into the tank inductor by a "tickler coil" (L2, right). Assuming the coupling is weak but sufficient to sustain oscillation, the oscillation frequency f is determined primarily by the LC circuit (tank circuit L1 and C in the figure on the right) and is approximately given by

This circuit was widely used in the regenerative radio receiver, popular until the 1940s. In that application, the input radio frequency signal from the antenna is magnetically