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Radio

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Radio

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  1. Radio

  2. *Warning*Heavy Science Content Ahead

  3. Baghdad battery – 250 BCE

  4. Electricity was a heavy duty toy for decades, including Ben Franklin and his kite, people rubbing cat skins on glass or amber rods, spinning sulfur balls, and sparking everything and everyone in sight

  5. Luigi Galvani - 1786 • Believed everything contained electricity • Looked for “animal magnetism” • Touched different metals to frogs’ legs which twitched

  6. Alessandro Volta - 1796

  7. Alessandro Volta - 1796 • Volta took Galvani’s experiment and showed that it was the current produced by the different metals that caused the twitch • Built a pile of alternating sandwiches of zinc and copper in an acid and created electicity

  8. Hans Christian Oersted - 1820

  9. Oersted’s experiment - 1820 • In a lecture in Copenhagen he performed an experiment to demonstrate there was no connection between electricity and magnetism by showing that an electric current passing through a wire wouldn’t affect a nearby compass needle

  10. Imagine his surprise when the needle swung the moment he turned on the current • He demonstrated that electricity created a magnetic field

  11. William Sturgeon - 1825 • Created the first electromagnet by wrapping wire around a soft iron bar and sending a current through the wire • Electricity can create magnetism

  12. Michael Faraday - 1826 • Reversed Sturgeon’s experiment • Showed that magnetism could create an electric current

  13. Samuel F. B. Morse - 1838

  14. Used a an on-off switch – the telegraph key – to turn an electric current on and off, sending pulses of current through a wire to an electromagnet that would click in time to the pulses

  15. Johannes Mueller - 1840

  16. Examined physical sensations • Can you feel colors • Can you hear shapes • Can you smell sounds • Discovered that each sense detects different things • We think this is obvious, but no one had proven it before. Remember “common sense”?

  17. Herman Hemholtz - 1857

  18. Meuller’s pupil • Investigated hearing • Noticed sound produced vibrations

  19. Did the vibrations operate at different frequencies? • They did • Thus, sound traveled at different frequencies • Used an electromagnet to attract the arms of a tuning fork, causing it to vibrate and produce sound

  20. Leon Scott de Martinville - phonautograph - 1857 • Attached a bristle to a membrane at the end of a cone, set the bristle to touch a piece of smoked glass • Spoke into the cone • membrane vibrated to the sound and the bristle etched a wavy line onto the smoked glass

  21. The Telephone - 1876 • Scott’s membrane, Faraday’s electromagnet, Oersted’s and Sturgeon’s electromagnet, Morse’s wire and electrical current, Heimholtz’s vibration, Scott’s membrane

  22. Bell and Gray

  23. Samuel Morse

  24. Heinrich Hertz - 1886

  25. Hemholtz’s pupil • Investigated whether electricity traveled in frequencies the way sound did

  26. Spark gap generator

  27. Hertz’ spark gap experiment

  28. Demonstrated that electricity traveled through air at specific frequencies, just like it did through wires

  29. Guglielmo Marconi - 1894

  30. Marconi radio

  31. Morse key

  32. Marconi and his radio

  33. Nikola Tesla

  34. Tesla coil - 1891 • Developed the first amplifier coil, the Tesla coil • Raised the voltage of an electrical current high enough to allow the air to conduct the current • Key to wireless transmission of radio waves

  35. Reginald Fessenden

  36. Felt that the variation in electrical amplitude created by a voice, just like on a telephone, could be carried by electrical wave of a radio signal • Did the first voice broadcast in 1900 • Short range • Poor quality • Needed far more power

  37. Ernst Alexanderson

  38. Developed the Alexanderson Alternator, a machine capable of generating the power, up to 100,000 hertz, that Fessenden needed to piggyback voice onto radio waves • In Dec. 1906, Fessenden did the first good voice and music broadcast, going hundreds of miles • Poetry and a Bible reading • A woman singing opera • A violin playing a Christmas carol

  39. Lee de Forest

  40. The audion tube is actually a Fleming valve (British term for tube) invented in England • de Forest simply added the bent wire

  41. De Forest’s audion tube - 1904

  42. Audion tube amplified the radio signal the way the Alexanderson generator increased the electrical power • de Forest didn’t know how the audion worked • Another man did

  43. Edwin Howard Armstrong