After many investigations i have the solution to improve the poor level of transmit power on Lora TTGO version 1 at 868 Mhz ( I suppose it is version 1.) The lora TTGo like this :
There are 2 issues :
Software :LMIC library is not clear on this side : Check radio.c file, and go to SX1276 power definition ( about line 476 ) : add this at the end of configuration file: writeReg(RegPaConfig,0b01111111) : It suppose you have a hardware witout Paboost connected.
Hardware:Is low cost, interresting but poor RF design. I remove all the parts at he RF filter. I apply the Semtech ref design to changes 8 capacitors and inductors, and use Pa output without Paboost option
Measurement are performed with radio laboratory equipement in conducted condition : about ±0,1 dBm absolute accuracy. That’s my job.
Before : 2dBm : about 1,6 mW ( with LMIC modification describe above)
After : 14dBm : 25mW. ( with LMIC same modification describe above)
Conclusion : some issue around lora TTGO could be the result of wrong parts…Simply apply Semtech refdesign could solve the issue, without hard optimisation, without network analyser and PCB effect compensation.
I don’t check the receiver parts. May be some errors on design again…
You cannot have this kind of issues with RFM95 module.