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Merge pull request #252 from cjcliffe/ssb_fix

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SSB mode FIR filter side-band supression
This commit is contained in:
Charles J. Cliffe 2016-01-10 16:24:03 -05:00
commit 12af109e84
4 changed files with 45 additions and 9 deletions
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25
src/modules/modem/analog/ModemLSB.cpp
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@ -2,8 +2,20 @@
ModemLSB::ModemLSB() : ModemAnalog() {
// half band filter used for side-band elimination
ssbFilt = resamp2_crcf_create(12,-0.25f,60.0f);
demodAM_LSB = ampmodem_create(0.5, 0.0, LIQUID_AMPMODEM_LSB, 1);
// options
float fc = 0.25f; // filter cutoff frequency
float ft = 0.05f; // filter transition
float As = 90.0f; // stop-band attenuation [dB]
float mu = 0.0f; // fractional timing offset
// estimate required filter length and generate filter
unsigned int h_len = estimate_req_filter_len(ft,As);
float h[h_len];
liquid_firdes_kaiser(h_len,fc,As,mu,h);
ssbFilt = firfilt_crcf_create(h,h_len);
ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
}
Modem *ModemLSB::factory() {
@ -15,7 +27,8 @@ std::string ModemLSB::getName() {
}
ModemLSB::~ModemLSB() {
resamp2_crcf_destroy(ssbFilt);
firfilt_crcf_destroy(ssbFilt);
nco_crcf_destroy(ssbShift);
ampmodem_destroy(demodAM_LSB);
}
@ -45,8 +58,12 @@ void ModemLSB::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *a
liquid_float_complex x, y;
for (int i = 0; i < bufSize; i++) { // Reject upper band
resamp2_crcf_filter_execute(ssbFilt,input->data[i],&x,&y);
ampmodem_demodulate(demodAM_LSB, x, &demodOutputData[i]);
nco_crcf_step(ssbShift);
nco_crcf_mix_up(ssbShift, input->data[i], &x);
firfilt_crcf_push(ssbFilt, x);
firfilt_crcf_execute(ssbFilt, &x);
nco_crcf_mix_down(ssbShift, x, &y);
ampmodem_demodulate(demodAM_LSB, y, &demodOutputData[i]);
}
buildAudioOutput(akit, audioOut, true);

3
src/modules/modem/analog/ModemLSB.h
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@ -16,6 +16,7 @@ public:
void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut);
private:
resamp2_crcf ssbFilt;
firfilt_crcf ssbFilt;
nco_crcf ssbShift;
ampmodem demodAM_LSB;
};

23
src/modules/modem/analog/ModemUSB.cpp
View File

@ -2,8 +2,20 @@
ModemUSB::ModemUSB() : ModemAnalog() {
// half band filter used for side-band elimination
ssbFilt = resamp2_crcf_create(12,-0.25f,60.0f);
demodAM_USB = ampmodem_create(0.5, 0.0, LIQUID_AMPMODEM_USB, 1);
// options
float fc = 0.25f; // filter cutoff frequency
float ft = 0.05f; // filter transition
float As = 90.0f; // stop-band attenuation [dB]
float mu = 0.0f; // fractional timing offset
// estimate required filter length and generate filter
unsigned int h_len = estimate_req_filter_len(ft,As);
float h[h_len];
liquid_firdes_kaiser(h_len,fc,As,mu,h);
ssbFilt = firfilt_crcf_create(h,h_len);
ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
}
Modem *ModemUSB::factory() {
@ -15,7 +27,8 @@ std::string ModemUSB::getName() {
}
ModemUSB::~ModemUSB() {
resamp2_crcf_destroy(ssbFilt);
firfilt_crcf_destroy(ssbFilt);
nco_crcf_destroy(ssbShift);
ampmodem_destroy(demodAM_USB);
}
@ -45,7 +58,11 @@ void ModemUSB::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *a
liquid_float_complex x, y;
for (int i = 0; i < bufSize; i++) { // Reject lower band
resamp2_crcf_filter_execute(ssbFilt,input->data[i],&x,&y);
nco_crcf_step(ssbShift);
nco_crcf_mix_down(ssbShift, input->data[i], &x);
firfilt_crcf_push(ssbFilt, x);
firfilt_crcf_execute(ssbFilt, &x);
nco_crcf_mix_up(ssbShift, x, &y);
ampmodem_demodulate(demodAM_USB, y, &demodOutputData[i]);
}

3
src/modules/modem/analog/ModemUSB.h
View File

@ -16,6 +16,7 @@ public:
void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut);
private:
resamp2_crcf ssbFilt;
firfilt_crcf ssbFilt;
nco_crcf ssbShift;
ampmodem demodAM_USB;
};