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DescriptionSmall spark gap transmitter.jpg	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.
Date	1909
Source	Downloaded 2010-03-02 from Walter Wentworth Massie and Charles Reginald Underhill (1909) Wireless Telegraphy and Telephony, Popularly Explained, D. Van Nostrand, New York, p.19, fig.7 on Google Books
Author	Charles Reginald Underhill
Permission (Reusing this file)	Public domain in USA – published prior to 1923 in USA

Public domain	This media file is in the public domain in the United States. This applies to U.S. works where the copyright has expired, often because its first publication occurred prior to January 1, 1931, and if not then due to lack of notice or renewal. See this page for further explanation.	United States
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