Software Defined Radio

Software Defined Radio
founder:	brmlab collective
depends on:
interested:	sargon biiter niekt0 pasky nephirus ruza sysop kiki tlapka
software license:	-
hardware license:	-
status:	active

Software Defined Radio is a computer peripheral that allows reception (and ideally also transmission) of arbitrary radio waves. Various peripherals have different frequency range, bandwidth and other capabilities. Best known are USRP (Universal Software Radio Peripherial) and RTL-SDR (extremely cheap DVB-T USB stick chipset).

On the software side, GNURadio is the most popular control software. Its modular design allows defining arbitrary signal decoding pathways visually.

We have SDR station on the table near our library (RadioLab), and some antennas on the roof. A radio-adsb.brm computer is using RTL-SDR to generate a live map of airplane traffic (ADSB-based) over Prague. Other activities (TETRA etc.) are planned or work in progress.

• setup WebSDR

We are saving up for one. If you'd like to Donate with comment “RadioLab”.

• Very cheap, http://www.alza.cz/genius-tvgo-dvb-t03-d163527.htm for 499CZK. Frequency range roughly 64MHz to 1700MHz, low bandwidth, reception only, but still interesting for many applications.

• 53 to 2211 MHz

TODO: Where/how to get a good antenna?

TODO: What are interesting frequencies to listen to without a super-strong antenna?

Pentium D, 1 GB, 40 GB, Ubuntu 12.04

“public” computer, you can tune in GQRX (run ~/gqrx/gqrx), experiment with gnuradio…

Remote listening - tune radio in brmlab, listen at home!

VNC:

xtightvncviewer -quality 7 -encodings tight 192.168.77.35:0

Maybe you will need to start a VNC server:

• LightDM login in case machine rebooted and autologin got stuck

root@radio-observer:~# x11vnc -display :0 -usepw -forever -auth /var/run/lightdm/root/\:0

• Desktop access:

radio@radio-observer:~$ x11vnc -display :0 -usepw -forever

• Audio: Vorbis compressed (for listening)

ssh radio@192.168.77.35 "parecord --channels=1 | oggenc -q "-1" -r -C 1 -" | ogg123 -

Uncompressed (e.g. for further processing)

ssh radio@192.168.77.35 "parecord --channels=1" | aplay -r 44100 -c 1 -f S16_LE

Average delay of this chain is 1-2 seconds.

Tunnel raw data - connect remote radio to your local receiver

ssh -A -L1234:192.168.77.35:1234 username@nat.brmlab.cz 'ssh radio@192.168.77.35 "killall rtl_tcp; rtl_tcp -a 0.0.0.0"'

Then start gqrx locally with

device="rtl_tcp=127.0.0.1:1234"

Works for me with 300000Hz bandwith.

P4, 1 GB, 60 GB, 10.04

currently there is a web-server with Virtual Radar map of planes running there

celeron, 512 MB, 80 GB, 10.04

celeron, 512 MB, 40 GB, 10.10

ADSB demodulator, Celeron@2.4GHz is enough (load ~0.9)

• Get rtl-sdr tool, compile.
• mkfifo /tmp/radio - we will use it to tunnel samples.
• Install GNURadio. (Debian Unstable version works fine.)
• Start gnuradio-companion and load http://al.robotfuzz.com/~al/rtl2832/rtl2832-fm.grc
• Switch sink from file to audio, adjust source file to /tmp/radio.
• As root, run ./rtl_sdr -f 94.6e6 - >/tmp/radio
• In gnuradio-companion, execute the flow graph (click on gear icon).
• You should hear CRo Radiozurnal. Quality of reception depends (hopefully) on the antenna.
• http://nat.brmlab.cz/~sysop/rds_rx.grc - stereo FM receiver with RDS decoder (original source here)

geiger.c (inspiration: Geiger on a Plane

Separate page

Separate page

First attempt: I was able to record GSM channel data with http://nat.brmlab.cz/~sysop/gsm.grc (recorded file here) and decode it with airprobe (gsm_receive.py with modified clock frequency here)

./gsm_receive_rtl.py -I dump.cfile -d 1 B0

That nice QT GUI we are using is called GQRX. (build with qmake)

• Heavens above Brmlab
• http://www.n2yo.com
• Úvod NOAA

• Gnuradio - DSP/SDR toolkit
• rtl-sdr - library and commandline tool for RTL2832U
• gr-osmosdr - Gnuradio (>= v3.5.3) sink for RTL2832U
• gain - patch for gr-osmosdr to set gain on F0012 tuner
• gr-baz - contains alternatiobe Gnuradio sink for RTL2832U
• gqrx - SDR receiver GUI in QT
• airprobe - gnuradio based GSM decoding tool
• http://www.kmitocty.cz/zaklady/tabulka2011.html - listening frequencies
• http://metroweb.cz/diskuze/viewtopic.php?p=64750#p64750 - frequencies used for FM communication in Prague subway
• http://old.avc-cvut.cz/avc.php?id=3622 - FEL ČVUT course on digital cellular network (czech)
• 24/192 Music Downloads ...and why they make no sense
• See also: Digital Signal Processing#Zdroje