FMout

FMout is a label used in electronics and communications to denote the output of a frequency modulation (FM) stage. The exact signal referred to by FMout varies by device and schematic, and there is no universal standard for what FMout carries. In practice, FMout can denote either the modulated RF output of an FM transmitter or the baseband audio output from an FM demodulator, depending on the context.

In FM transmitting hardware, FMout often labels the RF output of the modulator stage that feeds the subsequent upconverter or power amplifier and antenna. Its characteristics depend on the design of the transmitter and may be a high-frequency signal with modest amplitude control achieved through the RF chain and filtering. Because this path is part of the radio frequency front end, it typically requires impedance matching and filtering to the next stage.

In FM receivers and demodulators, FMout commonly denotes the audio signal that results after demodulation. This output is intended to drive an audio amplifier or line input and is usually a low-impedance, line-level or near-line-level signal. Levels and impedance vary with the particular demodulator design and any subsequent buffering or filtering. The signal is typically conditioned to remove unwanted remnants of the RF or pilot components before feeding audio stages.

In integrated circuits and development boards, FMout may be a pin or net name representing either an FM output or an auxiliary signal routed to a later block. The exact electrical characteristics are defined in the respective datasheet and reference designs.

See also: Frequency modulation, FM demodulation, FM transmitter, FM receiver.