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Implement DDC using a frequency xlating FIR filter
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,106 @@ | ||
| /* -*- c++ -*- */ | ||
| /* | ||
| * Gqrx SDR: Software defined radio receiver powered by GNU Radio and Qt | ||
| * http://gqrx.dk/ | ||
| * | ||
| * Copyright 2020 Clayton Smith VE3IRR. | ||
| * | ||
| * Gqrx is free software; you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation; either version 3, or (at your option) | ||
| * any later version. | ||
| * | ||
| * Gqrx is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with Gqrx; see the file COPYING. If not, write to | ||
| * the Free Software Foundation, Inc., 51 Franklin Street, | ||
| * Boston, MA 02110-1301, USA. | ||
| */ | ||
| #include <math.h> | ||
| #include <gnuradio/filter/firdes.h> | ||
| #include <gnuradio/io_signature.h> | ||
|
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| #include "downconverter.h" | ||
|
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| #define LPF_CUTOFF 120e3 | ||
|
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||
| downconverter_cc_sptr make_downconverter_cc(unsigned int decim, double center_freq, double samp_rate) | ||
| { | ||
| return gnuradio::get_initial_sptr(new downconverter_cc(decim, center_freq, samp_rate)); | ||
| } | ||
|
|
||
| downconverter_cc::downconverter_cc(unsigned int decim, double center_freq, double samp_rate) | ||
| : gr::hier_block2("downconverter_cc", | ||
| gr::io_signature::make(1, 1, sizeof(gr_complex)), | ||
| gr::io_signature::make(1, 1, sizeof(gr_complex))), | ||
| d_decim(decim), | ||
| d_center_freq(center_freq), | ||
| d_samp_rate(samp_rate) | ||
| { | ||
| connect_all(); | ||
| update_proto_taps(); | ||
| update_phase_inc(); | ||
| } | ||
|
|
||
| downconverter_cc::~downconverter_cc() | ||
| { | ||
|
|
||
| } | ||
|
|
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| void downconverter_cc::set_decim_and_samp_rate(unsigned int decim, double samp_rate) | ||
| { | ||
| d_samp_rate = samp_rate; | ||
| if (decim != d_decim) | ||
| { | ||
| d_decim = decim; | ||
| lock(); | ||
| disconnect_all(); | ||
| connect_all(); | ||
| unlock(); | ||
| } | ||
| update_proto_taps(); | ||
| update_phase_inc(); | ||
| } | ||
|
|
||
| void downconverter_cc::set_center_freq(double center_freq) | ||
| { | ||
| d_center_freq = center_freq; | ||
| update_phase_inc(); | ||
| } | ||
|
|
||
| void downconverter_cc::connect_all() | ||
| { | ||
| if (d_decim > 1) | ||
| { | ||
| filt = gr::filter::freq_xlating_fir_filter_ccf::make(d_decim, {1}, 0.0, d_samp_rate); | ||
| connect(self(), 0, filt, 0); | ||
| connect(filt, 0, self(), 0); | ||
| } | ||
| else | ||
| { | ||
| rot = gr::blocks::rotator_cc::make(0.0); | ||
| connect(self(), 0, rot, 0); | ||
| connect(rot, 0, self(), 0); | ||
| } | ||
| } | ||
|
|
||
| void downconverter_cc::update_proto_taps() | ||
| { | ||
| if (d_decim > 1) | ||
| { | ||
| double out_rate = d_samp_rate / d_decim; | ||
| filt->set_taps(gr::filter::firdes::low_pass(1.0, d_samp_rate, LPF_CUTOFF, out_rate - 2*LPF_CUTOFF)); | ||
| } | ||
| } | ||
|
|
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| void downconverter_cc::update_phase_inc() | ||
| { | ||
| if (d_decim > 1) | ||
| filt->set_center_freq(d_center_freq); | ||
| else | ||
| rot->set_phase_inc(-2.0 * M_PI * d_center_freq / d_samp_rate); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,61 @@ | ||
| /* -*- c++ -*- */ | ||
| /* | ||
| * Gqrx SDR: Software defined radio receiver powered by GNU Radio and Qt | ||
| * http://gqrx.dk/ | ||
| * | ||
| * Copyright 2020 Clayton Smith VE3IRR. | ||
| * | ||
| * Gqrx is free software; you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation; either version 3, or (at your option) | ||
| * any later version. | ||
| * | ||
| * Gqrx is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with Gqrx; see the file COPYING. If not, write to | ||
| * the Free Software Foundation, Inc., 51 Franklin Street, | ||
| * Boston, MA 02110-1301, USA. | ||
| */ | ||
| #pragma once | ||
|
|
||
| #if GNURADIO_VERSION < 0x030800 | ||
| #include <gnuradio/filter/freq_xlating_fir_filter_ccf.h> | ||
| #else | ||
| #include <gnuradio/filter/freq_xlating_fir_filter.h> | ||
| #endif | ||
|
|
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| #include <gnuradio/blocks/rotator_cc.h> | ||
| #include <gnuradio/hier_block2.h> | ||
|
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| class downconverter_cc; | ||
|
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| typedef boost::shared_ptr<downconverter_cc> downconverter_cc_sptr; | ||
| downconverter_cc_sptr make_downconverter_cc(unsigned int decim, double center_freq, double samp_rate); | ||
|
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| class downconverter_cc : public gr::hier_block2 | ||
| { | ||
| friend downconverter_cc_sptr make_downconverter_cc(unsigned int decim, double center_freq, double samp_rate); | ||
|
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| public: | ||
| downconverter_cc(unsigned int decim, double center_freq, double samp_rate); | ||
| ~downconverter_cc(); | ||
| void set_decim_and_samp_rate(unsigned int decim, double samp_rate); | ||
| void set_center_freq(double center_freq); | ||
|
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| private: | ||
| unsigned int d_decim; | ||
| double d_center_freq; | ||
| double d_samp_rate; | ||
| std::vector<float> d_proto_taps; | ||
|
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| void connect_all(); | ||
| void update_proto_taps(); | ||
| void update_phase_inc(); | ||
|
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| gr::filter::freq_xlating_fir_filter_ccf::sptr filt; | ||
| gr::blocks::rotator_cc::sptr rot; | ||
| }; |