So you have the Yagi Mechanical® program, you are ready to design an antenna, but what is this ‘Wind Spec’ thing all about? Which one should you choose? Is it important to your design? With this quick read-through, hopefully all of your questions will be answered.
Let us start with the question ‘Is this important to your design?’ The answer: it depends. If you live in an area with relatively low wind speeds and very little gusting, and you are designing an antenna to sit on a 30-foot pole, then the Wind Spec you choose will probably not make much of a difference in your design. But if you live on the outer banks, in tornado alley, or anywhere else that gets a lot of high-speed wind, then it is very important to your design. Most likely, you fall somewhere in between, so keep reading and you can pick a Wind Spec that suits your needs whether they are big or small.
What is a Wind Spec? Spec is short for specification, or in other words, a set of guidelines. There are several specifications in Yagi Mechanical® for choosing how to account for the effect the wind has on your antenna when you get it up on top of a tower. No Wind Spec is equivalent to placing your antenna in a wind tunnel, with a steady windspeed. This neither accounts for anything special in real world conditions, nor does it do any more than say “if you design your antenna for 90 mph winds with this, it will generally hold up under conditions where the wind does not reach that speed.” More than likely, if you are designing an antenna for your own personal use and you design it for 100 mph in an area where the gusts never reach 100 mph, then No Wind Spec should be fine.
EIA-222-C is the next step up. It still does not take into account factors like height, but it is based on real wind situations and can be used with maximum speeds from different zones (Zone A = 86.6 mph, Zone B = 100 mph, Zone C = 111.8 mph) to be even more accurate. So if you live in zone A and design at 90 mph with EIA-222-C, you can be pretty sure that your antenna will hold up. Most of the U.S. is in zone A, with most of the Atlantic and Gulf shores, the northern great plains, areas west of Lake Michigan, western Washington state, and parts of northern California in zone B, and south Florida and east North Carolina in zone C. Note that although this spec is included in Yagi Mechanical®, its use is not recommended because it is virtually an obsolete spec.
If you want a more detailed calculation, take another step up and use the UBC-97 spec. This is a very flexible spec, and useful if you want to factor in geographical features, height, and windspeed. By choosing a wind exposure level, you can use UBC-97 to get results much more applicable for your location. The different wind exposures are defined as the following: Exposure B is a site with 20% or more of the surrounding mile of land covered by buildings, forest, or anything else which impedes the wind; Exposure C is a mostly flat and open site, with a half mile or more empty terrain surrounding it; Exposure D is a site with basic wind speeds of 80 mph or more, and has a large body of water nearby, and unobstructed.
The last Wind Spec is EIA-222-F/G. It is a modern revision of EIA-222-C and it takes the height of the antenna into consideration, resulting in a much more conservative design. But it has the added advantage of using maximum speeds according to counties rather than the generic zones. A listing of these speeds can be found here. - https://wirelessestimator.com/content/standards/eia_tia_222/rev-g-windspeed-general
So which Wind Spec should you choose? The decision is yours. The most hassle-free choice is to use No Wind Spec. You get totally worthwhile results without having to worry about what zone you are in or how high you plan to mount your antenna. But if you want results that are more accurate and localized, the EIA and UBC specs are a better fit.