What is the phase difference between the I and Q RF signals that software-defined radio (SDR) equipment uses for modulation and demodulation?

In Software-Defined Radio (SDR) technology, signals are often processed using two components: In-phase (I) and Quadrature (Q). The fundamental characteristic of these two signals is that they are exactly 90 degrees out of phase with each other. This 90-degree orthogonal relationship is crucial because it allows the two signals to act independently, enabling the mathematical representation of any phase, frequency, or amplitude variation. Distractors like zero or 180 degrees represent signals that are either in-phase or simply inverted, which would not provide the two-dimensional signal space required for complex modulation.