The nRF5 SDK for Mesh provides a PA/LNA module with APIs for interfacing external Front End Modules (FEMs) to increase the range of Bluetooth Low Energy communication.

The FEMs are controlled by the enable signals that turn on a power amplifier (PA) or a low noise amplifier (LNA) (see the following figure). To ensure sufficient ramp-up time, these signals must be activated some time before the start of the radio transmission or reception.

Interfacing PA/LNA with nRF52

The Mesh PA/LNA module enables users to control such external components using GPIOs that are synchronized to the radio operation. The PA/LNA module drives the chosen GPIO pins according to the chosen polarity (Active High/Active Low).

See the following section for an example of how to use the PA/LNA module. You can find more information about the available APIs in the PA/LNA API documentation.

Adding PA/LNA support to the application

This section describes how to add PA/LNA support to the light_switch/server example. For more information about this example, see Light switch example and Light switch server details and Mesh APIs.

To add the PA/LNA support:

Select the unused GPIO pins that can be used by the PA/LNA module.
- For this example, we use GPIO 25 for controlling the LNA and GPIO 24 for controlling the PA.
- Let's assume that the control signals required by the external hardware module are Active High. The Mesh PA/LNA module uses the nRF52832 PPI and nRF52832 GPIOTE hardware modules to generate these signals.
Select the unused PPI channels 0 and 1, and the GPIOTE channel 0.
Make the following changes in light_switch/server/src/main.c:
1. Include the required module header file: mesh_pa_lna.h
2. Create a static global variable of type mesh_pa_lna_gpiote_params_t and initialize it with the selected values:
  static mesh_pa_lna_gpiote_params_t m_pa_lna_params = {
  .lna_cfg = {
  .enable = 1,
  .active_high = 1,
  .gpio_pin = 25
  },
  .pa_cfg = {
  .enable = 1,
  .active_high = 1,
  .gpio_pin = 24
  },
  .ppi_ch_id_set = 0,
  .ppi_ch_id_clr = 1,
  .gpiote_ch_id = 0
  };
3. Enable the PA/LNA module by calling mesh_pa_lna_gpiote_enable() after the call to mesh_init():
```
mesh_pa_lna_gpiote_enable(&m_pa_lna_params);
```
Build the example by following the instructions in Building the mesh stack and examples.
Run the example by following the instructions in Building the mesh stack and examples for commands required to program a device using `nrfjprog`.

If you connect a logic analyzer to the GPIO pins 25 and 24, you will see them toggling.

The unprovisioned device sends the unprovisioned node beacons every two seconds (NRF_MESH_PROV_BEARER_ADV_UNPROV_BEACON_INTERVAL_MS) and scans for the incoming provisioning invite for the rest of the time.

GPIO waveforms after enabling PA/LNA module

You will see brief Active High pulses on the GPIO pin 24, which is used for the PA control. Similarly, the GPIO pin 25 (used for the LNA control) is almost always ON, except for the time when the radio switches to the next advertising channel for scanning or for sending advertisements.