Introduction to Radios and Waves

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Introduction to Radios and Waves

• Information Technology
• 2006-2007

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So what is a radio?

• A radio is a device which either receives or
  transmits waves in the radio frequency.
• The transmitter takes some sort of message (it
  could be the sound of someone's voice, pictures
  for a television, data for a radio modem or
  whatever), encodes it onto a sine wave and
  transmits it with radio waves.
• The receiver receives the radio waves and decodes
  the message from the sine wave it receives. Both
  the transmitter and receiver use antennas to
  radiate and capture the radio signal.

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Basic AM Radio Receiver
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What are some examples?

• A baby monitor?
• 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

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Is a cell phone a radio?

• A cell phone is also a radio and is a much more
  sophisticated device. 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

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What are waves and how do they work with radios?

• Electromagnetic Spectrum

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Do all waves look the same?

• No, the frequency and amplitude of waves vary
  depending upon what type of signal generator is
  creating them.

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How do we measure waves?

• Waves are put into categories based on their
  frequency range and amplitude.
• The majority of all radio signals fall within the
  following groupings
• Very Low Frequency (VLF) 9 kHz - 30 kHz 33 km -
  10 km
• Low Frequency (LF) 30 kHz - 300 kHz 10 km - 1 km
• Medium Frequency (MF) 300 kHz - 3 MHz 1 km - 100
  m
• High Frequency (HF) 3 MHz - 30 MHz 100 m - 10 m
• Very High Frequency (VHF) 30 MHz - 300 MHz 10 m -
  1 m
• Ultra High Frequency (UHF) 300 MHz - 3 GHz 1 m -
  100 mm
• Super High Frequency (SHF) 3 GHz - 30 GHz 100 mm
  - 10 mm
• Extremely High Frequency (EHF) 30 GHz - 300 GHz
  10 mm - 1 mm

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So where do FM and AM fit?

• FM stands for frequency modulation.
• Frequency modulation (FM) is a form of modulation
  which represents information as variations in the
  instantaneous frequency of a carrier wave.
• AM stands for amplitude modulation.
• Amplitude modulation (AM) varies the strength of
  the transmitted signal in relation to the
  information being sent, for example, changes in
  the signal strength can be used to reflect sounds
  being reproduced for a speaker or light intensity
  for a television pixel.

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What happens to sound when I change a waveform?

• Imagine you are standing on the sidewalk as a
  ambulance turns the corner down the street. They
  ambulance turns on its siren as it drives past
  you and turns down the next street.
• How will the ambulance sound before and after it
  drives past you?
• Lets listen

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Who uses radios?

• Civilian Personnel
• Emergency Services Units
• VHF, HF
• Amateur Radio Operators
• Citizen Band, UHF, HF
• Radio Stations
• FM, AM and Satellite (digital-radio)
• Military Personnel
• VHF, HF, Satellite

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Wave Generation Activity

• Using Crocodile Clips, create a signal generator
  which produces a wave with the following
  specifications
• (Calibrate the graph to Voltage, 10 to -10
  volts, 0.1uS)
• 50 Mhz (frequency)
• 10 Volts (amplitude)
• What frequency range does this signal fall
  within?
• How does increasing the signals frequency effect
  the waves shape? Please sketch an example
• How does increasing the signals amplitude effect
  the shape of the wave? Please sketch an example.
• If you are trying to transmit a radio signal over
  a long distance, should a radio operator increase
  the frequency or the amplitude? Why?