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 n Properties of EM Waves n Choice of Frequencies n Radio Wave Production n Radio Wave Propagation n Radio Wave Reception n Television n Radar

3. Properties of EM Waves n Transverse n Propagates in Vacuum n Any Frequency Possible n Frequency X Wavelength = c n c = 3x10 8 m/s (in vacuum) E B

4. Transverse EM Wave

5. The Electromagnetic Spectrum

6. Choice of Frequencies n Lower Limit (~10 5 Hz, 3 km) u Bandwidth (data rate) u Antenna size u Project ELF n Upper Limit (~10 9 Hz, 30 cm) u Propagation - line of sight u Sources and Detectors u Radar / Microwaves

7. Radio Wave Production n Transmitter u Spectral purity (min interference) u Power level (W to kW) n Antenna u Size (~ wavelength) u Types u Polarization n Modulator u CW, AM, FM, SSB, TV, Digital

8. Dipole Antenna

9. Types of Modulation

10. Radio Wave Propagation n Diffraction versus Line-of-Sight u Low Frequency / High Frequency n Role of Ionosphere u MUF (f = 9n 1/2, n in particles/m 3 ) u Day/Night Variation (Skip) u Sunspots (11-year Cycle) u Magnetic Storms u Multihop Propagation u Long-Delayed Echoes (?)

11. Ionosphere

12. Density versus Height

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

14. Annual Sunspot Numbers

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

16. Superhetrodyne Receiver

17. Demodulation

18. Television n 50-890 MHz (6 MHz Channels) n FM Audio, SSB Video n 525 Lines @ 30 Frames / second n Interlacing (Alternating Lines) n Synch Pulses n Luminance / Chrominance n High-Definition TV (HDTV) n Cable versus On-Air

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