Radio Communications

J. C. SprottDepartment 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

Radio Wave Reception

Television

Radar

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

The Electromagnetic Spectrum

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

Transmitter Spectral purity (min interference) Power level (W to kW)

Antenna Size (~ wavelength) Types Polarization

Modulator CW, AM, FM, SSB, TV, Digital

Dipole Antenna

Types of Modulation

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

Density versus Height

Role of the Ionosphere100 MHz

1 MHz

10 MHz

Earth

Annual Sunspot Numbers

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

Demodulation

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

Pulsed (Air Traffic Control)

Doppler (Police)

Microwave Ovens (2.45 GHz / 12

cm wavelength)

Weather Radar