Here is a YouTube video about Quadrature Oscillators Made from FlipFlops, and is part of a growing collection of videos I have found to be useful. The reason is using a pair of D-type flip flops to generate quadrature (I and Q) signals from a crystal oscillator suitable for driving a quadrature mixer in a SDR and understanding science related to software defined radio.
This tutorial, "Quadrature Oscillators Made from FlipFlops" is free education you can watch, which will help you deepen your knowledge and be better prepared for licence exams, schoolwork, or operating radio equipment.