Buzz
Gallery of Cell Phone ImagesMany of us encounter electromagnetic interference quite frequently. For instance:
- If I place my cell phone on my desk near my computer, I hear loud static through the speakers every time the phone connects with the tower. Similarly, my car's tape player emits static noise whenever I make a call on my cell phone.
- When I dial a number on my home's cordless phone, the number can be heard through the baby monitor.
- It's not unusual for a truck to pass by and have its CB radio interfere with the FM station I'm listening to.
- We’ve all experienced motors causing radio or TV static.
Technically, none of these occurrences should happen. For example, a truck's CB radio doesn't transmit on FM radio bands, so my radio should never pick up CB signals. However, all transmitters tend to emit weaker signals on harmonic sidebands, which is how the FM radio picks up the CB. The same principle applies to the wireless phone interfering with the baby monitor. In the case of the cell phone affecting the computer speakers, the speaker wires act as antennas, picking up sidebands in the audible range.
These issues aren't critical — they're just annoyances. However, notice how frequently they occur. In an airplane, similar issues can lead to serious problems.
An airplane is equipped with various radios for different tasks. One radio allows the pilots to communicate with ground control and air traffic control (ATC). Another radio broadcasts the plane's location to ATC systems. There are also radar units for navigation and weather monitoring, among others. All of these radios operate on specific frequencies, transmitting and receiving information. If a cell phone is turned on, it can transmit up to 3 watts of power. Should its signal overlap with any frequency the plane is using, messages between people or computers may become unclear. If a wire in the plane has inadequate shielding, it could pick up the cell phone's signals in a similar way to how my computer's speakers do. This could lead to corrupted messages between equipment inside the plane. Many hospitals now use wireless networks for connecting devices. For example, the heart monitor in How Emergency Rooms Work has an antenna that links it to the nursing station via a wireless network. If a cell phone causes interference, it can disrupt communication between devices. This happens even if the phone is simply turned on, as the phone and tower regularly exchange data every few minutes.
The ban on laptops and CD players during takeoff and landing addresses a similar concern, but this caution might fall under the principle of 'better safe than sorry.' A poorly shielded laptop could emit significant radio interference at its operating frequency, which could, in theory, cause issues.
