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+<pre>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                RTLSDR usage                                  +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                    INDEX                                     +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ 1. Setup rtlsdr
+   1.1. Get sources
+   1.2. Drivers
+   1.3. Check if works
+ 2. Collection of tools
+   2.1. FM
+   2.2. Spectrum diagram
+   2.3. ADSB
+   2.4. AFSK1200
+ 3. Projects where rtlsdr used
+   3.1. WebSDR
+ 4. Problems
+   4.1. Sync errors
+ 5. Links
+ 6. Changelog
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                               1.Setup rtlsdr                                 +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+By rtlsdr usually call RTL2832U chip based tv-tunners which
+can be used for not just recievin DVB-T frequencies but much more
+and yes price is ~$10 it mean that anyone can just buy and try
+without "loosing" money.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+1.1.Get sources
+
+
+Main development repository is on http://sdr.osmocom.org/trac/wiki/rtl-sdr
+on github you can find more repos with experminental 
+features (https://github.com/keenerd/rtl-sdr).
+
+Getting sources from git:
+  git clone git://git.osmocom.org/rtl-sdr.git
+
+I prefer using plain binaries without any kind of installation. Just
+compile and use binary without any troubles.
+Build:
+  cmake .
+  make
+
+All binaries is in src dir
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+1.2.Drivers
+
+
+Linux kernel have some drivers for rtlsdr stick and DVB-T. When you will plug
+rtlsdr then kernel probably will load DVB-T drivers and you will not able
+to use you rtlsdr for sdr. Way yo fix is it add some drivers to black list and
+next time when you will plug rtlsdr this drivers will not be loaded.
+
+Check if rtlsdr related drivers is loaded:
+  lsmod | grep rtl28
+
+If there is some drivers then balcklist driver by creating file
+in /etc/modprobe.d/ with content:
+  blacklist dvb_usb_rtl28xxu
+
+Next thing that could appear is permissions on rtlsdr usage when its pluged in.
+To allow everyone to use create file in /etc/udev/rules.d/ with content:
+  SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", ATTRS{idProduct}=="2838", \
+  GROUP="adm", MODE="0666", SYMLINK+="rtl_sdr"
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+1.3.Check if works
+
+How to test if rtlsdr works? Run one of commands:
+  rtl_test
+
+I like to run rtl_adsb as you can see there that something is recieved and
+you see that everything "works":
+  rtl_adsb
+
+There should be line by line showing up some "hex" lines. If some data is showen
+then adsb data from plains is recieved.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                            2.Collection of tools                             +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+2.1.FM
+
+Get some sound trancmited from FM radio stations.
+
+  rtl_fm -f 96.3e6 -M wbfm -s 200000 -r 48000 - | aplay -r 48k -f S16_LE
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+2.2.Spectrum diagram
+
+Scan spectrum to find some activities on different frequencies.
+Good link with all description is http://kmkeen.com/rtl-power/ . 
+Main usage of rtl_power is :
+
+  rtl_power -f 76M:108M:125k -i 1 fm_stations.csv
+
+and then draw image :
+
+  heatmap.py fm_stations.csv fm_stations.png
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+2.3.ADSB
+
+ADS-B ( Automatic dependent surveillance broadcast ) in simple words airplain
+geoposition, speed, height and flight number broadcasting. You can recieve
+this data and see how many plains is around and sometimes flight number.
+
+rtlsdr have default one rtl_adsb programm but it shows only recieved data,
+without any decoding. Here is dump1090 specifically for rtlsdr and nothing
+more:
+
+  https://github.com/antirez/dump1090
+
+description howto install could be found also here
+
+  http://www.satsignal.eu/raspberry-pi/dump1090.html
+
+Using in interactive mode with height in metrs:
+  
+  dump1090 --interactive --metric
+
+Output:
+
+  Hex    Flight   Altitude  Speed   Lat       Lon       Track  Messages Seen .  
+  ------------------------------------------------------------------------------
+  71be01          10052     1009    36.434    33.544    45    9         1 sec
+  424913 SDM6329  10966     711     36.440    33.405    221   65        0 sec
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+2.4.AFSK1200
+
+Gqrx is graphical SDR software where you can travel across frequencies
+and in real time search for some transmission.
+
+  http://gqrx.dk/
+
+It have builtin AFSK1200 demodulator or in simple words ham radio packets.
+And you could try to see what people sending in tex around the world.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                        3.Projects where rtlsdr used                          +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+3.1.WebSDR
+
+WebSDR probably best site where you can go and click on some radio reciever 
+and liste what happends in some particular country. WebSDR site contains
+about 80 radio recievers around the world that can be accessed trought web
+interface. 
+  http://websdr.org/
+
+If you whant setup your own radio reciever read FAQ, prepare mail and send mail
+after that you could recieve precompiled websdr software with is easy
+to setup with rtlsdr stick.
+
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                 4.Problems                                   +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+4.1.Sync errors
+
+Once there was sync error when was trying to use rtl_test or rtl_adsb.
+To fix that changes for better quality usb cable.
+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++                                   5.Links                                    +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+[1] http://kmkeen.com/rtl-demod-guide/
+[2] http://kmkeen.com/rtl-power/
+[3] http://sdr.osmocom.org/trac/wiki/rtl-sdr
+[4] http://www.rtl-sdr.com/
+[5] https://github.com/antirez/dump1090
+[6] http://gqrx.dk
+</pre>
+
+```c
+
+#include <stdint.h>
+#include <arpa/inet.h>
+#include <stdio.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#define _GNU_SOURCE
+#include <getopt.h>
+
+
+struct ihex_binrec {
+	struct ihex_binrec *next; /* not part of the real data structure */
+        uint32_t addr;
+        uint16_t len;
+        uint8_t data[];
+};
+
+/**
+ * nybble/hex are little helpers to parse hexadecimal numbers to a byte value
+ **/
+static uint8_t nybble(const uint8_t n)
+{
+       if      (n >= '0' && n <= '9') return n - '0';
+       else if (n >= 'A' && n <= 'F') return n - ('A' - 10);
+       else if (n >= 'a' && n <= 'f') return n - ('a' - 10);
+       return 0;
+}
+
+static uint8_t hex(const uint8_t *data, uint8_t *crc)
+{
+       uint8_t val = (nybble(data[0]) << 4) | nybble(data[1]);
+       *crc += val;
+       return val;
+}
+
+static int process_ihex(uint8_t *data, ssize_t size);
+static void file_record(struct ihex_binrec *record);
+static int output_records(int outfd);
+
+static int sort_records = 0;
+static int wide_records = 0;
+static int include_jump = 0;
+
+static int usage(void)
+{
+	fprintf(stderr, "ihex2fw: Convert ihex files into binary "
+		"representation for use by Linux kernel\n");
+	fprintf(stderr, "usage: ihex2fw [<options>] <src.HEX> <dst.fw>\n");
+	fprintf(stderr, "       -w: wide records (16-bit length)\n");
+	fprintf(stderr, "       -s: sort records by address\n");
+	fprintf(stderr, "       -j: include records for CS:IP/EIP address\n");
+	return 1;
+}
+
+int main(int argc, char **argv)
+{
+	int infd, outfd;
+	struct stat st;
+	uint8_t *data;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "wsj")) != -1) {
+		switch (opt) {
+		case 'w':
+			wide_records = 1;
+			break;
+		case 's':
+			sort_records = 1;
+			break;
+		case 'j':
+			include_jump = 1;
+			break;
+		default:
+			return usage();
+		}
+	}
+
+	if (optind + 2 != argc)
+		return usage();
+
+	if (!strcmp(argv[optind], "-"))
+	    infd = 0;
+	else
+		infd = open(argv[optind], O_RDONLY);
+	if (infd == -1) {
+		fprintf(stderr, "Failed to open source file: %s",
+			strerror(errno));
+		return usage();
+	}
+	if (fstat(infd, &st)) {
+		perror("stat");
+		return 1;
+	}
+	data = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, infd, 0);
+	if (data == MAP_FAILED) {
+		perror("mmap");
+		return 1;
+	}
+
+	if (!strcmp(argv[optind+1], "-"))
+	    outfd = 1;
+	else
+		outfd = open(argv[optind+1], O_TRUNC|O_CREAT|O_WRONLY, 0644);
+	if (outfd == -1) {
+		fprintf(stderr, "Failed to open destination file: %s",
+			strerror(errno));
+		return usage();
+	}
+	if (process_ihex(data, st.st_size))
+		return 1;
+
+	return output_records(outfd);
+}
+
+static int process_ihex(uint8_t *data, ssize_t size)
+{
+	struct ihex_binrec *record;
+	uint32_t offset = 0;
+	uint32_t data32;
+	uint8_t type, crc = 0, crcbyte = 0;
+	int i, j;
+	int line = 1;
+	int len;
+
+	i = 0;
+next_record:
+	/* search for the start of record character */
+	while (i < size) {
+		if (data[i] == '\n') line++;
+		if (data[i++] == ':') break;
+	}
+
+	/* Minimum record length would be about 10 characters */
+	if (i + 10 > size) {
+		fprintf(stderr, "Can't find valid record at line %d\n", line);
+		return -EINVAL;
+	}
+
+	len = hex(data + i, &crc); i += 2;
+	if (wide_records) {
+		len <<= 8;
+		len += hex(data + i, &crc); i += 2;
+	}
+	record = malloc((sizeof (*record) + len + 3) & ~3);
+	if (!record) {
+		fprintf(stderr, "out of memory for records\n");
+		return -ENOMEM;
+	}
+	memset(record, 0, (sizeof(*record) + len + 3) & ~3);
+	record->len = len;
+
+	/* now check if we have enough data to read everything */
+	if (i + 8 + (record->len * 2) > size) {
+		fprintf(stderr, "Not enough data to read complete record at line %d\n",
+			line);
+		return -EINVAL;
+	}
+
+	record->addr  = hex(data + i, &crc) << 8; i += 2;
+	record->addr |= hex(data + i, &crc); i += 2;
+	type = hex(data + i, &crc); i += 2;
+
+	for (j = 0; j < record->len; j++, i += 2)
+		record->data[j] = hex(data + i, &crc);
+
+	/* check CRC */
+	crcbyte = hex(data + i, &crc); i += 2;
+	if (crc != 0) {
+		fprintf(stderr, "CRC failure at line %d: got 0x%X, expected 0x%X\n",
+			line, crcbyte, (unsigned char)(crcbyte-crc));
+		return -EINVAL;
+	}
+
+	/* Done reading the record */
+	switch (type) {
+	case 0:
+		/* old style EOF record? */
+		if (!record->len)
+			break;
+
+		record->addr += offset;
+		file_record(record);
+		goto next_record;
+
+	case 1: /* End-Of-File Record */
+		if (record->addr || record->len) {
+			fprintf(stderr, "Bad EOF record (type 01) format at line %d",
+				line);
+			return -EINVAL;
+		}
+		break;
+
+	case 2: /* Extended Segment Address Record (HEX86) */
+	case 4: /* Extended Linear Address Record (HEX386) */
+		if (record->addr || record->len != 2) {
+			fprintf(stderr, "Bad HEX86/HEX386 record (type %02X) at line %d\n",
+				type, line);
+			return -EINVAL;
+		}
+
+		/* We shouldn't really be using the offset for HEX86 because
+		 * the wraparound case is specified quite differently. */
+		offset = record->data[0] << 8 | record->data[1];
+		offset <<= (type == 2 ? 4 : 16);
+		goto next_record;
+
+	case 3: /* Start Segment Address Record */
+	case 5: /* Start Linear Address Record */
+		if (record->addr || record->len != 4) {
+			fprintf(stderr, "Bad Start Address record (type %02X) at line %d\n",
+				type, line);
+			return -EINVAL;
+		}
+
+		memcpy(&data32, &record->data[0], sizeof(data32));
+		data32 = htonl(data32);
+		memcpy(&record->data[0], &data32, sizeof(data32));
+
+		/* These records contain the CS/IP or EIP where execution
+		 * starts. If requested output this as a record. */
+		if (include_jump)
+			file_record(record);
+		goto next_record;
+
+	default:
+		fprintf(stderr, "Unknown record (type %02X)\n", type);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static struct ihex_binrec *records;
+
+static void file_record(struct ihex_binrec *record)
+{
+	struct ihex_binrec **p = &records;
+
+	while ((*p) && (!sort_records || (*p)->addr < record->addr))
+		p = &((*p)->next);
+
+	record->next = *p;
+	*p = record;
+}
+
+static int output_records(int outfd)
+{
+	unsigned char zeroes[6] = {0, 0, 0, 0, 0, 0};
+	struct ihex_binrec *p = records;
+
+	while (p) {
+		uint16_t writelen = (p->len + 9) & ~3;
+
+		p->addr = htonl(p->addr);
+		p->len = htons(p->len);
+		if (write(outfd, &p->addr, writelen) != writelen)
+			return 1;
+		p = p->next;
+	}
+	/* EOF record is zero length, since we don't bother to represent
+	   the type field in the binary version */
+	if (write(outfd, zeroes, 6) != 6)
+		return 1;
+	return 0;
+}
+```
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