Experiment with headphones

README.md

@@ -32,4 +32,4 @@ See the [blog post](https://blog.porucha.net/2024/pico-sdr/) for more informatio
 
 4. Open `grc/PicoSDR-WBFM.grc` in GNU Radio Companion, adjust carrier frequency to match your favorite FM radio station and press `F6`.
 
-5. Alternatively [gqrx](https://www.gqrx.dk/) works fine with `rtl_tcp` input mode. Maximum sample rate seem to be 400 ksps, above that the samples are dropped. Make sure to adjust LNA gain to +30 dB. It's not accurate, but it does control bias strength which in turn does affect analog gain.
+5. Alternatively [gqrx](https://www.gqrx.dk/) works fine with `rtl_tcp` input mode. Maximum sample rate seem to be 400 ksps, above that the samples are dropped.

grc/PicoSDR-WBFM.grc

@@ -49,7 +49,7 @@ blocks:
   id: variable
   parameters:
     comment: ''
-    value: '200_000'
+    value: '192_000'
   states:
     bus_sink: false
     bus_source: false
@@ -78,7 +78,7 @@ blocks:
   parameters:
     affinity: ''
     alias: ''
-    audio_decimation: '8'
+    audio_decimation: '4'
     comment: ''
     deemph_tau: 75e-6
     maxoutbuf: '0'
@@ -100,7 +100,7 @@ blocks:
     device_name: ''
     num_inputs: '2'
     ok_to_block: 'True'
-    samp_rate: samp_rate // 8
+    samp_rate: samp_rate // 4
   states:
     bus_sink: false
     bus_source: false
@@ -150,15 +150,15 @@ blocks:
     alias: ''
     beta: '6.76'
     comment: ''
-    cutoff_freq: samp_rate / 16
-    decim: '8'
+    cutoff_freq: samp_rate / 8
+    decim: '4'
     gain: '1'
     interp: '1'
     maxoutbuf: '0'
     minoutbuf: '0'
     samp_rate: samp_rate
     type: fir_filter_fff
-    width: samp_rate / 16
+    width: samp_rate / 8
     win: window.WIN_HAMMING
   states:
     bus_sink: false
@@ -205,7 +205,7 @@ blocks:
     ant8: ''
     ant9: ''
     args: '"rtl_tcp"'
-    bb_gain0: '0'
+    bb_gain0: '20'
     bb_gain1: '20'
     bb_gain10: '20'
     bb_gain11: '20'
@@ -374,7 +374,7 @@ blocks:
     freq7: 100e6
     freq8: 100e6
     freq9: 100e6
-    gain0: '0'
+    gain0: '10'
     gain1: '10'
     gain10: '10'
     gain11: '10'
@@ -438,7 +438,7 @@ blocks:
     gain_mode7: 'False'
     gain_mode8: 'False'
     gain_mode9: 'False'
-    if_gain0: '0'
+    if_gain0: '20'
     if_gain1: '20'
     if_gain10: '20'
     if_gain11: '20'
@@ -677,7 +677,7 @@ blocks:
     name: '"FM Demodulation"'
     nconnections: '1'
     size: '512'
-    srate: samp_rate // 8
+    srate: samp_rate // (2 ** 3)
     stemplot: 'False'
     style1: '1'
     style10: '1'
@@ -856,4 +856,4 @@ connections:
 
 metadata:
   file_format: 1
-  grc_version: 3.10.11.0
+  grc_version: 3.10.9.2

grc/PicoSDR.grc

@@ -45,23 +45,11 @@ blocks:
     coordinate: [168, 8.0]
     rotation: 0
     state: enabled
-- name: decimation
+- name: samp_rate
   id: variable
   parameters:
     comment: ''
-    value: '4'
-  states:
-    bus_sink: false
-    bus_source: false
-    bus_structure: null
-    coordinate: [352, 8.0]
-    rotation: 0
-    state: enabled
-- name: rf_rate
-  id: variable
-  parameters:
-    comment: ''
-    value: '200_000'
+    value: '50_000'
   states:
     bus_sink: false
     bus_source: false
@@ -69,38 +57,6 @@ blocks:
     coordinate: [264, 8.0]
     rotation: 0
     state: enabled
-- name: samp_rate
-  id: variable
-  parameters:
-    comment: ''
-    value: rf_rate // decimation
-  states:
-    bus_sink: false
-    bus_source: false
-    bus_structure: null
-    coordinate: [456, 8.0]
-    rotation: 0
-    state: enabled
-- name: analog_agc_xx_0
-  id: analog_agc_xx
-  parameters:
-    affinity: ''
-    alias: ''
-    comment: ''
-    gain: '1.0'
-    max_gain: '65536'
-    maxoutbuf: '0'
-    minoutbuf: '0'
-    rate: 1e-4
-    reference: '0.7'
-    type: complex
-  states:
-    bus_sink: false
-    bus_source: false
-    bus_structure: null
-    coordinate: [360, 312.0]
-    rotation: 0
-    state: enabled
 - name: analog_quadrature_demod_cf_0
   id: analog_quadrature_demod_cf
   parameters:
@@ -114,7 +70,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [768, 616.0]
+    coordinate: [640, 536.0]
     rotation: 0
     state: true
 - name: blocks_message_debug_0
@@ -129,7 +85,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1056, 112.0]
+    coordinate: [928, 32.0]
     rotation: 0
     state: true
 - name: blocks_probe_rate_0
@@ -149,7 +105,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [768, 120.0]
+    coordinate: [640, 40.0]
     rotation: 0
     state: true
 - name: digital_costas_loop_cc_0
@@ -167,33 +123,9 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [768, 424.0]
+    coordinate: [640, 344.0]
     rotation: 0
     state: true
-- name: low_pass_filter_0
-  id: low_pass_filter
-  parameters:
-    affinity: ''
-    alias: ''
-    beta: '6.76'
-    comment: ''
-    cutoff_freq: samp_rate / 8
-    decim: decimation
-    gain: '1'
-    interp: '1'
-    maxoutbuf: '0'
-    minoutbuf: '0'
-    samp_rate: rf_rate
-    type: fir_filter_ccf
-    width: samp_rate / 8
-    win: window.WIN_HAMMING
-  states:
-    bus_sink: false
-    bus_source: false
-    bus_structure: null
-    coordinate: [520, 284.0]
-    rotation: 0
-    state: enabled
 - name: osmosdr_source_0
   id: osmosdr_source
   parameters:
@@ -232,7 +164,7 @@ blocks:
     ant8: ''
     ant9: ''
     args: '"rtl_tcp"'
-    bb_gain0: '0'
+    bb_gain0: '20'
     bb_gain1: '20'
     bb_gain10: '20'
     bb_gain11: '20'
@@ -401,7 +333,7 @@ blocks:
     freq7: 100e6
     freq8: 100e6
     freq9: 100e6
-    gain0: '0'
+    gain0: '10'
     gain1: '10'
     gain10: '10'
     gain11: '10'
@@ -465,7 +397,7 @@ blocks:
     gain_mode7: 'False'
     gain_mode8: 'False'
     gain_mode9: 'False'
-    if_gain0: '0'
+    if_gain0: '20'
     if_gain1: '20'
     if_gain10: '20'
     if_gain11: '20'
@@ -533,7 +465,7 @@ blocks:
     minoutbuf: '0'
     nchan: '1'
     num_mboards: '1'
-    sample_rate: rf_rate
+    sample_rate: samp_rate
     sync: sync
     time_source0: ''
     time_source1: ''
@@ -548,7 +480,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [104, 244.0]
+    coordinate: [152, 164.0]
     rotation: 0
     state: enabled
 - name: qtgui_const_sink_x_0
@@ -640,7 +572,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1056, 408.0]
+    coordinate: [928, 328.0]
     rotation: 0
     state: true
 - name: qtgui_time_sink_x_0
@@ -737,7 +669,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [768, 312.0]
+    coordinate: [640, 232.0]
     rotation: 0
     state: true
 - name: qtgui_time_sink_x_0_0
@@ -834,7 +766,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1056, 592.0]
+    coordinate: [928, 512.0]
     rotation: 0
     state: true
 - name: qtgui_time_sink_x_0_1
@@ -931,7 +863,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1056, 480.0]
+    coordinate: [928, 400.0]
     rotation: 0
     state: true
 - name: qtgui_waterfall_sink_x_0_0
@@ -992,22 +924,20 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [768, 208.0]
+    coordinate: [640, 128.0]
     rotation: 0
     state: true
 
 connections:
-- [analog_agc_xx_0, '0', low_pass_filter_0, '0']
 - [analog_quadrature_demod_cf_0, '0', qtgui_time_sink_x_0_0, '0']
 - [blocks_probe_rate_0, rate, blocks_message_debug_0, print]
 - [digital_costas_loop_cc_0, '0', qtgui_const_sink_x_0, '0']
 - [digital_costas_loop_cc_0, '0', qtgui_time_sink_x_0_1, '0']
-- [low_pass_filter_0, '0', analog_quadrature_demod_cf_0, '0']
-- [low_pass_filter_0, '0', blocks_probe_rate_0, '0']
-- [low_pass_filter_0, '0', digital_costas_loop_cc_0, '0']
-- [low_pass_filter_0, '0', qtgui_time_sink_x_0, '0']
-- [low_pass_filter_0, '0', qtgui_waterfall_sink_x_0_0, '0']
-- [osmosdr_source_0, '0', analog_agc_xx_0, '0']
+- [osmosdr_source_0, '0', analog_quadrature_demod_cf_0, '0']
+- [osmosdr_source_0, '0', blocks_probe_rate_0, '0']
+- [osmosdr_source_0, '0', digital_costas_loop_cc_0, '0']
+- [osmosdr_source_0, '0', qtgui_time_sink_x_0, '0']
+- [osmosdr_source_0, '0', qtgui_waterfall_sink_x_0_0, '0']
 
 metadata:
   file_format: 1

src/CMakeLists.txt

@@ -1,5 +1,4 @@
 cmake_minimum_required(VERSION 3.21)
-set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 include($ENV{PICO_SDK_PATH}/pico_sdk_init.cmake)
 

src/cordic.h

@@ -0,0 +1,50 @@
+#pragma once
+
+/*
+ * Copyright (c) 2020 STMicroelectronics.
+ * All rights reserved.
+ *
+ * This software component is licensed by ST under BSD 3-Clause license,
+ * the "License"; You may not use this file except in compliance with the
+ * License. You may obtain a copy of the License at:
+ *
+ * https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#define CORDIC_MAXITER 9
+#define CORDIC_PI 0x10000000
+
+static int CORDIC_ZTBL[] = { 0x04000000, 0x025C80A4, 0x013F670B, 0x00A2223B, 0x005161A8, 0x0028BAFC,
+			     0x00145EC4, 0x000A2F8B, 0x000517CA, 0x00028BE6, 0x000145F3, 0x0000A2FA,
+			     0x0000517D, 0x000028BE, 0x0000145F, 0x00000A30 };
+
+inline static __attribute__((__unused__)) int fast_atan2(int y, int x)
+{
+	int k, tx, z = 0, fl = 0;
+
+	if (x < 0) {
+		fl = ((y > 0) ? +1 : -1);
+		x = -x;
+		y = -y;
+	}
+
+	for (k = 0; k < CORDIC_MAXITER; k++) {
+		tx = x;
+
+		if (y <= 0) {
+			x -= (y >> k);
+			y += (tx >> k);
+			z -= CORDIC_ZTBL[k];
+		} else {
+			x += (y >> k);
+			y -= (tx >> k);
+			z += CORDIC_ZTBL[k];
+		}
+	}
+
+	if (fl != 0) {
+		z += fl * CORDIC_PI;
+	}
+
+	return z;
+}

src/vendor/pico-stdio-usb-simple

@@ -1 +1 @@
-Subproject commit ed4858dda407ec66626aade9b7c6ad6016539f4c
+Subproject commit b6b09e34b844326a156bc6734146a88111138473