As a Cub
Scout leader I was always looking for something a bit different for the
try beyond the standard fare suggested in the hand books.
A popular project from decades past was a
crystal radio. Working only off the
energy provided by the radio waves, it still seems magical to me but
command the same attention of the boys with today’s high tech toys? I would say it worked quite well.
So at the suggestion of some, I’m putting
this out via the wonders of the high tech internet of today so people
the high tech of years gone by.
assembled, the radio does a good job of picking up strong AM broadcast
here in the Chicago
suburbs. It is not very selective
meaning you will hear more than one station if there are multiple
stations in your area as there are in the Chicago
area. For the electrically inclined,
this radio does not use a tuning capacitor as that would raise the cost
what would be acceptable for a scout project. The
capacitance needed comes from the turn to turn
capacitance of the
coil and by using an antenna that is much shorter than the wave length
many ways to approach this project. In a
more traditional approach, building each part of the radio could be
done over a
series of den meetings. I had no
way to store all the parts so this project is designed to be assembled
boys in about one hour with parents help. To
do this, some of the parts need to be set up ahead of
time. The instructions in part 1 are made
non-electrically inclined co-leaders in mind on how to set this up for
a den meeting. Parts used are meant
to be readily
available. Part 2 is meant to be
out at the meeting as instructions for assembly by a Cub Scout and
assistant. I had these built at our
regular meeting room in a grade school which I think is lead lined as
gets no cell phone service. We could not
tell if the radios were working until the kids got them home. When they did not work I told them to bring
them to my house where most problems were caused by bad connections or
needed a little more sanding for the wiper to make contact. I also used a continuity tester to check the
wiring each scout made to ensure the radios would work when they got
1. Get the
PARTS for one
up as needed. I had a beveled edge cut on the board and
stained it. I used brass screws and
washers. I did this to make it look just
a bit classier than it normally would have looked.
I assembled all the parts below into plastic
bags to make a small kit for each scout. I bought extra diodes and ear
phones as they are obtained from surplus sellers and may have varying
inch PVC pipe cut to a length of 4 inches
X 7 X ¾ inch pine board
feet of 28 gauge ENAMELED copper wire, make sure it is enamel coated
bare copper. I got my wire from a local
motor repair shop. The owner was happy
to help scouts and gave me what was left on a spool which was more than
for radios for two dens.
ohm carbon resistor. This can be between
30,000 and 100,000 ohms. Resistors come
in various sizes which do not matter in this project, the photo shows a
size resistor. If you know a Ham Radio
Operator they might have boxes of these that you can get from them a
than from Radio Shack. If you find or
have a bunch of salvaged resistors, you can determine the total
reading the color code rings. The code
can be found at
large metal paper clip
feet of insulated hook up wire
ear phone, make sure this is a ceramic ear phone and NOT a magnetic
head phone or ear buds. Only the ceramic
ear phone has the high efficiency that can covert the weak radio signal
into something that can be heard.
1N34A signal diode. Make sure this is a
signal diode and not a
zener or power supply diode.
of this writing, 2008, you can get diodes and ceramic ear phones at….
can also find information on
wire. About 30-100 feet of insulated
wire. Length is not crucial as long as
it is over 30 feet. If you live far away
from big AM stations, go longer.
will also need a soldering iron and rosin core solder
grit sand paper
2. Make the
I did this
with the help of another adult but a scout could help instead.
the PVC into 4 inch sections.
one 1/16 inch pilot hole at each end of the coil for mounting screws. Use a template to do this so you can drill
pilot holes on the board in the right spot later.
a ¼ inch hole on the opposite side of the pilot holes.
This hole has to be big enough for a screw
driver blade to go through later when you mount the coil to the board.
one more pair of 1/16 inch holes at a point 90 degrees from the first
holes. This will be where you can pull
the coil wire through the PVC to secure it and pull the wire out of the
the PVC later.
slid the PVC over the end of a variable speed drill.
I strung about 12 inches of wire off a spool
through one of the holes mentioned in the step above.
While wearing gloves, I guided the wire into
a coil of about a 2 inch length while my partner slowly ran the drill. The overall size is not very crucial. Just try to keep the windings from crossing
over each other. You want a smooth coil
that the slider will more on smoothly. When
you have the coil wound. Pull the last end
through the other hole tightly to keep
the coil with a clear lacquer to keep it in place and set it aside to
your boards to 5 X 7 inch sections.
the template from drilling the pilot holes for the coils and the
pattern shown on the drawing and photo, drill two pilot holes for
coil and 5 pilot holes for the screws used to connect the wires. Make sure the holes are close enough the
connect the leads of the resistor and diodes later.
4. Make the
the paper clip
the paper clip into a ‘S’ shape
one end into a circle that will fit onto one of the washers
the other end back as seen on the photo
a partner, hold the clip on the washer.
the washer and the clip with the soldering iron and solder the washer
you have a hot soldering iron, solder 2 inch sections of hook up wire
wire end of the ear phone. This will
make hook up to the screws easier.
clip and hook up wires
the ground clip by attaching it to a segment of hook up wire about 4
with the insulation stripped off the ends. Coil it up for storage.
two hook up wire segments by cutting two, 2 inch segments and stripping
insulation off the ends.
I use an
antenna made of insulated hook up wire about 40 feet long.
I use insulated wire to avoid any problems or
poor performance caused by accidental contact with a metal object. Coil it up for storage.
coil to the board and using the sand paper, sand of the enamel on the
the coil where the slider will make contact. You
may need to sand a bit more after each radio is
assembled. Place it and the other parts in
a bag along
with the instructions below. The
assembly tool needed would be a screw driver appropriate for the type
parts and simple antenna, in 5 steps we’ll build a radio that will pick
several radio stations all without batteries.
The parts consist of
Hook up wire
Ground wire and alligator
Washers and screws
coil comes already mounted to the board. Holes
for screws are pre-drilled. The only tool
need is a screw driver.
When attaching wires,
Attach them UNDER the
and wrap CLOCKWISE
two pieces of hook up wire, washer, wiper, and screw as shown in the
drawing. Tighten the screw to hold the
parts in place but ensure the wiper can move back and forth on the coil.
a screw and washer on the right side of the coil and attach the wire on
right side of the coil to the screw. Also
attach the antenna wire and one end of the diode.
a screw and washer on the left side of the coil and attach the wire on
side of the coil along with the hook up wire going to the wiper and the
a screw and washer on the middle front part of the board and attach the
hook up wire going to the wiper, one end of the resistor, and one of
for the earphone.
a screw and washer on the right front part of the board and attach the
end of the resistor, the other wire for the earphone, and the other end
you’ll probably not be able to pick up much of anything indoors at
home you should be able to pick up most of the bigger AM radio stations. Stations from far away can be heard after
how to set up your crystal radio.
Under ANY circumstances
This radio into a
A good antenna and a good
ground are essential in getting
the best performance from this simple radio.
The antenna wire is
insulated so it can be run through a
closed window as long as you do not pinch it very hard.
Wire run out 2nd
floor window to nearby tree
Wire run out second floor
window to a tree branch or fence
post where no one will walk into it.
OK but not the best
Wire run along a first or
second floor bedroom or hallway
Wire run along a basement
Wire run along the basement
Wire run inside any metal
Make sure ground connection
is to clean bare metal.
Steel ground rod for your
house wiring, usually found below
your electric meter, have an adult connect this.
Cold water pipe
Sink faucet as long as you
have metal piping going to sink.
Outside of electric
conduit, have an adult connect this.
Steel I beam house support
OK but not the best
Metal Window frame
A longer ground wire (20ft)
just laid on the floor.
Ground wire wrapped around
metal drain pipe or water pipe.
How to work the radio
With the radio connected to
an antenna and good ground, and
wiper in the middle of the coil, you should hear one or more stations
same time. Try moving the wiper to
different positions on the coil. Different
stations should change in loudness as you move
If you hear nothing, then
make sure you have good
connections. Remember that this radio
works best with a good ground and antenna.
How it works
Radio stations convert
sounds into radio waves and send out
the waves everywhere. Radio waves travel across the crystal radio
the time. Radio waves make electricity flow between the antenna wire
ground wire. This electricity is connected to the crystal radio. The
radio uses a tuner to tune the electricity to receive just one station.
uses a detector to convert this radio wave electricity back to sound
electricity. It uses a sensitive earphone to convert the sound
sound you can hear.