Chaos, Communication and Consciousness Module PH19510

1
Chaos, Communication and ConsciousnessModule
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 (3x108 m/s)
• f frequency (Hz)
• ? wavelength (m)

4
The Electromagnetic Spectrum
nm
(l) wavelength ? ? (f) frequency
5
The Electromagnetic Spectrum
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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
Refraction

• 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

Transmitter
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The Radio Spectrum
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Absorbtion in the atmosphere
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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

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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

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The Retina

• Imaging surface of eye
• 650mm2 (12)
• 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)

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The Eye - Colour Perception
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Moving Pictures

• Eye has persistence of vision
• ? 40ms (25Hz)
• Rapidly changing images seen as continuous motion

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

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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

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The Cathode Ray Tube (CRT)
Fluorescent Screen
Control Grid
Heater
Cathode
Focus Coil
Deflection Coils
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Orthicon Tube
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Electrons win over atoms

• Nov 1936 BBC trial
• 2 months
• Electronic system wins

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Review of Lecture

• Radio Waves Propagation
• The Eye
• Moving Pictures
• Mechanical TV
• Electronic TV