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You also should consider the ability of the tower to support the antenna wind loads. Two forces and a moment are important; Axial Force (Fa), Side Force (Fs), and Moment (Fmt). See Figure 7. Re-evaluation of the exist tower structure is especially important if, due to the migration, the antenna type is being changed. Figure 8 displays the maximum wind forces and mo- ments produced by various types of 8-foot diameter antennas. As an example, assume a 2-GHz system where the tower was originally designed to support the wind load of 2-GHz grid antennas. Migration to the 6.5 GHz band requires upgrading these antennas from grids to shielded (HP/UHX) antennas. When the antenna is changed from a grid to a shielded type, the magnitude of wind loads that the tower must support are almost doubled! Reinforcing of tower members may be required to support the additional wind load. |
 Figure 7 - Tower Wind Loading, Wind Forces and Moments |
| Antenna Type | Fa Max., lb | Fs Max., lb | Fmt Max., ft-lb |
|---|---|---|---|
| Grid, no ice | 1115 | 620 | -1820 |
| Standard, w/o radome | 3460 | 950 | -3940 |
| Standard, w/radome | 1790 | 1075 | +3720 |
| HP/UHX | 2560 | 1200 | -3570 |