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| Keywords: Poulsen's arc radiotelephone transmitter.jpg Poulsen arc radiotelephone transmitter built by Valdamar Poulsen around 1904 The Poulsen arc was an early radio transmitter technology that was used briefly until the mid 1920s when it was superseded by vacuum tube transmitters It was the first transmitter which produced undamped sinusoidal waves and so could be amplitude modulated AM to transmit sound <br/><br/> The photo shows Poulsen's first AM transmitter The Poulsen arc is on the right It consists of a rectangular arc chamber containing two electrodes to which a DC voltage of about 500 volts was applied creating a continuous electric arc A resonant circuit consisting of a capacitor on desk to right of arc chamber and inductor behind arc chamber was connected across the arc The negative resistance of the arc canceled the positive resistance of the tuned circuit exciting sinusoidal radio frequency oscillating currents in the circuit The arc was between the poles of an electromagnet cylindrical objects attached to each side of the chamber which created a magnetic field across the arc The arc chamber was filled with alcohol vapor from alcohol dripping from the cup on top These two features enabled the arc to oscillate at a high enough frequency for radio transmission The tuned circuit was attached through the transmission line on the wall to an outdoor wire antenna which radiated the energy as radio waves The carbon microphone center was connected directly in the antenna wire The sound waves striking the microphone's diaphragm put varying pressure on carbon granules varying its resistance thus varying the current allowed through to the antenna To handle the high power of the transmitter the microphone consists of three separate units attached to a single mouthpiece 1908 Retrieved October 10 2013 from https //books google com/books id ySTOAAAAMAAJ pg PA426 Gustav Eichhorn Jonathan Adolf Wilhelm Zenneck 1908 Jahrbuch der Drahtlosen Telegrafie und Telephonie Yearbook of Wireless Telegraphy and Telephony Verlag Von S Hirzel Leipzig Germany p 426 fig 1 on Google Books Gustav Eichhorn Jonathan Adolf Wilhelm Zenneck other versions PD-old-70-1923 Uploaded with UploadWizard Poulsen arc transmitters ImageNote 1 1040 664 138 163 1342 986 2 Arc chamber ImageNoteEnd 1 ImageNote 2 924 684 117 89 1342 986 2 Electromagnet ImageNoteEnd 2 ImageNote 3 1173 682 91 86 1342 986 2 Electromagnet ImageNoteEnd 3 ImageNote 4 778 701 141 117 1342 986 2 Variable tank capacitor ImageNoteEnd 4 ImageNote 5 889 575 158 99 1342 986 2 Tank inductor ImageNoteEnd 5 ImageNote 6 627 501 117 158 1342 986 2 High power carbon microphone in antenna lead has three driver units in series ImageNoteEnd 6 ImageNote 7 604 386 148 79 1342 986 2 Transmit/receive switch ImageNoteEnd 7 ImageNote 8 654 188 117 117 1342 986 2 Lightning arrester ImageNoteEnd 8 ImageNote 9 176 615 401 191 1342 986 2 Receiver ImageNoteEnd 9 ImageNote 10 1092 584 50 70 1342 986 2 Alcohol cup ImageNoteEnd 10 ImageNote 11 589 17 178 112 1342 986 2 Pass-through bushing in wall to outdoor wire antenna ImageNoteEnd 11 | ||||
