Working <a href="https://en.wikipedia.org/wiki/spark_gap_transmitter" class="extiw" title="w:spark gap transmitter">spark gap radiotelegraph transmitter</a> for sending <a href="https://en.wikipedia.org/wiki/Morse_code" class="extiw" title="w:Morse code">Morse code</a> in the Electric Museum in <a href="https://en.wikipedia.org/wiki/Frastanz" class="extiw" title="w:Frastanz">Frastanz</a>, Austria. Invented by <a href="//commons.wikimedia.org/wiki/Guglielmo_Marconi" title="Guglielmo Marconi">Guglielmo Marconi</a> in 1895, spark gap transmitters were used until about 1920.  This low power induction coil transmitter worked off low voltage DC power, and may have been a shipboard transmitter.
<a href="//commons.wikimedia.org/wiki/User:Asurnipal" title="User:Asurnipal">Asurnipal</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>