To control the power output of the E22 module, we need to know how its power settings in the meshtastic app correlate to the actual output power. To test the power output, I used an RF-Power-Meter-V5.0. This device has a linear measurement range from -40dbM to 0dbm. I used 40db of attenuation to make sure the max power of 30dbm would not excede these limits. The test setup is below.
To get a baseline and confirm my setup is working properly, I connected my Heltec V3 to the power meter and set the meshtastic output to 22dbm. The max output from the heltec device should be 21dbm. This test confirmed my setup was working properly.
Next I connected the Lilygo with the E22 module to the test setup and set the Meshtastic power setting to 22dbm. I was only getting about 24dbm, but after troubleshooting I realized it was because one of the edge connections on the E22 module was an antenna output. This was connected to a header pin and run into the breadboard. After removing this header pin, the output was 30dbm as expected. Image of pin removal below.
Now that I was getting the expected output, I took readings with meshtastic power settings set to 22dbm, 20dbm, 18dbm, 16dbm, and 14dbm. Below are the results with links to the readings.
| Power Setting | Power Output | Link to Reading |
|---|---|---|
| 22dbm | 30dbm | Reading |
| 20dbm | 27dbm | Reading |
| 18dbm | 24.7dbm | Reading |
| 16dbm | 23.3dbm | Reading |
| 14dbm | 19.7dbm | Reading |
You can see the output is pretty linear above a power setting of 16dbm giving an output about 7 dbm above the setting. It seems to fall off under 16dbm, but since the output was below the 21dbm available from stock devices, I quit taking readings. At the Meshtastic setting of 22dbm, we did get the full 30dbm advertised for the module.