APs that require external antennas need special care. You need to configure the antennas properly, consider what role the AP serves (AP or bridge), and consider where the antennas are placed.
For more information on Wi-Fi antennas, flip back to Chapter 2, "Cisco Antennas."
Ideally, you locate the AP as close as possible to the antennas. The farther the signal has to travel across the cabling between the AP and the antenna, the more signal reduction (also known as RF attenuation) you experience. For instance, if you are locating an antenna in a courtyard to service clients roaming outside, don't place the AP in a closet, dozens of feet away from the antenna. Instead, place the AP outside in a weatherproof enclosure, so it's closer to the antenna. An even better idea is to use a 1300 series, which is weatherproof.
Signal loss depends on what type of cable you use. Cisco offers two types of cable. One is similar to LMR400 and has a loss of 6.7dB per 100 feet, whereas the other is similar to LMR600 with 4.4dB per 100 feet. For every 3dB, you lose about half the signal's power. This loss occurs on both transmission and reception. You can use higher-quality cable to reduce signal loss over longer cables, but keep in mind that higher-quality cable is more expensive.
In addition, if you use an 802.11a product, cable loss is an even more significant issue. Loss increases with frequency, and coaxial cable has even more attenuation with 5-GHz signals than 2.4-GHz signals.