My Homemade 70cm “Cheap Yagi”
I got the inspiration to build this antenna from an article authored by Kent Britain (WA5VJB)
I have reposted that article in PDF format here
The original article is on Kent's website
The antenna is rather easily made with the following materials:
A wooden stick about 36” long and about ½” – ¾” thick. The antenna only needs about 28” but the rest can be used as a handle or for mounting purposes.
Some #8 aluminum ground wire for the reflector and directors. I found some of the wire that Radio Shack used to sell.
A piece of #10 AWG solid copper wire for the driven element. I made the curved part exactly as indicated in the article, and I made the long top part about 2” longer than specified so I'd have room to shorten it as needed while tuning.
The dimensions can be found in the article – look for the section describing the 450MHz antenna on page 4. Be sure to cut the elements precisely, and to space them just as described in the article.
The wire used in this project bends somewhat easily. I was fussy and made my elements as straight as I could. If one knocks the antenna against something, the elements will bend. Just bend them back into place by hand and eyeball the alignment.
I tried tuning the antenna with my dual needle SWR meter and an HT. The mistake I made was that I took measurements at 5MHz intervals. I should have taken measurements at 1MHz intervals. I quickly realized this mistake when I began to use the antenna analyzer.
I borrowed an antenna analyzer from a fellow ham, which allowed me to quickly tune the antenna to about 443 MHz (my chosen sweet spot). Trim off pieces of the driven element (the copper wire) that are very small, say, 1/8”, until you get close to the desired sweet spot, and then take off very tiny pieces of about 1/16” in length. I was surprised that reducing the driven element's length by 1/16” moved the sweet spot about 1-2 MHz(!) once I got close to the desired frequency.
Note that the bandwidth of the antenna is around 5-6 MHz, so it won't cover all of the repeaters in the 440-450 MHz range. One will note in the picture below that I have it mounted for vertical polarization.
It seems to be working well based on signal reports from others, even though it was tested from inside my house with 5W or less. I've gotten great reports from at least 30 miles away.
Here are some pictures:
This picture is of the yagi in my house on its mounting stand, which is made of wood and a short piece of PVC pipe. Eventually, I may mount it outside, after appropriately weatherproofing the antenna.
Here is a picture of the plot of the SWR values versus frequency. Of course, your version will probably be a little bit different.
Here is a photo of the yagi mounted onto a PVC mast, shared with my 2m homebrew cubical quad. The antenna has found a new home in my attic. The additional PVC pipe on the right is a counterweight. A PVC tee cross was used to connect all 4 pieces of pipe together.
Many thanks to fellow hams Ernie (N1AEW) and Allison (KB1GMX) and Bo (WA1QYM) for helping in many ways as I constructed this antenna. Thank you, Kent (WA5VJB) for designing this antenna in the first place. :-)
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This page was most recently updated on May 20, 2012.