added RTLSDR bias tee support

TLeconte#116

README.md

@@ -58,6 +58,8 @@ for the RTLSDR device
 
  -p ppm :		set rtl ppm frequency correction
 
+ -B bias : 		Enable (1) or Disable (0) the bias tee (default is 0)
+
 for the AirSpy device
  -g gain :              set airspy gain (0..21)
 

acarsdec.c

@@ -55,6 +55,7 @@ int skip_reassembly = 0;
 int gain = -100;
 int ppm = 0;
 int rtlMult = 160;
+int bias = 0;
 #endif
 
 #ifdef WITH_AIR
@@ -111,7 +112,7 @@ static void usage(void)
 #endif
 #ifdef WITH_RTL
 	fprintf(stderr,
-		" [-g gain] [-p ppm] -r rtldevicenumber  f1 [f2] ... [fN]");
+		" [-g gain] [-p ppm] [-B bias] -r rtldevicenumber  f1 [f2] ... [fN]");
 #endif
 #ifdef WITH_AIR
 	fprintf(stderr,
@@ -173,6 +174,7 @@ static void usage(void)
 		" -g gain\t\t: set rtl gain in db (0 to 49.6; >52 and -10 will result in AGC; default is AGC)\n");
 	fprintf(stderr, " -p ppm\t\t\t: set rtl ppm frequency correction\n");
 	fprintf(stderr, " -m rtlMult\t\t\t: set rtl sample rate multiplier: 160 for 2 MS/s or 192 for 2.4 MS/s (default: 160)\n");
+	fprintf(stderr, " -B bias\t\t\t: Enable (1) or Disable (0) the bias tee (default is 0)\n");
 	fprintf(stderr,
 		" -r rtldevice f1 [f2]...[f%d]\t: decode from rtl dongle number or S/N rtldevice receiving at VHF frequencies f1 and optionally f2 to f%d in Mhz (ie : -r 0 131.525 131.725 131.825 )\n", MAXNBCHANNELS, MAXNBCHANNELS);
 #endif
@@ -242,7 +244,7 @@ int main(int argc, char **argv)
 	idstation = strdup(sys_hostname);
 
 	res = 0;
-	while ((c = getopt_long(argc, argv, "HDvarfdsRo:t:g:m:Aep:n:N:j:l:c:i:L:G:b:M:P:U:T:", long_opts, NULL)) != EOF) {
+	while ((c = getopt_long(argc, argv, "HDvarfdsRo:t:g:m:Aep:n:N:j:l:c:i:L:G:b:M:P:U:T:B:", long_opts, NULL)) != EOF) {
 
 		switch (c) {
 		case 'v':
@@ -288,6 +290,9 @@ int main(int argc, char **argv)
 		case 'm':
 			rtlMult = atoi(optarg);
 			break;
+		case 'B':
+			bias = atoi(optarg);
+			break;
 #endif
 #ifdef	WITH_SDRPLAY
 		case 's':

acarsdec.h

@@ -142,6 +142,7 @@ extern int mdly;
 extern int hourly, daily;
 
 extern int ppm;
+extern int bias;
 extern	int	lnaState;
 extern	int	GRdB;
 extern int initOutput(char*,char *);

rtl.c

@@ -308,6 +308,13 @@ int initRtl(char **argv, int optind)
 		return 1;
 	}
 
+	r = rtlsdr_set_bias_tee(dev, bias);
+	if (verbose) 
+		fprintf(stderr, "Set Bias Tee to %d\n", bias);
+	if(r < 0){
+		fprintf(stderr, "WARNING: Failed to set bias tee\n");
+		return 1;
+	}
 	return 0;
 }