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Rad Pic1
Here’s a radio modem using an “iPod” FM Transmitter and a regular FM receiver. Using the programs provided, you can send messages between two computers at 9600 bps – Link.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.


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Comments

  1. DavidO says:

    Uhhm, why would you want to?

  2. FCC says:

    Also, this is technically illegal and could potentially net you a fine of several thousand dollars if someone A) noticed and B) decided to be an asshole about it. Radio waves are not to be meddled with lightly, unless you have a license.

  3. Michael Spencer (callsign NO0K) says:

    Yes this is technically illegal, but I figure I could shed some more light on what is specifically illegal, why, and what you can do to make this legal again:

    First, every radio device operates in a specific radio service. Nearly all radio services, like the one this short-range transmitter broadcasts on, both require a license for any transmission above a certain Effective Radiated Power level AND requires that a transmitter be either type-accepted or be specifically approved by the FCC.

    So essentially the only thing illegal about this project was opening the kit up and connecting an external antenna. Once the transmitter was modified it was no-longer type accepted for the radio service it operates in. So feel free to do this as long as you don’t modify your transmitter.

    Bandwidth wise, FM broadcast signals are pretty wide-band, so you are going to reach the practical limit of your audio sending/receiving gear long before you run out of bandwidth. With a very clear radio channel and a better method of encoding/decoding data, you may be able to approach a good fraction of a megabit per second with this method.

    If this kind of thing interests you, consider ham radio. The amateur radio service lets you use home-built or modified radios, so this kind of experimentation is welcome and encouraged. There’s quite a lot of data being sent and received via HF nowadays, with a variety of interesting encoding methods. (Think of it as the world’s most expensive-to-join and most well-regulated IRC channel.) So as long as you obey regulations: transmit nothing offensive, stay within the amateur radio service (which is pretty HUGE and has many chunks of prime spectrum), transmit at legal power (max of 1500 watts in most bands), identify your transmissions legally (get a callsign and use it on the air), and use amateur radio spectrum for non-profit or public-service use only, you can do pretty much anything you want.

    It’s kinda scary really: if you read the FCC’s federal regulations for the amateur radio service, the paragraphs about the purpose of the service show a GREAT understanding of the hacker ethic, encoded into federal law. Look at that, a federally protected “right to hack” (radio-wise that is) for anyone with a ham radio license. :-)

    So if this kind of project REALLY gets your gears turning, AND if you think you have enough spare money for parts for radio hardware projects, consider getting a ham radio license. arrl.org is a good place to start. Be warned: ARRL does have a bit of a commercial interest in seeing the hobby grow, but you don’t HAVE to join them. Use some free practice-test sites on the Internet and study on your own, and you should be able to pass the Technician and General class license tests without the ARRL’s help. (And who knows — if you’re in the Omaha area, maybe I’ll be one of the three VE’s grading your license test! :-) )

  4. Michael Spencer (callsign NO0K) says:

    Yes this is technically illegal, but I figure I could shed some more light on what is specifically illegal, why, and what you can do to make this legal again:

    First, every radio device operates in a specific radio service. Nearly all radio services, like the one this short-range transmitter broadcasts on, both require a license for any transmission above a certain Effective Radiated Power level AND requires that a transmitter be either type-accepted or be specifically approved by the FCC.

    So essentially the only thing illegal about this project was opening the kit up and connecting an external antenna. Once the transmitter was modified it was no-longer type accepted for the radio service it operates in. So feel free to do this as long as you don’t modify your transmitter.

    Bandwidth wise, FM broadcast signals are pretty wide-band, so you are going to reach the practical limit of your audio sending/receiving gear long before you run out of bandwidth. With a very clear radio channel and a better method of encoding/decoding data, you may be able to approach a good fraction of a megabit per second with this method.

    If this kind of thing interests you, consider ham radio. The amateur radio service lets you use home-built or modified radios, so this kind of experimentation is welcome and encouraged. There’s quite a lot of data being sent and received via HF nowadays, with a variety of interesting encoding methods. (Think of it as the world’s most expensive-to-join and most well-regulated IRC channel.) So as long as you obey regulations: transmit nothing offensive, stay within the amateur radio service (which is pretty HUGE and has many chunks of prime spectrum), transmit at legal power (max of 1500 watts in most bands), identify your transmissions legally (get a callsign and use it on the air), and use amateur radio spectrum for non-profit or public-service use only, you can do pretty much anything you want.

    It’s kinda scary really: if you read the FCC’s federal regulations for the amateur radio service, the paragraphs about the purpose of the service show a GREAT understanding of the hacker ethic, encoded into federal law. Look at that, a federally protected “right to hack” (radio-wise that is) for anyone with a ham radio license. :-)

    So if this kind of project REALLY gets your gears turning, AND if you think you have enough spare money for parts for radio hardware projects, consider getting a ham radio license. arrl.org is a good place to start. Be warned: ARRL does have a bit of a commercial interest in seeing the hobby grow, but you don’t HAVE to join them. Use some free practice-test sites on the Internet and study on your own, and you should be able to pass the Technician and General class license tests without the ARRL’s help. (And who knows — if you’re in the Omaha area, maybe I’ll be one of the three VE’s grading your license test! :-) )

  5. NO0K (dupe poster extraordinaire) says:

    The first post errored out, I promise! *cries* If someone could delete the dupe and delete this post, I’d appreciate it.

  6. NO0K (dupe poster extraordinaire) says:

    The first post errored out, I promise! *cries* If someone could delete the dupe and delete this post, I’d appreciate it.

  7. Ben cartwright says:

    o F*ck i was sooooo going to do this as a project awwww i have to think of somthing else :-(

  8. Matt says:

    This is not “technically illegal”. It only has to be approved by the FCC if it is over a certain power level. Whether you built it yourself or modified something makes no difference if it doesn’t reach over a certain power level and as long as it doesn’t cause interference with other devices.

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