 cm	135 cm	23,5 cm	503,5 cm

Effective tube lengths (add a part for pushing in)