Tuned Transmitter, by Guglielmo Marconi, 1899. Marconi’s first tuned transmitter, completed at the Haven Hotel, Poole. The square wooden frame carries two windings, one linked to the Leyden jar and the brass balls that form a spark-gap. The single turn of the second winding was connected between an aerial and earth
It uses a very high Q Spider Coil. The coil is wound with 660/46 Litz and the Q is in excess of 1000, too high to measure on my HP 4342A Q Meter. The radio has only one tuned circuit, the spider coil using a "Holy Grail" silver and ceramic variable capacitor. The antenna is coupled to the spider coil with the smaller non-resonant spider coil. This coil does not resonate anywhere in the broadcast band, if it it did it would try to inject stations at its resonant point.