The Construction Principles for "open-sleeve"-Elements

The construction principles of the Duoband-Yagis depends on the "open-sleeve"- elements. The developping of these elements are shown down. You can construct not only "open-sleeve"-radiators, it is possible to use "open-sleeve"-directors, too.

First step: A tube ("sleeve") will be pushed over the dipole for f1. You will get a second resonance on another (higher) frequency f2.

Second step: The tube ("sleeve") will be replaced by two skeleton elements nearby ("open-sleeve"). You will get a second resonance on another frequency f2, too. Adjusting length and distance are much easier than with a tube element.

Third step: You need only one skeleton element for resonance on a second frequency f2. With the length of this "open-sleeve"-element you set the frequency f2, with the distance the radiation resistance for f2.

It is possible, to get a second resonance with a definend radiation resistance (impedance) with such an element. You can add more than one element for more resonances with one feedpoint.

The diameter and distance of all elements is very critical, a little difference causes severe changes in the parameters!

A special case is the combining of 145MHz and 435MHz, because 435MHz is an harmonic of 145MHz and the dipole 1 for 2m has a 3/2-lambda-resonance on 70cm.

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

Now we add the 70cm-open-sleeve-element to the 2m-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 70cm with 50 +/- j 0 Ohm.

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