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

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

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

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

The Electromagnetic Spectrum

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

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

Ionospheric Propagation Ionosphere km 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

The Radio Spectrum

Absorbtion in the atmosphere

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

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

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

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)

The Eye - Colour Perception

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

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

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

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

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

Orthicon Tube

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

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