Lets assume you want your own radio station. Or maybe you just need to broadcast an important message on a local radio station. The proper route would be to either buy an FM license from the FCC, or if your only needing to broadcast a message once on a local station you would call the station up and negotiation a price to pay for your message to be heard.
However the air is free, and sending out radio waves on any given frequency is also free and extremely easy to do. Even though you may be risking legal issues if you do so.
Knowing that anyone with the right tools can send out signals on almost any frequency means that anyone can hijack a radio station and play their content instead of the radio stations content.
The only things needed to take over a radio station is an FM transmitter and an antenna. This is where the Raspberry Pi comes into the picture.
Note: When performing this I only did it for 5 minutes at a very low strength at time when most people in my area where most likely sleeping. I also tuned my radio in to the station I was hijacking hoping to get dead air. Since I did get dead air I felt I was safe.
First we will download the official Raspberry Pi OS known as Raspbian. I used Raspbian Lite you can choose to use the Pixel image if you want. After downloading the image we burn it to our SD Card. Since I use Linux to burn the image to the SD Card I will type the following commands.
sudo dd if=raspbian.img of=/dev/mmcblk0 bs=1M conv=fsync && sudo sync && sync
While the image is burning we will download a program called PiFM. This allows us to turn our Raspberry Pi into an FM Transmitter.
Once the image is done burning we will mount the sdcard and navigate to the pi users home directory.
Next we copy the PiFM GZ file to the location. And extract the files from the GZ file, then we will delete the GZ file.
cp $HOME/pifm.tar.gz /run/media/sdcardname/home/pi/
tar -zxvf pifm.tar.gz
Next we will copy some audio files to the SD Card. In this example we will only copy one audio file.
cp $HOME/Music/audio.mp3 /run/media/sdcardname/home/pi/
Now that we have done all of this. We will remove the SD Card from our computer.
Now on the GPIO 14 pin of our Raspberry Pi, we will connect a wire. The wire will act as our antena. I actually rigged a fairly strong antena up with a wired cloths hanger and wrapping a 28 Guage copper wire around it. I then simply attached the end of the copper wire to the GPIO 4 pin.
Now we place the SD Card into the Raspberry Pi and boot it up. Once it is running we will log in to the Raspberry Pi and type the following commands.
sudo ./pifm left_right.wav 103.1 22050 stereo
ffmpeg -i audio.mp3 -f s16le -ar 22.05k -ac 1 - | sudo ./pifm -
Based upon the above commands if we tune our FM radio to the channel 103.1 we will here the MP3 file that we have on our Raspberry Pi. If we want to broadcast on a different station we will simply change 103.1 to a different number. If we want to hijack a certain local station we can use Radio Locator and type our location in to get a list of all of our local radio stations.
Note: I’m not a lawyer and I’m simply trying to interpret the FCC license Article 47 Part 15. Please consult a lawyer.
e-CFR Code Of Regulations
According to the FCC broadcasting without a license is allowed for both FM and AM as long as AM’s power does not go above a 1 WATT. For FM your allowed to broadcast between the frequencies of 88MHz and 108MHz and a radius of 60 meters as long as it is not affecting any licensed radio stations.
This is why when you purchase an FM Transmitter to make an MP3 play music through your car speakers your legally allowed to do. Because it isn’t breaking any laws. However be aware that if your less than 60 meters away from the radio station that your broadcasting on and your interfering with the station your then in violation.
Some areas have more FM radio pirates than others. And in those areas the FCC is watching more closely. Below is a map of the FCC violators.
The FCC usually wont take action if they receive no complaints, and if they only receive one or two complaints they wont take action. However the more complaints they receive the more likely they will take action.