Simple toolkit to decode Iridium signals

Requisites

• Python (2.7)
• NumPy (scipy)

License

Unless otherwise noted in a file, everything here is (c) Sec & schneider and licensed under the 2-Clause BSD License

Example usage

Capture with hackrf or rad1o and multiprocessing

Note: The rad1o has to be in hackrf-mode

hackrf_transfer  -r /dev/stdout -f 1627000000 -a 1 -l 40 -g 20 -s 2000000 | python2 extractor.py -c 1627000000 -r 2000000 -f hackrf --jobs 2 | grep "A:OK" | tee outfile

This writes to outfile. Pager messages can be decoded with

python2 iridium-parser.py outfile

Extracting Iridium packets from raw data

To capture and demodulate Iridium packets use extractor.py. You can either process a file offline or stream data into the tool.

Command line options:

-o, --offline: Process a file offline

By default, the extractor will drop samples if the computing power available is not enough to keep up. If you have an already recorded file, use the -o,--offline option to not drop any samples. In this case the extractor will pause reading the file (or input stream) until it can process more samples again.

-q: Queue length

The internal queue is filled with samples where the detector has detected activity in the file. By default it is 12000 elements long (roughly 4 GB at 2 Maps). You can tweak the length of the queue with this option

-c: Center frequency

The center frequency of the samples data in Hz.

-r: Sample rate

The sample rate of the samples in sps

-f: Input file format

File Format	extractor.py format option
complex uint8 (RTLSDR)	rtl
complex int8 (hackrf, rad1o)	hackrf
complex int16 (USRP with specrec from gr-analysis)	sc16
complex float (GNURadio, uhd_rx_cfile	float

-j, --jobs

The number of processes to spawn which demodulate packets. The detector runs in the main process.

Main Components

Detector

detector-fft.py

Searches through the file in 1 ms steps to scan for activity and copies these parts into snippets called <rawfilename>-<timestamp>.det

Cut and Downmix

cut-and-downmix.py

Mixes the signal down to 0 Hz and cuts the beginning to match the signal exactly. Output is <detfile>-f<frequency>.cut

Demod

demod.py

Does manual DQPSK demodulation of the signal and outputs <cutfile>.peaks (for debugging) <cutfile>.data the raw bit stream and on stdout an ASCII summary line.

Parser

iridium-parser.py

Takes the demodulated bits and tries to parse them into a readable format.

Supports some different output formats (-o option).