FRF

fRF is a shorthand appearing in technical writings to denote a radio-frequency frequency, typically written as f_RF or fRF. It is not a standardized term with a single universally accepted definition; rather, its meaning depends on the context and field, where it generally represents a specific RF carrier or drive frequency used in a system.

In wireless communications, fRF is commonly used to designate the carrier frequency around which an RF front end operates. It appears in equations describing modulation, filtering, upconversion and downconversion, as well as in the specification of antenna bandwidth. The RF chain is typically analyzed with fRF alongside intermediate frequency (fIF) and baseband (fBB).

In magnetic resonance imaging and spectroscopy, fRF refers to the frequency of the applied radio-frequency pulses that excite spins or drive transitions. Proton MRI, for example, uses a resonance condition that sets the fRF based on the main magnetic field strength, commonly in the tens to hundreds of megahertz range depending on the system.

Other uses include general RF testing and calibration, where fRF is the frequency of a test signal, and schematic notations in which fRF is a variable parameter for the RF portion of a circuit. Because fRF denotes frequency, its exact value is chosen to match the target RF band and the device under test.

Because of varying conventions, readers should verify the intended meaning of fRF in any given document.