Explore the Airwaves with Weekend Projects

In just a few hours you can make a completely batteryless AM radio receiver with a range of around 25 miles. Built with a small assortment of components, some scrap wood, and a beverage bottle tightly wound with magnet wire, we call this project Bottle Radio. Similar to other “crystal radio” projects, the crystal in this build is contained inside a germanium diode, which rectifies incoming audio signal. The radio operates on the power from radio waves, and receives signal from a long wire antenna. When this signal enters the diode, it contains positive and negative peaks, however the diode, only allowing signal to pass in the forward direction, converts the alternating current of the signal into direct current. That current then vibrates a diaphragm inside a crystal earphone, allowing you to hear the radio without any visible power source!

If it sounds difficult, it’s not. In fact once you have your parts in hand, this project will only take a couple hours to assemble. Watch the video below to see how the entire circuit works, and we also provide some tips on the project page for extending the range of your receiver using a loop antenna and RF amplifier.

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7 Responses to Explore the Airwaves with Weekend Projects

Dave Bell on July 13th, 2012 at 2:01 pm said:

Excellent project! Crystal sets, classic or modernized are always a winner.
A couple of comments:

“As radio stations slowly move away from the AM band, the “window of opportunity” to experience this remarkable technology is dwindling.”
In many markets, AM radio is alive and well, and any exodus of stations is actually favorable to this kind of radio, as crowding is reduced.

And please! It’s siliCON, not siliCONE!
The latter is a non-carbon based lifeform, er, I mean hydrocarbon replacement.

A schematic would also be nice, for those who can (still) read one…

Dave

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craig on July 13th, 2012 at 7:16 pm said:

Having built many crystal radios myself, I found how well SOME amplified computer speakers work in place of the weak, quiet and often hard-to-obtain crystal earphone. I have a favorite hand-wound variometer crystal radio and amped speakers that I use for workshop listening. Even Dennis Miller can sound good on a warm mellow crystal set, ha de cha-cha.

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- Nick Normal on July 19th, 2012 at 10:34 am said:
  
  +1!
  
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Andy Pober on July 15th, 2012 at 1:18 pm said:

As a kid I remember many kits with these parts. One was for a “Rocket Radio” tuned by a an extendable nosecone on a shaft. Very Buck Rogers.

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Jon Adair on July 19th, 2012 at 3:20 pm said:

I’ve built a few different types (but none with a real crystal). I even have a reproduction Rocket Radio around. Unfortunately a really strong local AM station overwhelms most others.

You can homebrew different semiconductors instead of the diode – including the classic “Foxhole radio” with a blued or rusted razor blade and graphite pencil lead. It’s a bit harder to homebrew a speaker or earphone but it can be done.

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Rick Crammond on July 20th, 2012 at 5:19 pm said:

Crystal radios are fun!

For a real interesting time, hook up the audio output from the crystal radio to your computer sound in.

It works especially well with a Mac and the software Audio Hijack. The gain, pitch, reverb, etc. can be changed at will, and then a whole assortment of sounds become instantly available in real time.

See my Instructable, “Spooky Tesla Spirit Radio” at http://www.instructables.com/id/Spooky-Tesla-Spirit-Radio/
for more info on how to do that.

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