From 52c3760e902647db215bdc63d37afd1855d2472a Mon Sep 17 00:00:00 2001
From: Brumi-2021 <86470699+Brumi-2021@users.noreply.github.com>
Date: Wed, 5 Mar 2025 04:27:18 +0100
Subject: [PATCH] Adding Wefax demodulation mode inside Audio App (#2539)

* Adding_new_WFAX_GUI_mode_Audio_App

* Wefax_APT_demodulation_structure

* Solving REC Apt signal.wav from WFAX

* clang format issues

* correcting comments
---
 .../application/apps/analog_audio_app.cpp     | 34 ++++++-
 .../application/apps/analog_audio_app.hpp     | 29 ++++--
 firmware/application/baseband_api.cpp         | 12 +--
 firmware/application/baseband_api.hpp         |  3 +-
 firmware/application/freqman.hpp              |  1 +
 firmware/application/freqman_db.cpp           |  9 +-
 firmware/application/receiver_model.cpp       | 32 +++++--
 firmware/application/receiver_model.hpp       | 10 +-
 firmware/baseband/audio_output.cpp            |  2 +-
 firmware/baseband/dsp_demodulate.cpp          | 35 +++++--
 firmware/baseband/dsp_demodulate.hpp          | 12 +++
 firmware/baseband/dsp_hilbert.cpp             | 85 ++++++++++++++++
 firmware/baseband/dsp_hilbert.hpp             | 13 +++
 firmware/baseband/proc_am_audio.cpp           | 28 ++++--
 firmware/baseband/proc_am_audio.hpp           |  4 +-
 firmware/common/dsp_fir_taps.hpp              | 96 +++++++++++++++++--
 firmware/common/dsp_iir_config.hpp            |  6 ++
 firmware/common/dsp_sos_config.hpp            | 20 +++-
 firmware/common/message.hpp                   |  7 +-
 19 files changed, 383 insertions(+), 55 deletions(-)

diff --git a/firmware/application/apps/analog_audio_app.cpp b/firmware/application/apps/analog_audio_app.cpp
index 4726f44b5..b55250a7c 100644
--- a/firmware/application/apps/analog_audio_app.cpp
+++ b/firmware/application/apps/analog_audio_app.cpp
@@ -102,6 +102,24 @@ WFMOptionsView::WFMOptionsView(
     };
 }
 
+/* AMFMAptOptionsView *********************************************************/
+
+AMFMAptOptionsView::AMFMAptOptionsView(
+    Rect parent_rect,
+    const Style* style)
+    : View{parent_rect} {
+    set_style(style);
+
+    add_children({
+        &label_config,
+        &options_config,
+    });
+
+    freqman_set_bandwidth_option(AMFM_MODULATION, options_config);  // adding the common message from freqman.cpp to the options_config
+    options_config.set_by_value(receiver_model.amfm_configuration());
+    receiver_model.set_amfm_configuration(5);  // Fix index 5 manually, not from freqman: set to  RX AM (USB+FM) mode to demod audio tone, and get Wefax_APT signal.
+}
+
 /* SPECOptionsView *******************************************************/
 
 SPECOptionsView::SPECOptionsView(
@@ -176,8 +194,8 @@ AnalogAudioView::AnalogAudioView(
 
     auto modulation = receiver_model.modulation();
     // This app doesn't handle "Capture" mode.
-    if (modulation > ReceiverModel::Mode::SpectrumAnalysis)
-        modulation = ReceiverModel::Mode::SpectrumAnalysis;
+    if (modulation > ReceiverModel::Mode::SpectrumAnalysis)  // This two should be together in the last index position : SpectrumAnalysis = 4, and  Capture = 5
+        modulation = ReceiverModel::Mode::SpectrumAnalysis;  // For sw simplicity , Wefax_mode,  should NOT be added between.
 
     options_modulation.set_by_value(toUType(modulation));
     options_modulation.on_change = [this](size_t, OptionsField::value_t v) {
@@ -346,6 +364,12 @@ void AnalogAudioView::on_show_options_modulation() {
             text_ctcss.hidden(true);
             break;
 
+        case ReceiverModel::Mode::AMAudioFMApt:
+            widget = std::make_unique<AMFMAptOptionsView>(options_view_rect, Theme::getInstance()->option_active);
+            waterfall.show_audio_spectrum_view(false);
+            text_ctcss.hidden(true);
+            break;
+
         case ReceiverModel::Mode::SpectrumAnalysis:
             widget = std::make_unique<SPECOptionsView>(this, nbfm_view_rect, Theme::getInstance()->option_active);
             waterfall.show_audio_spectrum_view(false);
@@ -387,6 +411,9 @@ void AnalogAudioView::update_modulation(ReceiverModel::Mode modulation) {
         case ReceiverModel::Mode::WidebandFMAudio:
             image_tag = portapack::spi_flash::image_tag_wfm_audio;
             break;
+        case ReceiverModel::Mode::AMAudioFMApt:  // TODO pending to update it.
+            image_tag = portapack::spi_flash::image_tag_am_audio;
+            break;
         case ReceiverModel::Mode::SpectrumAnalysis:
             image_tag = portapack::spi_flash::image_tag_wideband_spectrum;
             break;
@@ -421,6 +448,9 @@ void AnalogAudioView::update_modulation(ReceiverModel::Mode modulation) {
         case ReceiverModel::Mode::WidebandFMAudio:
             sampling_rate = 48000;
             break;
+        case ReceiverModel::Mode::AMAudioFMApt:  // TODO  Wefax mode.
+            sampling_rate = 12000;
+            break;
         default:
             break;
     }
diff --git a/firmware/application/apps/analog_audio_app.hpp b/firmware/application/apps/analog_audio_app.hpp
index 33153376a..29f01d514 100644
--- a/firmware/application/apps/analog_audio_app.hpp
+++ b/firmware/application/apps/analog_audio_app.hpp
@@ -53,6 +53,24 @@ class AMOptionsView : public View {
         }};
 };
 
+class AMFMAptOptionsView : public View {
+   public:
+    AMFMAptOptionsView(Rect parent_rect, const Style* style);
+
+   private:
+    Text label_config{
+        {0 * 8, 0 * 16, 2 * 8, 1 * 16},
+        "BW",
+    };
+
+    OptionsField options_config{
+        {3 * 8, 0 * 16},
+        6,  // Max option length
+        {
+            // Using common messages from freqman_ui.cpp In HF USB , Here  we only need USB Audio demod, + post-FM demod fsubcarrier FM tone to get APT signal.
+        }};
+};
+
 class NBFMOptionsView : public View {
    public:
     NBFMOptionsView(Rect parent_rect, const Style* style);
@@ -206,12 +224,11 @@ class AnalogAudioView : public View {
     OptionsField options_modulation{
         {0 * 8, 0 * 16},
         4,
-        {
-            {" AM ", toUType(ReceiverModel::Mode::AMAudio)},
-            {"NFM ", toUType(ReceiverModel::Mode::NarrowbandFMAudio)},
-            {"WFM ", toUType(ReceiverModel::Mode::WidebandFMAudio)},
-            {"SPEC", toUType(ReceiverModel::Mode::SpectrumAnalysis)},
-        }};
+        {{" AM ", toUType(ReceiverModel::Mode::AMAudio)},
+         {"NFM ", toUType(ReceiverModel::Mode::NarrowbandFMAudio)},
+         {"WFM ", toUType(ReceiverModel::Mode::WidebandFMAudio)},
+         {"WFAX", toUType(ReceiverModel::Mode::AMAudioFMApt)},  // Added to handle  HF  WeatherFax , SSB (USB demod) + Tone_Subcarrier FM demod
+         {"SPEC", toUType(ReceiverModel::Mode::SpectrumAnalysis)}}};
 
     AudioVolumeField field_volume{
         {28 * 8, 0 * 16}};
diff --git a/firmware/application/baseband_api.cpp b/firmware/application/baseband_api.cpp
index e288d9d66..452a63b1a 100644
--- a/firmware/application/baseband_api.cpp
+++ b/firmware/application/baseband_api.cpp
@@ -66,12 +66,12 @@ static void send_message(const Message* const message) {
 
 void AMConfig::apply() const {
     const AMConfigureMessage message{
-        taps_6k0_decim_0,  // common FIR filter taps pre-decim_0 to all 5 x AM mod types.(AM-9K, AM-6K, USB, LSB, CW)
-        taps_6k0_decim_1,  // common FIR filter taps pre-decim_1 to all 5 x AM mod. types.
-        decim_2,           // var decim_2 FIR taps filter , variable values, depending selected  AM mod(AM  9k / 6k all rest AM modes)
-        channel,           // var channel FIR taps filter , variable values, depending selected  AM mode, each one different  (DSB-9K, DSB-6K, USB-3K, LSB-3K,CW)
-        modulation,        // var parameter .
-        audio_12k_hpf_300hz_config};
+        taps_6k0_decim_0,              // common FIR filter taps pre-decim_0 to all 6 x AM mod types.(AM-9K, AM-6K, USB, LSB, CW, WFAX)
+        taps_6k0_decim_1,              // common FIR filter taps pre-decim_1 to all 6 x AM mod. types. (")
+        decim_2,                       // var decim_2 FIR taps filter , variable values, depending selected  AM mod(AM  9k / 6k and all rest AM modes)
+        channel,                       // var channel FIR taps filter , variable values, depending selected  AM mode, each one different  (DSB-9K, DSB-6K, USB-3K, LSB-3K,CW,WFAX)
+        modulation,                    // var parameter . enum class Modulation : int32_t {DSB = 0, SSB = 1, SSB_FM = 2}
+        audio_12k_iir_filter_config};  // var parameter , 300 Hz hpf all except Wefax (1.500Hz lpf)
     send_message(&message);
     audio::set_rate(audio::Rate::Hz_12000);
 }
diff --git a/firmware/application/baseband_api.hpp b/firmware/application/baseband_api.hpp
index a594fc273..e8e1bd584 100644
--- a/firmware/application/baseband_api.hpp
+++ b/firmware/application/baseband_api.hpp
@@ -36,9 +36,10 @@
 namespace baseband {
 
 struct AMConfig {
-    const fir_taps_real<32> decim_2;  // added to handle two types decim_2 9k, 6k
+    const fir_taps_real<32> decim_2;  // added to handle two var types decim_2 9k, 6k
     const fir_taps_complex<64> channel;
     const AMConfigureMessage::Modulation modulation;
+    const iir_biquad_config_t audio_12k_iir_filter_config;  // added to handle two var IIR filter types : 300 hpf(as before) , 1500Hz lpf for Wefax.
 
     void apply() const;
 };
diff --git a/firmware/application/freqman.hpp b/firmware/application/freqman.hpp
index 74bf9198e..18c179f26 100644
--- a/firmware/application/freqman.hpp
+++ b/firmware/application/freqman.hpp
@@ -41,6 +41,7 @@ enum freqman_entry_modulation : uint8_t {
     AM_MODULATION = 0,
     NFM_MODULATION,
     WFM_MODULATION,
+    AMFM_MODULATION,  // Added for Wefax.
     SPEC_MODULATION
 };
 
diff --git a/firmware/application/freqman_db.cpp b/firmware/application/freqman_db.cpp
index 89eb52b14..59613e682 100644
--- a/firmware/application/freqman_db.cpp
+++ b/firmware/application/freqman_db.cpp
@@ -51,7 +51,7 @@ options_t freqman_modulations = {
     {"SPEC", 3},
 };
 
-options_t freqman_bandwidths[4] = {
+options_t freqman_bandwidths[5] = {
     {
         // AM
         {"DSB 9k", 0},
@@ -72,6 +72,10 @@ options_t freqman_bandwidths[4] = {
         {"180k", 1},
         {"200k", 0},
     },
+    {
+        // AMFM for Wefax-
+        {"USB+FM", 5},  // Fixed RX demodul AM config Index 5 : USB+FM for Audio Weather fax (Wfax) tones.
+    },
     {
         // SPEC -- TODO: these should be indexes.
         {"12k5", 12500},
@@ -99,8 +103,7 @@ options_t freqman_bandwidths[4] = {
         {"4500k", 4500000},
         {"5000k", 5500000},
         {"5500k", 5500000},  // Max capture, needs /4 decimation, (22Mhz sampling ADC).
-    },
-};
+    }};
 
 // TODO: these should be indexes.
 options_t freqman_steps = {
diff --git a/firmware/application/receiver_model.cpp b/firmware/application/receiver_model.cpp
index f7c795555..2dcf6b03a 100644
--- a/firmware/application/receiver_model.cpp
+++ b/firmware/application/receiver_model.cpp
@@ -39,13 +39,14 @@ using namespace portapack;
 
 namespace {
 
-static constexpr std::array<baseband::AMConfig, 5> am_configs{{
+static constexpr std::array<baseband::AMConfig, 6> am_configs{{
     // we config here all the non COMMON parameters to each AM modulation type in RX.
-    {taps_9k0_decim_2, taps_9k0_dsb_channel, AMConfigureMessage::Modulation::DSB},  // AM DSB-C  BW 9khz  (+-4k5)  commercial EU bandwidth .
-    {taps_6k0_decim_2, taps_6k0_dsb_channel, AMConfigureMessage::Modulation::DSB},  // AM DSB-C  BW 6khz  (+-3k0)  narrow AM , ham equipments.
-    {taps_6k0_decim_2, taps_2k8_usb_channel, AMConfigureMessage::Modulation::SSB},  // SSB USB   BW 2K8   (+ 2K8)
-    {taps_6k0_decim_2, taps_2k8_lsb_channel, AMConfigureMessage::Modulation::SSB},  // SSB LSB   BW 2K8   (- 2K8)
-    {taps_6k0_decim_2, taps_0k7_usb_channel, AMConfigureMessage::Modulation::SSB},  // SSB USB   BW 0K7   (+ 0K7)  used to get audio tone from CW Morse, assuming tx shifted +700hz aprox
+    {taps_9k0_decim_2, taps_9k0_dsb_channel, AMConfigureMessage::Modulation::DSB, audio_12k_hpf_300hz_config},            // AM DSB-C  BW 9khz  (+-4k5)  commercial EU bandwidth .
+    {taps_6k0_decim_2, taps_6k0_dsb_channel, AMConfigureMessage::Modulation::DSB, audio_12k_hpf_300hz_config},            // AM DSB-C  BW 6khz  (+-3k0)  narrow AM , ham equipments.
+    {taps_6k0_decim_2, taps_2k8_usb_channel, AMConfigureMessage::Modulation::SSB, audio_12k_hpf_300hz_config},            // SSB USB   BW 2K8   (+ 2K8)  SSB ham equipments.
+    {taps_6k0_decim_2, taps_2k8_lsb_channel, AMConfigureMessage::Modulation::SSB, audio_12k_hpf_300hz_config},            // SSB LSB   BW 2K8   (- 2K8)  SSB ham equipments.
+    {taps_6k0_decim_2, taps_0k7_usb_channel, AMConfigureMessage::Modulation::SSB, audio_12k_hpf_300hz_config},            // SSB USB   BW 0K7   (+ 0K7)  To get audio tone from CW Morse, assuming tx shifted +700hz aprox
+    {taps_6k0_decim_2, taps_2k6_usb_wefax_channel, AMConfigureMessage::Modulation::SSB_FM, audio_12k_lpf_1500hz_config},  // SSB USB+FM  to demod. Subcarrier FM Audio Tones to get APT Weather Fax.
 }};
 
 static constexpr std::array<baseband::NBFMConfig, 3> nbfm_configs{{
@@ -145,6 +146,17 @@ void ReceiverModel::set_am_configuration(uint8_t n) {
     }
 }
 
+uint8_t ReceiverModel::amfm_configuration() const {
+    return settings_.amfm_config_index;
+}
+
+void ReceiverModel::set_amfm_configuration(uint8_t n) {
+    if (n < am_configs.size()) {
+        settings_.amfm_config_index = n;
+        update_modulation();
+    }
+}
+
 uint8_t ReceiverModel::nbfm_configuration() const {
     return settings_.nbfm_config_index;
 }
@@ -303,6 +315,10 @@ void ReceiverModel::update_modulation() {
             update_am_configuration();
             break;
 
+        case Mode::AMAudioFMApt:  // Wefax , first step , USB demodulation from the AMAudio group, index 2 (USB+3K), TODO +FM subcarrier demod ?
+            update_amfm_configuration();
+            break;
+
         case Mode::NarrowbandFMAudio:
             update_nbfm_configuration();
             break;
@@ -321,6 +337,10 @@ void ReceiverModel::update_am_configuration() {
     am_configs[am_configuration()].apply();
 }
 
+void ReceiverModel::update_amfm_configuration() {
+    am_configs[amfm_configuration()].apply();  // update with different index for Wefax.
+}
+
 void ReceiverModel::update_nbfm_configuration() {
     nbfm_configs[nbfm_configuration()].apply(squelch_level());
 }
diff --git a/firmware/application/receiver_model.hpp b/firmware/application/receiver_model.hpp
index ecdb32236..36ab728c1 100644
--- a/firmware/application/receiver_model.hpp
+++ b/firmware/application/receiver_model.hpp
@@ -40,8 +40,9 @@ class ReceiverModel {
         AMAudio = 0,
         NarrowbandFMAudio = 1,
         WidebandFMAudio = 2,
-        SpectrumAnalysis = 3,
-        Capture = 4
+        AMAudioFMApt = 3,  // Added to handle  HF  WeatherFax , SSB (USB demod) + Tone_Subcarrier FM demod
+        SpectrumAnalysis = 4,
+        Capture = 5
     };
 
     struct settings_t {
@@ -54,6 +55,7 @@ class ReceiverModel {
         bool rf_amp = false;
         Mode mode = Mode::NarrowbandFMAudio;
         uint8_t am_config_index = 0;
+        uint8_t amfm_config_index = 0;
         uint8_t nbfm_config_index = 0;
         uint8_t wfm_config_index = 0;
         uint8_t squelch_level = 80;
@@ -87,6 +89,9 @@ class ReceiverModel {
     uint8_t am_configuration() const;
     void set_am_configuration(uint8_t n);
 
+    uint8_t amfm_configuration() const;
+    void set_amfm_configuration(uint8_t n);
+
     uint8_t nbfm_configuration() const;
     void set_nbfm_configuration(uint8_t n);
 
@@ -140,6 +145,7 @@ class ReceiverModel {
 
     void update_modulation();
     void update_am_configuration();
+    void update_amfm_configuration();
     void update_nbfm_configuration();
     void update_wfm_configuration();
 
diff --git a/firmware/baseband/audio_output.cpp b/firmware/baseband/audio_output.cpp
index 2a35db70a..313661dd6 100644
--- a/firmware/baseband/audio_output.cpp
+++ b/firmware/baseband/audio_output.cpp
@@ -72,7 +72,7 @@ void AudioOutput::on_block(const buffer_f32_t& audio) {
     if (do_processing) {
         const auto audio_present_now = squelch.execute(audio);
 
-        hpf.execute_in_place(audio);
+        hpf.execute_in_place(audio);  // IIRBiquadFilter name is "hpf", but we will call with "hpf-coef" for all  except WFAX with "lpf-coef".
         deemph.execute_in_place(audio);
 
         audio_present_history = (audio_present_history << 1) | (audio_present_now ? 1 : 0);
diff --git a/firmware/baseband/dsp_demodulate.cpp b/firmware/baseband/dsp_demodulate.cpp
index 695668a16..835e279fb 100644
--- a/firmware/baseband/dsp_demodulate.cpp
+++ b/firmware/baseband/dsp_demodulate.cpp
@@ -24,6 +24,8 @@
 #include "complex.hpp"
 #include "fxpt_atan2.hpp"
 #include "utility_m4.hpp"
+#include "dsp_hilbert.hpp"
+#include "dsp_modulate.hpp"
 
 #include <hal.h>
 
@@ -63,12 +65,7 @@ buffer_f32_t SSB::execute(
 
     return {dst.p, src.count, src.sampling_rate};
 }
-/*
-static inline float angle_approx_4deg0(const complex32_t t) {
-        const auto x = static_cast<float>(t.imag()) / static_cast<float>(t.real());
-        return 16384.0f * x;
-}
-*/
+
 static inline float angle_approx_0deg27(const complex32_t t) {
     if (t.real()) {
         const auto x = static_cast<float>(t.imag()) / static_cast<float>(t.real());
@@ -82,6 +79,32 @@ static inline float angle_precise(const complex32_t t) {
     return atan2f(t.imag(), t.real());
 }
 
+buffer_f32_t SSB_FM::execute(    // Added to handle WFAX (HF weather map )-
+    const buffer_c16_t& src,     // input arg , pointer Complex c16 i,q buffer.
+    const buffer_f32_t& dst) {   // input arg , pointer f32 buffer audio demodulated
+    complex16_t* src_p = src.p;  // removed const ; init src_p pointer with the mem address pointed by src.p.
+    const auto src_end = &src.p[src.count];
+    auto dst_p = dst.p;
+    float mag_sq_lpf_norm;
+
+    while (src_p < src_end) {
+        // FM APT audio tone demod: real part (USB-differentiator)  and AM tone demodulation + lpf (to remove the subcarrier.)
+        real_to_complex.execute((src_p++)->real(), mag_sq_lpf_norm);
+        *(dst_p++) = mag_sq_lpf_norm;  // already normalized/32.768f and clipped to +1.0f for the wav file.
+
+        real_to_complex.execute((src_p++)->real(), mag_sq_lpf_norm);
+        *(dst_p++) = mag_sq_lpf_norm;
+
+        real_to_complex.execute((src_p++)->real(), mag_sq_lpf_norm);
+        *(dst_p++) = mag_sq_lpf_norm;
+
+        real_to_complex.execute((src_p++)->real(), mag_sq_lpf_norm);
+        *(dst_p++) = mag_sq_lpf_norm;
+    }
+
+    return {dst.p, src.count, src.sampling_rate};
+}
+
 buffer_f32_t FM::execute(
     const buffer_c16_t& src,
     const buffer_f32_t& dst) {
diff --git a/firmware/baseband/dsp_demodulate.hpp b/firmware/baseband/dsp_demodulate.hpp
index d965ca080..1cb48699b 100644
--- a/firmware/baseband/dsp_demodulate.hpp
+++ b/firmware/baseband/dsp_demodulate.hpp
@@ -23,6 +23,7 @@
 #define __DSP_DEMODULATE_H__
 
 #include "dsp_types.hpp"
+#include "dsp_hilbert.hpp"
 
 namespace dsp {
 namespace demodulate {
@@ -47,6 +48,17 @@ class SSB {
     static constexpr float k = 1.0f / 32768.0f;
 };
 
+class SSB_FM {  // Added to handle WFAX-
+   public:
+    buffer_f32_t execute(
+        const buffer_c16_t& src,
+        const buffer_f32_t& dst);
+
+   private:
+    static constexpr float k = 1.0f / 32768.0f;
+    dsp::Real_to_Complex real_to_complex;  // It is a member variable of SSB_FM.
+};
+
 class FM {
    public:
     buffer_f32_t execute(
diff --git a/firmware/baseband/dsp_hilbert.cpp b/firmware/baseband/dsp_hilbert.cpp
index 642fa3d69..8f62dae85 100644
--- a/firmware/baseband/dsp_hilbert.cpp
+++ b/firmware/baseband/dsp_hilbert.cpp
@@ -21,6 +21,7 @@
 
 #include "dsp_hilbert.hpp"
 #include "dsp_sos_config.hpp"
+#include "utility_m4.hpp"
 
 namespace dsp {
 
@@ -83,4 +84,88 @@ void HilbertTransform::execute(float in, float& out_i, float& out_q) {
     n = (n + 1) % 4;
 }
 
+Real_to_Complex::Real_to_Complex() {
+    // No need to call a separate configuration method like "Real_to_Complex()" externally before using the execute() method
+    // This is the constructor for the Real_to_Complex class.
+    // It initializes the member variables and calls the configure function for the sos_input, sos_i, and sos_q filters.
+    // to ensure the object is ready to use right after instantiation.
+
+    n = 0;
+
+    sos_input.configure(full_band_lpf_config);
+    sos_i.configure(full_band_lpf_config);
+    sos_q.configure(full_band_lpf_config);
+    sos_mag_sq.configure(quarter_band_lpf_config);  // for APT LPF subcarrier filter. (1/4 Nyquist fs/2 = 1/4 * 12Khz/2 = 1.5khz)
+}
+
+void Real_to_Complex::execute(float in, float& out_mag_sq_lpf) {
+    // Full_band LPF  means a LP filter with f_cut_off = fs/2; Full band = Full max band = 1/2 * fs_max =  1.0 x f_Nyquist = 1 * fs/2 = fs/2
+    float a = 0, b = 0;
+    float out_i = 0, out_q = 0, out_mag_sq = 0;
+    // int32_t packed;
+
+    float in_filtered = sos_input.execute(in) * 1.0f;  // Anti-aliasing full band LPF,  fc = fs/2= 6k, audio filter front-end.
+
+    switch (n) {
+        case 0:
+            a = in_filtered;
+            b = 0;
+            break;
+        case 1:
+            a = 0;
+            b = -in_filtered;
+            break;
+        case 2:
+            a = -in_filtered;
+            b = 0;
+            break;
+        case 3:
+            a = 0;
+            b = in_filtered;
+            break;
+    }
+
+    float i = sos_i.execute(a) * 1.0f;  // better keep <1.0f to minimize recorded APT(t) black level artifacts.-
+    float q = sos_q.execute(b) * 1.0f;
+
+    switch (n) {  // shifting down -fs4 (fs = 12khz , fs/4 = 3khz)
+        case 0:
+            out_i = i;
+            out_q = q;
+            break;
+        case 1:
+            out_i = -q;
+            out_q = i;
+            break;
+        case 2:
+            out_i = -i;
+            out_q = -q;
+            break;
+        case 3:
+            out_i = q;
+            out_q = -i;
+            break;
+    }
+
+    n = (n + 1) % 4;
+
+    /*   res = __smuad(val1,val2);  	p1 = val1[15:0] × val2[15:0]
+                                                p2 = val1[31:16] × val2[31:16]
+                                                res[31:0] = p1 + p2
+                                        return res; */
+
+    // Not strict Magnitude complex calculation, it is a cross multiplication (lower 16 bit real x lower 16 imag) + 0 (higher 16 bits comp),
+    // but better visual results comparing real magnitude calculation, (better map diagonal lines reproduction, and less artifacts in APT signal(t)
+    out_mag_sq = __SMUAD(out_i, out_q);                        // "cross-magnitude" of the complex (out_i + j out_q)
+    out_mag_sq_lpf = sos_mag_sq.execute((out_mag_sq)) * 2.0f;  // LPF quater band = 1.5khz APT signal
+
+    out_mag_sq_lpf /= 32768.0f;  // normalize ;
+    // Compress clipping positive APT signal [-1.5 ..1.5] input , converted to [-1.0 ...1.0] with "S" compressor gain shape.
+    if (out_mag_sq_lpf > 1.0f) {
+        out_mag_sq_lpf = 1.0f;  // clipped signal  at +1.0f,  APT signal is positive, no need to clip -1.0
+    } else {
+        out_mag_sq_lpf = out_mag_sq_lpf * (1.5f - ((out_mag_sq_lpf * out_mag_sq_lpf) / 2.0f));
+    }
+}
+
 } /* namespace dsp */
diff --git a/firmware/baseband/dsp_hilbert.hpp b/firmware/baseband/dsp_hilbert.hpp
index 8aad9ea9c..11596a5dd 100644
--- a/firmware/baseband/dsp_hilbert.hpp
+++ b/firmware/baseband/dsp_hilbert.hpp
@@ -39,6 +39,19 @@ class HilbertTransform {
     SOSFilter<5> sos_q = {};
 };
 
+class Real_to_Complex {
+   public:
+    Real_to_Complex();  // Additional initialization
+    void execute(float in, float& out_mag_sq_lpf);
+
+   private:
+    uint8_t n = 0;
+    SOSFilter<5> sos_input = {};
+    SOSFilter<5> sos_i = {};
+    SOSFilter<5> sos_q = {};
+    SOSFilter<5> sos_mag_sq = {};
+};
+
 } /* namespace dsp */
 
 #endif /*__DSP_HILBERT_H__*/
diff --git a/firmware/baseband/proc_am_audio.cpp b/firmware/baseband/proc_am_audio.cpp
index a1304c464..a1e0c8330 100644
--- a/firmware/baseband/proc_am_audio.cpp
+++ b/firmware/baseband/proc_am_audio.cpp
@@ -27,6 +27,7 @@
 #include "event_m4.hpp"
 
 #include <array>
+#include "dsp_hilbert.hpp"
 
 void NarrowbandAMAudio::execute(const buffer_c8_t& buffer) {
     if (!configured) {
@@ -44,16 +45,28 @@ void NarrowbandAMAudio::execute(const buffer_c8_t& buffer) {
     // TODO: Feed channel_stats post-decimation data?
     feed_channel_stats(channel_out);
 
-    auto audio = demodulate(channel_out);
+    auto audio = demodulate(channel_out);  // now 3 AM demodulation types : demod_am, demod_ssb, demod_ssb_fm (for Wefax)
     audio_compressor.execute_in_place(audio);
     audio_output.write(audio);
 }
 
 buffer_f32_t NarrowbandAMAudio::demodulate(const buffer_c16_t& channel) {
-    if (modulation_ssb) {
-        return demod_ssb.execute(channel, audio_buffer);
-    } else {
-        return demod_am.execute(channel, audio_buffer);
+    switch (modulation_ssb) {  // enum class Modulation : int32_t {DSB = 0, SSB = 1, SSB_FM = 2}
+        case (int)(AMConfigureMessage::Modulation::DSB):
+            return demod_am.execute(channel, audio_buffer);
+            break;
+
+        case (int)(AMConfigureMessage::Modulation::SSB):
+            return demod_ssb.execute(channel, audio_buffer);
+            break;
+
+        case (int)(AMConfigureMessage::Modulation::SSB_FM):  // Added to handle Weather Fax mode.
+            // chDbgPanic("case SSB_FM demodulation");                   // Debug.
+            return demod_ssb_fm.execute(channel, audio_buffer);  // Calling a derivative of demod_ssb (USB) , but with different FIR taps + FM audio tones demod.
+            break;
+
+        default:
+            break;
     }
 }
 
@@ -98,8 +111,9 @@ void NarrowbandAMAudio::configure(const AMConfigureMessage& message) {
     channel_filter_high_f = message.channel_filter.high_frequency_normalized * channel_filter_input_fs;
     channel_filter_transition = message.channel_filter.transition_normalized * channel_filter_input_fs;
     channel_spectrum.set_decimation_factor(1.0f);
-    modulation_ssb = (message.modulation == AMConfigureMessage::Modulation::SSB);
-    audio_output.configure(message.audio_hpf_config);
+    // modulation_ssb = (message.modulation == AMConfigureMessage::Modulation::SSB);  // originally we had just 2 AM types of demod. (DSB , SSB)
+    modulation_ssb = (int)message.modulation;              // now sending by message , 3 types of AM demod :   enum class Modulation : int32_t {DSB = 0, SSB = 1, SSB_FM = 2}
+    audio_output.configure(message.audio_hpf_lpf_config);  // hpf in all AM demod modes (AM-6K/9K, USB/LSB,DSB), except Wefax (lpf there).
 
     configured = true;
 }
diff --git a/firmware/baseband/proc_am_audio.hpp b/firmware/baseband/proc_am_audio.hpp
index d63481186..8f651bb5b 100644
--- a/firmware/baseband/proc_am_audio.hpp
+++ b/firmware/baseband/proc_am_audio.hpp
@@ -63,9 +63,11 @@ class NarrowbandAMAudio : public BasebandProcessor {
     int32_t channel_filter_transition = 0;
     bool configured{false};
 
-    bool modulation_ssb = false;
+    // bool modulation_ssb = false;  // Origianlly we only had 2 AM demod types {DSB = 0, SSB = 1} , and we could handle it with bool var , 1 bit.
+    int8_t modulation_ssb = 0;  // Now we have 3 AM demod types we will send now index integer  {DSB = 0, SSB = 1, SSB_FM = 2}
     dsp::demodulate::AM demod_am{};
     dsp::demodulate::SSB demod_ssb{};
+    dsp::demodulate::SSB_FM demod_ssb_fm{};  // added for Wfax mode.
     FeedForwardCompressor audio_compressor{};
     AudioOutput audio_output{};
 
diff --git a/firmware/common/dsp_fir_taps.hpp b/firmware/common/dsp_fir_taps.hpp
index 7ba171a32..c04fe190d 100644
--- a/firmware/common/dsp_fir_taps.hpp
+++ b/firmware/common/dsp_fir_taps.hpp
@@ -553,14 +553,14 @@ constexpr fir_taps_real<32> taps_6k0_decim_2{
     }},
 };
 
-// IFIR prototype filter fs=48000 ; pass=4500 (cutt off -3dBs) , stop=8000 (<-60dBs), decim=4, fout=12000
+// IFIR prototype filter fs=48000 ; pass=4500 (cutoff -3dBs) , stop=8000 (<-60dBs), decim=4, fout=12000
 // For Europe AM commercial  broadcasting stations in LF/MF/HF, Emissions Designator 9K00A3E Bandwidth: 9.00 kHz (derivated from taps_6k0_decim_2 )
-// Pre-decimate LPF FIR filter design Created with SciPy Python with the "window method", num_taps = 32, cut_off = 5150. sample_rate = 48000 # Hz,
-// Created with h = signal.firwin(num_taps, cut_off, nyq=sample_rate/2, window=('chebwin',50)) , achieving good  STOP band plot < -60 dB's with some ripple.
+// Pre-decimate LPF FIR filter design Created with SciPy Python with the "window method", num_taps = 32, cutoff = 5150. sample_rate = 48000 # Hz,
+// Created with h = signal.firwin(num_taps, cutoff, nyq=sample_rate/2, window=('chebwin',50)) , achieving good  STOP band plot < -60 dB's with some ripple.
 // post-scaled h taps to avoid decimals , targeting <= similar int values as previous taps_6k0_dsb_channel peak < 32.767 (2 exp 15) and similar H(f)gain
 constexpr fir_taps_real<32> taps_9k0_decim_2{
-    .low_frequency_normalized = -4500.0f / 48000.0f,  // Negative -cutt off freq -3dB (real achieved data ,in the plot and measurements)
-    .high_frequency_normalized = 4500.0f / 48000.0f,  // Positive +cutt off freq -3dB (idem)
+    .low_frequency_normalized = -4500.0f / 48000.0f,  // Negative -cutoff freq -3dB (real achieved data ,in the plot and measurements)
+    .high_frequency_normalized = 4500.0f / 48000.0f,  // Positive +cutoff freq -3dB (idem)
     .transition_normalized = 3500.0f / 48000.0f,      // 3500 Hz = (8000 Hz - 4500 Hz) (both from plot H(f) curve plot)
     .taps = {{-53, -30, 47, 198, 355, 372, 89, -535,
               -1307, -1771, -1353, 370, 3384, 7109, 10535, 12591,
@@ -644,14 +644,14 @@ constexpr fir_taps_complex<64> taps_6k0_dsb_channel{
     }},
 };
 
-// Channel filter: fs=12000, pass=4500 (cutt off -3dBs), stop=4940 (<-60dBs), decim=1, fout=12000   (*1) real frec pass / stop , based on plotted  H(f) curve)
+// Channel filter: fs=12000, pass=4500 (cutoff -3dBs), stop=4940 (<-60dBs), decim=1, fout=12000   (*1) real frec pass / stop , based on plotted  H(f) curve)
 // For Europe AM commercial broadcasting stations in LF/MF/HF, Emissions Designator 9K00A3E Bandwidth: 9.00 kHz (derivative from  taps_6k0_dsb_channel)
-// FIR filter design created with SciPy Python using "window method"; selected design parameters: num_taps = 64, cut_off = 4575. sample_rate = 12000 # Hz,
-// Created with : h = signal.firwin(num_taps, cut_off, nyq=sample_rate/2, window=('chebwin',50)) , achieving real plot curve (*1) with peak stop band ripple -60dBs.
+// FIR filter design created with SciPy Python using "window method"; selected design parameters: num_taps = 64, cutoff = 4575. sample_rate = 12000 # Hz,
+// Created with : h = signal.firwin(num_taps, cutoff, nyq=sample_rate/2, window=('chebwin',50)) , achieving real plot curve (*1) with peak stop band ripple -60dBs.
 // post-scaled h taps to avoid decimals , targeting <= similar int values as previous taps_6k0_dsb_channel peak < 32.767 (2 exp 15), (29625)  and similar H(f)gain
 constexpr fir_taps_complex<64> taps_9k0_dsb_channel{
-    .low_frequency_normalized = -4500.0f / 12000.0f,  // Negative -cutt off freq -3dB (in the H(f) curve plot)
-    .high_frequency_normalized = 4500.0f / 12000.0f,  // Positive +cutt off freq -3dB (in the H(f) curve plot)
+    .low_frequency_normalized = -4500.0f / 12000.0f,  // Negative -cutoff freq -3dB (in the H(f) curve plot)
+    .high_frequency_normalized = 4500.0f / 12000.0f,  // Positive +cutoff freq -3dB (in the H(f) curve plot)
     .transition_normalized = 440.0f / 12000.0f,       // 440Hz = (4940 Hz -4500 Hz)  cut-3dB's (both data comes from H(f) curve plot and confirmed by  measurements )
     .taps = {{
         {2, 0},
@@ -945,6 +945,82 @@ constexpr fir_taps_complex<64> taps_0k7_usb_channel{
     }},
 };
 
+// USB AM+FM for Wefax (Weather fax RX) , based USB AM with truncated Differentiator band limmited cuttoff 2.400Hz for Audio Tones FM dem. ///////////////////
+
+// IFIR prototype filter: fs=12000, pass=2600, stop=3200, decim=1, fout=12000       // stop band minimum att < -48 dB's (+3300 Hz min atten peak) , rest <50 to -60dB's
+constexpr fir_taps_complex<64> taps_2k6_usb_wefax_channel{
+    .low_frequency_normalized = 0,
+    .high_frequency_normalized = 2600.0f / 12000.0f,
+    .transition_normalized = 600.0f / 12000.0f,
+    .taps = {{{-14 + 2},
+              {-11 - 5},
+              {-2 - 8},
+              {6 - 5},
+              {13 + 1},
+              {15 + 14},
+              {0 + 26},
+              {-22 + 13},
+              {-13 - 11},
+              {7 - 1},
+              {-20 + 17},
+              {-47 - 37},
+              {33 - 89},
+              {122 + 8},
+              {19 + 131},
+              {-124 + 26},
+              {1 - 123},
+              {158 + 52},
+              {-94 + 245},
+              {-363 - 91},
+              {36 - 468},
+              {524 - 37},
+              {67 + 531},
+              {-552 + 5},
+              {136 - 686},
+              {1013 + 258},
+              {-204 + 1527},
+              {-2104 + 168},
+              {-900 - 2529},
+              {2577 - 1881},
+              {2868 + 2122},
+              {-1209 + 3570},
+              {-3768 - 52},
+              {-1043 - 3412},
+              {2634 - 1801},
+              {2083 + 1693},
+              {-861 + 1927},
+              {-1507 - 318},
+              {95 - 1041},
+              {692 + 100},
+              {-189 + 519},
+              {-478 - 241},
+              {210 - 481},
+              {454 + 122},
+              {-35 + 372},
+              {-262 + 7},
+              {4 - 166},
+              {116 + 40},
+              {-66 + 108},
+              {-117 - 62},
+              {33 - 117},
+              {95 - 2},
+              {19 + 57},
+              {-23 + 13},
+              {3 - 7},
+              {6 + 16},
+              {-20 + 16},
+              {-25 - 9},
+              {-8 - 19},
+              {4 - 12},
+              {7 - 4},
+              {7 + 4},
+              {2 + 12},
+              {-7 + 13}
+
+    }}
+
+};
+
 // WFM 200KF8E emission type //////////////////////////////////////////////
 
 // IFIR image-reject filter: fs=3072000, pass=100000, stop=484000, decim=4, fout=768000
diff --git a/firmware/common/dsp_iir_config.hpp b/firmware/common/dsp_iir_config.hpp
index 177475df8..93e93d179 100644
--- a/firmware/common/dsp_iir_config.hpp
+++ b/firmware/common/dsp_iir_config.hpp
@@ -55,6 +55,12 @@ constexpr iir_biquad_config_t audio_12k_hpf_300hz_config{
     {0.89485861f, -1.78971721f, 0.89485861f},
     {1.00000000f, -1.77863178f, 0.80080265f}};
 
+// scipy.signal.butter(2, 1500 / 6000.0, 'low', analog=False)
+constexpr iir_biquad_config_t audio_12k_lpf_1500hz_config{
+    // Added to lpf the audio in wefax mode , before sending to SD card or spk.
+    {0.09763107f, 0.19526215f, 0.09763107f},
+    {1.00000000f, -0.94280904f, 0.33333333f}};
+
 // scipy.signal.butter(2, 300 / 4000.0, 'highpass', analog=False)
 constexpr iir_biquad_config_t audio_8k_hpf_300hz_config{
     {0.84645925f, -1.69291851f, 0.84645925f},
diff --git a/firmware/common/dsp_sos_config.hpp b/firmware/common/dsp_sos_config.hpp
index 6a0ecb00f..b55dc01d6 100644
--- a/firmware/common/dsp_sos_config.hpp
+++ b/firmware/common/dsp_sos_config.hpp
@@ -25,7 +25,7 @@
 #include "dsp_iir.hpp"
 
 // scipy.signal.iirfilter(ftype="ellip", N = 10, rp = 0.5, rs = 60.0, Wn = 0.5, btype = 'lowpass', output="sos")
-
+// 3khz cutofff  @fs:12Khz , used in Hilbert
 constexpr iir_biquad_df2_config_t half_band_lpf_config[5] = {
     {0.02339042f, 0.0411599f, 0.02339042f, 1.0f, -0.95317621f, 0.33446485f},
     {1.0f, 0.82196114f, 1.0f, 1.0f, -0.50327735f, 0.63611027f},
@@ -33,4 +33,22 @@ constexpr iir_biquad_df2_config_t half_band_lpf_config[5] = {
     {1.0f, 0.14394122f, 1.0f, 1.0f, -0.04368236f, 0.94798064f},
     {1.0f, 0.08720754, 1.0f, 1.0f, 0.00220944f, 0.98743139f}};
 
+// scipy.signal.iirfilter(ftype="ellip", N = 10, rp = 0.5, rs = 60.0, Wn = 0.99, btype = 'lowpass', output="sos")
+// 6khz cutofff @fs:12Khz , used in WFAX demod.
+constexpr iir_biquad_df2_config_t full_band_lpf_config[5] = {
+    {0.88095275f, 1.76184993f, 0.88095275f, 1.0f, 1.89055677f, 0.89616378f},
+    {1.0f, 1.99958798f, 1.0f, 1.0f, 1.9781807f, 0.98002549f},
+    {1.0f, 1.99928911f, 1.0f, 1.0f, 1.99328036f, 0.99447816f},
+    {1.0f, 1.99914562f, 1.0f, 1.0f, 1.997254f, 0.99828526f},
+    {1.0f, 1.99909558f, 1.0f, 1.0f, 1.9986187f, 0.99960319f}};
+
+// scipy.signal.iirfilter(ftype="ellip", N = 10, rp = 0.5 , rs = 60.0, Wn = 0.25, btype = 'lowpass', output="sos")
+// 1.5khz cutofff  @fs:12Khz, used in WFAX demod.
+constexpr iir_biquad_df2_config_t quarter_band_lpf_config[5] = {
+    {0.00349312f, 0.00319397f, 0.00349312f, 1.0f, -1.53025211f, 0.6203438f},
+    {1.0f, -0.83483341f, 1.0f, 1.0f, -1.47619047f, 0.77120659f},
+    {1.0f, -1.23050154f, 1.0f, 1.0f, -1.43058949f, 0.9000896f},
+    {1.0f, -1.33837384f, 1.0f, 1.0f, -1.41007744f, 0.96349953f},
+    {1.0f, -1.36921549f, 1.0f, 1.0f, -1.40680439f, 0.9910884f}};
+
 #endif /*__DSP_SOS_CONFIG_H__*/
diff --git a/firmware/common/message.hpp b/firmware/common/message.hpp
index a619816ca..080519255 100644
--- a/firmware/common/message.hpp
+++ b/firmware/common/message.hpp
@@ -585,6 +585,7 @@ class AMConfigureMessage : public Message {
     enum class Modulation : int32_t {
         DSB = 0,
         SSB = 1,
+        SSB_FM = 2,  // Added new for RX Wefax mode,  to demodulate APT signal ,FM modulated inside audio subcarrier tones, and then up broadcasted in SSB USB .
     };
 
     constexpr AMConfigureMessage(
@@ -593,14 +594,14 @@ class AMConfigureMessage : public Message {
         const fir_taps_real<32> decim_2_filter,
         const fir_taps_complex<64> channel_filter,
         const Modulation modulation,
-        const iir_biquad_config_t audio_hpf_config)
+        const iir_biquad_config_t audio_hpf_lpf_config)
         : Message{ID::AMConfigure},
           decim_0_filter(decim_0_filter),
           decim_1_filter(decim_1_filter),
           decim_2_filter(decim_2_filter),
           channel_filter(channel_filter),
           modulation{modulation},
-          audio_hpf_config(audio_hpf_config) {
+          audio_hpf_lpf_config(audio_hpf_lpf_config) {
     }
 
     const fir_taps_real<24> decim_0_filter;
@@ -608,7 +609,7 @@ class AMConfigureMessage : public Message {
     const fir_taps_real<32> decim_2_filter;
     const fir_taps_complex<64> channel_filter;
     const Modulation modulation;
-    const iir_biquad_config_t audio_hpf_config;
+    const iir_biquad_config_t audio_hpf_lpf_config;
 };
 
 // TODO: Put this somewhere else, or at least the implementation part.