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You can also use RPi as FM stereo transmitter without additional hardware - https://github.com/Miegl/PiFmAdv https://github.com/Miegl/PiFmAdv

by magnat 8y ago

jdietrich 8y ago
You can, but you definitely shouldn't.
- jcims 8y ago
  Yeah I was able to easily jam my mobile phone with a Pi by transmitting on a fundamental with harmonics the phone’s band. The range was pretty short but it nuked the signal. I used it to show my youngest what can happen if you aren’t careful with RF.
  - lostlogin 8y ago
    That’s a project with appeal - dangerous, but appealing.
- markovbot 8y ago
  Why not
  - caltelt 8y ago
    From the github repo readme: > In most countries, transmitting radio waves without a state-issued licence specific to the transmission modalities (frequency, power, bandwidth, etc.) is illegal.
    - userbinator 8y ago
      In practice, it's more like "if you get caught if it's illegal" --- and depending on what you're doing, getting caught can be very easy (e.g. broadcasting in an active band at enough power that your neighbours notice), or pretty much impossible (e.g. if you transmit inside a Faraday cage or at powers so low it doesn't reach the other side of the room). Or as the old saying goes, "If no one else can hear you, they won't know you're saying anything."
    - Fnoord 8y ago
      The Nokia N900 had a FM transmitter, allowing you to stream to e.g. your car radio. Nowadays we got different solutions and this is mostly redundant (though still possibly of use in what we now call "older" cars). The transmitter was very short range, and therefore it was legal.
  - dTal 8y ago
    It works by toggling a GPIO pin on and off. This results in a square wave carrier signal, which means you get an infinite stack of odd harmonics - 3f, 5f etc. This means you're not just transmitting on the frequency you meant to, but on every odd multiple of that frequency (with correspondingly decreasing amplitude of 1/3, 1/5 etc) all the way up the entire spectrum. It's very easy to accidentally clobber something like that. The only reason regulators haven't come down like a ton of bricks is the amplitude on PiFM is really too small to be very harmful - you're unlikely to mess up anything beyond the range of your own home, maybe your neighbors. If someone with a little knowledge tried to hook it up to an amplifier however, they're gonna have a bad time real darn quick...

You can also use RPi as FM stereo transmitter without additional hardware - https://github.com/Miegl/PiFmAdv https://github.com/Miegl/PiFmAdv

by magnat 8y ago

You can also use RPi as FM stereo transmitter without additional hardware - https://github.com/Miegl/PiFmAdv https://github.com/Miegl/PiFmAdv

jdietrich 8y ago

You can, but you definitely shouldn't.

jcims 8y ago
Yeah I was able to easily jam my mobile phone with a Pi by transmitting on a fundamental with harmonics the phone’s band. The range was pretty short but it nuked the signal. I used it to show my youngest what can happen if you aren’t careful with RF.
- lostlogin 8y ago
  That’s a project with appeal - dangerous, but appealing.
markovbot 8y ago
Why not
- caltelt 8y ago
  From the github repo readme: > In most countries, transmitting radio waves without a state-issued licence specific to the transmission modalities (frequency, power, bandwidth, etc.) is illegal.
  - userbinator 8y ago
    In practice, it's more like "if you get caught if it's illegal" --- and depending on what you're doing, getting caught can be very easy (e.g. broadcasting in an active band at enough power that your neighbours notice), or pretty much impossible (e.g. if you transmit inside a Faraday cage or at powers so low it doesn't reach the other side of the room). Or as the old saying goes, "If no one else can hear you, they won't know you're saying anything."
  - Fnoord 8y ago
    The Nokia N900 had a FM transmitter, allowing you to stream to e.g. your car radio. Nowadays we got different solutions and this is mostly redundant (though still possibly of use in what we now call "older" cars). The transmitter was very short range, and therefore it was legal.
- dTal 8y ago
  It works by toggling a GPIO pin on and off. This results in a square wave carrier signal, which means you get an infinite stack of odd harmonics - 3f, 5f etc. This means you're not just transmitting on the frequency you meant to, but on every odd multiple of that frequency (with correspondingly decreasing amplitude of 1/3, 1/5 etc) all the way up the entire spectrum. It's very easy to accidentally clobber something like that. The only reason regulators haven't come down like a ton of bricks is the amplitude on PiFM is really too small to be very harmful - you're unlikely to mess up anything beyond the range of your own home, maybe your neighbors. If someone with a little knowledge tried to hook it up to an amplifier however, they're gonna have a bad time real darn quick...