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rpitx-app-note
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András Retzler 2015-11-08 15:41:19 +01:00
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@ -20,22 +20,22 @@ These examples will use the raw audio file `music48000.raw` and `speech48000.raw
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.
We will play these files in a loop, you can stop it with Ctrl+C.
**Generate AM modulation:**
cat music48000.raw | csdr convert_i16_f | csdr gain_ff 1.0 | csdr dsb_fc | csdr add_dcoffset_cc | sudo rpitx -i- -m IQFLOAT -f 28400
(while true; do cat music48000.raw; done) | 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.
**Generate USB modulation:**
cat speech48000.raw | csdr convert_i16_f | csdr dsb_fc | csdr bandpass_fir_fft_cc 0 0.1 0.01 | csdr gain_ff 2.0 | csdr shift_addition_cc 0.2 | sudo rpitx -i- -m IQFLOAT -f 28400
(while true; do cat speech48000.raw; done) | csdr convert_i16_f | csdr dsb_fc | csdr bandpass_fir_fft_cc 0 0.1 0.01 | csdr gain_ff 2.0 | csdr shift_addition_cc 0.2 | sudo rpitx -i- -m IQFLOAT -f 28400
**Generate LSB modulation:**
cat speech48000.raw | csdr convert_i16_f | csdr dsb_fc | csdr bandpass_fir_fft_cc -0.1 0 0.01 | csdr gain_ff 2.0 | csdr shift_addition_cc 0.2 | sudo rpitx -i- -m IQFLOAT -f 28400
(while true; do cat speech48000.raw; done) | csdr convert_i16_f | csdr dsb_fc | csdr bandpass_fir_fft_cc -0.1 0 0.01 | csdr gain_ff 2.0 | csdr shift_addition_cc 0.2 | sudo rpitx -i- -m IQFLOAT -f 28400
* It's the matter of the filter which sideband do we select:
* `csdr bandpass_fir_fft_cc -0.1 0` is the lower sideband
@ -44,5 +44,10 @@ A raw audio file differs from a .wav file because it doesn't have any headers to
**Generate NFM modulation:**
cat music48000.raw | csdr convert_i16_f | csdr gain_ff 7000 | csdr convert_f_samplerf 20833 | sudo rpitx -i- -m RF -f 28400
(while true; do cat music48000.raw; done) | csdr convert_i16_f | csdr gain_ff 7000 | csdr convert_f_samplerf 20833 | sudo rpitx -i- -m RF -f 28400
**Generate WFM modulation:**
(while true; do cat music48000.raw; done) | csdr convert_i16_f | csdr gain_ff 70000 | csdr convert_f_samplerf 20833 | sudo rpitx -i- -m RF -f 28400
* Frequency deviation is set much higher with `csdr gain_ff 70000`, that's the only difference between this and NFM.