Complex sentence: In Tesla's more advanced (magnifier) design, the secondary LC circuit is composed of a tightly coupled air-core transformer secondary coil driving the bottom of an isolated third coil helical resonator.
Split into simpler sentences: In Tesla's more advanced (magnifier) design, a third coil is added. The secondary LC circuit is composed of a tightly coupled air-core transformer secondary coil driving the bottom of a separate third coil helical resonator.