File:EB1911 Telegraph - two coupled oscillation circuits.jpg

English: The antenna may have oscillations excited in it inductively. F. Braun suggested in 1898 that the oscillator discharge of a Leyden jar should be sent through the primary coil, of a transformer and the secondary coil should be interposed between the antenna and an earth connexion. Marconi imparted practical utility to this idea by tuning the two circuits together, and the arrangement now employed is as follows:— A suitable condenser C, or battery of Leyden jars, has one coating connected to one spark ball and the other through a coil of one turn with the other spark ball of a discharger S. These spark balls are connected either to the secondary circuit of an induction coil I, or to that of an alternating current transformer having a secondary voltage of 20,000 to 100,000 volts. Over the coil of one turn is wound a secondary circuit of 5 or 10 turns, of which one end is connected to the earth through a variable inductance and the other end to an antenna or radiating wire A (see figure). These two circuits are so adjusted that the closed oscillation circuit, consisting of the condenser, primary coil and spark gap, has the same natural time period of oscillation as the open circuit consisting of the antenna, secondary coil and adjustable inductance. When this is the case, if discharges are made across the spark gap oscillations are excited in the closed circuit, and these induce other syntonic oscillations in the antenna circuit.