English: Photo of a small spark-gap transmitter, an early type of radio transmitter used during the wireless telegraphy era before 1920. This example is a small demonstration unit from a 1909 book on radio. The source text says that in a practical transmitter the small inductor (coil) shown would be replaced by a larger coil.
Public domain in USA - published prior to 1923 in USA
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{{Information |Description=Photo of a small spark-gap transmitter. |Source=Downloaded 2010-03-02 from [http://books.google.com/books?id=2MA3AAAAMAAJ&pg=PA19 Walter Wentworth Massie and Charles Reginald Underhill (1909) ''Wireless Telegraphy and Telep
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