At this stage, I remembered how “great” it was to catch FM radio broadcasting in my amplifier while playing electric guitar and decided to use my old rusty G-string as an antenna for this RPi FM project.
No multiple connectors, just a plain piece of wire powered by a bit of heavy metal magic :D
In the real world, antenna theory and design is a “rocket science”. If you really want to send long-range FM signals with your RPi, you should learn it and build your antenna accordingly necessary wavelength (we are still working in VHF and HF bands), power consumption and other parameters. But for a couple of simple tests, a piece of string or the wire works perfectly.
There are not so many bands where we can legally check our RPi FM radio station. But still, there are some bands where you can check your FM transmitters. For initial checks, I used Citizen Band within 27 MHz.
This is easy, just run something like this in your RPi bash shell:
# sudo ./pi_fm_adv --audio sound.wav --freq 27.0
Legal Note: Such activities are illegal in most countries. Don’t do it, be a good boy.
Let’s have some fun and check whether RPi allows us to intrude broadcast radio signal. “Together with my friend, we performed broadcast signal intrusion against radio receiver inside his car” - I would say if we really did it :D
There is a video of how it could have been:
You can see that RPi Zero completely replaces the original signal. Even with a limited in its length antenna it still remains extremely powerful. Nice way to listen only music you like in your Uber :D
As you can see, the embedded ability for FM transmitting in your RPi is an amazing thing! You can use it pure legally, transmitting signals in open frequencies.
But if you are interested in applying your device in Red Teaming operations, this is still useful because of the ability to intrude broadcast signals. How would your company employees act if the radio says them to leave their office and keep their PCs unlocked?
Just take a powerful antenna with you and enjoy it!