Application note on using rpitx

Using with csdr to modulate streaming input

You will need the dev branch of csdr for doing this.
Setup instructions:

git clone https://github.com/simonyiszk/csdr.git
cd csdr
git fetch
git checkout dev
make && sudo make install 

Note that it should be already done, if you installed qtcsdr.

Modulate from raw audio file

These examples will use the raw audio file testsound48000.raw, which is present in this repo. You can get this file by:

git clone https://github.com/ha7ilm/rpitx-app-note
cd rpitx-app-note; ls  #There is your file.

A raw audio file differs from a .wav file because it doesn't have any headers to store its parameters, just the samples after each other.

Generate AM modulation:

cat testsound48000.raw | csdr convert_i16_f | csdr gain_ff 1.0 | csdr dsb_fc | csdr add_dcoffset_cc | sudo rpitx -i- -m IQFLOAT -f 28400

• The part csdr gain_ff 1.0 can be changed to increase/decrease modulation.
• The -f 28400 at the end gives the transmit frequency in kHz.