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Migration may also have a considerable impact on tow- er structural requirements. You should receive tower rigidity and wind loading factors before placing the new equipment on your tower. Tower Rigidity, Twist and Sway Requirements EIA/TIA Standard 222E specifies the tower twist and sway rigidity requirements that manufacturers must meet or exceed in their tower design. (see Figure 5). This requirement ensures that the antenna will remain operation- al (within 10 dB of nominal) during windy conditions. The EIA/TIA Standard specifies the maximum allowable tower twist and sway based on the half-power (3 dB) |
beamwidth of the antenna. The narrower the half-power beamwidth, the more restrictive the tower twist and sway requirements. Figure 6 displays the EIA/TIA Standard 222E maximum allowable tower twist and sway requirements for an 8 foot diameter antenna operating in the 2-GHz, 6.5-GHz and 10.5 GHz Operational Fixed, private microwave bands. As the frequency is increased from 2 GHz to 6.5 GHz, the maximum allowable tower twist and sway decreases from 3.5° to 1.0‚. The change requires an increase in tower rigidity by the substantial factor of 3.5. If your tower was originally designed to satisfy the rigidity specifications for a 2-GHz system, migration to the 6.5 GHz band may require tower stiffening to satis- fy the increased twist and sway requirements. |
| Antenna Type | Frequency MHz |
3 dB Beamwidth Degrees | Maximum Allowable Twist and Sway Degrees |
|---|---|---|---|
| PL8-18A | 1850-1990 | 4.5 | 3.5 |
| PL8-65D | 6425-7125 | 1.3 | 1.0 |
| PL8-105 | 10500-10700 | 0.9 | 0.7 |