Take A Break From Arduinos, And Build A Radio Transmitter

When you start watching [learnelectronic’s] two-part series about making a radio transmitter, you might not agree with some of his history lessons. After all, the origin of radio is a pretty controversial topic. Luckily, you don’t need to know who invented radio to enjoy it.

The first transmitter uses a canned oscillator, to which it applies AM modulation. Of course, those oscillators are usually not optimized for that service, but it sort of works. In part two he reduces the frequency to 1 MHz at which point it can be listened to on a standard AM radio, before adding an amplifier so any audio source can modulate the oscillator. There’s a lot of noise, but the audio is clearly there.

This is far from practical of course, but combined with a crystal radio it could make an awesome weekend project for a kid you want to hook on electronics. The idea that a few simple parts could send and receive audio is a pretty powerful thing. If you get ready to graduate to a better design, we have our collection.

12 thoughts on “Take A Break From Arduinos, And Build A Radio Transmitter

    1. I have to agree…. a simple transistor oscillator would have a much better waveform with fewer harmonics and a much more solid transmit frequency. A square wave is just wrong for making transmitters as your energy is spread out to all kinds of frequencies you don’t want or need it at. Those canned oscillators also contain local decoupling so modulating their Vcc isn’t a terribly grand way of getting information through them.

      1. The decoupling capacitor is probably a 0.1uF ceramic inside the can. For a 10kHz signal, the cap has an impedance of 160 ohms. The driver circuit just need to have lower impedance to brute force its way.

        Also note that the average amplifier would be unstable driving a such a high capacitive load without stability issue. That topic is a bit advanced for OP’s target group however.

    2. I’m afraid I have to agree. I couldn’t watch past the first few minutes. Talking about “tank circuits”, either RC or LC, without any explanation beyond that, showing a plot of a sine wave with the axes labeled “space” and “time”, facepalm. I can’t imagine how a person new to radio could get any useful knowledge from this.

  1. Clarke’s Second Law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

    The video is clearly a first step. I might suggest a resistor from the output into a capacitor isolated shunt diode with an audio modulated DC bias current. Modulated RF output off high side of diode.
    Keep at it. This is how a hobby starts and maybe even a vocation. A really good reference source is the ARRL handbook.
    Electronics is supposed to be fun and discovery and I can see it in your enthusiasm. Keep at it Good luck. 73.

  2. Projects for kids are great, but having government heavies talk about licenses and approved bands can dampen their enthusiasm.

    Is there a power limit specified for these kind of projects? To be sure you cause minimum disruption, and reduce the chance the local authorities come after you?

      1. That’s for type approved equipment or equipment with a declaration of conformity similar to the ones used in Europe. This thing is simply an illicit transmitter.
        Just declare it an experimental clock generator and see if its below EMC limits (it probably is), with this power you don’t disturb anyone except maybe you next-door HAM operator.

      2. Well, you link to the rules, but obviously haven’t read them. The limits are different for different frequency ranges, but that’s not everything. At most frequencies, the limits are for maximum field strength at a given distance from your antenna, so this depends on both the power being delivered to the antenna and the antenna’s gain. Part 15 is pretty complicated, but it’s the responsibility of everyone who builds a transmitter and intends to operate it without a license, to understand whatever sections of the regulations apply.

  3. Great to see many learning, experimenting, monitoring, listening, receiving and transmitting. Learnelectronics has some other great videos too.

    The fourth step in learning from where I was taught was teaching last I know… after watching/listening, reading/problem solving and applying/experimenting.

    We definitely need more on board listening and monitoring from underground to out in space… especially if you didn’t sign a non-disclosure agreement relating to the signals filth.

    “After all, the origin of radio is a pretty controversial topic. Luckily, you don’t need to know who invented radio to enjoy it.”

    Yeah, for sure and I thought what got me into radio was a pretty controversial topic. Wow!

    Then I started studying amateur radio, electronics and RF engineering again and was amazed at how controversial the topic of RF alone is post first bachelor degree in science (say ionizing vs nonionizing radiation and considering states of matter effects with high and low energies…, RF specific effects, thermal effects, non-thermal effects, etc.) and then the history of radio and other physics theories.

    Interesting regarding the early “practical” versus “non-practical” opinions based on the scientists perspectives.

    Novelty magic parlor tricks to… ??? most might not believe what can be done still to this day and like “it isn’t practical” or is it like this fine young lady notes as still magic (watch from 2:49 to 3:12):

    https://youtu.be/53sAEQ0rYyU?t=169

    I like how this video also notes controversial capabilities of radio reception also:
    https://www.gaia.com/article/oldest-conspiracies-proven-true-project-echelon (watch the first video from 30 to 33 seconds at least).

  4. My very first thing I ever built over some 50 years ago was an AM transmitter that went 100m easy very clear audio even though it used an old carbon telephone mike, used AC128 coil was 100turns on ferrite. Rod from old radio tuning cap was 365pf air cored it wasn’t small lol but did it ever work everyone would say it just sounded like a close radio station, then we discovered FM stereo, luckily there was an IC BA****? This made spy bugs a reality it was all built on top of a 9v battery, they were good cheap with right antenna it could go some considerable distance all in full stereo toowhen we tired of all that we ventured into pirate radio on 27MHz mainly USA and Australia it relied on a thing called Skip where signals bounced of ionosphere it would fade in and out but we all had loads of fun met new folks learned a lot most of us modified our Rigs to the USA Citizen Band We envied our Yank mates thier CB was 5Watts output, whereas in NZ it was legally sped at 1/2 Watt even so it all still worked when conditions were right it was almost like they weren’t in another country, we all had pirate names, like SawDoctor, Bones, Frogsticker of course mine was Silverdragon. To commemorate any contacts we would exchange QSL cards. Indeed I still have? A 100 page folder full of cards from all over the world I got a card from almost all states in USA. Often the Radio Inspectors would drive around looking for us Pirates tehe, I had a huge 27MHz Groundplane antenna on my roof, how hard could it be? As I got older I transitioned into HAM Radio but it wasn’t as much fun for some reason but there you have it.

    1. Here in the US many CBers don’t care about the 5W legal limit and run amplifiers running into thousands of watts (often without proper output filtering). No wonder you could hear them all the way into your country! (kidding, I understand about how skip works.)
      The FCC (US regulatory agency for RF) seems to have given up on tracking and prosecuting all but the absolute worst offenders, which can be a bit of a thorn in the side of hams and CBers alike. Never had any trouble myself, either as a ham or a CBer.
      I will say that I had more youthful fun with the CB radio as a 17 year old, but now in my 40s I enjoy ham radio much, much more.

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