The input/output terminals of a mixer, are identified as RF, LO and IF. In most double balanced mixers, the LO and RF are either transformer or transmission line-coupled to the mixer diodes, and therefore have a limited low-frequency response; while the IF port is usually direct-coupled with an essentially unlimited low frequency response. In upconverting applications, the low frequency input signal is often applied to IF port with the higher-frequency output signal being taken from the RF port.