We’re going retro this month to bring you this tutorial on how to make a radio.
This project and all Geek Pack Hack activities must be undertaken with a suitable adult completing their own risk assessment and supervising their children at all times.
We live in an age where digital electronics make it possible to stream live broadcasts from anywhere in the world. And yet it still seems amazing that a simple electronic circuit can grab radio waves right out of the air– no computer needed.
Even more amazingly, the basic AM “crystal radio” that we describe here doesn’t even need a battery to work! We do add a battery-powered amplifier to make it easier to hear, but people have been making similar non-powered crystal radios for decades.
As our friend recently described it, it’s like you can scrape the big record player in the sky.
Do be aware that the strength of AM signals is different in different locations. Various types of electromagnetic radiation can also interfere with your AM receiver. Our radio was able to pick up one station clearly and sometimes a second station very faintly, depending on our location.
You’ll have to experiment with setting up your radio so that it works well.
As with most of our projects, kids can have a lot of fun participating, but they’ll need the help of an adult.
Before getting started, if you want a crash course in electricity basics, check out our post on electrical current, resistance, and voltage.
If you aren’t already familiar with breadboards, might want to check out this post on how to use a breadboard.
We’ll explain the parts we used, and then we’ll give you step-by-step instructions for how to make a radio.
You can check out our video tutorial here and subscribe to our YouTube channel to keep up with new projects.
We explain everything below as well (but you have to watch if you want to see what we heard when we tuned in!)
Radio Waves Facts
Radio waves are electromagnetic waves just like visible light, but they have a longer wavelength.
Sound can be sent from a radio transmitter to a receiver as an electromagnetic radio wave with a changing shape.
AM waves have longer wavelengths than FM waves.
There are also a variety of other technologies that involve radio waves. Some examples include GPS, Wi-Fi, Bluetooth, and cell phones.
Many objects in outer space actually emit radio waves as well, which can be detected and studied to learn about the universe.
How is Radio Transmitted?
Since there are lots of radio stations, we need some way to be able to tune in to just the station we want to listen to.
Every AM radio station transmits a signal by combining the input sound waveform with a carrier wave that has a specific wavelength.
An AM radio has to tune in and process this combined signal by using a decoder to get the input sound we want to listen to.
How Does a Radio Receiver Work?
The standard AM crystal radio is a circuit with an antenna connected to an inductor and a capacitor.
The inductor in combination with the capacitor can be tuned to different radio stations.
To decode the signal, AM crystal radios commonly use a germanium diode.
In the most simple crystal radios, you could connect a sensitive earpiece directly to the diode without any battery or other power source.
The sound from an unpowered crystal radio is very faint. It’s best listened to at night in a very quiet room!
To make it easier to hear, we connected the output from our crystal radio circuit to an audio amplifier.
And here’s what our AM crystal radio looked like.
Supplies to Make a Radio
9-volt battery connector (or just twist copper wire around the battery terminals)
18 AWG Enameled Copper Wire (“Magnet Wire”)
47 kΩ resistor
Electrolytic capacitors (0.1 uF and 220 uF)
Ceramic capacitors (10 nF, 47 pF, and two 680 pF capacitors)
Steps to Make a Radio
Step 1: Make the inductor
You can see the inductor in the above photo of our crystal radio– we’re holding it at the top of the image.
We created our inductor by winding enameled wire around a ferrite rod. By slowly sliding the ferrite rod in and out of the coil of wire, we can change the inductance of the circuit and tune the radio.
Our ferrite rod was 10 mm in diameter and 140 mm long.
First, cut a piece of paper so that it is the same width as the ferrite rod.
Loosely wrap the paper around the rod.
Tape the edge of the paper so that the rod can smoothly slide in and out of the paper.
Gently wind the enameled wire around the paper-covered rod to complete 35 turns. Leave enough wire at the ends so that you can later insert them into the breadboard.
Tape the coiled enameled wire to the paper.
Make sure that you can still slide the rod in and out of the coil
Step 2: Prepare your antenna and ground wires
Pull apart to separate the two insulated halves of the speaker wire.
Our ground and antenna wires were each 20 feet long.
Step 3: Wire up the circuit on the breadboard
See the wiring diagram below.
Grab all the pieces and start building the circuit!
It’s best to connect your battery after the rest of the circuit is complete.
We build this circuit using an earpiece rather than a speaker.
Step 4: Test out your radio!
It is very important that your crystal radio be connected to a good ground,
We stripped some of the insulation off of the end of the ground speaker wire and taped the internal copper wire to a cold water pipe. That worked quite well.
Lay out the antenna wire as straight as possible to extend the full 20 feet.
You can tune the radio by SLOWLY moving the ferrite rod in and out of the inductor coil.
If you enjoyed this project or have questions, please let us know!
We’d love to hear from others who have experimented with crystal radios.
Are there other projects you’d like us to build? Please leave us a comment!
Check out all of our cool engineering projects.
We also have a helpful basic electronics page that teaches skills such as how to use a breadboard and multimeter.