I have been thinking for awhile about making a UHF Yagi antenna and spent a fair amount of time trying out several online calculators. Results from the calculators vary quite a bit, and that may cause a builder to spend a lot of time trimming and adjusting to get an antenna that is a good performer.
Why would anyone want to build an antenna when they can be easily purchased? A couple reasons come to mind. First, you may not want to spend a lot of money to buy a commercial antenna. Some will work fine and some will not. Althought the advertisements emphacize great performance is possible, results are not always up to the specs. We have all been there. Second, you will learn more by building and experimenting. And you can continue to tweak the DIY antenna until it performs to your expectations.
What about getting parts? (Think: The Shack) Parts can be obtained from several sources and you may even have some onhand already. You will have to add the ingenuity to put things together so it is sturdy as well as functional. There are plenty of videos on YouTube which can be helpful. One I just recently watched that had some great information was a presentation for the Sierra Nevada Amateur Radio Society by John Portune, W6NBC. The presentation is based on a detailed study back in 1948 by the Bureau of Standards (Now NIST) on the Yagi Uda antenna. The study is titled NBS Technical Note 688 and can be easily found on the internet search. Lots of math, so it’s not for those that hate math, for sure. However, John pretty well simplifies the concepts into just a few steps to actually build a Yagi. The video at this link (https://www.youtube.com/watch?v=gabzyN22pg4&t=66s is worth watching. John provides some good guidance on what materials he recommends for the boom, elements, and hair pin matching component.
In order to simplify all the element lengths and separation distances I have created a shared spreadsheet to compute the values based on John’s steps. The sheet is on my Google drive and can be accessed by going to this link: https://docs.google.com/spreadsheets/d/1RtRfx_vKAGwh7i9g1nsfz3iGNCStz1k3jGT_kzBYIn8/edit?usp=sharing
There are four tabs for the sheet: Instructions, Notes, Calculator, and Examples. If you go to the Calculator sheet, all you have to do is enter the frequency you want to make a Yagi for and press the Enter/Return key. The calculations should be completed showing the wavelength in different units. Element Spacing, Reflector Length, Driven Element Length, and Director Lengths are calculated.
Once the antenna is built you can tune it. John covers what to do for tuning, but it may take some experimenting and trial and error to get it just how you want it. With a 3-element you may see about 7 db gain relative to a dipole; 5-element about 9 dbd, and 6-element about 10 dbd. If you install it vertically you may be able to reach repeaters that are farther away than you reach currently. It will also make simplex contacts easier. Mounting it horizontally would allow for some pretty nice sideband contacts.
Also remember: Parts may be obtained at The Shack.
Let me know if you have questions or suggestions. w9wrp@yahoo.com
73, Bill
Comments