Yagi-Uda the III.

No, this is not the name of another royal baby… it’s about my third attempt to build a 2m antenna for my SOTA activations. In my earlier iterations I was unable to strike the balance between size/weight and usability.

What happened so far:

Yagi - UltralightMy first attempt to build a Yagi-Uda antenna was based on a design by  Paul/KD5IVP. It worked, but had some crucial flaws for my endeavors. It was a 3-element antenna made out of piano wire and a carbon fiber arrow as a boom. Very small and  lightweight indeed but in high winds/gusts the elements were flapping like a seagull during take-off. It’s demise came on it’s second outing… the arrow broke in half while bushwhacking up a mountain and I lost some of the piano wires in the woods. To read more about it and to see it in action check out this post.

 

Yagi - TapemeasureI then moved on to a tape measure 3-element antenna based on a design by Joe/WB2HOL. It worked well and accompanied me on several activations –  even a few 14ers (Summits higher than 14’000 ft / 4267m). My main gripe with this antenna is that it is delicate to transport as well. The steel tape gets kinked easily since the antenna is strapped to the outside of my backpack. It’s rather easy to replace the director and reflector, but soldering the coax to the steel radiator is another story. It turned out that this design is also vulnerable to high winds and your arms start to feel the weight after a few minutes without support. You can see the antenna in action in this video, around 3:30 into the clip.

 

The one?
I continued my research for a suitable 2m Yagi-Uda which would fit my requirements:

  • Lightweight (but sturdy enough to withstand high winds)
  • Easy and save to transport
  • Easy to build (even for me)

I eventually stumbled onto IZ2UUF’s Website –  an Italian radio amateur who enjoys hiking and playing with radios as well. He designed an 4-element Yagi-Uda weighing only 80 grams (~2.9 ounces)!! All elements fit into the fiberglass boom (fishing rod) for easy transport with no matching network necessary. The description to build the antenna focused on the critical parts with excellent pictures to support the instructions.

Davide/IZ2UUF modeled the antenna with 4NEC2, a free antenna modeling software package. Since he shared his input file with me, I took the opportunity to download the free SW and to learn more about antenna modelling. After a few more e-mail exchanges with him I was convinced by his design and started to source all the parts.

The final productI did not have afiberglass fishing pole available and opted to use a plastic one I had lying around. Davide is using aluminum welding rods for his elements which I could not find at the desired length/diameter here in the US. I therefore ordered aluminum alloy 6061 rods instead (1/8″ x 6′ ) from a supplier in IL (for details see the resource section below). My build also differs in the connector (BNC instead SMA). All these changes resulted in a slightly heavier (194 g / 6.8 ounces) first version compared to Davide’s antenna. My boom alone is heavier than Davide’s complete antenna (96 g / 3.4 oz). However, I am planning to improve/reduce the weight in version two.

 

I had a chance to use the antenna over the week-end during the CO-14er event. All I can say so far is that it worked well and that the weight is not an issue at all… huge improvement to the tape-measure version.

 

 

Mount Evans 4339 m/14264 ft - WØ/FR-ØØ3

For more pictures, a weight comparison and resources head over to my blog.

73, Matt/KØMOS

Matt Schnizer, KØMOS, is a special contributor to AmateurRadio.com and writes from Colorado, USA. Contact him at k0mos at schnizer.com.

One Response to “Yagi-Uda the III.”

  • Arie JZ11CLS:

    Hello Matt,
    According to your experiments, which one is the best resonator on this Yagi matters? Ignore the impedance. Gamma match, t-match, etc?

    I can not decide by my self regarding this. Because with my own made FS meter, they all look like equal.

    73. Arie JZ11CLS Indonesia

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