setTxPower seems to have no effect

[Henry-Pease]

Both with measuring the output on my laptop with an SDR dongle and by looking at the RSSI from another module, I see no difference between setTxPower(17) and setTxPower(20), or even setting it at 0, 1, or 2 -- no drop in power. Adding the second parameter for PA_BOOST pin also doesn't seem to make a difference, although when I specify PA_OUTPUT_RFO_PIN I do see the power drop dramatically.

I'm using a custom PCB that's basically just a copy of the sparkfun ESP32 LoRa board, which uses the RFM95 LoRa module. Any idea if the setTxPower function is actually implemented / should be working differently than what I'm seeing?

Thanks!

[IoTThinks]

Last time, I also tried to do the same thing. Normally, a board may support either RFO or PA_BOOST but not both.

I tried the PA_BOOST, and set TX_Power also. RFO doesnt seem available for my board so there is a huge drop of RSSI.

When I changed TX_Power, the RSSI did change too but not much. You can try to disable AGC and measure again. AGC may affect RSSI and SNR.

[tausday]

Hello i have see the same. PLS Check the Register REG_PA_DAC its 0x4d. U can check it with:

LoRa.dumpRegisters(Serial);

If it's 0x84 the boost is not enabled If it's 0x87 the boost is enabled

I have checked at my Heltec at is was x84, so i have add LoRa.setTxPower(20,PA_OUTPUT_PA_BOOST_PIN); After LoRa.begin(868E6) was successfully loaded.

Now i have 0x87 and the RSSI was dropped from -86dBmm to -79dBmm U can see it in LoRa.cpp between 425-460

Give it a Try

[IoTThinks]

@tausday By right, when setting setTxPower, REG_PA_DAC should already be either 0x87 or 0x84. https://github.com/sandeepmistry/arduino-LoRa/blob/master/src/LoRa.cpp#L447

I also see the same effect like you. But I always feel +10dBm difference is not very big enough. :D A bad tuned attenna may easily drop the RSSI much more than the setTxPower can gain.