thank you all for your excellent replies: I'm going to make the BFO calibration procedure, and listening by myself on my good old DEGEN 1103 chines receiver.
And yes, I was surprised at first by the too higly pitched received modulation: it is a good second facts that leads to a BFO calibration problem.
I will let you know!
All in all this uBitx is a great transceiver for the price, and for many like me a chance to transmit with something else but commercial hardware.
