By the way, *amazing blackout* happened at some point around 4-5 AM local time (2-3 AM UTC). The K increased to 6+ at that time.

Nonetheless, at 90º phase, the peaks of the pump match the peaks and valleys of the resonant signal. This little kick increases the voltage of the varactor. In general, increasing the reverse voltage of the varactor reduces its capacitance. Since V = Q/C, and at the peak and valleys I = 0 (making Q a conserved quantity), reducing C means increasing V, making this resonant back-and-forth stay for way longer before fading away.

This configuration is called a "degenerate parametric amplifier" because the pump frequency is twice the signal frequency. The interesting aspect of this circuit is that the gain is strongly dependent of the phase of the pump frequency. In fact, at 0º phase we do not see much amplification. Neither at 180º nor at 270º

Now, how is this supposed to work: if I leave this circuit with the pump disabled (PUMP = 2V), this behaves as a simple tank circuit with resonance frequency at 1.42 GHz. Delivering a pulse to the tank makes it go back an forth a few times at 1.42 GHz until it gets dissipated mostly by R1.