Fix signal processing, use files

1 files changed, 56 insertions, 31 deletions

diff --git a/talk.ipynb b/talk.ipynb
index d8e8de0..220e47e 100644
--- a/talk.ipynb
+++ b/talk.ipynb
@@ -24,7 +24,6 @@
     "## Yuval Adam\n",
     "\n",
     " - Full stack developer and systems architecture consultant\n",
-    " - But I also like to play with radios\n",
     " - https://yuv.al\n",
     " - @yuvadm\n",
     "\n"
@@ -42,7 +41,7 @@
     "\n",
     " - I never learned physics, RF engineering or signal processing\n",
     " - But radios are pretty cool!\n",
-    " - Hopefully in 25 minutes I can show you some neat things\n",
+    " - Hopefully I can show you some neat things\n",
     " - Slides and code @ https://github.com/yuvadm/radio-pyconil-2018"
    ]
   },
@@ -54,10 +53,11 @@
     }
    },
    "source": [
-    "## Agenda\n",
+    "## Radio Waves\n",
+    "\n",
+    "![static/dipole.gif](static/dipole.gif)\n",
     "\n",
-    " - What are radio waves?\n",
-    " - Hardware vs software radio"
+    "*Source: https://en.wikipedia.org/wiki/Antenna_(radio)*\n"
    ]
   },
   {
@@ -68,20 +68,22 @@
     }
    },
    "source": [
-    "## Radio Waves\n",
-    "\n",
-    "![static/dipole.gif](static/dipole.gif)\n",
+    "## Hardware Radio\n",
     "\n",
-    "*Source: https://en.wikipedia.org/wiki/Antenna_(radio)*\n"
+    "![static/radio.jpg](static/radio.jpg)"
    ]
   },
   {
    "cell_type": "markdown",
-   "metadata": {},
+   "metadata": {
+    "slideshow": {
+     "slide_type": "subslide"
+    }
+   },
    "source": [
     "## Hardware Radio\n",
     "\n",
-    "![static/radio.jpg](static/radio.jpg)"
+    "![static/gsm.jpg](static/gsm.jpg)"
    ]
   },
   {
@@ -201,6 +203,17 @@
    ]
   },
   {
+   "cell_type": "markdown",
+   "metadata": {
+    "slideshow": {
+     "slide_type": "slide"
+    }
+   },
+   "source": [
+    "## GQRX"
+   ]
+  },
+  {
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
@@ -219,15 +232,13 @@
     "sdr.center_freq = 91.8e6      # 91,800,00 Hz frequency for the radio station\n",
     "sdr.gain = 'auto'             # tune the gain (AKA \"volume\") automatically\n",
     "\n",
-    "samples = sdr.read_samples(1.2e6 * 8)  # collect samples during 8 seconds\n",
-    "sdr.close()\n",
-    "\n",
-    "print(samples[:5])"
+    "samples = sdr.read_samples(1.2e6 * 10)\n",
+    "sdr.close()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "slideshow": {
      "slide_type": "subslide"
@@ -235,16 +246,20 @@
    },
    "outputs": [],
    "source": [
-    "# Load the samples into a numpy array\n",
+    "# Alternatively, load previously captured samples from rtl_sdr\n",
+    "# and convert them from unsigned 8-bit samples to a complex IQ array\n",
     "\n",
     "import numpy as np\n",
     "\n",
-    "samples = np.array(samples).astype('complex64')"
+    "raw = np.fromfile('/tmp/samples.in', np.uint8).astype(np.float64)\n",
+    "raw += -127\n",
+    "raw /= 2**7\n",
+    "samples = (raw[0::2] + 1j * raw[1::2]).astype(np.complex64)"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
    "metadata": {
     "slideshow": {
      "slide_type": "subslide"
@@ -265,7 +280,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 3,
    "metadata": {
     "slideshow": {
      "slide_type": "subslide"
@@ -274,14 +289,14 @@
    "outputs": [],
    "source": [
     "# Apply the Frequency DEmodulation\n",
-    "# We use something called polar discriminator\n",
+    "# We use something called a polar discriminator\n",
     "\n",
     "samples = np.angle(samples[1:] * np.conj(samples[:-1]))"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 4,
    "metadata": {
     "slideshow": {
      "slide_type": "subslide"
@@ -302,7 +317,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 5,
    "metadata": {
     "slideshow": {
      "slide_type": "subslide"
@@ -316,22 +331,32 @@
     "AUDIO_RATE = 50e3\n",
     "DECIMATION_RATE = int(BANDWIDTH / AUDIO_RATE)  # Decimation factor of 4\n",
     "\n",
-    "samples = signal.decimate(samples, DECIMATION_RATE)"
+    "samples = signal.decimate(samples, DECIMATION_RATE)\n",
+    "\n",
+    "# Amplify the signal volume\n",
+    "samples *= 10000\n",
+    "samples = samples.astype('int16')"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "slideshow": {
-     "slide_type": "subslide"
-    }
-   },
+   "execution_count": 6,
+   "metadata": {},
    "outputs": [],
    "source": [
     "# HIT IT\n",
     "\n",
-    "whatever.play(samples)"
+    "import alsaaudio\n",
+    "\n",
+    "device = alsaaudio.PCM(alsaaudio.PCM_PLAYBACK, device='default')\n",
+    "device.setchannels(1)\n",
+    "device.setrate(50000)\n",
+    "device.setformat(alsaaudio.PCM_FORMAT_S16_LE)\n",
+    "device.setperiodsize(120)\n",
+    "\n",
+    "# Write data in chunks\n",
+    "for s in np.array_split(samples, 120):\n",
+    "    device.write(s)"
    ]
   },
   {