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Bridging the Ether JCARCJCARC Programprogram Aprilapril 20152015 Byby AH6EZAH6EZ Early Radio Discoveries

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Bridging the Ether JCARCJCARC Programprogram Aprilapril 20152015 Byby AH6EZAH6EZ Early Radio Discoveries Bridging the Ether JCARCJCARC ProgramProgram AprilApril 20152015 ByBy AH6EZAH6EZ Early Radio Discoveries • 1831 Faraday discovered principle of electro-magnetic induction • 1842 Henry : electrical spark between 2 conductors induces magnetism in needles at 30m • 1867 Maxwell : theory on electro-magnetism, predicted existence of electrical waves in ether • 1879 Hughes : tube of iron filings conductive from electrical sparks at 500 meters • 1882 Bell/Preece tx inductive England-Isle Wight signals during a cable disorder • 1887 Hertz , discovers electrical sparks based on wave-phenomena in the ether, confirmed Maxwell theories, and that waves travel at the speed of light • 1890 Branly attracts attention to properties of tubes with iron filings • 1896 Marconi demo of wireless telegraphy using coherer to English telegraph-office • 1897 Marconi : 22km path Isle Wight to England viable • 1901 Marconi uses syntonised (tuned) receivers and transmitters • 1901, first signals sent across Atlantic Ocean from Poldhu to New Foundland • 1902 Marconi develops the magnetic detector • 1903 Schlömilch develops the electrolytic detector Preece 1885 Wireless Induction ¼ mile ¼ mile ¼ mile ¼ mile ¼ mile Branley 1890 experiment Galvanometer Coherer tube Leyden jar Lodge named the device a coherer in 1894 Lodge Muirhead Coherer • Small metallic cup contains globule of mercury • Drop of oil forms infinitely thin insulating film over it • Small iron disc with sharp edge slowly rotated above mercury • By adjusting screw, lower edge of disc just touches the oil • Low pressure to not puncture the film of oil • Coherer, dry cell, telephone rcvr or syphon recorder in series • Electrical oscillations breaks down insulating film of oil • Resets automatically, needs no tapping arrangement Marconi Coherer 95% Nickel 5% Silver filings in a vacuum Physics of the Coherer • At rest = high resistance • After triggered = much lower resistance • Must be tapped or shaken to reset • Ordinary electro-static attraction? • Microscopic sparks pass between the fillings and slightly weld them together? • Welds broken by tapping? Marconi’s 1895 Coherer Receiver 1896 Marconi Receiver using coherer He used RF chokes, I used ferrite beads He used relay to key a telegraph sounder, I used an LED Marconi Decoherer Something like this is needed to “tap” the coherer to reset it after every trigger Syphon Recorder Invented by Lord Kelvin in 1870 for oceanic cable telegraphy Plus and minus pulses Captured on paper By a suspended ink pen 1896 Marconi Coherer 1896 Marconi Coherer 1896 Marconi Coherer and Decoherer Solenoid 1896 Marconi Coherer Sensitive Telegraph Sounder 1896 Marconi Coherer and Case Marconi Coherer Tilt Table for adjusting sensitivity Later tuned version Marconi Magnetic Detector Patent 1902, used until 1918 Standard shipboard spark receiver Spring driven iron wire loop that is magnetized and de-magnetized by the received signal with a primary and secondary transformer effect such that high-impedance headphones can hear the sounds caused by magnetic field collapsing with hysterisis Carborundum Detector • Consists simply of a small carborundum crystal held between two brass springs • It works because carborundum has what is termed an unilateral conductivity • Typically a battery bias is used to adjust sensitivity Electrolytic Coherer • Platinum cup containing a solution of dilute acid (electrolyte) • Cup forms 1 electrode, is Wollaston wire sealed in glass tube • Connection made to wire by metal tube in which the electrode is mounted • Detector w/hi-impedance phones in series tapped across two points of pot • Current passes thru detector polarizing it, gas formed at electrodes, hi res • If AC current, sound is heard, self-restoring • Atmospheric disturbances reduce sensitivity Hot Wire Barretter - Invented 1902 by Fessenden, found limited use in early receivers - Highly sensitive thermo resistor - Permitted reception of amplitude modulated voice signals - Coherer (standard detector of the time) can’t - DC bias to most sensitive point - RF heats and cools the thin wire •(Resistance changes) - Used today for Microwave Bolometer Marconi Podhu, England Station 400 wires suspended in an inverted cone 200-foot circle of 20, 200 feet high masts Mostly destroyed in 1901 storm Rebuilt Podhu Station This temporary rebuilt antenna using just 2 towers was used for Transatlantic tests in 1901 Podhu with flags for 1903 Royal visit Four wooden lattice towers, 200 feet high, placed at corners of 200ft square. 1903: Prince and Princess of Wales visited and climbed to top of one tower Poldhu station was closed in 1933. In 1937 site was cleared Poldhu Amateur Radio Club (GB2GM) started operating from hut at site in 1991 Written in 1914 • In 1914 the tube was not yet common for use as a detector. Various systems were being improved • The detectors used in Radio-Telegraphy may be broadly divided into two classes: – potential actuated - joined across the terminals of the condenser – current actuated - connected in series with the condenser • Detectors may also be further subdivided into classes – imperfect contact devices, such as the Marconi coherer – rectifying devices, such as the Fleming valve and carborundum detector – electrolytic detectors, as those of Fessenden and Schlomilch – thermo-electric type, galena against graphite, and other combinations – alternation of their magnetic properties: the Marconi magnetic detector Fleming Valve Carbon or tungsten filament and plate The beginnings of a rectifier tube Magnetostrictive Materials • Nickel, Iron, Cobalt • Change shape (10ppm) when magnetized • Terfenol-D (Terbium, Dysprosium, Iron) 1400ppm • NiMnGa alloys • Galfenol Radio Controlled Toys • Spark gap transmitter • Radicon Bus 1950’s • Radicon Tank 1967 A Thousand Questions for Marconi… My first Coherer… 104 years of knowledge and 2 days of experiments… What went wrong? (18 volts and door bell !) Second Coherer is surviving… But pretty deaf… Coherers Actually Work ! 6v for Decoherer 9v for Coherer Buzzer is Spark Gap Filing Transmitter Coherer Motor Driven Gear LED for Is Decoherer Visually Decoding CW I am MAN… I made RADIO….
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  • The Stage Is Set
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