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horiz0n, 02/19/2016 10:51 PM

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[[PageOutline]]
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= rtl-sdr =
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DVB-T sticks based on the Realtek RTL2832U can be used as a cheap SDR, since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation. The possibility of this has been discovered by the V4L/DVB kernel developer [http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/44461/focus=44461 Antti Palosaari].
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== Specifications ==
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The RTL2832U outputs 8-bit I/Q-samples, and the highest theoretically possible sample-rate is 3.2 MS/s, however, the highest sample-rate without lost samples that has been tested so far is 2.8 MS/s. The frequency range is highly dependent of the used tuner, sticks that use the Elonics E4000 offer the best range (64 - 1700 MHz).
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== Supported Hardware ==
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So far, the following devices are supported:
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 * ezcap EzTV668 USB 2.0 DVB-T/DAB/FM stick (Elonics E4000 tuner) (sources: [http://www.aliexpress.com/product-gs/486876635-DVB-T-Digital-TV-USB-Dongle-Stick-With-FM-DAB-DAB--wholesalers.html AliExpress], [https://www.dealextreme.com/p/dvb-t-digital-tv-usb-dongle-stick-with-fm-dab-dab-44326 Dealextreme])
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 * ezcap EzTV666 USB 2.0 DVB-T/DAB/FM stick (Elonics E4000 tuner, [attachment:EZTV666.JPG picture])
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 * Hama nano DVB-T stick (Elonics E4000 tuner)
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 * Terratec NOXON DAB/DAB+ USB-Stick (Fitipower FC0013 tuner)
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People over at reddit [http://www.reddit.com/r/RTLSDR/comments/rbqfz/rtlsdr_compatibility_list_work_in_progress_please/ are collecting a list] of other devices that are compatible.
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Other sticks based on the RTL2832U might be added in the future as well.
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This is the PCB of the ezcap-stick:[[br]][[br]]
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[[Image(ezcap_top.jpg,50%)]][[br]]
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More pictures can be found [http://www.steve-m.de/pictures/rtl-sdr/ here].
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== Software ==
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rtl-sdr is a commandline tool that can initialize the RTL2832, tune to a given frequency, and record the I/Q-samples to a file.
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The code can be checked out with:
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{{{
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git clone git://git.osmocom.org/rtl-sdr.git
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}}}
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It can also be browsed on http://cgit.osmocom.org/cgit/rtl-sdr/
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=== Progress ===
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 * A [http://cgit.osmocom.org/cgit/gr-osmosdr/ GNU Radio source block] for [http://sdr.osmocom.org/trac/ OsmoSDR] and rtlsdr is being created. '''Please install a recent gnuradio (>= v3.5.3) to use it.'''
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 * Current progress: Rework to a library, support for multiple devices, tuner autodetection, FC0012 support
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 * the librtlsdr-branch has been merged  to master
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=== Building the software ===
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==== rtlsdr library & capture tool ====
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You have to install development packages for libusb1.0 and can either use cmake or autotools to build the software.
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Please note: prior pulling a new version from git and compiling it, please do a "make uninstall" first to properly remove the previous version.
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Building with cmake:
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{{{
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cd rtl-sdr/
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mkdir build
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cd build
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cmake ../
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make
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}}}
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Building with autotools:
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{{{
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cd rtl-sdr/
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autoreconf -i
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./configure
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make
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}}}
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The build executable (rtl_sdr) can be found in rtl-sdr/src/.
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==== Gnuradio Source ====
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The gnuradio source requires the rtl-sdr package and a recent gnuradio (>= v3.5.3) to be installed.
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Please note: prior pulling a new version from git and compiling it, please do a "make uninstall" first to properly remove the previous version.
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Building with cmake:
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{{{
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git clone git://git.osmocom.org/gr-osmosdr
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cd gr-osmosdr/
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mkdir build
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cd build/
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cmake ../
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make
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make install
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ldconfig
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}}}
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==== Automated installation ====
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Marcus D. Leech has kindly integrated the forementioned build steps into his gnuradio installation script at [http://www.sbrac.org/files/build-gnuradio]. This is the most user-friendly option so far.
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=== Usage ===
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Example: To tune to 392.0 MHz, and set the sample-rate to 1.8 MS/s, use:
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{{{
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./rtl-sdr /tmp/out.bin -s 1.8e6 -f 392e6
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}}}
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If the device can't be opened, make sure you have the appropriate rights to access the device (udev-rules, or running it as root).
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=== Known problems ===
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 * If the samples are written to a harddrive, and not a ramdisk, samples may get dropped. An improved version with proper buffering and asynchronous usage of libusb is in the works.
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== Using the data ==
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To convert the data to a standard cfile, following GNU Radio Block can be used:[[br]]
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[[br]][[Image(rtl2832-cfile.png)]][[br]][[br]]
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The GNU Radio Companion flowgraph (rtl2832-cfile.grc) is attached to this page. It is based on the FM demodulation flowgraph posted by Alistair Buxton [http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/44461/focus=44525 on this thread].
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Please note: for realtime operation you may use fifos (mkfifo) to forward the iq data from the capture utility to the GRC flowgraph.
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What has been successfully tested so far is the reception of FM/AM radio, [http://tetra.osmocom.org/ TETRA], [http://gmr.osmocom.org/ GMR], [http://svn.berlin.ccc.de/projects/airprobe/ GSM], [https://github.com/bistromath/gr-air-modes ADS-B] and [https://github.com/smunaut/osmo-pocsag POCSAG].
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[[br]][[br]]
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[[Image(rtl-sdr-gmr.png)]][[br]]
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Multiple GMR-carriers can be seen in a spectrum view with the full 3.2 MHz bandwidth (at 3.2 MS/s).
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