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rpitx-app-note
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András Retzler 2015-11-08 15:31:31 +01:00
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@ -15,7 +15,7 @@ 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:
These examples will use the raw audio file `music48000.raw` and `speech48000.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.
@ -24,12 +24,25 @@ A raw audio file differs from a .wav file because it doesn't have any headers to
**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
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
* 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
**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
* It's the matter of the filter which sideband do we select:
* `csdr bandpass_fir_fft_cc -0.1 0` is the lower sideband
* `csdr bandpass_fir_fft_cc 0 0.1` is the upper sideband
* I have experienced that if the SSB signal is in the center of the I/Q signal, then it won't be okay, so I shift it a bit. So the exact frequency should be around: `rpitx frequency + 48000*0.2 = rpitx frequency + 9600 Hz`
**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