Airband VOR receiver and trasmitter (#3244)

* First test * Reorder includes for consistency and fix string dereference in VorCdiIndicator * Add memory section and linker script entry for vor_rx application * Testing VOR TX * Moving VOR TX to SD * Code refactoring to align with guidelines * Add TODO comment to verify radial sign convention in vor_tx_config * Remove unnecessary set_dirty() calls in VorRxView methods * Update Course Deviation Indicator label and adjust UI element positions * Update VorTxView to run prepared image from memory map * Update build condition in nightly release workflow to include workflow_dispatch event * Reverting action changes * Adjust Course Deviation Indicator layout and refine painting logic * Refactor VorRxView UI elements for improved layout and clarity * Add calibration field and update radial calculation logic in VorRxView * Enhance VOR processing: add renormalization to phase oscillator, improve signal handling, and update configuration parameters * Implement radial smoothing and TO/FROM state handling in VorRxView; update VOR processing logic * Setting comments inline * Refactor VorCdiIndicator and VorRxView: change normalize_signed_degrees to use int32_t, update radial smoothing to use fixed point arithmetic to reduce flash usage * Update external app address end to 0xAE0B0000 * Update set_vor_tx_config to include enabled parameter for consistency * Refactor VorRx to omit decim_2 stage and update comments for clarity on VOR processing * Add RSSI, Channel, and Audio fields to VorRxView to mimic existing apps * Refactor VorRxView labels and status messages * Update VorRxView calibration field range to allow full circle input * Completing Ident transmission logic * Fixing TX gain and moving log label * Refactor VOR phase calculations and update radial offset handling for accurate bearing representation * Add low-pass filters to strip 9960 Hz subcarrier from audio output
2026-09-12 09:39:30 +00:00 · 2026-07-04 08:49:21 +02:00
parent 7481aefe9f
commit b5d84fcc4d
20 changed files with 1765 additions and 1 deletions
@@ -0,0 +1,150 @@
+/*
+ * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
+ * Copyright (C) 2026 PortaPack Mayhem
+ *
+ * This file is part of PortaPack.
+ *
+ * This program 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 2, or (at your option)
+ * any later version.
+ *
+ * This program 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 this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __PROC_VOR_RX_H__
+#define __PROC_VOR_RX_H__
+
+#include "baseband_processor.hpp"
+#include "baseband_thread.hpp"
+#include "rssi_thread.hpp"
+
+#include "dsp_decimate.hpp"
+#include "dsp_demodulate.hpp"
+#include "dsp_iir.hpp"
+#include "audio_compressor.hpp"
+
+#include "audio_output.hpp"
+#include "spectrum_collector.hpp"
+
+#include <array>
+#include <cstdint>
+#include <cmath>
+
+// Standalone VOR receiver baseband.
+// Demodulates the AM channel at 48 kHz (so the 9960 Hz subcarrier stays
+// representable) and decodes the 30 Hz reference vs. variable phase to derive
+// the radial.
+class VorRx : public BasebandProcessor {
+   public:
+    VorRx();
+
+    void execute(const buffer_c8_t& buffer) override;
+    void on_message(const Message* const message) override;
+
+   private:
+    static constexpr size_t baseband_fs = 3072000;
+    // VOR keeps the channel at 48 kHz instead of the AM audio 12 kHz, so the
+    // 9960 Hz subcarrier stays below Nyquist. The standard AM decim_2 stage is
+    // therefore omitted (its ~4.5 kHz low-pass would remove the subcarrier).
+    static constexpr size_t channel_filter_decimation_factor = 1;
+
+    std::array<complex16_t, 512> dst{};
+    const buffer_c16_t dst_buffer{
+        dst.data(),
+        dst.size()};
+    std::array<float, 32> audio{};
+    const buffer_f32_t audio_buffer{
+        audio.data(),
+        audio.size()};
+
+    dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0{};
+    dsp::decimate::FIRC16xR16x32Decim8 decim_1{};
+    dsp::decimate::FIRAndDecimateComplex channel_filter{};
+    int32_t channel_filter_low_f = 0;
+    int32_t channel_filter_high_f = 0;
+    int32_t channel_filter_transition = 0;
+    bool configured{false};
+    bool vor_enabled{false};
+
+    static constexpr float vor_reference_hz{30.0f};
+    static constexpr float vor_subcarrier_hz{9960.0f};
+    // 100 ms at 48 kHz (exactly 3 cycles of 30 Hz)
+    static constexpr uint32_t vor_window_samples{4800};
+    // One-pole low-pass to isolate the +/-480 Hz FM subcarrier baseband
+    // after quadrature down-conversion (corner ~600 Hz at 48 kHz).
+    static constexpr float vor_sub_lp_alpha{0.9245f};
+    // Fixed phase lag the receive chain adds to the recovered 30 Hz reference
+    // tone, expressed in degrees at 30 Hz. It comes almost entirely from the
+    // one-pole subcarrier low-pass above (~2.75 deg of lag at 30 Hz for
+    // alpha = 0.9245) plus a ~0.1 deg half-sample delay in the FM
+    // differentiator. Because the reference tone is delayed, the raw radial
+    // (reference - variable) reads low by this amount, so we add it back.
+    // Value verified by a TX->RX loopback (proc_vor_tx fed through this
+    // decoder): every transmitted radial decoded ~3.2 deg low before this
+    // correction, and on-bearing afterwards.
+    static constexpr float vor_ref_phase_lag_deg{3.2f};
+
+    struct PhaseOscillator {
+        float sin_v{0.0f};
+        float cos_v{1.0f};
+        float step_sin{0.0f};
+        float step_cos{1.0f};
+
+        void configure(float frequency_hz, float sample_rate_hz);
+        float cosine() const { return cos_v; }
+        float sine() const { return sin_v; }
+        void advance();
+        void renormalize();
+    } vor_reference_osc{}, vor_subcarrier_osc{};
+    // 30 Hz DFT accumulators for the variable (AM) and reference (FM) tones.
+    float vor_ref_i{0.0f};
+    float vor_ref_q{0.0f};
+    float vor_var_i{0.0f};
+    float vor_var_q{0.0f};
+    float vor_dc_sum{0.0f};
+    // Subcarrier quadrature down-converter / FM-demodulator state.
+    float vor_sub_lp_i{0.0f};
+    float vor_sub_lp_q{0.0f};
+    float vor_sub_prev_i{0.0f};
+    float vor_sub_prev_q{0.0f};
+    uint32_t vor_sample_count{0};
+
+    dsp::demodulate::AM demod_am{};
+    // Two cascaded 2nd-order Butterworth low-passes (4th-order total) that strip
+    // the 9960 Hz FM subcarrier out of the audio before it reaches the speaker.
+    // The channel is kept wide (48 kHz) so the subcarrier survives for the
+    // radial decode, so it must be filtered out of the audible path here.
+    IIRBiquadFilter audio_lpf_1{};
+    IIRBiquadFilter audio_lpf_2{};
+    FeedForwardCompressor audio_compressor{};
+    AudioOutput audio_output{};
+
+    SpectrumCollector channel_spectrum{};
+
+    /* NB: Threads should be the last members in the class definition. */
+#ifdef PRALINE
+    BasebandThread baseband_thread{baseband_fs, this, baseband::Direction::Receive,
+                                   /*auto_start*/ false};
+    RSSIThread rssi_thread{/*auto_start*/ false};
+#else
+    BasebandThread baseband_thread{baseband_fs, this, baseband::Direction::Receive};
+    RSSIThread rssi_thread{};
+#endif
+
+    void configure(const AMConfigureMessage& message);
+    void configure_vor(const VorRxConfigureMessage& message);
+    void process_vor_metrics(const buffer_f32_t& audio);
+    void send_vor_status(uint16_t phase_deg, uint16_t radial_deg, uint16_t ref_level, uint16_t var_level, uint8_t quality, bool valid, bool to_from);
+    static uint16_t normalize_degrees(float degrees);
+};
+
+#endif /*__PROC_VOR_RX_H__*/