MilRadioComms.com - Military Radio & Aircraft Frequencies

This is project using the Raspberry Pi and the Dongle. I've been thinking of how I could stream audio online without tieing up a "real" computer. I've been streaming Military Aviation Communications audio for years. But sometimes I don't like streaming from the computer that I do "real" work on, this got me thinking of a new project for the Raspberry Pi computer. At this time the project isn't complete but it is just to prove the concept that it will work. This project is no more than me experimenting with the Raspberry Pi and Linux style of operating system, both new to me.

Some applications for this type of setup would be to mount this very small dongle/Raspberry system at the antenna to avoid coax losses. It would be great if powered from a battery/solar panel. You could set one at your Ham Radio repeater site and stream the repeaters audio online. Put one at your friends house if he lives close to something you would like to monitor but you're too far away for a good signal....The possibilities are endless. Please if you think of some good uses share them with me....

If you don't have any experience using the Raspberry Pi computer you first need to see my article Raspberry Pi - Getting It Ready for Neat Scanner Projects. That article will guide you through installing an operating system, setting up the networking, and getting the Raspberry Pi computer and Dongle to talk to each other.

Picture of the Self-Contained Dongle Radio Streaming via the Raspberry Pi's Wifi dongle.
Click on Picture for larger image


As a first test I installed and confirgured the required software on the Raspberry Pi computer. I then tuned the SDR Dongle to a NOAA weather radio frequency (162.400 MHz), and using ezstream and lame software I had the Raspberry Pi stream the audio to an Icecast 2 server via a wifi link. Since I now can get audio from the Raspberry Pi to Icecast, this means I could stream scanner audio to any web service that accepts Icecast such as LiveATC.net

Steps on How to Stream Dongle Audio Through Raspberry Pi to an Icecast Server

• 1) Install ezstream, this will stream mp3 audio to an IceCast server, type the following command: sudo apt-get install ezstream
• 2) Install lame, this will handle the MP3 audio encoding. It takes the output from the Dongle and converts it to MP3 format. Type the following command: sudo apt-get install lame

• 1) Type cd this will put you in your home dirctory (the directory you are put into when you login).
• 2) Type pwd, you should see "/home/pi". We're just making sure you are really in your home directory.
• 3) We now will use nano to create a file called ezstream.xml, type sudo nano ezstream.xml
• 4) In the window below you'll see a template you can use for the ezstream.xml file. Click somewhere on the text below, then hit CTRL A to select the entire window. Next hit CTRL C to copy the text to your clipboard. Now return to your PuTTY window, select the window with your mouse, then hit the RIGHT mouse button. This will copy the contents of your clipboard to the ezstream.xml file you have open in nano.
  • Below you'll see a template you can use for the ezstream.xml file:
    <ezstream> <url>your_icecast_stream_server</url> <sourcepassword>sourcepassword</sourcepassword> <format>MP3</format> <filename>stdin</filename> <!-- Important: For streaming from standard input, the default for continuous streaming is bad. Set <stream_once /> to 1 here to prevent ezstream from spinning endlessly when the input stream stops: --> <stream_once>1</stream_once> <!-- The following settings are used to describe your stream to the server. It's up to you to make sure that the bitrate/quality/samplerate/channels information matches up with your input stream files. --> <svrinfoname>A name for your stream</svrinfoname> <svrinfourl>a_clever_url</svrinfourl> <svrinfogenre>Rock_HipHop_Swing</svrinfogenre> <svrinfodescription>A description of your stream</svrinfodescription> <svrinfobitrate>128</svrinfobitrate> <svrinfoquality>2.0</svrinfoquality> <svrinfochannels>1</svrinfochannels> <svrinfosamplerate>44100</svrinfosamplerate> <!-- Turn off YP directory advertising --> <svrinfopublic>0</svrinfopublic> </ezstream>
  
  
• 5) Next you'll make some changes to the ezstream.xml file. Do Not Use Your Mouse while in nano, it just screws things up!. User your up arrow key to move to the top of the file.
• 6) The 2nd line of text says your_icecast_stream_server replace the text between the "url" tags with the following: http://192.168.1.105:8080/stream_raspberry, but use the IP address of your IceCast machine.
• 7) The next line says sourcepassword, change that to what you set the source password in IceCast.
• 8) While using your down arrow key, move down the file until you find svrinfobitrate, change the 128 to 16
• 9) Move down until you see svrinfosamplerate, change the 44100 to 22000
• 10) You will see other informational items in the ezstream.xml file such as description of stream, URL, and so on. These don't need to be change.
• 11) You're done editing the file, to save the file hit CTRL O, then hit Enter to write the file. Then to exit nano hit CTRL X
• 12) Are you getting excited yet? We're almost ready to test it out!

• -M fm | wbfm | am | usb | lsb | raw
• Selects a demodulator.
  • -M fm narrow band FM
  • -M wbfm wide band FM
  • -M am amplitude modulation
  • -M lsb lower sideband
  • -M usb upper sideband
  • -M raw raw output, 2x16 bit IQ pairs. Purely debugging and no sane person has any use for this.
• -f "freq" | "start:stop:step"
  • Tune to a frequency. Value can be specified as an integer (89100000), a float (89.1e6) or as a metric suffix (89.1M). Multiple values or ranges will be scanned.
• -s "sample_rate"
  • Bandwidth of signal.
• -d "index"
  • When using multiple dongles, this indicated which. You can also identify dongles by the text in the serial number field of the EEPROM.
• -g "gain"
  • A floating point gain value. The dongle will use the closest gain setting available.
• -p "error"
  • Correct for the parts-per-million error in the crystal.
• -F 0 | 9
  • Enable a higher quality downsampling FIR than the default boxcar filter. -F 0 is okay to use while -F 9 is still a work in progress.
• -A std | fast | lut
  • Choose how arctan is computed. Options select between the standard (floating) lib, a fast polynomial integer approximation and a precomputed look-up-table.
• -E dc | deemp | direct | offset
  • -E dc dc blocking filter
  • -E deemp de-emphasis filter for WBFM
  • -E direct direct sampling mode
  • -E offset offset tuning mode (E4000 only)
• -l "squelch level"
  • Squelch is required for scanning multiple frequencies, to indicated when a frequency should be skipped. When used with a single frequency the output will be muted instead. Default value is 0/off. Squelch values are extremely sensitive to external conditions (noise and antenna) as well as the other options used. For example, squelch should be halved when the sample rate is doubled. When in doubt, start at zero and work upwards.
• -t "squelch delay"
  • The number of squelch hits to count up to. Default value is 20. So the squelch must be trigger 20 times consecutively before rtl_fm moves on to the next channel. Negative delay values cause rtl_fm to exit instead of hopping to another channel or muting the output. This is useful for scripts or trunked systems.
• -r "output rate"
  • In some odd circumstances you might want to apply an extra low pass downsampling/resampling stage. This is for that, but most of the time it is rarely needed. It will also change the output rate. It is also a very poor quality resampler. Use sox for resampling.