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SSB FIR kaiser -> Simple IIR Lowpass

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This commit is contained in:
Charles J. Cliffe 2016-02-02 21:26:24 -05:00
parent 090d751482
commit 1523d55b6c
4 changed files with 9 additions and 31 deletions
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22
src/modules/modem/analog/ModemLSB.cpp
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@ -3,20 +3,9 @@
ModemLSB::ModemLSB() : ModemAnalog() { ModemLSB::ModemLSB() : ModemAnalog() {
// half band filter used for side-band elimination // half band filter used for side-band elimination
demodAM_LSB = ampmodem_create(0.25, 0.25, LIQUID_AMPMODEM_LSB, 1); demodAM_LSB = ampmodem_create(0.25, 0.25, LIQUID_AMPMODEM_LSB, 1);
// options ssbFilt = iirfilt_crcf_create_lowpass(6, 0.25);
float fc = 0.25f; // filter cutoff frequency
float ft = 0.05f; // filter transition
float As = 90.0f; // stop-band attenuation [dB]
float mu = 0.5f; // fractional timing offset
// estimate required filter length and generate filter
unsigned int h_len = estimate_req_filter_len(ft,As);
float *h = (float *) malloc(h_len * sizeof(float));
liquid_firdes_kaiser(h_len,fc,As,mu,h);
ssbFilt = firfilt_crcf_create(h,h_len);
ssbShift = nco_crcf_create(LIQUID_NCO); ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25); nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
free(h);
} }
Modem *ModemLSB::factory() { Modem *ModemLSB::factory() {
@ -28,7 +17,7 @@ std::string ModemLSB::getName() {
} }
ModemLSB::~ModemLSB() { ModemLSB::~ModemLSB() {
firfilt_crcf_destroy(ssbFilt); iirfilt_crcf_destroy(ssbFilt);
nco_crcf_destroy(ssbShift); nco_crcf_destroy(ssbShift);
ampmodem_destroy(demodAM_LSB); ampmodem_destroy(demodAM_LSB);
} }
@ -57,13 +46,12 @@ void ModemLSB::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *a
return; return;
} }
liquid_float_complex x; liquid_float_complex x, y;
for (int i = 0; i < bufSize; i++) { // Reject upper band for (int i = 0; i < bufSize; i++) { // Reject upper band
nco_crcf_step(ssbShift); nco_crcf_step(ssbShift);
nco_crcf_mix_up(ssbShift, input->data[i], &x); nco_crcf_mix_up(ssbShift, input->data[i], &x);
firfilt_crcf_push(ssbFilt, x); iirfilt_crcf_execute(ssbFilt, x, &y);
firfilt_crcf_execute(ssbFilt, &x); ampmodem_demodulate(demodAM_LSB, y, &demodOutputData[i]);
ampmodem_demodulate(demodAM_LSB, x, &demodOutputData[i]);
} }
buildAudioOutput(akit, audioOut, true); buildAudioOutput(akit, audioOut, true);

3
src/modules/modem/analog/ModemLSB.h
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@ -16,7 +16,8 @@ public:
void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut); void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut);
private: private:
firfilt_crcf ssbFilt; iirfilt_crcf ssbFilt;
// firfilt_crcf ssbFilt;
nco_crcf ssbShift; nco_crcf ssbShift;
ampmodem demodAM_LSB; ampmodem demodAM_LSB;
}; };

13
src/modules/modem/analog/ModemUSB.cpp
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@ -3,20 +3,9 @@
ModemUSB::ModemUSB() : ModemAnalog() { ModemUSB::ModemUSB() : ModemAnalog() {
// half band filter used for side-band elimination // half band filter used for side-band elimination
demodAM_USB = ampmodem_create(0.25, -0.25, LIQUID_AMPMODEM_USB, 1); demodAM_USB = ampmodem_create(0.25, -0.25, LIQUID_AMPMODEM_USB, 1);
// options ssbFilt = iirfilt_crcf_create_lowpass(6, 0.25);
float fc = 0.25f; // filter cutoff frequency
float ft = 0.05f; // filter transition
float As = 90.0f; // stop-band attenuation [dB]
float mu = 0.5f; // fractional timing offset
// estimate required filter length and generate filter
unsigned int h_len = estimate_req_filter_len(ft,As);
float *h = (float *) malloc(h_len * sizeof(float));
liquid_firdes_kaiser(h_len,fc,As,mu,h);
ssbFilt = firfilt_crcf_create(h,h_len);
ssbShift = nco_crcf_create(LIQUID_NCO); ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25); nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
free(h);
} }
Modem *ModemUSB::factory() { Modem *ModemUSB::factory() {

2
src/modules/modem/analog/ModemUSB.h
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@ -16,7 +16,7 @@ public:
void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut); void demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *audioOut);
private: private:
firfilt_crcf ssbFilt; iirfilt_crcf ssbFilt;
nco_crcf ssbShift; nco_crcf ssbShift;
ampmodem demodAM_USB; ampmodem demodAM_USB;
}; };