It is generally true that ETSI EN 300 328 allows 20 dBm RF output power in all such cases when equipment is using wide band modulations other than FHSS (Frequency Hopping Spread Spectrum). In these cases PSD (Power Spectral Density) also must be tested, which allows 10 dBm / 1 MHz.
These restrictions apply to those BLE devices, where adaptive frequency hopping is not enabled. In the case of 125 kbps, 500 kbps and 1 Mbps PHY (~1 MHz bandwidth) it means that the maximum radiated power allowed is 10 dBm. In the case of 2 Mbps PHY it is a few tenths dB more.
Based on FCC part 15.247 in the case of wideband digital modulation the output power can go up to 30 dBm and the power spectral density must be below 8 dBm / 3 KHz.
In the case of 500 kbps (coded), 1 Mbps and 2 Mbps PHY 30 dBm limitation is applied.
In the case of 125 Kbps coded PHY the device doesn’t pass the 8 dBm/ 3 KHz PSD limit with full power, thus the maximum output power allowed is 14 dBm.
Since Bluetooth stack takes the strictest regulation, thus the maximum output power is 10 dBm in those cases when AFH is not enabled (or AFH is enabled but no more than 15 channels are available). This stack limitation (10 dBm EIRP) is valid in for all PHYs and devices.
|Power Limits Without AFH|
|FCC||125 kbps coded PHY||
500 kbps, 1Mbps and 2 Mbps
|Supported by stack||10|
When adaptive frequency hopping is allowed (and at least 15 channels is available) the only one limitation is maximum 20 dBm EIRP. There isn’t any restriction for PSD.
If AFH is used, the maximum output power, which is allowed by FCC, can be 30 dBm and there isn’t any PSD limitation. FCC contains a restricted band from 2483.5 MHz to 2500 MHz and due to this in several cases power limitation is needed on the edge channels.
Considering regulations of FCC and ETSI, when AFH is applied and at least 15 channels are available, the maximum conducted output power, which is allowed by BLE stack, is 20 dBm on all channels except of on channel 37 and 38 (physical channels not logical channels) . The output power is limited to 18 dBm on channel 37 and 15.3 dBm on channel 38 in the case of all PHYs. There isn’t any limitation on channel 39, because the upper channel is only used for advertisements, so with the low duty cycle correction advertisements can be sent at full power.
|Power Limits With AFH|
|FCC||channel 37||channel 38||
all other channels
|Supported by stack||18||15.3||20|