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Fix SSB drift with re-write of SSB demod w/o ampmodem

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This commit is contained in:
Charles J. Cliffe 2016-02-03 21:24:37 -05:00
parent 7f1c0a700d
commit 52fefab980
4 changed files with 21 additions and 9 deletions
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11
src/modules/modem/analog/ModemLSB.cpp
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@ -2,10 +2,11 @@
ModemLSB::ModemLSB() : ModemAnalog() {
// 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);
ssbFilt = iirfilt_crcf_create_lowpass(6, 0.25);
ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
c2rFilt = firhilbf_create(5, 90.0);
}
Modem *ModemLSB::factory() {
@ -19,7 +20,8 @@ std::string ModemLSB::getName() {
ModemLSB::~ModemLSB() {
iirfilt_crcf_destroy(ssbFilt);
nco_crcf_destroy(ssbShift);
ampmodem_destroy(demodAM_LSB);
firhilbf_destroy(c2rFilt);
// ampmodem_destroy(demodAM_LSB);
}
int ModemLSB::checkSampleRate(long long sampleRate, int /* audioSampleRate */) {
@ -51,7 +53,10 @@ void ModemLSB::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *a
nco_crcf_step(ssbShift);
nco_crcf_mix_up(ssbShift, input->data[i], &x);
iirfilt_crcf_execute(ssbFilt, x, &y);
ampmodem_demodulate(demodAM_LSB, y, &demodOutputData[i]);
nco_crcf_mix_down(ssbShift, y, &x);
// Liquid-DSP AMPModem SSB drifts with strong signals near baseband (like a carrier?)
// ampmodem_demodulate(demodAM_LSB, y, &demodOutputData[i]);
firhilbf_c2r_execute(c2rFilt, x, &demodOutputData[i]);
}
buildAudioOutput(akit, audioOut, true);

5
src/modules/modem/analog/ModemLSB.h
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@ -17,7 +17,8 @@ public:
private:
iirfilt_crcf ssbFilt;
// firfilt_crcf ssbFilt;
firhilbf c2rFilt;
nco_crcf ssbShift;
ampmodem demodAM_LSB;
// firfilt_crcf ssbFilt;
// ampmodem demodAM_LSB;
};

13
src/modules/modem/analog/ModemUSB.cpp
View File

@ -2,10 +2,11 @@
ModemUSB::ModemUSB() : ModemAnalog() {
// 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);
ssbFilt = iirfilt_crcf_create_lowpass(6, 0.25);
ssbShift = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_frequency(ssbShift, (2.0 * M_PI) * 0.25);
c2rFilt = firhilbf_create(5, 90.0);
}
Modem *ModemUSB::factory() {
@ -19,7 +20,8 @@ std::string ModemUSB::getName() {
ModemUSB::~ModemUSB() {
iirfilt_crcf_destroy(ssbFilt);
nco_crcf_destroy(ssbShift);
ampmodem_destroy(demodAM_USB);
firhilbf_destroy(c2rFilt);
// ampmodem_destroy(demodAM_USB);
}
int ModemUSB::checkSampleRate(long long sampleRate, int /* audioSampleRate */) {
@ -46,12 +48,15 @@ void ModemUSB::demodulate(ModemKit *kit, ModemIQData *input, AudioThreadInput *a
return;
}
liquid_float_complex x,y;
liquid_float_complex x, y;
for (int i = 0; i < bufSize; i++) { // Reject lower band
nco_crcf_step(ssbShift);
nco_crcf_mix_down(ssbShift, input->data[i], &x);
iirfilt_crcf_execute(ssbFilt, x, &y);
ampmodem_demodulate(demodAM_USB, y, &demodOutputData[i]);
nco_crcf_mix_up(ssbShift, y, &x);
// Liquid-DSP AMPModem SSB drifts with strong signals near baseband (like a carrier?)
// ampmodem_demodulate(demodAM_USB, y, &demodOutputData[i]);
firhilbf_c2r_execute(c2rFilt, x, &demodOutputData[i]);
}
buildAudioOutput(akit, audioOut, true);

1
src/modules/modem/analog/ModemUSB.h
View File

@ -17,6 +17,7 @@ public:
private:
iirfilt_crcf ssbFilt;
firhilbf c2rFilt;
nco_crcf ssbShift;
ampmodem demodAM_USB;
};