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Radio Communications. J. C. Sprott Department of Physics University of Wisconsin - Madison Presented to Physics 208 on April 6, 2006. http://sprott.physics.wisc.edu/lectures.htm. Outline. Properties of EM Waves Choice of Frequencies Radio Wave Production Radio Wave Propagation

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radio communications

Radio Communications

J. C. Sprott

Department of Physics

University of Wisconsin - Madison

Presented to

Physics 208

on April 6, 2006

http://sprott.physics.wisc.edu/lectures.htm

outline
Outline
  • Properties of EM Waves
  • Choice of Frequencies
  • Radio Wave Production
  • Radio Wave Propagation
  • Radio Wave Reception
  • Television
  • Radar
properties of em waves
Properties of EM Waves
  • Transverse
  • Propagates in Vacuum
  • Any Frequency Possible
  • Frequency X Wavelength = c
  • c = 3x108 m/s (in vacuum)

E

B

choice of frequencies
Choice of Frequencies
  • Lower Limit (~105 Hz, 3 km)
    • Bandwidth (data rate)
    • Antenna size
    • Project ELF
  • Upper Limit (~109 Hz, 30 cm)
    • Propagation - line of sight
    • Sources and Detectors
    • Radar / Microwaves
radio wave production
Radio Wave Production
  • Transmitter
    • Spectral purity (min interference)
    • Power level (W to kW)
  • Antenna
    • Size (~ wavelength)
    • Types
    • Polarization
  • Modulator
    • CW, AM, FM, SSB, TV, Digital
radio wave propagation
Radio Wave Propagation
  • Diffraction versus Line-of-Sight
    • Low Frequency / High Frequency
  • Role of Ionosphere
    • MUF (f = 9n1/2, n in particles/m3)
    • Day/Night Variation (Skip)
    • Sunspots (11-year Cycle)
    • Magnetic Storms
    • Multihop Propagation
    • Long-Delayed Echoes (?)
ionosphere
Ionosphere

Ionosphere

role of the ionosphere
Role of the Ionosphere

100 MHz

10 MHz

1 MHz

Earth

radio wave reception
Radio Wave Reception
  • Antenna
    • Reciprocity Theorem
    • Size (Practical Limits)
  • Receiver
    • Superhetrodyne
    • IF, AGC, AFC
  • Demodulator (Detector)
  • Stereo (Subcarrier - sum/difference)
  • Signal-to-Noise Ratio
television
Television
  • 50-890 MHz (6 MHz Channels)
  • FM Audio, SSB Video
  • 525 Lines @ 30 Frames / second
  • Interlacing (Alternating Lines)
  • Synch Pulses
  • Luminance / Chrominance
  • High-Definition TV (HDTV)
  • Cable versus On-Air
radar
Radar
  • Pulsed (Air Traffic Control)
  • Doppler (Police)
  • Microwave Ovens (2.45 GHz / 12 cm wavelength)
  • Weather Radar
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