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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. Properties of EM Waves Choice of Frequencies Radio Wave Production Radio Wave Propagation

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Radio Communications

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  1. 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

  2. Outline • Properties of EM Waves • Choice of Frequencies • Radio Wave Production • Radio Wave Propagation • Radio Wave Reception • Television • Radar

  3. Properties of EM Waves • Transverse • Propagates in Vacuum • Any Frequency Possible • Frequency X Wavelength = c • c = 3x108 m/s (in vacuum) E B

  4. Transverse EM Wave

  5. The Electromagnetic Spectrum

  6. 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

  7. 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

  8. Dipole Antenna

  9. Types of Modulation

  10. 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 (?)

  11. Ionosphere Ionosphere

  12. Density versus Height

  13. Role of the Ionosphere 100 MHz 10 MHz 1 MHz Earth

  14. Annual Sunspot Numbers

  15. Radio Wave Reception • Antenna • Reciprocity Theorem • Size (Practical Limits) • Receiver • Superhetrodyne • IF, AGC, AFC • Demodulator (Detector) • Stereo (Subcarrier - sum/difference) • Signal-to-Noise Ratio

  16. Superhetrodyne Receiver

  17. Demodulation

  18. 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

  19. Radar • Pulsed (Air Traffic Control) • Doppler (Police) • Microwave Ovens (2.45 GHz / 12 cm wavelength) • Weather Radar

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