Serge, I would suggest displaying the received RSSI values during all testing phases.
This way you will have a good idea if everything is setup properly. I just solved a problem here where I mistakenly thought the setHighPower() function was referring to the "transmit power level", whereas in fact it selects which radio you are using, HW or W. So, my bad.
I had it set wrong because I am using the RFM69 radio with an Arduino ProMini board, and the voltage regulator is only good for about 125mA, so I was wanting to throttle back the transmit power level, which is actually set using setPowerLevel(). So in fact, my RFM69 radio was not working properly, and the RSSI values were correspondingly very poor, and which indicated something was wrong in my setup.
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Felix, since you mention wanting to see clone boards, attached is a picture of my current radio lashup before being finalized. ProMini controlling RFM69 radio. Your library example software works fine.
Also, for reference, I've been using 2 of your Moteino-Mega boards to implement an SUV alarm. 433-MHz, 55000 bps, and 100mW xmit power. Recently I did some range testing, and had good RSSI of about -85 with the one node inside the SUV, and the other node 500' away inside a metal frame commercial building. Very happy with that. I had previously tried RFM12 going just 60' from condo to inside the SUV, and reception was unreliable.