Building a Weatherproof YAGI
By using 1/2-inch copper tubing for the elements and 3/4 inch for the boom, the antenna can be made strong enough to deal with ice formations on the elements. This is a good size element for a UHF YAGI, but for either 2 meters or 220 MHz the usage of 1 inch copper tubing for the boom and 3/4 inch for the elements would be better. Type M copper tubing is the best choice as it is harder than type L. You will also need caps to seal off the elements to keep water out of the boom and the elements where it could freeze and split the tubing.
The formulas for making a YAGI for any band can be found in any of the handbooks published by The ARRL or any of the other antenna books that deal with antenna construction. Also, the formulas can be found here in antenneX, in last month’s issue. Aside from the antenna dimensions which are determined from the formulas, you will need a torch and acid core solder to make your beam. It goes without saying that the beam will have to be a “plumbers delight” beam and you will have to use either a gamma match or other similar matching system. You will also need a drill press or other method of boring the holes in the boom accurately. A tubing cutter is required, unless you want to use a hacksaw.
After you have determined the element lengths and spacing from the formulas, the elements have to be cut to length and the spacing on the boom marked for drilling. A center punch will make the hole drilling easier to start, as the center punched dimple will keep the drill from sliding off of the boom. After the holes are drilled through the boom, the elements need to be inserted through the boom and centered correctly through the boom. Once this is done, the elements and the boom need to be cleaned where they will be soldered together and then all elements soldered in place.
If you have correctly cut the elements, the antenna should then be ready for you to set the matching network correctly for minimum SWR. After you have finished setting the matching system for minimum SWR, you need to seal the matching network for weather protection as well. Do not forget to solder the end caps on the boom and the elements to keep moisture out of them. You can paint the antenna with epoxy for even more protection.
Lastly, be sure your antenna feedline connection is also weatherproofed. I found that covering a tape wrapped connection with a layer of hot glue and using a torch with a low flame to melt the glue into a smooth layer makes a connection that is nearly impossible to penetrate after the glue has cooled and hardened. I have a splice I cut off of a connection with the thought of salvaging the connectors and the barrel connector. I had to give it up until later on in the next century as it was too hard to get that glue off. So, be sure your connections have no shorts in them before you use this method of sealing. If you do want to use this method, usually the heat never gets too hot for the coax, but you can pour water over the connection to cool it off if desired.
This is only one approach to getting an antenna that will better endure the blows of Old Man Frost. There are others I am sure, but this one has been used in some of the worst areas in the mountains on this continent and at last report the antennas were doing fine except for the one that took a direct hit by lightening, although it was repairable.
Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF
Last Updated : 8th March 2024