201 lines
6.8 KiB
Plaintext
201 lines
6.8 KiB
Plaintext
Dump1090 README
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===
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Dump 1090 is a Mode S decoder specifically designed for RTLSDR devices.
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The main features are:
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* Robust decoding of weak messages.
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* Single bit errors correction using the 24 bit CRC.
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* Ability to decode DF11, DF17 messages.
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* Ability to decode DF formats like DF0, DF4, DF5, DF16, DF20 and DF21
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where the checksum is xored with the ICAO address by brute forcing the
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checksum field using recently seen ICAO addresses.
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* Decode raw IQ samples from file (using --ifile command line switch).
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* Interactive mode where aircrafts currently detected are shown
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as a list refreshing as more data arrives.
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Installation
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---
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Type "make".
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Normal usage
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---
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To capture traffic directly from your RTL device and show the captured traffic
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on standard output, just run the program without options at all:
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./dump1090
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To just output hexadecimal messages:
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./dump1090 --raw
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To run the program in interactive mode:
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./dump1090 --interactive
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In iteractive mode it is possible to have a less information dense but more
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"arcade style" output, where the screen is refreshed every second displaying
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all the recently seen aircrafts with some additional information such as
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altitude and flight number, extracted from the received Mode S packets.
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Using files as source of data
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---
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To decode data from file, use:
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./dump1090 --ifile /path/to/binfile
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The binary file should be created using rtl_sdr like this (or with any other
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program that is able to output 8-bit unsigned IQ samples at 2Mhz sample rate).
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rtl_sdr -f 1090000000 -s 2000000 -g 50 output.bin
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In the example rtl_sdr a gain of 50 is used, simply you should use the highest
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gain availabe for your tuner. This is not needed when calling Dump1090 itself
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as it is able to select the highest gain supported automatically.
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It is possible to feed the program with data via standard input using
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the --ifile option with "-" as argument.
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Additional options
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---
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Dump1090 can be called with other command line options to set a different
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gain, frequency, and so forth. For a list of options use:
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./dump1090 --help
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Everything is not documented here should be obvious, and for most users calling
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it without arguments at all is the best thing to do.
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Reliability
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---
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By default Dump1090 tries to fix single bit errors using the checksum.
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Basically the program will try to flip every bit of the message and check if
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the checksum of the resulting message matches.
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This is indeed able to fix errors and works reliably in my experience,
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however if you are interested in very reliable data I suggest to use
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the --no-fix command line switch in order to disable error fixing.
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Performances and sensibility of detection
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---
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In my limited experience Dump1090 was able to decode a big number of messages
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even in conditions where I encountered problems using other programs, however
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no formal test was performed so I can't really claim that this program is
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better or worse compared to other similar programs.
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If you can capture traffic that Dump1090 is not able to decode properly, drop
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me an email with a download link. I may try to improve the detection during
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my free time (this is just an hobby project).
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Antenna
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---
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Mode S messages are transmitted in the 1090 Mhz frequency. If you have a decent
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antenna you'll be able to pick up signals from aircrafts pretty far from your
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position, especially if you are outdoor and in a position with a good sky view.
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You can easily build a very cheap antenna following the istructions at:
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http://antirez.com/news/46
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With this trivial antenna I was able to pick up signals of aircrafts 200+ Km
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away from me.
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Debug mode
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---
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The Debug mode is a visual help to improve the detection algorithm or to
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understand why the program is not working for a given input.
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In this mode messages are displayed in an ASCII-art style graphical
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representation, where the individial magnitude bars sampled at 2Mhz are
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displayed.
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An index shows the sample number, where 0 is the sample where the first
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Mode S peak was found. Some additional background noise is also added
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before the first peak to provide some context.
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It is possible to display different categories of messages:
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--debug 1 Displays all the messages correctly demoudulated.
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A correctly demodulated message is just one that
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makes sense as a Mode S message, the preamble makes
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sense, and there are no message errors, that is,
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no adiacet samples describing bits are the same
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magnitude.
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--debug 2 Only messages with demodulation errors are displayed,
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That is, only messages where one or more adiacent
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samples that should describe bits are the same
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magnitude.
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--debug 3 Correctly deooded messages with Bad CRC are displayed.
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--debug 4 Correctly deooded messages with good CRC are displayed.
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--debug 5 Preamble detection failed in some way (specified when
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dumping the samples) even if the current sample level
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is greater than MODES_DEBUG_NOPREAMBLE_LEVEL (set to
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25 by default).
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How this program works?
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---
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The code is very documented and written in order to be easy to understand.
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For the diligent programmer with a Mode S specification on his hands it
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should be trivial to understand how it works.
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The algorithms I used were obtained basically looking at many messages
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as displayed using a trow-away SDL program, and trying to model the algorithm
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based on how the messages look graphically.
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How to test the program?
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---
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If you have an RTLSDR device and you happen to be in an area where there
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are aircrafts flying over your head, just run the program and check for signals.
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However if you don't have an RTLSDR device, or if in your area the presence
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of aircrafts is very limited, you may want to try the sample file distributed
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with the Dump1090 distribution under the "testfiles" directory.
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Just run it like this:
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./dump1090 --ifile testfiles/modes1.bin
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What is --strip mode?
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---
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It is just a simple filter that will get raw IQ 8 bit samples in input
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and will output a file missing all the parts of the file where I and Q
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are lower than the specified <level> for more than 32 samples.
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Use it like this:
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cat big.bin | ./dump1090 --snip 25 > small.bin
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I used it in order to create a small test file to include inside this
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program source code distribution.
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Contributing
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---
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Dump1090 was written during some free time during xmas 2012, it is an hobby
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project so I'll be able to address issues and improve it only during
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free time, however you are incouraged to send pull requests in order to
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improve the program. A good starting point can be the TODO list included in
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the source distribution.
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Credits
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---
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Dump1090 was written by Salvatore Sanfilippo <antirez@gmail.com> and is
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released under the BSD three clause license.
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