Understanding Antenna Wind Load
When installing an antenna, a valid question to ask is “What is the impact of the wind blowing on the antenna?” For most home installations, the impact is negligible and isn’t a major concern. The way the effect of the wind on an antenna is measured is called the wind load. In order to determine the wind load, we need to determine the surface area of the antenna that will be impacted by the wind, and how easily the wind moves over it (the drag coefficient). We also need to know the expected wind in the location of the antenna. There can be a lot of math involved in these calculations, but in most cases for OTA antennas, the wind load is low enough that it isn’t a concern.
As stated above, the wind load of an antenna is a combination of how much surface area the antenna has, it’s drag coefficient (how easily the wind moves over it), and how much wind is pushing against the antenna. The generic formula for calculating wind load is F = A x P x Cd, where F is the wind load, A is the surface area of the antenna (usually given in square feet), P is the wind pressure (calculated from another formula) and Cd is the drag coefficient.
An OTA antenna has lots of open spaces for the wind to move through it, but it will still block some of the wind. Since the surface area of most OTA antennas is small, and the elements are generally round, the Cd will be quite low. With a small surface area and a low Cd, the wind load will also be low, so damage from wind is not expected. As a result, most OTA antennas don’t list the wind load. If the winds are high enough to damage the antenna, that is probably the least of your concerns as you will probably also have trees down and other damage.
The place where wind loading can become a concern is when installing a tower. It’s important to determine if local ordinances require a building permit for the tower. Local building codes will likely require a more involved formula with more variables. The Electronic Industries Alliance and the Uniform Building Code both have different formulas for calculating wind load, which may require detailed measurements and calculations. This may require the services of a structural engineer to sign off on the design.
In many cases, a tower properly mounted against a building will likely not be a concern, but guyed towers must be engineered properly. The height of the tower, and size of the antennas being installed on it, and the expected winds in your location will determine how many guy wires are needed, and at what heights on the tower they need to be attached. If you are considering installing a tower for your OTA antenna, seeking the assistance of an experienced tower installation company is advised.
The bottom line is that for most antenna installations, wind load is probably not a major concern. As long as everything is mounted properly and securely, your antenna should be fine. The only place it may become a concern is when installing tower. For professional wind load calculations on a particular installation you will want to provide your antenna weight and dimension specifications to a qualified engineer along with your specific installation location, height and mounting structure specifications.