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!