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  • Hi gang! I'm listening to my portable crystal radio. All the power comes from the radio waves.

  • Notice there's no ground connection. And the antenna is in here.

  • As you can see there's not a lot to it. There's a crystal earpiece for listening

  • to.

  • Here's the adjustable capacitor for tuning in a radio station.

  • Here's a diode.

  • And this is the coil that the capacitor resonates with.

  • But the trick is that this coil also acts as the antenna.

  • This type of antenna is called a loop antenna, for reasons you can probably guess.

  • Here's how I made it. I started with an extra large pizza box.

  • I could have just wrapped the coil around the outside of the box but I wanted it

  • protected. So I put it on the inside. That meant the coil needed some internal structure inside

  • the box. I decided to use the corners of the box's cover for that.

  • Start by making the corners of the box's lid like this.

  • The actual dimensions don't matter much, except that this length here needs to be

  • about one inch longer than the box is deep.

  • Then cut the corners off the lid.

  • You should now have two pieces from the front and two pieces still attached at the

  • back.

  • Next we need to make slots for this piece to go through the box.

  • First use one of the pieces to mark the where the slot should you go for all four corners.

  • Then cut them.

  • And then tape the pieces in place.

  • And there's the finish box.

  • Next we need to make the tuning capacitor.

  • We need two pieces of aluminum foil cut six inches by six inches each.

  • A piece of paper cut seven inches by nine inches.

  • A paper towel roll.

  • And some tape. It doesn't matter what kind.

  • Tape one of the pieces of aluminum foil to the paper towel roll near one end.

  • Tape the other piece of aluminum foil

  • on one end of the piece of paper.

  • Next, take the paper with the aluminum foil and wrap it around the tube.

  • Wrap it around tightly,

  • but not so tightly that you can't slide it back and forth.

  • Next, I'm going to make electrical contact with the aluminum foil for each of these pieces.

  • To do that I've got this wire, and I'll strip it bare for a long length.

  • And then

  • wrap it around like this

  • and twist it on.

  • And there we go. That's contact with one end.

  • Now repeat the same thing for this end right here.

  • And there we go. Two wires now attached

  • to the variable capacitor.

  • Finally, I cut a tab out of the top of the box for putting the capacitor on

  • when in use.

  • Next is to make the loop antenna coil. I'm using twenty six gauge (AWG) wire and doing

  • fourteen turns.

  • Twenty two gauge, eighteen gauge and so on will also work. Just make sure it's insulated.

  • As you can see the more turns you have, the harder it is to pull the wire. But doing

  • like I'm doing here works quite well.

  • Finally, I cut the wire, leaving long ends to work with.

  • And then secure the ends in place by putting them through holes one corner.

  • Next to connect it all together.

  • Here's the wiring diagram but I'll show you each connection as I make it.

  • First remove the insulation from the ends of the coil wires.

  • Open the capacitor to its fullest length. That's so that you know how much wire is needed

  • to reach inside the box.

  • Then connect one end of the coil to one of the capacitor wires. It doesn't

  • matter which one.

  • Then connect the other end of the coil to the other capacitor wire.

  • Then connect one wire to either of the places where you connected the coil

  • and capacitor wires together.

  • Next for the diode.

  • It has to be a germanium diode. In my case part number 1N34.

  • Find the end of the diode that doesn't have the stripe on it. Connect the other end

  • of that wire to that end of the diode.

  • Next, connect another wire to the end of the diode with the stripe on it.

  • The other end of that wire goes out the top of the box.

  • Connect another wire to the other place where you connected the coil and capacitor wires

  • together and run the other end out of the top of box.

  • Now you can close the box.

  • Lastly, the earpiece. For this circuit it has to be a crystal earphone, also called a

  • crystal earpiece. I'm using on I made myself by hot-gluing a hollow tube

  • to the opening of a piezoelectric buzzer.

  • Connect the wires of the earphone to the wires you just ran out of the top of the box

  • in the previous steps.

  • And you're ready to test.

  • To test it, start with the capacitor in some position and rotate the box. The flat side of

  • the box should be facing a radio station. If you don't know where one is, then keep

  • slowly rotating it.

  • If you don't find something, then readjust the capacitor and try again.

  • Nice and loud right there. It sounds like news.

  • I'll put it in the microphone.

  • Hopefully you heard that.

  • Loud and clear.

  • Well thanks for watching! Check out my youtube channel, rimstarorg, for more

  • videos like this. That includes one on how to make your own crystal earphone. One

  • with a bunch of crystal radio troubleshooting tips. And for variety,

  • one on how a rocket works to get from Earth to orbit using SpaceX's Falcon 9

  • as an example.

  • And don't forget to subscribe if you like these videos or give a thumbs-up or leave

  • a question or comment below.

  • See you in a bit!

Hi gang! I'm listening to my portable crystal radio. All the power comes from the radio waves.

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B2 capacitor coil wire diode antenna aluminum foil

Portable Crystal Radio using Loop Antenna and Pizza Box

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    Why Why posted on 2013/04/06
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