Hello! Long story short: hackrf sink code to convert from GR complex to hackrf 8-bit format fails by generating wrong bits on ARM when I do TX on Raspberry PI 2 . Evil hides here: lib/hackrf/hackrf_sink_c.cc outbuf[i] = inbuf[i]*127; Since on ARM GCC treats all "char" as unsigned(this is chosen implementation) it generates wrong bits, so my advice is to compile on ARM gr-osmocom with flag -fsigned-char. This is probably most effective way to solve this, it solved my TX problems.