Doppler-shifted cyclotron resonance between electrons and narrowband whistler mode waves is employed in a new feedback model to account for observed signal growth and emission triggering in controlled experiments using the Siple Station, Antarctica, VLF transmitter. The interaction region (IR) is centered on the magnetic equator and is treated like an unstable feedback amplifier with a delay line. The temporal growth rate is given by &lgr; = (G-1)/T, where G is the loop gain and T is the effective loop delay. For G1 the system is unstable and can generate self-excited oscillations. The self-excited oscillations reach saturation when G falls to unity, which occurs when the electron transit time through the interaction region is comparable with the phase bunching time. At signal levels well below saturation the model predicts exponential temporal growth. Saturation fields just inside and outside the plasmapause are estimated to be 1 m&ggr; and 12 m&ggr;, respectivley, consistent with measurements. Because of a progressive loop phase shift the stimulated radiation can cancel the input signal at a certain point (located near the input to the IR) in time and space, giving the rise to transient conditions resembling those at the tail-end of the triggering signal. It is postulated that this temporary null may be the cause of emission triggering, and hence the region arond this point is called the ''triggering window.''