From 3823c8efce1fd3f9b51debb5569c9419dbb38a89 Mon Sep 17 00:00:00 2001
From: Alexandru Csete <oz9aec@gmail.com>
Date: Sun, 11 Sep 2016 12:39:54 +0200
Subject: [PATCH] Custom FIR kernels for Airspy.

---
 lib/airspy/airspy_fir_kernels.h | 101 ++++++++++++++++++++++++++++++++
 lib/airspy/airspy_source_c.cc   |  49 +++++++++++++++-
 2 files changed, 149 insertions(+), 1 deletion(-)
 create mode 100644 lib/airspy/airspy_fir_kernels.h

diff --git a/lib/airspy/airspy_fir_kernels.h b/lib/airspy/airspy_fir_kernels.h
new file mode 100644
index 0000000..e15f4e1
--- /dev/null
+++ b/lib/airspy/airspy_fir_kernels.h
@@ -0,0 +1,101 @@
+#pragma once
+
+#define KERNEL_16_110_LEN   7
+const float KERNEL_16_110[] =
+{
+    -0.031835079193115234f,
+     0.000000000000000000f,
+     0.281831502914428710f,
+     0.500007271766662600f,
+     0.281831502914428710f,
+     0.000000000000000000f,
+    -0.031835079193115234f
+};
+
+#define KERNEL_8_100_LEN    11
+const float KERNEL_8_100[] =
+{
+     0.006633400917053223f,
+     0.000000000000000000f,
+    -0.051035523414611816f,
+     0.000000000000000000f,
+     0.294403314590454100f,
+     0.499997496604919430f,
+     0.294403314590454100f,
+     0.000000000000000000f,
+    -0.051035523414611816f,
+     0.000000000000000000f,
+     0.006633400917053223f
+};
+
+#define KERNEL_4_90_LEN     15
+const float KERNEL_4_90[] =
+{
+    -0.002474188804626465f,
+     0.000000000000000000f,
+     0.016965746879577637f,
+     0.000000000000000000f,
+    -0.067680597305297852f,
+     0.000000000000000000f,
+     0.303180575370788570f,
+     0.500017046928405760f,
+     0.303180575370788570f,
+     0.000000000000000000f,
+    -0.067680597305297852f,
+     0.000000000000000000f,
+     0.016965746879577637f,
+     0.000000000000000000f,
+    -0.002474188804626465f
+};
+
+#define KERNEL_2_80_LEN     47
+const float KERNEL_2_80[KERNEL_2_80_LEN] =
+{
+    -0.000198006629943848f,
+     0.000000000000000000f,
+     0.000576853752136230f,
+     0.000000000000000000f,
+    -0.001352190971374512f,
+     0.000000000000000000f,
+     0.002729177474975586f,
+     0.000000000000000000f,
+    -0.004988193511962891f,
+     0.000000000000000000f,
+     0.008499503135681152f,
+     0.000000000000000000f,
+    -0.013788580894470215f,
+     0.000000000000000000f,
+     0.021713137626647949f,
+     0.000000000000000000f,
+    -0.033980011940002441f,
+     0.000000000000000000f,
+     0.054944872856140137f,
+     0.000000000000000000f,
+    -0.100657463073730470f,
+     0.000000000000000000f,
+     0.316457390785217290f,
+     0.500000000000000000f,
+     0.316457390785217290f,
+     0.000000000000000000f,
+    -0.100657463073730470f,
+     0.000000000000000000f,
+     0.054944872856140137f,
+     0.000000000000000000f,
+    -0.033980011940002441f,
+     0.000000000000000000f,
+     0.021713137626647949f,
+     0.000000000000000000f,
+    -0.013788580894470215f,
+     0.000000000000000000f,
+     0.008499503135681152f,
+     0.000000000000000000f,
+    -0.004988193511962891f,
+     0.000000000000000000f,
+     0.002729177474975586f,
+     0.000000000000000000f,
+    -0.001352190971374512f,
+     0.000000000000000000f,
+     0.000576853752136230f,
+     0.000000000000000000f,
+    -0.000198006629943848f
+};
diff --git a/lib/airspy/airspy_source_c.cc b/lib/airspy/airspy_source_c.cc
index 25f73d4..bbeb3aa 100644
--- a/lib/airspy/airspy_source_c.cc
+++ b/lib/airspy/airspy_source_c.cc
@@ -40,6 +40,7 @@
 #include <gnuradio/io_signature.h>
 
 #include "airspy_source_c.h"
+#include "airspy_fir_kernels.h"
 
 #include "arg_helpers.h"
 
@@ -638,12 +639,58 @@ std::string airspy_source_c::get_antenna( size_t chan )
 
 double airspy_source_c::set_bandwidth( double bandwidth, size_t chan )
 {
+  if (bandwidth == 0.f)
+    return get_bandwidth( chan );
+
+  {
+    int     ret;
+    int     decim;
+    int     size;
+    const float  *kernel;
+
+    decim = (int)(_sample_rate / bandwidth);
+//    if (decim < 2)
+//    {
+//      kernel = 0;
+//      size = 0;
+//    }
+//    else
+    if (decim < 4)
+    {
+      kernel = KERNEL_2_80;
+      size = KERNEL_2_80_LEN;
+    }
+    else if (decim < 8)
+    {
+      kernel = KERNEL_4_90;
+      size = KERNEL_4_90_LEN;
+    }
+    else if (decim < 16)
+    {
+      kernel = KERNEL_8_100;
+      size = KERNEL_8_100_LEN;
+    }
+    else
+    {
+      kernel = KERNEL_16_110;
+      size = KERNEL_16_110_LEN;
+    }
+
+    if (size)
+    {
+      std::cout << "  Airspy decim:" << decim
+                << "  kernel size:" << size << std::endl;
+      ret = airspy_set_conversion_filter_float32(_dev, kernel, size);
+      AIRSPY_THROW_ON_ERROR(ret, "Failed to set IQ conversion filter")
+    }
+  }
+
   return get_bandwidth( chan );
 }
 
 double airspy_source_c::get_bandwidth( size_t chan )
 {
-  return 10e6;
+  return _sample_rate;
 }
 
 osmosdr::freq_range_t airspy_source_c::get_bandwidth_range( size_t chan )