1. Physical Objects—Trees, masonry, buildings, and other physical structures are some of the most common sources of interference. The density of the materials used in a building's construction determines the number of walls the signal can pass through while maintaining adequate strength.
2. Radio Frequencies— Wireless technologies such as 802.11b/g use a range of 2.4GHz, as do many other devices, such as cordless phones and microwaves. Devices that share the channel can cause noise and weaken the signals.
3. Electrical Interference—Electrical interference comes from devices such as computers, refrigerators, fans, lighting fixtures, or motorized devices. The impact that electrical interference has on the signal depends on the proximity of the electrical device to the wireless access point.
4. Environmental Factors—Weather conditions can have a huge impact on wireless signal integrity. Lightning, for example, can cause electrical interference, and fog can weaken signals as they pass through.
5. Improper Installation—The root cause most Wi-Fi issues is installation. Improper cabling, use of low quality devices (access points, switches, routers, etc.), and poor positioning of Wi-Fi devices are the most likely culprits.