second required to sample directly at 5 GHz. A vector signal generator will typically use I/Q data alongside some programmed frequency to generate its signal. And similarly a vector signal analyser can provide a stream of I/Q data in its output. Many modulation schemes, e.g. quadrature amplitude modulation rely heavily on I/Q. Alternating current (AC) circuits The term alternating current applies to a voltage vs. time function that is sinusoidal with a frequency When it is applied to a typical (linear time-invariant) circuit or device, it causes a current that is also sinusoidal. In general there is a constant phase difference, φ, between any two sinusoids. The input sinusoidal voltage is usually defined to have zero phase, meaning that it is arbitrarily chosen as a convenient time reference. So the phase difference is attributed to the current function, e.g. whose orthogonal components are and as we have seen. When φ happens to be such that the in-phase component is zero, the current and voltage sinusoids are said to be in quadrature, which means they are orthogonal to each other. In that case, no average (active) electrical power is consumed. Rather power is temporarily stored by the device and given back, once every seconds. Note that the term in quadrature only implies that two sinusoids are orthogonal, not that they are components of another sinusoid. See also IQ imbalance Constellation diagram Phasor Polar modulation Quadrature amplitude modulation Single-sideband modulation Notes References Further reading Steinmetz, Charles Proteus (1917). Theory and Calculations of Electrical Apparatus 6 (1 ed.). New York: McGraw-Hill Book Company. B004G3ZGTM. External links I/Q Data for Dummies Signal processing Radio electronics