Open-sleeve principles VHF-Duoband principles Duoband-Yagi 6m/10m 10m-Dipole+ 3-El.- 6 m Triband-Yagi 6m/4m/2m   Duoband-Dipol 2m/70cm 2m/70cm 2+2/3 El. 2m/70cm 4+5 El. 2m/70cm 5+8 El. 2m-Moxon+2-El.-70cm

The vertical DK7ZB-Duoband-Dipole for 2m/70cm

This dipole for 2m with an open-sleeve- element for 70 cm must be mounted in front of a mast. Otherwise the feedpoint impedance for 2 m is 72 Ohm and not 50 Ohm. The mast acts as a reflector. Gain on 2 m is 2,6 dBd and on 70 cm is 4,6 dBd. The elements are made of 10x1 mm aluminium tubes. Do not use other diameters!

The radiator has a length of 936 mm from tip to tip with 10 mm spacing. The choke has 5 turns of RG174 on 25 mm.

Position of the elements are measured from center of element to outer side of the mast. 

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Element (10mm) 

Position

Length

2m-Dipole

280mm

936mm (tip to tip)

70cm-open-sleeve-element

307mm

316mm

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For a better pattern on 70 cm we should add a 70-cm-reflector. So we come to a vertical polarized 2-Element-Yagi for 70 cm.

The gain increases to 5,4 dBd on 70 cm, on 2 m we have no changes.

The 70-cm-open-sleeve-element must get a new length and an other position.

 

 

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 Element

Position

Length

70cm-Reflector

150mm

324mm

2m-Dipole

280mm

936mm (tip to tip)

70cm-open-sleeve-element

309mm

313mm

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