Radio communications
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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


Transverse em wave

Transverse EM Wave


The electromagnetic spectrum

The Electromagnetic Spectrum


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


Dipole antenna

Dipole Antenna


Types of modulation

Types of Modulation


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


Density versus height

Density versus Height


Role of the ionosphere

Role of the Ionosphere

100 MHz

10 MHz

1 MHz

Earth


Annual sunspot numbers

Annual Sunspot Numbers


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


Superhetrodyne receiver

Superhetrodyne Receiver


Demodulation

Demodulation


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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