Handiham World for 23 March 2011
Welcome to Handiham World!
The power of ice combined with wind is evident once again! As those of us whose antennas have had to weather many winters can tell you, there is little worse for an antenna system than ice combined with wind. I was reminded of this earlier today when I opened my email and found a message from AA9BB in Lacrosse, Wisconsin. It had a link to a story about the 2,000 foot WEAU TV transmitting tower that collapsed near Fairchild, WI during the ice and wind storm that moved through last night. We are still having a pretty terrible Spring blizzard from the same weather system here in the Twin Cities. Fortunately no one was hurt in the tower collapse, which was only discovered when the station engineer paid a call to the transmitter site to determine why the station had gone off the air. While there will obviously need to be an investigation into exactly why this tall tower fell, my money would be on the wind and ice combination causing the design limits to be exceeded.
When the wind blows, most amateur radio antennas will not be damaged. Wire antennas have little wind loading area, and beam antennas are made to flex in the wind. The problem comes when weather conditions are just exactly right to allow freezing rain to fall and turn to ice upon hitting the ground or your ham radio antenna. The extra weight of the ice can be several times the weight of the antenna itself, putting considerable strain on the supporting system components like insulators, guy wires, masts, and towers. This is bad enough, but then suppose that the wind picks up. As storm fronts move through, the weather conditions will change. There can be periods of regular rain followed by freezing rain as the temperature plummets, and then the wind can shift and pick up as the freezing rain picks up or turns to snow. Imagine the terrible wind load and strain on the supports as the antenna whips in the wind, pushed all the more by the greater wind loading due to the coating of ice. When the design limits are reached, the antenna or its supporting structure will fail.
What can you do about ice and wind? My feeling is that moving to someplace with a better climate might be the only sure-fire answer. Some places are more prone to ice storms than others, though, and about all you can do is build your wire antennas to withstand greater loads by using compression-style insulators instead of the “dog bone” style. Compression insulators are much less likely to break because more pull on the wires actually compresses the insulators instead of pulling them apart. Better quality wire can help, too, as can good, heavy-duty hardware at all supporting points. Antenna towers that telescope down during high wind conditions can help protect your antenna investment. At least the antenna will be closer to the ground where the wind may be less, and the entire structure presents less of a wind load when telescoped in the down position.
My wire antennas are not that great. One is a commercial Windom about 125 feet long and the other is an end-fed wire, also about 125 feet. Neither one was mounted with heavy-duty hardware, so if they come down in an ice storm with lots of wind, I wouldn’t be surprised. What I am doing is sort of playing the odds, since we don’t get those conditions together too often here. My Butternut vertical can pretty much take care of itself because it has almost no horizontal surfaces to collect heavy ice. Flexing in the wind just breaks the ice off and it falls harmlessly to the ground around the base. It is really the horizontal surfaces that you have to protect the most from icing. How much is an airline ticket to Florida? Can’t afford that? Try getting some compression insulators – they’re a lot cheaper.
Patrick Tice, WA0TDA
Handiham System Manager