Bottle Radio

By Steve Hobley
Time Required: 3-4 hours

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Crystal radio technology has been around for many years. This “bottle radio” take on a crystal radio requires no power source, operates on the power from radio waves, and receives signal from a long wire antenna. As radio stations slowly move away from the AM band, the “window of opportunity” to experience this remarkable technology is dwindling. On that note, the closer you are to an AM station or transmitter, the more likely you are to hear distinct radio waves with this project.

The “crystal” in question is contained inside a germanium diode, and is used to rectify the radio signal so that our ears can hear it. Since this project has no power source, the signal can be quite weak – crystal earphones are a fun way to hear low-amp signal (due to their sensitivity), or, alternatively, you could hook up a 9V mini-amplifier.

For more information on this battery-less technology check out this Wikipedia article.

Steps

Step #1: Winding the coil.

NextPrev

Unsurprisingly, the first thing we'll need is a bottle. I'm using a brown glass bottle. Remove the label and rinse it clean.
Next, we need one of our three spools of magnet wire. Here we'll be using the red 30-gauge wire.
When winding a coil, it's intuitive to wind "hand over bottle," but this introduces a twist in the wire, something we don't want. A better way to wind a twist-less coil is to put the spool of wire on some kind of spindle and rotate the bottle slowly. Start by sticking down the free end with tape (start at the bottom of the bottle, leaving around 6" of lead wire for connecting later).
Be careful of the wire. You don't want it to "cross over" itself while winding. Try to keep a constant tension and apply tape as needed to save your position as you wind. You want to make the coils as smooth and closely packed as possible.
Once complete (using the whole spool) you should have something that looks like image 2 (leave about 8-10" of lead wire at the top, for connecting later). Next we will sandpaper the wire, but before that, apply fast drying sprayable lacquer or shellac (if available) to hold the wire in position. If you don't, you risk loosening the wire when you sandpaper the wire. The lacquer will hold it all together. Also, don't use too much, otherwise you risk waiting over an hour for it to dry.
The last step is to take a small piece of 150 grit sandpaper, and carefully sand off the red coating in a vertical line (image 3), then gently sand the ends of the wire to expose the copper.

Conclusion

There are actually many ways of making a crystal radio set; this is just one of them. If you can find a 365pF variable capacitor, you can try making a crystal radio like this one, reputed to be an excellent fixed-coil radio.

Steve Hobley

This week, I have been mostly working on...

I've been tinkering around with bits of technology since I was five years old. I used to take the telephone apart at home, just to see how it worked.

After a couple of years I could even put it back together again - and sometimes it would continue to work.

28 Responses to Bottle Radio

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Steve Hobley on July 23rd, 2012 at 1:26 pm said:

David makes very good points – you’ll need to use some judgement when selecting your coat hangers – mine were bare metal but I’ve seen the enameled ones. I remember being apprehensive about sanding the coil surface, but it turns out to be easier than it looks. Using a substantial gauge wire and sandpaper 150 grit+ has minimal risk, I’ve made dozens of coils over the years without too many issues.

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raymond on July 29th, 2012 at 11:27 am said:

can you give us a tutorial about that.?

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Nick Normal on January 29th, 2013 at 9:04 pm said:

Hi Brian,
The diode between E/D is a germanium diode – you can see it being installed in the video, here: http://youtu.be/9VqVaFMQd2o?t=5m34s

The diode rectifies the incoming signal, essentially turning the alternating signal into a direct signal, so yes it is necessary! Note that silicon diodes won’t work in place of the NTE109, but other germanium diodes can be used depending on your incoming signal. Feel free to experiment!

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Nick Normal on January 29th, 2013 at 9:06 pm said:

Hi Ebel,

Did you make your tube coil radio yet?

cheers, Nick

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wtrham1996 on March 23rd, 2013 at 7:19 am said:

I cannot access the RF amplifer circuit to built this project. I clicked on “here” and it would not open. Why? You need to fix the link.

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Lina Nawed on April 18th, 2013 at 2:37 am said:

I would also like to know how to build the RF amplifier, the link doesn’t work for me either. Please Help!

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gg91114 on July 8th, 2013 at 4:27 pm said:

Does the color of the type effect performance? I am using the green color after the red got extremely tangled and construction is still underway, Thanks.

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Robert Lominick on July 9th, 2013 at 2:41 pm said:

You can build a simple amp with a darlington transistor, two 150k resistors. Go to Techlib, here is the link: http://www.techlib.com/electronics/audioamps.html#class-a

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Qiang Jiabao on October 13th, 2013 at 5:53 am said:

Hi !Could anyone help me.I try to do this radio but it doesn’t work.

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- Qiang Jiabao on October 13th, 2013 at 5:57 am said:
  
  I think it’s antenna’s problem but the radio didn’t say how to do it.
  
  Reply ↓
maria alejandra on November 23rd, 2013 at 2:54 pm said:

i need help in doesnt work. i did everuthing as the video said, but still didnt work pleasee help

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- maria alejandra on November 23rd, 2013 at 3:17 pm said:
  
  I used a 28 awg cable could that be?
  help
  
  Reply ↓
binary options trading on November 29th, 2013 at 2:48 pm said:

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Glass Scratch Removal Kit on December 23rd, 2013 at 5:29 am said:

This post is truly inspiring. I like your post and everything you share with us is current and very informative, I want to bookmark the page so I can return here from you that you have done a fantastic job..

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Jan on May 27th, 2014 at 1:10 am said:

Im making this at the moment, one question.

How many twists with magnet wire do you need around the bottle?

Answer a.s.a.p. please.

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- Pjr McCarty on May 27th, 2014 at 10:07 pm said:
  
  Use all the wire on the spool – the kind they recommend. Fill the whole space of the fat end of the bottle.
  
  Reply ↓
James on June 5th, 2014 at 10:27 am said:

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jim on July 4th, 2014 at 12:02 pm said:

Does this radio have FM and AM?

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travbm on March 22nd, 2018 at 8:51 am said:

Instead of a resistor I found the 300mh side of a transformer drove my crystal ear piece louder. I think any high inductor up to 1 henry should work down to 1300 uh.

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Sogou.com on August 22nd, 2019 at 7:41 pm said:

This site was… how do you say it? Relevant!! Finally I have found something which helped me.
Thanks!

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