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steve-m, 02/19/2016 10:51 PM


PageOutline = rtl-sdr =

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 V4L developer [http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/44461/focus=44461 Antti Palosaari].

Specifications

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).

Supported Hardware

So far, the following devices are supported:

Other sticks based on the RTL2832U might be added in the future as well.

This is the PCB of the ezcap-stick:brbr
Image(ezcap_top.jpg,50%)br
More pictures can be found [http://www.steve-m.de/pictures/rtl-sdr/ here].

Software

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.

The code can be checked out with: {{{
git clone git://git.osmocom.org/rtl-sdr.git
}}}

It can also be browsed on http://cgit.osmocom.org/cgit/rtl-sdr/

=== Building the software ===
To build it, simply run 'make' in the src/-directory and make sure you have libusb1.0-0-dev installed.

=== Usage ===

Example: To tune to 392.0 MHz, and set the sample-rate to 1.8 MS/s, use:

{{{
./rtl-sdr /tmp/out.bin -s 1800000 -f 392000000
}}}

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).

=== Known problems ===

  • 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.
Using the data

To convert the data to a standard cfile, following GNU Radio Block can be used:br
brImage(rtl2832-cfile.png)brbr
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].

What has been successfully tested so far is the reception of [http://tetra.osmocom.org/ TETRA] and [http://gmr.osmocom.org/ GMR].
brbr
Image(rtl-sdr-gmr.png)br
Multiple GMR-carriers can be seen in a spectrum view with the full 3.2 MHz bandwidth (at 3.2 MS/s).

Updated by steve-m almost 6 years ago · 10 revisions

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