Homebrew 12/17
Meter Yagi
by W4VAS

 

 

Being a tightwad, and low on cash, and needing a decent antenna for the WARC bands,
I began looking into different options for a gain antenna for 12 and 17 meters.
The main goal was performance with a secondary goal for low cost.
I looked at the sleeve driven antennas and the commercially made antennas (Cushcraft A3WS)
and decided to make my own variation of a 3 element trap yagi.
The sleeve driven antenna was excellent design, but the cost of aluminum drove the price up pretty high.
If you have a good stock of used aluminum for elements, that might be a better route.
I had very little aluminum to start with so materials cost mattered.

After downloading the Quick Yagi V4 application and doing some testing,
I have settled on a design that should work. The plans for the A3WS gave me some ideas.
Once I put the aluminum together and put the traps on it, the lengths were quite a bit longer than I had thought.
Obviously, the coax traps are not as inductive on 12 meters as the commercially made traps.

I had some used 7/8” tubing and purchased the rest in 72” lengths from http://www.cycle-24.com.
On the driven and director, the 7/8” stick was 3’ long and on the reflector, I used a 4’ stick. (So it would be long enough)
All other 72” sticks (3/4” 5/8” ½”) were cut in half making them 3’ and telescoped downward from 7/8” to ½” at both sides of the trap
and the very end after the trap was 3/8” tube for adjusting the 17 meter lengths.

I took a Ύ” OD ½” ID 6” long stick of fiberglass as a coil form and design frequency is 24.5 mhz.
(Research on the internet gleaned that you want the resonant frequency just outside the desired band).
(My grid-dip meter dips at 24 MHZ on these traps, so we are good there)

Here are the measurements of the elements as they ended up in the finished antenna.
           
(I used a 2” X 2” .062 thick 14’ long boom. ($42 at Metal Supermarkets in Tucker, GA 5-21-12)

Reflector element 240 inches total between the traps 20.5 inches past the trap.

7’ 3” space

Driven element 216.5 inches total between the traps 18” past the traps

6’ 3” space

Director 193 total between the traps 17.5” past the traps

 

I took a 1’ long piece of Ύ OD fiberglass for the insulator in the middle of the driven element.


 

I also used 6” long pieces of the same tube for the traps. (3/4” OD ½” ID)


 

I used a Ό” think 4” X 12” piece of aluminum stock and made a boom to mast bracket.

 

Trap design: Get the trap program from VE6YP


Use it to design your traps. As you can see, I used the small 50 ohm coax that was originally
used in 10Base2 networking. (I had a partial spool of it, so I made good use of what was left).
 You can use RG59, RG59 etc and the length are calculated for you using this app. (FREE!!!)
  If you set the app to use Metric, your measurements are more precise and easier to measure.
I added 40mm to the total and removed 20 mm outer insulation from each end to connect things us.
I drilled a hole into the center of the fiberglass tube and used some fairly stiff hookup wire to connect the shield
at one end to the center of the other end and use hemostats to guide the wire through the holes.
This made a clean, nice looking trap.
I then drilled holes on each end and used an eyelet and a sheet metal thread screw to attach trap wire to the element.
Just make sure there is a good mechanical connection from the trap to the aluminum on both sides of the trap.
Also, make sure all the traps are electrically the same direction.
I decided to make the “center conductor” point to the “Center” of the antenna.
(It was just easier to remember). It may not matter, but what the heck.

 

I have had this antenna in the air for a couple years now, and I must say, it is FANTASTIC!
I recently installed a HEX beam, and it works good, but can't match this antenna.

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