--- vtrtlsdr.c.orig	2015-12-27 19:44:51.974350707 +0100
+++ vtrtlsdr.c	2015-12-27 23:08:04.130494884 +0100
@@ -22,6 +22,10 @@
 //  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 //  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
+// Changelog:
+// 20151227: added direct sampling option
+//           changed minimum sample rate to 226k
+//           -- Jacek Lipkowski <sq5pf@lipkowski.org>
 
 #include "config.h"
 #include "vtport.h"
@@ -40,7 +44,7 @@
 static double srcal = 1.0;               // Sample rate calibration coefficient
 static unsigned int sample_rate = 0;                     // Nominal sample rate
 
-static double frequency = 0;                                 // Tuner frequency
+static double frequency = -1;                                 // Tuner frequency
 static int gain = 0;                 // Tuner gain, units of 0.1dB, 0 = use AGC
 
 static timestamp timebase = timestamp_ZERO;            // Base of our timestamp
@@ -52,6 +56,10 @@
 static int UFLAG = FALSE;                            // Set TRUE with -u option
 static int QFLAG = FALSE;                         // -q option: invert Q signal
 
+
+// -D option: direct sampling: 0 (off), 1 (I input), 2 (Q input)
+static int direct_sampling = 0; 
+
 ///////////////////////////////////////////////////////////////////////////////
 //  Timestamping                                                             //
 ///////////////////////////////////////////////////////////////////////////////
@@ -254,6 +262,9 @@
 
    open_device();
 
+   if( rtlsdr_set_direct_sampling(dev, direct_sampling) != 0)
+	   VT_bailout( "RTL set direct sampling failed");
+
    if( rtlsdr_set_sample_rate(dev, sample_rate) < 0)
       VT_bailout( "cannot set RTL sample rate");
 
@@ -266,7 +277,7 @@
 
    VT_report( 1, "frequency %.0f Hz", frequency);
    uint32_t actual_freq = rtlsdr_get_center_freq( dev);
-   if( !actual_freq) VT_bailout( "error setting frequency");
+   if ((!direct_sampling)&&( !actual_freq)) VT_bailout( "error setting frequency");
    VT_report( 1, "actual freq %d Hz", actual_freq);
 
    VT_report( 1, "frequency correction: %d ppm",
@@ -486,7 +497,7 @@
        "  -L name   Specify log file\n"
        "  -d device Device number (default 0)\n"
        "  -d ?      List available devices\n"
-       "  -r rate   Sample rate 1000000 to 3200000\n"
+       "  -r rate   Sample rate 226000 to 3200000\n"
        "\n"
        "  -F hertz  Tuner frequency, Hertz\n"
        "  -g gain   Tuner gain (dB, default 0 = auto)\n"
@@ -494,6 +505,7 @@
        "  -q        Invert the Q signal\n"
        "\n"
        "  -u        No sample rate tracking\n"
+       "  -D type   Turn on direct sampling mode (0-off, 1-I input, 2-Q input)\n"
        "  -T stamp  Start time when using -u\n"
        "            (default is to use system clock)\n"
        "\n"
@@ -509,12 +521,36 @@
 
    while( 1)
    {
-      int c = getopt( argc, argv, "vBd:r:g:F:T:L:uq?");
+      int c = getopt( argc, argv, "vBd:r:g:F:T:L:uqiD:?");
 
       if( c == 'v') VT_up_loglevel();
       else
-      if( c == 'B') background = 1;
-      else
+	      if( c == 'B') background = 1;
+	      else
+		      if( c == 'D') {
+			      switch (*optarg) {
+				      case '1':
+				      case 'I':
+				      case 'i':
+					      direct_sampling=1;
+					      break;
+
+				      case '2':
+				      case 'Q':
+				      case 'q':
+					      direct_sampling=2;
+					      break;
+				      case '0':
+					      direct_sampling=0;
+					      break;
+
+				      default:
+					      fprintf(stderr,"Unknown direct sampling option: [%s]\n",optarg);
+					      exit(1);
+			      }
+
+		      }
+		      else
       if( c == 'L') VT_set_logfile( "%s", optarg);
       else
       if( c == 'd')
@@ -564,10 +600,13 @@
    if( sample_rate <= 0)
       VT_bailout( "invalid or missing sample rate, needs -r");
    if( sample_rate > 3200000) VT_bailout( "max sample rate 3200000");
-   if( sample_rate < 1000000) VT_bailout( "min sample rate 1000000");
+   if( sample_rate < 226000) VT_bailout( "min sample rate 226000");
+
+   if (frequency < 0)
+      VT_bailout( "invalid frequency");
 
-   if( frequency <= 0)
-      VT_bailout( "invalid or missing frequency, needs -F");
+   if ((!direct_sampling)&&(frequency == 0))
+      VT_bailout( "missing frequency, needs -F");
 
    if( background)
    {