An apparatus may include an exciter, disposed within a resonance chamber, to generate an RF power signal. The apparatus may include a resonator coil, disposed within the resonance chamber, to receive the RF power signal, and generate an RF output signal; and a pickup loop assembly, to receive the RF output signal and output a pickup voltage signal. The pickup loop assembly may include a pickup loop, disposed within the resonance chamber; and a variable attenuator, disposed at least partially between the resonator coil and the pickup loop. The variable attenuator may include a configurable portion, movable from a first position, attenuating a first amount of the RF output signal, to a second position, attenuating a second amount of the RF output signal, different from the first amount.