6 ms·

Same. Here's a Pi-based FM transmitter that uses no additional hardware except for an antenna: http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry

Same. Here's a Pi-based FM transmitter that uses no additional hardware except for an antenna: http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...

dTal 5y ago
Note: do not use this. The carrier wave is a square wave which means you spill ungodly amounts of RF into harmonic sidebands. If you dare to plug this into an amplifier - at least without a lowpass filter - expect a firm knock on your door.
- klysm 5y ago
  Isn’t the point that you use this without an amp though
  - dTal 5y ago
    It's still illegal (and possibly dangerous) even without the amp - you're just much less likely to actually interfere with anything because the range is short. But you still shouldn't use it.
    - klysm 5y ago
      Out of curiosity, what laws does it violate?
      - SV_BubbleTime 5y ago
        All manner of jamming and FCC broadcast rules.
        klysm 5y ago
        Yeah but specifically, I just don’t know anything about these laws and it seems fine to be doing it at low power
        gsich 5y ago
        Low power means nobody is going to notice.
        rfdave 5y ago
        Lolz. Low power in the wrong place can be a problem.
        rfdave 5y ago
        For the most part, transmitting radio in the US is only allowed in a few frequency bands, referred to as the ISM band. These have pretty strict transmit power and duty cycle limits. If you get a ham radio license, then many more bands open up to you.
        wiml 5y ago
        Title 47, part 15, holds the relevant regulations. Subparts 5, 15, and 23 are probably where you should start. TBH, if you keep your radiated power low and make a reasonable attempt not to interfere with other users (be aware of bands' uses and where your harmonics and spurs are falling), you'll be completely fine, the worst you'll get is an official notice from the FCC telling you to stop. I'd also suggest seeking out some ham radio experimenter groups to learn from, even if you don't want a ham license, there's a lot of practical knowledge to be shared.
    - omginternets 5y ago
      Could you elaborate? As someone who has been interested in hacking SDRs for a while (but with zero prior knowledge outside of programming), I'm often worried that I have a poor barometer for what is legally dangerous. This stuff seems innocuous enough, but isn't always. I don't know what I don't know, so any additional context is welcome.
      - haswell 5y ago
        Generally speaking: - Listening is typically OK (with some exceptions). - Transmitting is a minefield, and you could interfere with critical systems, cause outages, and get in trouble. Imagine interfering with aircraft communication systems on accident because there’s an airport nearby. Things can get pretty serious pretty quickly.
        parsecs 5y ago
        What are exceptions to listening? I'm pretty sure you can listen wherever and however you want.
        wdfx 5y ago
        You're not strictly allowed to decode and read pager messages.
        deleted 5y ago
        [deleted]
        cnorthwood 5y ago
        It depends on the country you're in. In the UK for example, you're only allowed to listen to broadcast, amateur radio, or transmissions to which you are the intended recipient
        omginternets 5y ago
        Thanks! Say I wanted to transmit, what’s the general process for navigating the minefield? One of the things I’d like to do is build a software-defined radio (using an rpi, for example) and use it to send something like Ethernet packets over the air.
    - netr0ute 5y ago
      Problem is, the kinds of people who are interested in this kind of thing don't care if it's illegal or not.
      - haswell 5y ago
        They'll start to care pretty quickly when they get a visit from a 3-letter agency (just one example [0]). - [0] https://www.jdsupra.com/legalnews/fcc-enforcement-bureau-targets-6301570/ https://www.jdsupra.com/legalnews/fcc-enforcement-bureau-tar...
        CamperBob2 5y ago
        Realistically, that's not going to happen unless a harmonic lands within the ATC band or a GPS subband. The trouble is, that's entirely possible. This sort of thing needs a good enclosure, or at least some board-level shielding.
        lstepnio 5y ago
        99.999999999% not going to happen. On the remote chance does, expect a simple educational talk.
    - mlyle 5y ago
      You're pretty damn likely to be inside the part 15 mask which is hundreds of microvolts/meter (30m away) up at UHF+. The total energy inside a single GPIO squarewave is on the order of 30mW; harmonics are a tiny fraction of this, and most will not be radiated efficiently. (Not to mention that edge rates/stray capacitance will limit their energy in the first place). The big question is whether the fundamental frequency is compliant. A perfect squarewave has ~81% of its energy in the fundamental frequency.
londons_explore 5y ago
I wrote that code. It's mostly broken nowadays because newer pi's use different hardware and new Linux distributions lock down the ability to poke random memory without the kernel having a proper driver. There are other pifm projects which use the same general idea and work properly though.
- gregsadetsky 5y ago
  Amazing, thanks! Would you have a links to those other projects or their names? Would love to read more.
pqb 5y ago
Funny, in last weekend I was playing with various projects [0][1][2] based on the idea from this article. It was impressive how long range Raspberry Pi achieved even without the cable antenna. They do work - transmit audio over the FM waves, but sadly the quality (buzzing noise) is far from expectations. Initially, I thought it is just my Raspi 3B, but when dived into the issues section on GitHub, I noticed more people were claiming they had similar problems. Do you know what could cause such degradation? Is there any better solution to transmit FM in a home? Worrying fact is it also spams close ranges making them unable to listen. Have you applied any filter making it more stricter about the wave range it will take? [0]: https://github.com/ChristopheJacquet/PiFmRds https://github.com/ChristopheJacquet/PiFmRds [1]: https://github.com/markondej/fm_transmitter https://github.com/markondej/fm_transmitter [2]: https://github.com/miegl/PiFmAdv https://github.com/miegl/PiFmAdv

dTal 5y ago

Note: do not use this. The carrier wave is a square wave which means you spill ungodly amounts of RF into harmonic sidebands. If you dare to plug this into an amplifier - at least without a lowpass filter - expect a firm knock on your door.

klysm 5y ago
Isn’t the point that you use this without an amp though
- dTal 5y ago
  It's still illegal (and possibly dangerous) even without the amp - you're just much less likely to actually interfere with anything because the range is short. But you still shouldn't use it.
  - klysm 5y ago
    Out of curiosity, what laws does it violate?
    - SV_BubbleTime 5y ago
      All manner of jamming and FCC broadcast rules.
      - klysm 5y ago
        Yeah but specifically, I just don’t know anything about these laws and it seems fine to be doing it at low power
        gsich 5y ago
        Low power means nobody is going to notice.
        rfdave 5y ago
        Lolz. Low power in the wrong place can be a problem.
        rfdave 5y ago
        For the most part, transmitting radio in the US is only allowed in a few frequency bands, referred to as the ISM band. These have pretty strict transmit power and duty cycle limits. If you get a ham radio license, then many more bands open up to you.
        wiml 5y ago
        Title 47, part 15, holds the relevant regulations. Subparts 5, 15, and 23 are probably where you should start. TBH, if you keep your radiated power low and make a reasonable attempt not to interfere with other users (be aware of bands' uses and where your harmonics and spurs are falling), you'll be completely fine, the worst you'll get is an official notice from the FCC telling you to stop. I'd also suggest seeking out some ham radio experimenter groups to learn from, even if you don't want a ham license, there's a lot of practical knowledge to be shared.
  - omginternets 5y ago
    Could you elaborate? As someone who has been interested in hacking SDRs for a while (but with zero prior knowledge outside of programming), I'm often worried that I have a poor barometer for what is legally dangerous. This stuff seems innocuous enough, but isn't always. I don't know what I don't know, so any additional context is welcome.
    - haswell 5y ago
      Generally speaking: - Listening is typically OK (with some exceptions). - Transmitting is a minefield, and you could interfere with critical systems, cause outages, and get in trouble. Imagine interfering with aircraft communication systems on accident because there’s an airport nearby. Things can get pretty serious pretty quickly.
      - parsecs 5y ago
        What are exceptions to listening? I'm pretty sure you can listen wherever and however you want.
        wdfx 5y ago
        You're not strictly allowed to decode and read pager messages.
        deleted 5y ago
        [deleted]
        cnorthwood 5y ago
        It depends on the country you're in. In the UK for example, you're only allowed to listen to broadcast, amateur radio, or transmissions to which you are the intended recipient
      - omginternets 5y ago
        Thanks! Say I wanted to transmit, what’s the general process for navigating the minefield? One of the things I’d like to do is build a software-defined radio (using an rpi, for example) and use it to send something like Ethernet packets over the air.
  - netr0ute 5y ago
    Problem is, the kinds of people who are interested in this kind of thing don't care if it's illegal or not.
    - haswell 5y ago
      They'll start to care pretty quickly when they get a visit from a 3-letter agency (just one example [0]). - [0] https://www.jdsupra.com/legalnews/fcc-enforcement-bureau-targets-6301570/ https://www.jdsupra.com/legalnews/fcc-enforcement-bureau-tar...
      - CamperBob2 5y ago
        Realistically, that's not going to happen unless a harmonic lands within the ATC band or a GPS subband. The trouble is, that's entirely possible. This sort of thing needs a good enclosure, or at least some board-level shielding.
      - lstepnio 5y ago
        99.999999999% not going to happen. On the remote chance does, expect a simple educational talk.
  - mlyle 5y ago
    You're pretty damn likely to be inside the part 15 mask which is hundreds of microvolts/meter (30m away) up at UHF+. The total energy inside a single GPIO squarewave is on the order of 30mW; harmonics are a tiny fraction of this, and most will not be radiated efficiently. (Not to mention that edge rates/stray capacitance will limit their energy in the first place). The big question is whether the fundamental frequency is compliant. A perfect squarewave has ~81% of its energy in the fundamental frequency.

londons_explore 5y ago

I wrote that code. It's mostly broken nowadays because newer pi's use different hardware and new Linux distributions lock down the ability to poke random memory without the kernel having a proper driver. There are other pifm projects which use the same general idea and work properly though.

gregsadetsky 5y ago
Amazing, thanks! Would you have a links to those other projects or their names? Would love to read more.

pqb 5y ago

Funny, in last weekend I was playing with various projects [0][1][2] based on the idea from this article. It was impressive how long range Raspberry Pi achieved even without the cable antenna. They do work - transmit audio over the FM waves, but sadly the quality (buzzing noise) is far from expectations. Initially, I thought it is just my Raspi 3B, but when dived into the issues section on GitHub, I noticed more people were claiming they had similar problems. Do you know what could cause such degradation? Is there any better solution to transmit FM in a home? Worrying fact is it also spams close ranges making them unable to listen. Have you applied any filter making it more stricter about the wave range it will take? [0]: https://github.com/ChristopheJacquet/PiFmRds https://github.com/ChristopheJacquet/PiFmRds [1]: https://github.com/markondej/fm_transmitter https://github.com/markondej/fm_transmitter [2]: https://github.com/miegl/PiFmAdv https://github.com/miegl/PiFmAdv