Super Simple FM Transmitter

Making your own FM radio is practically a rite of passage for hackers. How about making a small FM transmitter?

Originally designed by the Japanese multimedia artist [Tetsuo Kogawa], this simple FM transmitter can be built with only 10 components and about an hour of your time. The method shown here is one of the easiest to build, and it’s called the Manhattan Style — the same method used when [Bill Meara] built his BITX radio. It’s unique in that instead of using traces it uses one copper PCB which is used for all ground connections, and then small islands of the same PCB glued on top to form nodes for the circuit to connect to. Besides being an extremely easy way to make a PCB without any fancy tools, it also makes you think about circuits in a different light. In fact, it gives “floating ground” a whole new meaning!

While its 10 component count is impressive, it can’t beat this 3 component FM transmitter we shared a year ago! Stick around after the break to see how to make your very own.

29 thoughts on “Super Simple FM Transmitter

  1. i think with analog dying it is pretty doubtful that the law is even being enforced.

    heck there was a sing along microphone and the transmitter for the verbot toy in the 80’s was simply fm transmitters.

    i think the law is more concerned about taking down emergency signals like the police or 911 dispatch .

    also radio is not the only form of emergency broadcast there is tv and even door to door evacuation calls.

    though if you do find that it can broadcast outside the house or even property then that may be reason for alarm and then you may want to check with the law.

      1. I’m here in Florida, the pirate radio capitol of North America. While the verbiage sounds scary, the ‘enforcement’ is pretty soft. My experience was with a 24 hour pirate FM station with a broadcast radius of 3-4 miles. Our dealings with the FCC were mostly limited to knocks on the door from agents asking to inspect the equipment, a polite refusal to let them in and them leaving to get a warrant while we packed up the gear and went to the next available space. This went on for years. There was eventually a police raid, equipment seizure and a few arrests after a new group took over the station and got very cocky and radical, but basically, if we stayed low key they didn’t go out of their way to haul us to jail or fine us. Of course none of us will ever get legitimate licenses, but that’s a small price to pay.
        I’m not encouraging anyone to broadcast illegally- I just want to ease anyone’s fears about playing with this kind of low power circuit. Have fun, be polite and use common sense. The FCC is just another under-paid, over-worked bureaucracy- they don’t have time to bust hobbyists and artists.

        1. The radio spectrum is clogged with enough licensed crap that makes it difficult to tune what few listenable stations still exist. The last thing we need is more pirate clowns intentionally muddying up the band. Non-licensed FM transmitters (limited to a few microwatts) are more than enough to cover your home with tuneable audio… that’s the point of the circuit in this article, and using it doesn’t make you a pirate if you ensure that the output level and your antenna efficiency are sufficiently in check. But intentionally running at higher power levels than allowed, such as you discussed having done in the past, is just plain douche-y.

          Honestly, by the time you’re capable of building a transmitter of sufficient power to break the rules and to do so with a clean signal that isn’t too wide or over-modulated (ie, to respect the technical standards), you’re smart/wise enough to not actually do so. Those that are all “omg, I built a leet circuit with more powerz” lack the skill & finess to build transmitters that are clean and that could avoid notice (by not trampling all over adjacent stations, for example). So, in that way at least, the system is sufficiently darwinian (assuming they don’t give themselves RF burns in the meantime).

          Nonetheless, intentionally breaking the rules in ways which bring harm (economic) or inconvenience to others is not a responsible behavior. If you’re out in the country where your signal isn’t going to interfere with others, then what the heck, go for it… But if you’re in a populated area and you just want to get noticed by being a nuisance, there are far better ways to do it than by building/operating illegal transmitters. There’s the difference.

          I expect some flaming for this, but being a responsible adult does, in fact, require cooperation with the rules of the group.

      2. Not sure if you would want to peruse this issue. But, if you think about it most store bought FM transmitters meant for Ipod’s and portable audio devices to transmit sound whether music or any form of audio via FM. Belkin, RCA, APPLE themselves numerous others would be facing FCC fines left and right. 300′ or 92 meters at an output of 50 NANOwatts.

        If this thing pushes 1 watt I would be impressed. I wouldn’t worry too much about the FCC unless neighbors start complaining or if out knock out half a city block of am/fm/uhf/vhf signals or a whole cable system. The FCC has bigger fish to fry….

        1. Nowhere near 1W, even 50mW still would be way too generous…
          Also, kinda useless when you can buy all-in-one chip solutions that have a PLL and stereo encoder, all that for a few bucks. Unlike the cheap PLL stuff, this will drift (frequency) like crazy.
          If there’s anything worth pursuing, it’s building a cheap DDS transmitter where all the hard stuff happens in software ;-)

      1. In grained in every living creature is the instinct to survive.

        The Long Answer:
        Getting a job, which by the way is a false and misleading statement, makes survival easier to do. No one gets a job, one seeks and is given a job. Getting implies that it is all in the hands of the job seeker when in fact, it is completely out of the hands of the job seeker. The employer can refuse to hire for any bigoted reason imaginable, and there is nothing the job seeker can do about it.

        So if all employers refuse to hire a particular individual, employers have made that individual unemployable, placed him or her in a life threatening situation and by extension made him or her disabled. It is one of the most cruel and dispicable things society can do to an individual.

        I feel a rant comming on so I think I’ll move on to the short answer.

        The Short Answer:
        It’s something to do in the mean time.

    1. Well, IMO, this reply is pretty much off target with respect to the original post, still very interesting with respect to new toys to buy and play with. I just ordered three MMR-70, one for my SE-phone, one for my Raspberry and one to tinker with. But, buddy, if you have to ask ‘why bother’, you’ve definitely come to the wrong site.

      1. Not really. Its all about level you want to operate at.
        You want to start making wooden wheels for your car? Weave baskets?
        This is electronics archeology. Its useful to know how it works, but not useful to make it.

        We cant all stop looking forward and stagnate fixing old tube radios.

        1. First: Thanks for your reply.
          ‘The level you want to operate at’ – exactly right! What do we have here: a few parts worth a few cents doing something interesting. Something I can throw together in an afternoon and twiddle around using my clumsy fingers and an oscilloscope.
          So, you say this is electronics archeology, I say it’s a way to investigate on things that are the very fundamentals of our everyday life. I can’t have a look at the gate capacity of one of the billions FETs in todays microprocessor, but I can have a look at this pennywhistle schematic and try to understand it. Base-capacity in bipolar transistors.->pn depletion zone->varactors? Does this ring a bell? Cascode? Input impedance? Miller effect? There are information threads to follow and things to learn from here. And while this schematic or the actual device are irrelevant, this information is not.

          What’s true in this almost useless contraption is true in whatever solid state electronics an engineer might come across in her professional life.

          I don’t know where you’re from and at what stage of your professional life you are at the moment, but if your education system trains intelligent people to despise this kind of rainy sunday experiment just because you don’t learn anything you could not read in a book and you don’t build anything you could not buy from China better and cheaper, I would be concerned. Very concerned. ’cause then it will not be long until the only way to get such a device – or any device – is to buy it from China.

          If you compare this to making baskets, then you have completely not understood that all your world is made of wicker, so to say, even if it’s so finely woven that you can’t see it.

  2. The design isn’t actually new. It is the same as the one-transistor FM transmitter that has been around for decades:

    The only different is that the circuit diagram has been changed so it is easier to build. It is, however, much more difficult to understand that way. The design is quite ingenious – the transistor is used both for the FM modulation and to drive the oscillator. The audio input changes the base voltage of the transistor which leads to a variation of the junction capacitance of the base-emitter diode. This change in capacitance modulates the frequency of the LC circuit.

  3. Way back I’ve seen small self-sticking boards for DIL8/14/16/etc, TO100 and other ‘difficult’ form-factors to help build circuits this way. Did it myself too once or twice for HF circuits, using bits of copper-clad perfboard (preferred the type with strips per row, connecting three holes each time). Glued them down or soldered short solid core wires to the appropriate pads and the ground plane, Soldered the part on, then the components and interconnecting wires.

    You do want to have a beefy soldering iron for the ground plane connections.

  4. Let’s see, hmmm.

    A low cost transmitter plugged into the audio out of the TV.
    A low cost receiver plugged intot he audio in of speekers sitting acrossed the room.
    And you have a low cost wireless speaker system in your home.

    I do have a set of wireless headphones with such a setup but they don’t work all that well. I guess I could hack it up and have the setup I’d like. The speakers on the TV while adequate when everythings off, are a bit far away when the furnace comes on requiring an excessive amount of volume increase. And living in an apartment, I am qutie sensitive regarding how much noise I make, even though the neighbors are not.

    1. It just occured to me that if I tune an FM Radio to the frequency of the transmitter, I would achieve the same thing without all the fuss.

      Now the question is: which would use the least amount of energy. The external speakers would likely require an amplifier. Whereas a readio has all of that built in.

      On the other hand, if I add to the FM transmitter, circuitry that provides a wireless power supply, then the speakers will shut down when the telivision turns off.

  5. It’s November of 2018 as I am writing this. I just found this website and I am seriously impressed. I never even gave any thought to building my own FM trans. But now that I have found this place, I kinda wanna look into it a bit further. I hope everybody here is still active and reading and approving these comments

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