An inexpensive Software Defined Radio using the DVB-T dongles based on the Realtek RTL2832U.
- Osmocom rtl-sdr site: http://sdr.osmocom.org/trac/wiki/rtl-sdr
- rtl-sdr software download: http://cgit.osmocom.org/cgit/rtl-sdr/
- Dump 1090 Mode S decoder specifically designed for RTLSDR devices: https://github.com/antirez/dump1090
Building rtl-sdr on Mac OS X
First I got the code from http://cgit.osmocom.org/cgit/rtl-sdr/
I followed the instructions from http://sdr.osmocom.org/trac/wiki/rtl-sdr
cd rtl-sdr/ autoreconf -i ./configure make sudo make install sudo ldconfig
The first problem was after ./configure, namely:
configure: error: Package requirements (libusb-1.0 >= 1.0) were not met
Turns out I had an ancient version of libusb.
sudo port install libusb solved that.
With the programs built, the next step was running rtl_test:
$ rtl_test -t Found 1 device(s): 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle Found Rafael Micro R820T tuner Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6 No E4000 tuner found, aborting.
So far so good.
Next I tried running rtl_fm, which lets you demodulate a FM signal. AM is supposedly also supported. I say supposedly because I could not get rtl_fm to work properly. It would run, and write demodulated sound data to a file, but playing it back always produced gibberish. Also, the files were way too large for the specified sample rate and length of time the program was running. The documentation for rtl_fm is sketchy. For example, the list of options includes:
[-s sample_rate (default: 24k)]
which naturally makes you suspect -s sets the sample rate. It does no such thing, it actually sets the IF bandwidth. Again, supposedly.
After several hours of trying to get rtl_fm to work properly, I threw in the towel, and moved on to rtl_tcp, which acts as a little TCP server, sending I/Q data to a connected client. I had much better luck here. Running the program produced the following:
$ ./rtl_tcp Found 1 device(s). Found Rafael Micro R820T tuner Using ezcap USB 2.0 DVB-T/DAB/FM dongle Tuned to 100000000 Hz. listening... Use the device argument 'rtl_tcp=127.0.0.1:1234' in OsmoSDR (gr-osmosdr) source to receive samples in GRC and control rtl_tcp parameters (frequency, gain, ...).
I then connected to it via telnet in another console window:
$ telnet 127.0.0 1234</code>
And the rtl_tcp server program responded with:
and proceeded to send I/Q data to my telnet session, which spewed it to the window. Mission accomplished.
Next I wrote a small program to open a connection to the rtl_tcp server, and grab all the received data, count the number of bytes per second, and display it once per second, as a quick and dirty test to see if everything was working OK. I got around 4M bytes per second, which is correctly for a 2 MHz sample rate (the data is 8 bit I/Q, so there are two bytes per sample).
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