1. Chaos, Communication and Consciousness Module PH19510 Lecture 7 Radio Propagation & Television

2. Overview Radio Waves & Propagation The Eye Moving Pictures Mechanical TV Electronic TV

3. Wavelength and Frequency Wavelength and frequency are related by: where: c = speed of light (3x10 8 m/s) f = frequency (Hz) = wavelength (m)

4. The Electromagnetic Spectrum ( ) wavelength   (f) frequency nm

5. The Electromagnetic Spectrum

6. The Valve Age 1907 Triode Valve – Electronic Amplification Further developments  More Electrodes (grids)  Higher powers Circuits  Amplifiers  Oscillators

7. Radio Propagation Light travels in straight lines How does radio work out of line of sight ? Diffraction around obstacles Refraction from ionosphere

8. Ionospheric Propagation Ionosphere 50-600km Gradual refraction Radio Freq  1MHz – 15MHz  20m – 300m Hop distance  300km – 2300km (single) Multi-hop possible Time of day dependent Sunspot dependent Ionosphere Transmitter Refraction

9. The Radio Spectrum

10. Absorbtion in the atmosphere

11. Broadcast Radio 1909 First ‘broadcast’ station San Jose, CA  Human voice & music 1920 Licensed public radio in US 1920 Marconi broadcasting from Chelmsford 1922 Formation of BBC in UK

12. The Human Eye Superb imaging device Sensitive to  Intensity  Colour  Movement Stereo Pair  3D vision up to 1m  Redundancy Resolve 1mm lines/spaces at 1m

13. The Structure Of The Eye Lens  Focus incoming light Iris  Variable aperture  Regulate light input Retina  Imaging Surface Fovea  High resolution colour Optic Nerve  Transmit signals to brain

14. The Retina Imaging surface of eye 650mm 2 (1” 2 ) Light sensed by rods & cones Rods  Sensitive light intensity 130 million Cones  Sensitive to Red, Green, Blue  7 million  Concentrated in fovea (centre of vision)

15. The Eye - Colour Perception

16. Moving Pictures Eye has persistence of vision  = 40ms (25Hz) Rapidly changing images seen as continuous motion THAUMATROPE

17. Early Experiments Photoconductivity of selenium  Resistance depends on illumination Scanning disk Used for ‘fax’ in early C20th

18. John Logie Baird Scottish Inventor 1926 ‘televisor’ Electromechanical Nipkow Disk Initially 30 lines at 5fps Improved to 240 lines 1936

19. Electronic Imaging Systems Scanning electron beams Rosing & Zworkyin (Russia) 1907  Mechanical scanning + Cathode Ray tube Philo Farnsworth  Image Dissector (1926) Iconoscope  Based on vacuum tube technology

20. The Cathode Ray Tube (CRT) Heater Cathode Control Grid Anodes Fluorescent Screen Focus Coil Deflection Coils

21. Orthicon Tube

22. Electrons win over atoms Nov 1936 BBC trial 2 months Electronic system wins

23. Review of Lecture Radio Waves & Propagation The Eye Moving Pictures Mechanical TV Electronic TV