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.

The Construction Principles for Duoband-Yagis 2 m/70 cm

 

An interesting phenomenon is the 3/2-lambda resonance of 2-m-elements on the 70-cm-band. 

A dipole for 2m has a very interesting azimuth pattern on 70cm.

0 dB = 0,85 dBd
Now we add the 70-cm-open-sleeve-element to the 2-m-dipole. The currents change and we have the highest current in the parasitic fed open-sleeve element. With the correct distance we get one feedpoint for two bands, on 70 cm with 50 +/- j 0 Ohm.

Pattern of this construction

0 dB = 4,63 dBd

We can use this open-sleeve-construction as the radiating system in a Yagi for two bands.