spark transmitter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A source of alternating current, especially a now obsolete radio transmitter, that derives its output from the oscillating discharge of a capacitor to an inductor and across a spark gap.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an early radio transmitter using a discharge across a spark gap as the source of its power