Specific Absorption Rate (SAR) Power backoff in Sierra Wireless Modules
What is Specific Absorption Rate (SAR)?
SAR is a measure of the amount of radio frequency energy that can be absorbed by the body when using a mobile device such as a cellular phone.When cellular modules are integrated in to a host device such as PC, the SAR testing is applicable to the host device. The FCC limit for SAR level is 1.6 watts per kilogram (1.6 W/kg).
How to set SAR Power backoff in Sierra Wireless Modules?
Using the AT!MAXPWR command, the SAR Power back values can be set for each band. Note that any change to the maximum TX power for the band should be carefully evaluated as it may impact regulatory certification.
To set the SAR Power Backoff in Sierra Wireless modules, specify the band and the technology using the AT!MAXPWR command.
Examples of SAR Power Backoff,
- Get the Max power for LTE Band 4
- AT!MAXPWR?4,2
- Set the Max power for LTE Band 4 to 23 dbm
- AT!MAXPWR=4,2,23
- Get the Max power for WCDMA Band 3
- AT!MAXPWR?3,0
- Set the Max power for WCDMA Band 3 to 22 dbm
- AT!MAXPWR=3,0, 22
What are the LTE/WCDMA bands to specify the SAR Power backoff?
Here are the 3GPP bands for which the maximum power can be set the SAR Power Backoff using the AT!MAXPWR command.
| Band | Rx MHz | Tx MHz |
| 1 | 1920–1980 | 2110–2170 |
| 2 | 1850–1910 | 1930–1990 |
| 3 | 1710–1785 | 1805–1880 |
| 4 | 1710–1755 | 2110–2155 |
| 5 | 824–849 | 869–894 |
| 6 | 830–840 | 875–885 |
| 7 | 2500–2570 | 2620–2690 |
| 8 | 880–915 | 925–960 |
| 9 | 1749.9–1784.9 | 1844.9–1879.9 |
| 10 | 1710–1770 | 2110–2170 |
| 11 | 1427.9–1447.9 | 1475.9–1495.9 |
| 12 | 699–716 | 729–746 |
| 13 | 777–787 | 746–756 |
| 14 | 788–798 | 758–768 |
| 15 | Reserved | Reserved |
| 16 | Reserved | Reserved |
| 17 | 704–716 | 734–746 |
| 18 | 815–830 | 860–875 |
| 19 | 830–845 | 875–890 |
| 20 | 832–862 | 791–821 |
| 21 | 1447.9–1462.9 | 1495.9–1510.9 |
| 22 | Reserved | Reserved |
| 23 | 2000–2020 | 2180–2200 |
| 24 | 1626.5–1660.5 | 1525–1559 |
| 25 | 1850–1915 | 1930–1995 |
| 26–32 | Reserved | Reserved |
| 33 | 1900–1920 | 1900–1920 |
| 34 | 2010–2025 | 2010–2025 |
| 35 | 1850–1910 | 1850–1910 |
| 36 | 1930–1990 | 1930–1990 |
| 37 | 1910–1930 | 1910–1930 |
| 38 | 2570–2620 | 2570–2620 |
| 39 | 1880–1920 | 1880–1920 |
| 40 | 2300–2400 | 2300–2400 |
| 41 | 2496–2690 | 2496–2690 |
| 42 | 3400–3600 | 3400–3600 |
| 43 | 3600–3800 | 3600–3800 |
| 44-60 | Reserved | Reserved |
What tool can be used to set SAR Power Backoff?
Any tool such as AT Command Tester which can send AT commands to the Sierra Wireless modules can be used to set the SAR Power Backoff.
