VHF / UHF Dual Band Vertical Dipole Antenna

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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 available at the time.

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 ( Fig. 1 ). 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.

Fig. 1 – Dipole Antenna Polarization

Fig. 2 – VHF / UHF Vertical Dipole Antenna Details

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 ( Fig. 2 ) 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 a TV antenna my dad built back in 84′.

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 every year should be more than enough.

Fig. 3 – Electrical Connectors

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 ( Fig. 4 ).

This made it easier for me to adjust the SWR. The spacer between the 2m and the 70cm elements it’s a brass fitting ( Fig. 3 ). 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.

Fig. 4a – Plastic Bracket Detail

Fig. 4b – Antenna Elements Connection

Fig. 4c – Vertical Dipole Closeup View

Fig. 4d – Antenna Extension Tubes Detail

SWR ADJUSTMENT

A nanoVNA should be enough for you to properly adjust the SWR. Is a little time consuming, but I would recommend you to make the adjustments with the antenna installed ( Fig. 5 ). 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.

73, YO6DXE