The focus is layed on the results of experiments with a HF-Transmitter consisting of a pure Raspberry Pi. The Pi uses a digital coding and 4-FSK-Modulation for these experiments. There are also shown some measurement results and there are given some criteria about the quality of a RaspberryPi as a transmitter. Harmonics and mixer products are discussed and ideas, how to avoid them. It is compared with some simple experiments with GnuRadio on effects of digital interpolation and mixing.
Finally some results of short wave transmission with the output power of 10 mW in WSPR-mode is shown.