A typical baby monitor, with the receiver on the left and the transmitter on the right: The transmitter sits in the baby's room and is essentially a mini "radio station." The parents carry the receiver around the house to listen to the baby. Typical transmission distance is limited to about 200 feet (61 m).

Radio Basics: Real-life Examples

A baby monitor is about as simple as radio technology gets. There is a transmitter that sits in the baby's room and a receiver that the parents use to listen to the baby. Here are some of the important characteristics of a typical baby monitor:

  • Modulation: Amplitude Modulation (AM)
  • Frequency range: 49 MHz
  • Number of frequencies: 1 or 2
  • Transmitter power: 0.25 watts

(Don't worry if terms like "modulation" and "frequency" don't make sense right now -- we will get to them in a moment.)

A cell phone is also a radio and is a much more sophisticated device (see How Cell Phones Work for details). A cell phone contains both a transmitter and a receiver, can use both of them simultaneously, can understand hundreds of different frequencies, and can automatically switch between frequencies. Here are some of the important characteristics of a typical analog cell phone:

  • Modulation: Frequency Modulation (FM)
  • Frequency range: 800 MHz
  • Number of frequencies: 1,664 (832 per provider, two providers per area)
  • Transmitter power: 3 watts

A typical cell phone contains both a transmitter and a receiver, and both operate simultaneously on different frequencies. A cell phone communicates with a cell phone tower and can transmit 2 or 3 miles (3-5 km).