https://support.apple.com/en-us/HT201542

Potential sources of Wi-Fi and Bluetooth interference

Sources of interference

These things can cause interference with Wi-Fi networks and Bluetooth devices if they are nearby.

Microwave ovens

Using your microwave oven near your computer, Bluetooth device, or Wi-Fi base station might cause interference.

Direct Satellite Service (DSS)

The coax cable and connectors used with some types of satellite dishes can cause interference. Check the cabling for damage that could cause radio frequency interference (RF leakage). Try replacement cables if you suspect interference.

Power sources

Certain external electrical sources like power lines, electrical railroad tracks, and power stations can cause interference. Avoid locating your AirPort Base Station, AirPort Time Capsule, or Wi-Fi router near power lines in a wall, or near a breaker box.

2.4 GHz or 5 GHz phones

A cordless telephone that operates in the 2.4 GHz or 5 GHz range can cause interference with wireless devices or networks while taking calls.

Wireless RF video 

Wireless video transmitters that operate in the 2.4 GHz or 5 GHz bandwidth can cause interference with wireless devices or networks.

Wireless speakers

Wireless audio that operates in the 2.4 GHz or 5 GHz bandwidth can cause interference with other wireless devices or networks.

Certain external monitors and LCD displays

Certain displays can emit harmonic interference, especially in the 2.4GHz band between channels 11 and 14. This interference might be stronger if you're using a notebook computer with the lid closed and have an external monitor connected. Try changing your access point to use 5 GHz or a lower 2.4 GHz channel.

Poorly shielded cabling

External hard drives or other devices with poorly shielded cabling can interfere with your wireless devices. If disconnecting or turning off the device appears to help, try replacing the cable that connects the device to your computer.

Other wireless devices

Other wireless devices that operate in the 2.4 GHz or 5 GHz bandwidth (microwave transmitters, wireless cameras, baby monitors, a neighbor's Wi-Fi device) can cause interference with Wi-Fi or bluetooth connections.

Some devices might not specifically state that they operate in the 2.4 GHz or 5 GHz band. The product's documentation should indicate the bands the device uses to operate. These might be referred to as "Dual Band" or "Wi-Fi" or "Wireless" devices.

Wireless barriers

A device's location and building construction materials can affect Wi-Fi and Bluetooth performance. If possible, avoid barriers or change the placement of your Wi-Fi or Bluetooth devices for a clearer signal path. 

Examples:

• Your computer is underneath a metal desk and you try to use a wireless (Bluetooth) mouse on top of the desk. The metal in the desk might act as a shield between the mouse and your computer. You might not be able to pair the device to your computer, or the pointer might move erratically.
• Your AirPort Base Station is downstairs and your computer is upstairs. The material between the two floors is concrete with metal reinforcement. The floor might lower or block the Wi-Fi signal from your base station to your computer. You might see slower network speeds, lower signal strength, or might not be able to connect to your Wi-Fi network at all.

Radio Frequency (RF) reflective and absorbing obstructions include the following:

Type of Barrier	Interference Potential
Wood	Low
Synthetic material	Low
Glass	Low
Water	Medium
Bricks	Medium
Marble	Medium
Plaster	High
Concrete	High
Bulletproof glass	High
Metal	Very high

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