M11L3 Slides

• Amplitude

  A measure of the size of the disturbance a wave produces
• Radio Transmissions

  • Each radio station uses an assigned frequency to avoid interfering with other radio broadcasts
  • TV stations & Cell phone companies are also assigned specific frequencies
  • The remaining radio frequencies are assigned for other purposes, such as navigation and radio astronomy
• Carrier wave

  EM wave with the specific frequency that a station is assigned
• Radio Station transmissions

  1. Transmit a carrier wave

  2. Send information about sounds that you receive

  3. Sounds produced @ radio station are CONVERTED into electrical signals called SIGNAL WAVE

  4. Signal wave is used to modify the carrier wave
• Modulation

  Process of adding signal wave to carrier wave
• In 2009, full-power television stations in the United States began broadcasting only digital signals
• Digital signal

  An electric signal where there are only two possible values: ON and OFF
• Analog signal

  An electric signal whose values change smoothly overtime
• Telephones

  • Decades ago, telephones connected with wires
  • When you speak into a telephone, a microphone converts the sound waves into an electric signal
  • In a cell phone, this signal is transmitted to and from microwave towers using microwaves or radio waves
  • The towers, are several kilometers apart and each covers an area called a cell
  • If you move from one cell to another, an Automated Control station transfers the signal to the new cell and its tower
• Communications Satellites

  • Thousands have been launched into Earth's orbit
  • The sender broadcasts a microwave signal to the satellite
  • The satellite receives the signal, amplifies it, and transmits it to a particular region on Earth
  • Like cell phones, satellites are transceivers
  • To avoid interference, the satellite receives signals at one frequency and broadcasts signals at a different frequency
• The Global Positioning System (GPS)


  • A system of satellites, ground monitoring stations, and receivers that determine your exact location at or above Earth's surface
  • The 24 satellites necessary for 24-hour, around-the-world coverage became fully operational in 1995
  • Signals from 4 satellites used to determine the location of an object using a GPS receiver
• FM

  FM radio stations broadcast information by changing the Frequency of the carrier wave
• AM

  AM radio stations broadcast information by changing the AMPLITUDE of the carrier wave