nRF21540 RF Front-End Modules Nordic Semiconductor nRF21540 RF Front-End Modules (FEMs) support BLUETOOTH® Low Energy (BLE), IEEE 802.15.4 range extensions, and proprietary applications. These FEMs offer configurable gain Power Amplifier (PA) in the transmit path (Tx) and Low Noise Amplifier (LNA) in the receive path (Rx). The nRF21540 FEMs feature a highly configurable gain in the Transmit state, enabling the application to implement adaptive gain control algorithms. These modules can be controlled through IO pins and/or through the SPI interface, or a combination of both by writing to an internal control register.