Here is my dual band VHF - UHF vertical dipole antenna. It works great and it offers you the option to properly adjust the SWR.
I wanted to build a vertical dipole for the VHF radio I had on my sailboat. I was never happy with the commercial models I used in the past. Since I am back on land for a while, I decided to build a VHF – UHF dual band vertical dipole for amateur radio. Specifically for the 2m and the 70cm amateur radio bands. For me was important to install it on the roof and use it for repeaters and local coms. So far I’m really happy about the performance. I made it almost entirely from scrap materials I had on hand.
DIPOLE ANTENNA POLARIZATION
I noticed a little confusion when it comes to the polarization. Some think is omnidirectional, while others think is directional. The truth is that it can be either one of them. If you install the antenna horizontally, it will be slightly directional. But installed vertically, it becomes omnidirectional. Similar to a ground plane antenna. Down bellow you have a graphic that it will help you understand how it works.
BUILDING THE ANTENNA
This vertical dipole is really easy to build. If you watch the video above, you will understand exactly how to build it. I made this drawing representing a cross section to help you with the construction details.
Consider using materials of your choice. I used whatever I had available. For the plastic bracket you can use a 3D printed one. I just happen to have the plastic one from an antenna my dad built.
The drawing should be self explanatory and in a few hours you should have it ready. Built well it will last a really long time with not much maintenance. A cleanup once an year should be more than enough.
In case you can’t see the details in the video, here you have some photos. On the extensions I made some markings at 1cm distance from each other.
This made it easier to do SWR adjustments. The spacer between the 2m and the 70cm elements, was made using a brass fitting. You can find these in the electrical connectors. It worked for me so that it what I used. The brass makes a good contact with the elements and so far there was no corrosion.
A nanoVNA should be enough for you to properly adjust the SWR. Is a little time consuming, but I recommend you to make the adjustments with the antenna installed. Anything around or the height of the antenna will influence the SWR. Extend or insert the extension tube for each band until you are happy with the SWR reading for each band. I like adjusting the SWR for the 2m band first. Then I adjusted for the 70cm band. After that I go back and forward between bands to make sure nothing changed as they may influence each other. Once you are happy with the SWR readings, tighten the screws of the extension tubes.
I didn’t build an HF version for my (tr)uSDX Transceiver just yet. I know a dipole has a better performance than an EFHW… plus that is not as noisy. In the past I tested the difference between an EFHW and a dipole on the CB band. I was way more impressed about the dipole to be honest.
73 DE YO6DXE