This is a short build description of a 10-element yagi for the 70 cm band, based on a design by DK7ZB [1].

Boom

The boom is a 15x15 mm aluminium square tube with a length of 2 m which is very lightweight.

Elements

The elements are 10 mm aluminium tubes, which are connected to the boom by 3d-printed element holders.

Element Position Length
Reflector 0 mm 327 mm
Radiator 140 mm 315 mm
Director 1 235 mm 300 mm
Director 2 425 mm 287 mm
Director 3 650 mm 281 mm
Director 4 920 mm 272 mm
Director 5 1205 mm 269 mm
Director 6 1495 mm 269 mm
Director 7 1780 mm 274 mm
Director 8 1995 mm 269 mm

Simulation

The whole construction was modelled in Autodesk Inventor and a 3D field simulation was performed to verify the design.

E-field simulation

The farfield simulation results in a gain of 15.8 dBi, a 3 dB angular width of 32.5° and a front-to-back ratio of 30 dB.

Farfield simulation

Impedance Match

The feedpoint impedance of the radiating element is about 28 Ω. The simplest matching solution consists of two 75 Ω coaxial cables in parallel with a length of λ/4 [2]. The resulting line impedance of 37.5 Ω transforms the feedpoint impedance to 50 Ω. By coiling up the coax some common mode rejection can be achieved.


  1. DK7ZB: 10-Element-28Ohm-Yagi for 70cm ↩︎

  2. The DK7ZB-Match for Yagis ↩︎