TX Power with SX1276MB1MAS Shield with different Supply voltage


I noticed a big TX power difference on the SX1276MB1MAS Shield when supplying it with different voltages. My settings are as follows:

  • power output is set to +14dBm
  • frequency is set to 868MHz
  • measured with a sepctrum analyzer directly at the ANT_HF output

5.9dBm when powering the shield with 1.9V
12dBm when powering the shield with 3.6V
(The antenna has a additional gain of araound 2dBi, so with 3.6V we would have the required +14dB).

As the data sheet (5.1 Power Supply Strategy) says: “The SX1276/77/78/79 employs an internal voltage regulation scheme which provides stable operating voltage, and hence device characteristics, over the full industrial temperature and operating voltage range of operation. This includes up to +17 dBm of RF output power which is maintained from 1.8 V to 3.7 V and +20 dBm from 2.4 V to 3.7 V.”
I didn’t expect such an impact for different power supply levels.

Are there additional registers to get the full +14dB as set in the RegPaConfig register with 1.9V that I’m not aware of? Also the usage of the PA_BOOST wouldn’t be an option as the device has to operate at a very low power.