Bluetooth TX Power Settings#

Introduction#

The default TX power used by the Bluetooth stack is +8 dBm, meaning that all of the advertisement packets and data packets are transmitted with this power level (except if your device has a lower TX power capability). However, this can be changed both in positive and negative direction. The actual TX power is determined by both the user configuration and the actual circumstances. This document discusses how you can configure TX power and how the actual TX power will change.

Global Maximum and Minimum TX Power#

The global maximum TX power can be set with the sl_bt_system_set_tx_power(int16_t min_power, int16_t max_power, int16_t * set_min, int16_t * set_max ) API command. The unit of the TX power is 0.1 dBm. To ensure safe functioning, suspend radio operations for a short time while changing the TX power. For example, to set 2.3 dBm maximum TX power and 0 dBm minimum TX power, use the following commands:

sl_bt_system_halt(1);
gecko_cmd_system_set_tx_power(0, 23, &set_min, &set_max);
sl_bt_system_halt(0);

Note that, although you can set the TX power with 0.1 dBm granularity, the low power PA cannot be set to arbitrary TX levels – there are discrete power levels you can use. The set values are provided by the variables pointed to, by their arguments set_min and set_max. Always check these values because it can be much higher/lower than the TX power you want to set.

The minimum TX power setting has no effect in Bluetooth stack if the LE Power Control (LEPC) is not enabled. LEPC is a new feature introduced in BLE 5.2, which c