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Chaos, Communication and Consciousness Module PH19510

Chaos, Communication and Consciousness Module PH19510 . Lecture 6 Radio Days. Overview. Theoretical Beginnings Faraday & Maxwell First Transmission Hertz Practical Systems Marconi, Tesla, Braun Transmitting Information CW Amplitude Modulation. Michael Faraday (1791-1867).

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Chaos, Communication and Consciousness Module PH19510

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  1. Chaos, Communication and ConsciousnessModule PH19510 Lecture 6 Radio Days

  2. Overview • Theoretical Beginnings • Faraday & Maxwell • First Transmission • Hertz • Practical Systems • Marconi, Tesla, Braun • Transmitting Information • CW • Amplitude Modulation

  3. Michael Faraday (1791-1867) • Chemist, Physicist • Discovered electromagnetic induction • Changing current in a one coil induces current in another linked coil. • Faraday’ Law               ,

  4. Faraday and the £20 Note

  5. James Clerk Maxwell (1831-1879) • Mathematician • Brought together work of Faraday, Gauss, Ampere • 1864 presented “Maxwell’s Equations”

  6. No magnetic monopoles Electric Charges  Electric Fields Maxwell’s Equations Changing magnetic fields  Electric fields # Changing Electric fields Magnetic fields

  7. Divergence · • Scalar quantity • Measure of ‘outgoingness’ of field at a point • Flow across boundary of infinitesimally small sphere at point. • Expansion  +ve divergence • Contraction  -ve divergence

  8. Curl × • Vector • Rate of rotation of a field • Points along axis of rotation • Right hand rule • Example • Uniform rotation • Constant curl • Points into page

  9. No magnetic monopoles Electric Charges  Electric Fields Maxwell’s Equations Changing magnetic fields  Electric fields # Changing Electric fields Magnetic fields

  10. Consequence of Maxwell’s Equations • Electric and Magnetic Forces are linked • Wave nature of electromagnetism • Showed waves moved at speed of light • Suggested light was form of electromagnetic wave • 1873 Suggested propogation of EM waves

  11. Heinrich Rudolf Hertz • 1857 – 1894 • 1887 Proved Maxwell’s proposition that Electromagnetic Waves can travel over distance

  12. Hertz’s Experiment1 – Primary circuit Interrupter Capacitor • Current flows through coil •  magnetic field in core •  Interrupter Opens • Current dies away •  magnetic field dies away • Interrupter Closes • Current Flows • (repeat forever) Battery Primary Coil Core

  13. Antennae Plates Hertz’s Experiment2 – Secondary Circuit Secondary Coil • Many turns in secondary coil • Changing field in primary coil & core •  Very high voltage in secondary (10-20kV) • Sparks • Radiating Electromagnetic field from antennae plates Spark Gap

  14. Hertz’s Experiment3 – Receiver • Electromagnetic field induced in receiver loop • (Tiny) sparks appear in gap

  15. Need to make communications system • Spark transmitter produces broad band output • Splash across many frequencies • Due to rapid edge of spark • Tiny sparks only visible in dark

  16. The coherer • Tube filled with silver/nickel filings • Particles stick together (cohere) under influence of electric field • Allows large current to flow • Unstick particles mechanically (hammer) • Primitive amplifier

  17. Nikola Tesla (1856-1943) • 1893-1895 Investigated high frequency Currents • Produced reliable radio Frequency generator • ‘Narrow’ frequency band

  18. Guglielmo Marconi (1874-1937) • 1896 Demonstrates wireless telegraphy • 1901 Tuned Radio • Resonance • Coherer • Extensive use in ship/shore comms

  19. The Cat’s Whiskers • Karl Braun • 1874 Discovered point contact semiconductor junction • 1898 Cat’s Whisker • Simple Rectifier • Lead Sulphide • Phosphor Bronze spring contact

  20. CW Modulation • Continuous Wave • Radio Frequency Carrier • Turn carrier On & Off • Transmit information by length & timing of On/Off periods • Morse code • Simple Digital

  21. Simple Radio Reciever • Voltage induced in antenna by EM wave • Variable Capacitor & primary coil select required freq. • Diode & capacitor remove RF • Signal heard in earpiece

  22. Amplitude Modulation - AM • Transmit analogue signals – speech/music • Same as Frequency Division Multiplexing • Change amplitude of carrier depending on signal • Multiplication process:

  23. Amplitude Modulation #1 • Carrier Waveform

  24. Amplitude Modulation #2 • Signal Waveform

  25. Modulation Depth x 2 Amplitude Modulation #3 • Transmitted Waveform

  26. Demodulation of AM Signals • Rectify signal with diode • Remove carrier with low-pass filter • Signal remains

  27. Overview • Theoretical Beginnings • Faraday & Maxwell • First Transmission • Hertz • Practical Systems • Marconi, Tesla, Braun • Transmitting Information • CW • Amplitude Modulation

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