Added a bunch of notes about Radiosonde RX (help !)

firmware/application/ui_sonde.cpp

@@ -53,14 +53,14 @@ SondeView::SondeView(NavigationView& nav) {
 	field_frequency.set_value(receiver_model.tuning_frequency());
 	field_frequency.set_step(receiver_model.frequency_step());
 	field_frequency.on_change = [this](rf::Frequency f) {
-		receiver_model.set_tuning_frequency(f);
+		set_target_frequency(f);
 		field_frequency.set_value(f);
 	};
 	field_frequency.on_edit = [this, &nav]() {
 		// TODO: Provide separate modal method/scheme?
 		auto new_view = nav.push<FrequencyKeypadView>(receiver_model.tuning_frequency());
 		new_view->on_changed = [this](rf::Frequency f) {
-			receiver_model.set_tuning_frequency(f);
+			set_target_frequency(f);
 			field_frequency.set_value(f);
 		};
 	};
@@ -74,6 +74,8 @@ SondeView::SondeView(NavigationView& nav) {
 		static_cast<int8_t>(receiver_model.lna()),
 		static_cast<int8_t>(receiver_model.vga()),
 	});
+	
+	set_target_frequency(402000000);
 
 	/*logger = std::make_unique<SondeLogger>();
 	if( logger ) {
@@ -90,8 +92,15 @@ void SondeView::focus() {
 	field_vga.focus();
 }
 
-void SondeView::on_packet(const sonde::Packet& packet) {
+void SondeView::on_packet(const baseband::Packet& packet) {
-	text_debug.set("Got frame !");
+	std::string bin_string;
+	
+	for (size_t i = 0; i < 30; i++) {
+		bin_string += to_string_dec_uint(packet[i]);
+	}
+	
+	text_debug.set(bin_string);
+	
 	/*if( logger ) {
 		logger->on_packet(packet);
 	}*/
@@ -100,4 +109,13 @@ void SondeView::on_packet(const sonde::Packet& packet) {
 	}*/
 }
 
+void SondeView::set_target_frequency(const uint32_t new_value) {
+	target_frequency_ = new_value;
+	radio::set_tuning_frequency(tuning_frequency());
+}
+
+uint32_t SondeView::tuning_frequency() const {
+	return target_frequency_ - (sampling_rate / 4);
+}
+
 } /* namespace ui */

firmware/application/ui_sonde.hpp

@@ -67,6 +67,7 @@ public:
 
 private:
 	//std::unique_ptr<SondeLogger> logger { };
+	uint32_t target_frequency_ { };
 
 	FrequencyField field_frequency {
 		{ 0 * 8, 0 * 8 },
@@ -96,12 +97,16 @@ private:
 		Message::ID::SondePacket,
 		[this](Message* const p) {
 			const auto message = static_cast<const SondePacketMessage*>(p);
-			const sonde::Packet packet { message->type, message->packet };
+			//const sonde::Packet packet { message->type, message->packet };
-			this->on_packet(packet);
+			//this->on_packet(packet);
+			this->on_packet(message->packet);
 		}
 	};
 
-	void on_packet(const sonde::Packet& packet);
+	//void on_packet(const sonde::Packet& packet);
+	void on_packet(const baseband::Packet& packet);
+	void set_target_frequency(const uint32_t new_value);
+	uint32_t tuning_frequency() const;
 };
 
 } /* namespace ui */

firmware/baseband/proc_sonde.cpp

@@ -28,22 +28,23 @@
 #include "event_m4.hpp"
 
 SondeProcessor::SondeProcessor() {
-	decim_0.configure(taps_200k_decim_0.taps, 33554432);
+	decim_0.configure(taps_11k0_decim_0.taps, 33554432);
-	decim_1.configure(taps_200k_decim_1.taps, 131072);
+	decim_1.configure(taps_11k0_decim_1.taps, 131072);
 }
 
 void SondeProcessor::execute(const buffer_c8_t& buffer) {
 	/* 2.4576MHz, 2048 samples */
 
 	const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
-	const auto decimator_out = decim_1.execute(decim_0_out, dst_buffer);
+	const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
+	const auto decimator_out = decim_1_out;
 
-	/* 307.2kHz, 256 samples */
+	/* 38.4kHz, 32 samples */
 	feed_channel_stats(decimator_out);
 
 	for(size_t i=0; i<decimator_out.count; i++) {
-		if( mf_38k4_1t_19k2.execute_once(decimator_out.p[i]) ) {
+		if( mf.execute_once(decimator_out.p[i]) ) {
-			clock_recovery_fsk_19k2(mf_38k4_1t_19k2.get_output());
+			clock_recovery_fsk_4800(mf.get_output());
 		}
 	}
 }

firmware/baseband/proc_sonde.hpp

@@ -20,13 +20,61 @@
  * Boston, MA 02110-1301, USA.
  */
 
+/* Notes to self (or others, welcome !):
+ * Sharebrained wrote in matched_filter.hpp that taps should be those of a complex low-pass filter combined with a complex sinusoid, so
+ * that the filter shifts the spectrum where we want (signal of interest around 0Hz).
+ * 
+ * In this baseband processor, after decim_0 and decim_1, the signal ends up being sampled at 38400Hz (2457600 / 8 / 8)
+ * Since the applied shift in ui_sonde.cpp is -fs/4 = -2457600/4 = -614400Hz to avoid the DC spike, the FSK signal ends up being
+ * shifted by 614400 / 8 / 8 = 9600Hz. So decim_1_out should look like this:
+ * 
+ *   _______________|__/'\__________
+ * -C               A   B           C
+ * 
+ * A is the DC spike at 0Hz
+ * B is the FSK signal shifted right at 9600Hz
+ * C is the bandwidth edge at 19200Hz
+ * 
+ * Taps should be computed to shift the whole spectrum by -9600Hz ("left") so that it looks like this:
+ * 
+ *   ______________/'\______________
+ * -C               D               C
+ * 
+ * A should have been filtered off ?
+ * D is B around 0Hz now
+ * 
+ * Then the clock_recovery function should be happy :)
+ * 
+ * Mathworks.com says:
+ * In the case of a single-rate FIR design, we simply multiply each set of coefficients by (aka 'heterodyne with') a complex exponential.
+ * 
+ * Can SciPy's remez function be used for this ? See tools/firtest.py
+ * GnuRadio's firdes only outputs an odd number of taps
+ * 
+ * ---------------------------------------------------------------------
+ * 
+ * Looking at the AIS baseband processor:
+ * 
+ * Copied everything necessary to get decim_1_out (so same 8 * 8 = 64 decimation factor)
+ * The samplerate is also the same (2457600)
+ * After the matching filter, the data is decimated by 2 so the final samplerate for clock_recovery is 38400 / 2 = 19200Hz.
+ * Like here, the shift used is fs/4, so decim_1_out should be looking similar.
+ * The AIS signal deviates by 2400 (4800Hz signal width), the symbol rate is 9600.
+ * 
+ * The matched filter's input samplerate is 38400Hz, to get a 9600Hz shift it must use 4 taps ?
+ * To obtain unity gain, the sinusoid length must be / by the number of taps ?
+ * 
+ * See ais_baseband.hpp
+ * 
+ * */
+
 #ifndef __PROC_SONDE_H__
 #define __PROC_SONDE_H__
 
 #include "baseband_processor.hpp"
 #include "baseband_thread.hpp"
 #include "rssi_thread.hpp"
-#include "proc_tpms.hpp"
+#include "proc_ais.hpp"
 
 #include "channel_decimator.hpp"
 #include "matched_filter.hpp"
@@ -36,8 +84,6 @@
 #include "packet_builder.hpp"
 #include "baseband_packet.hpp"
 
-#include "ook.hpp"
-
 #include "message.hpp"
 #include "portapack_shared_memory.hpp"
 
@@ -63,13 +109,13 @@ private:
 		dst.size()
 	};
 
-	dsp::decimate::FIRC8xR16x24FS4Decim4 decim_0 { };
+	dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0 { };
-	dsp::decimate::FIRC16xR16x16Decim2 decim_1 { };
+	dsp::decimate::FIRC16xR16x32Decim8 decim_1 { };
+	dsp::matched_filter::MatchedFilter mf { baseband::ais::square_taps_38k4_1t_p, 2 };
 
-	dsp::matched_filter::MatchedFilter mf_38k4_1t_19k2 { rect_taps_307k2_38k4_1t_19k2_p, 8 };
+	// AIS: 19200, 9600
-
+	clock_recovery::ClockRecovery<clock_recovery::FixedErrorFilter> clock_recovery_fsk_4800 {
-	clock_recovery::ClockRecovery<clock_recovery::FixedErrorFilter> clock_recovery_fsk_19k2 {
+		19200, 4800, { 0.0555f },
-		38400, 19200, { 0.0555f },
 		[this](const float raw_symbol) {
 			const uint_fast8_t sliced_symbol = (raw_symbol >= 0.0f) ? 1 : 0;
 			this->packet_builder_fsk_4800_M10.execute(sliced_symbol);
@@ -78,7 +124,7 @@ private:
 	PacketBuilder<BitPattern, NeverMatch, FixedLength> packet_builder_fsk_4800_M10 {
 		{ 0b11001100110011001010011001001100, 32, 1 },
 		{ },
-		{ 102 * 8 },
+		{ 50 },	// { 102 * 8 },
 		[this](const baseband::Packet& packet) {
 			const SondePacketMessage message { sonde::Packet::Type::M10, packet };
 			shared_memory.application_queue.push(message);