FM Radio on Raspberry Pi

These tools require an RTL chipset based DVB-T dongle and strong radio signals. There are a bunch of scripts to listen to FM directly using the sox play command ... or as an IP feed from the IP address of the Raspberry Pi.

Required Hardware DVB-T or RTL_SDR Stick

Here is some general information about the hardware and software:

Clone the repo

$ cd ~/
$ git clone https://github.com/duracell80/RTLUtils.git
$ cd RTLUtils

$ sudo chmod +x *.sh

Install RTL_FM

To install only the SDR tools without a streamer

$ cd ~/RTLUtils
$ ./install.sh

After reboot and knowing a local FM station's frequency and already knowing your Pi is outputting sound ...

$ cd ~/RTLUtils
$ sudo chmod +x *.sh
$ ./tune_fm.sh 103.3M

Finding FM Station Frequencies using rtl_power

Follow these steps to create a file of presets containing your clearest stations. Increase the chances of scanning for and finding frequencies by hooking your SDR up to an FM antenna.

First Run The Scan

You may hear silence on some frequencies, I have set the script to ignore weak frequencies, just press "Cursor Up" on your keyboard to keep scanning what rtl_power found.

$ cd ~/RTLUtils
$ sudo chmod +x *.sh
$ ./scan_fm.sh

Save Your Clear Stations

With scan_fm running tune the radio by using the Up and Down arrow keys. The Left and Right arrow keys will allow the fine tune within that current frequency range. When you hear a clear station hit Shift+M to add that clear frequency to your station "memory" ... just like a real radio! You'll end up with a file called fm_preset.csv.

$ cd ~/RTLUtils
$ ./scan_fm.sh
$ cat fm_preset.csv

Here were my clear stations ...

Listen to Your Presets

Now that you have a list of frequencies tied to your SDR and local area you can tune these with the up and down cursor keys, you can use these frequencies later with rtl_fm_streamer.

$ cd ~/RTLUtils
$ ./start_fm.sh

Install RTL_FM with FM Server (FM over IP)

To install the SDR with a streamer

$ cd ~/RTLUtils
$ sudo chmod +x *.sh
$ ./install-streamer.sh
$ sudo reboot

From your PC or Phone's browser via port 2346 for FM station 103.3 ...
http://your-pi-ip:2346/103300000/2

IPRadio

To find your Pi's Ethernet address use "ifconfig eth0"
To find your Pi's WiFi address use "ifconfig wlan0"
To listen to 90.3FM over your network in stereo http://your-pi-ip:2346/90300000/1

Use Cases

This could be useful if you're wanting to listen to an FM station on your phone maybe in VLC without having to use Internet data to do so, using your Raspberry Pi as a conduit.

Recording an FM program using VLC.

Allowing distant family members the opportunity to listen to local sports commentary, otherwise not found online.

Listen in Browser

To listen to a local FM radio station over your local LAN after reboot and knowing the IP address of the Pi and a frequency to tune to such as 103.3; Open the URL in a web browser or VLC player such as ... http://192.168.1.180:2346/95500000 for 95.5FM. Add these as URL's to M3U or PLS files to use within Mopidy, Moode, Volumio or any other MPD player. Note as stated by rtl_fm_streamer's creator, this is a one dongle, one station, one client deal. It's not possible to tune to the same station from multiple devices at the same time. Switching between listening devices I have found it beneficial to stop and start the service or reboot the pi.

Starting and Stopping the Radio Server

$ sudo service rtl_fm stop
$ sudo service rtl_fm start

Reading the Status of the Radio Server

$ sudo service rtl_fm status

rtl_fm.service - RTL FM Server, turns local broadcast FM stations into online radio $
   Loaded: loaded (/etc/systemd/system/rtl_fm.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2020-06-07 07:54:30 BST; 2min 25s ago
 Main PID: 972 (rtl_fm_streamer)
    Tasks: 8 (limit: 2200)
   Memory: 13.9M
   CGroup: /system.slice/rtl_fm.service
           └─972 /usr/local/bin/rtl_fm_streamer

Jun 07 07:56:23 raspberrypi rtl_fm_streamer[972]: Start streaming on frequency: 103300000 Hz [stereo: 0]
Jun 07 07:56:23 raspberrypi rtl_fm_streamer[972]: Tuned to 103780000 Hz.
Jun 07 07:56:23 raspberrypi rtl_fm_streamer[972]: Mono demodulation
Jun 07 07:56:23 raspberrypi rtl_fm_streamer[972]: Waiting for connection...
Jun 07 07:56:46 raspberrypi rtl_fm_streamer[972]: Connected
Jun 07 07:56:46 raspberrypi rtl_fm_streamer[972]: Start streaming on frequency: 103300000 Hz [stereo: 0]
Jun 07 07:56:46 raspberrypi rtl_fm_streamer[972]: Tuned to 103780000 Hz.
Jun 07 07:56:46 raspberrypi rtl_fm_streamer[972]: Mono demodulation

You can tune to a stereo stream, depending on the capability of your Pi. Contact the rtl_fm_streamer maintainer. Knowing your local FM frequencies is very helpful and I recommend putting together a playlist of the stations you want to tune to, in this way you could mix local FM broadcasts with online streams in one playlist file. It is possible to listen to FM bands beyond what a normal HiFi can recieve. You could try SDR# on Windows to explore your local signals. In the US it might be possible to tune to a NOAA broadcast.

Lookup FM Frequencies Here

ToDo

Service: HD (Hybrid Digital) Radio
Service: RTL_TCP
Service: ATC Airband scanner

FM Glitches

Artists may be able to use these libraries with SoX or Alsa to create some pretty awesome sound glitches

SOS Transmissions from Mars via Public Radio
rtl_fm -M fm -s 32k -f 90.3M - | aplay -r 48000 -f S16_LE

Homealone Talkboy booking at night at The Ritz with NPR:
rtl_fm -M fm -r 24000 -s 250k -f 90.3M - | aplay -r 16000 -f S16_LE

Very slow playback: rtl_fm -M fm -s 250k -f 103.3M - | play -r 32k -t raw -e s -b 16 -c 1 -V1 -
Very fast playback: rtl_fm -M fm -s 250k -f 103.3M - | play -r 500k -t raw -e s -b 16 -c 1 -V1 -
Hyper fast : rtl_fm -M fm -r 24000 -s 250k -f 90.3M - | aplay -r 48000 -f S16_LE


Upside Down Transmission on Public Radio with Alsa
rtl_fm -M fm -s 250k -f 90.3M - | aplay -r 48000 -f S16_LE
rtl_fm -M fm -s 175k -f 90.3M - | aplay -r 48000 -f S16_LE

Enjoy!

moheshmohan / RTLUtils