Most of us experience electromagnetic interference on a fairly regular basis. For example:
• If you put your cell phone down on your desk near the computer, you can hear loud
static in your computer's speakers every time the phone and the tower handshake. In the
same way, your car's stereo produces loud static whenever you make a call on your cell
phone.
• When you dial a number on your home's wireless phone, you can hear the number being
dialed through the baby monitor.
• It is not uncommon for a truck to go by and have its CB radio overwhelm the FM station
you am listening to.
• Most of us have come across motors that cause radio or TV static.
None of these things, technically, should be happening. For example, a truck's CB radio is not
transmitting on the FM radio bands, so your radio should never hear CB signals. However, all
transmitters have some tendency to transmit at lower power on harmonic side bands, and this is
how the FM radio picks up the CB. The same thing holds true for the wireless phone crossing
over to the baby monitor. In the case of the cell phone affecting the computer's speakers, the wire
to each speaker is acting like an antenna, and it picks up side bands in the audible range.
These are not dire problems -- they are just a nuisance. But notice how common they are. In an
airplane, the same phenomena can cause big trouble.
An airplane contains a number of radios for a variety of tasks. There is a radio that the pilots use
to talk to ground control and air traffic control (ATC). There is another radio that the plane uses
to disclose its position to ATC computers. There are radar units used for guidance and weather
detection, and so on. All of these radios are transmitting and receiving information at specific
frequencies. If someone were to turn on a cell phone, the cell phone would transmit with a great
deal of power (up to 3 watts). If it happens to create interference that overlaps with radio
frequencies the plane is using, then messages between people or computers may be garbled. If
one of the wires in the plane has damaged shielding, there is some possibility of the wire picking
up the phone's signals just like my computer's speakers do. That could create faulty messages
between pieces of equipment within the plane.
Many hospitals have installed wireless networks for equipment networking. For example, in
case of a heart monitor, the black antenna sticking out of the top of the monitor connects it back
to the nursing station via a wireless network. If you use your cell phone and it creates
interference, it can disrupt the transmissions between different pieces of equipment. That is true
even if you simply have the cell phone turned on -- the cell phone and tower handshake with
each other every couple of minutes, and your phone sends a burst of data during each handshake.
The prohibition on laptops and CD players during takeoff and landing is addressing the same
issue, but the concerns here might fall into the category of "better safe than sorry." A poorly
shielded laptop could transmit a fair amount of radio energy at its operating frequency, and this
could, theoretically, create a problem.
• If you put your cell phone down on your desk near the computer, you can hear loud
static in your computer's speakers every time the phone and the tower handshake. In the
same way, your car's stereo produces loud static whenever you make a call on your cell
phone.
• When you dial a number on your home's wireless phone, you can hear the number being
dialed through the baby monitor.
• It is not uncommon for a truck to go by and have its CB radio overwhelm the FM station
you am listening to.
• Most of us have come across motors that cause radio or TV static.
None of these things, technically, should be happening. For example, a truck's CB radio is not
transmitting on the FM radio bands, so your radio should never hear CB signals. However, all
transmitters have some tendency to transmit at lower power on harmonic side bands, and this is
how the FM radio picks up the CB. The same thing holds true for the wireless phone crossing
over to the baby monitor. In the case of the cell phone affecting the computer's speakers, the wire
to each speaker is acting like an antenna, and it picks up side bands in the audible range.
These are not dire problems -- they are just a nuisance. But notice how common they are. In an
airplane, the same phenomena can cause big trouble.
An airplane contains a number of radios for a variety of tasks. There is a radio that the pilots use
to talk to ground control and air traffic control (ATC). There is another radio that the plane uses
to disclose its position to ATC computers. There are radar units used for guidance and weather
detection, and so on. All of these radios are transmitting and receiving information at specific
frequencies. If someone were to turn on a cell phone, the cell phone would transmit with a great
deal of power (up to 3 watts). If it happens to create interference that overlaps with radio
frequencies the plane is using, then messages between people or computers may be garbled. If
one of the wires in the plane has damaged shielding, there is some possibility of the wire picking
up the phone's signals just like my computer's speakers do. That could create faulty messages
between pieces of equipment within the plane.
Many hospitals have installed wireless networks for equipment networking. For example, in
case of a heart monitor, the black antenna sticking out of the top of the monitor connects it back
to the nursing station via a wireless network. If you use your cell phone and it creates
interference, it can disrupt the transmissions between different pieces of equipment. That is true
even if you simply have the cell phone turned on -- the cell phone and tower handshake with
each other every couple of minutes, and your phone sends a burst of data during each handshake.
The prohibition on laptops and CD players during takeoff and landing is addressing the same
issue, but the concerns here might fall into the category of "better safe than sorry." A poorly
shielded laptop could transmit a fair amount of radio energy at its operating frequency, and this
could, theoretically, create a problem.
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