Scientific Explorer Crystal Radio User manual

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You will also need the following things:
- pencil
- 4 thick books
- scissors or wire cutters
- magnifuing glass
- small screwdriver
WARNING:
This radio works without any electrical source. It must not be
connected to any electrical appliances or to an electric outlet.
Beware ofsharp points and rough edges.
rubber fiands

BTIILDING THE RADIO
Getting Started
A. Listen to the Earphone
BgF* putting the crystal radio together, you should examine two
of its parts, the earphone andthe ttiode.
lhe _earplone is one of the most important parts of your crystal ra_
dio. It is the earphone that changes itectricil impulses into"sound.
Any small electrical impulse will make the earphone click.
Many common things contain a tiny electric charge.
lut tle.earphone to your ear. Hold one bare wire end in your hand.
louch the other bare wir_e end to things around the hous6: a water
faucet, a metal window frame, or a ridiator.
WARNING:
Do not touch the wire to a wall socket, or to a lamp outlet, or
to anything that carries electricity.
B. The Crystal Diode
The heart gf your crystal radio, the part that contains the crystal, is
the diode. Be very-carefu! when you open the package that"con-
tFms your crystal diode! Diodes are made of glass and can break.
A diode is an electrical device that lets current pass only one way.
The reason that this is important is a complicatld or.. io, *itt
learn more about it later, in the section "ail"d "How Radio works,,.
Jf you have a magniffing glass, take a close look at the diode with
it. Inside the glass qbe-ia a tiny speck, a crystal of germanir-, or.
of the rarest metals in the world. Pressing against ifis ve.y hn"
wire. Can you see the crystal and the wirif (See Fig. 1)- '

Building the Radio
A. Prepare the Tirning Coil
1. The flrst step
coil. Start with
end of the wire.
2. Slide a rubber band over
one end ofyour coil tube.
Slide it down about ll2 in.
from the end of the tube.
(Fig.2)
B. Wind the Coil
in building the crystal radio is winding the tuning
the spool of wire. Take the tape offit, and find the
Fig.2
coil tube
Note: Adult help is advisablefor this task. Winding
the coil must be done very carefully and precisely, or yoar
radio will not work. Fig" J
1. Slip the spool of wire onto a
pencil. Rest the two ends of the
pencil on two thick books. Then
put two more books on top of
the pencils to hold them in place.
The spool can now turn freely on
the pencil. (Fig. 3)
2. Hold the end of the coil tube loosely in one hand, with your
thumb over the coil wire.
Now turn the coil tube with vour
other hand. Keep your thumb resting ttg' 4
on top of the wire, guiding the wire so
that it lies smooth and flat on the coil
tube. The wire must be wound so that it
is only one layer thick, with the wires
lying snugly side by side. The wires
should touch, but they should never
cross or overlap one another. (Fig. 4)
3. When you come to the end of the wire, finish up so that the wire
at the beginning of the coil and the wire at the end of the coil are on
the same side of the
F--/ rubberband

Fig.5
coil tube. Be sure you
have at least 3 inches
sticking out over the end
of the tube. (Fig. 5)
4. Slip another rubber
band over the tube and
wire to hold the end of
the wire in place. Make
sure your coils are neat and tight, and put the tuning coil aside.
C. Prepare the Base and Insert the CoiI
1. Place the plastic base face down, so that you don't see the printed let-
ters and words. Bend up the square back panel and bend in the two tabs.
2. Now bend up the two side panels. If there are circles of plastic in the
side panels, just push them out and throw them away.
3. Bend in the tabs on the side panels. Push them into the slits in the tabs
of the back panel. Make sure that the tabs lock securely in place. Don't
bend the front panel up yet.
4. Slip one end of the coil into one side of the base. Slip the other end
into the other side of the base.
5. Turn the coil so that the ends of the coil
wire are next to Hole D on one side of the
base and Hole B on the other. (Fig. 6)
Slip one wire through Hole B. Wind this
end around and through Hote B twice and
cut it off.
6. Slip the other wire through Hole D on the other side of the base. But
DON'T cut it off.
7. Your coil wire is covered with a film of thin, clear plastic insulating
material. Electricity cannot get through it. You have to clean this film off
the end of the coil wire that goes through HoIe D. Here's how:
A. Fold your piece of sandpaper, sand side in.
B. Put about 1 inch of the end of the coil
wire in Hole D into the folded sandpaper.
C. Squeeze the sandpaper and pull the end of the wire out
of the fold. Do this at least 10 times. Keep turning the wire.
Sand off the insulation all the way around. Save your
sandpper. You're going to use it again later.
__-_--/ rubber bands
7 ...--3 in. [?.s cm]
Fig. ri

D. Prepare the Earphone, the Diode, and the Connecting Wires
1. Unwind the 2 wires that are twisted together on your earphone, so
that each wire end is approximately 6 in. long. Tie a simple knot in
the wire so that the wire does not unwind any more. tsig.7
2. Make a small loop at the end of each diode
wire by bending the wire around the lead of a
pencil. (Fig. 7) The loops should be able to slip
over the end of one of the bolts supplied with
your kit.
3. Make a smallloop at one end of each connecting wire, the same
way you did with the diode.
E. Put the Earphone and lirning Rod onto the Base
1. Put one earphone wire into Hole D and out again through
Hole C.
2.Do the same with the other earphone wire on the other side of the
base. Put it in Hole B and out HoleA.
3. Make a smallloop at the end of each earphone wire around the
lead of a pencil.
4. Push the tuning rod into Hole 1. Push the rod in a little way and
slip the tuning ball onto it. Then push the rod all the way through
until the rod goes through Hole 2.
5. Turn the tuning rod so that the eye lines up with Hole 4. Your
radio should look like the drawings in Fig.8a & b.
Fig.8o
I*ft side Fig" sb Right side

F. Make Connections
Now you arcready to make connections.
1. Put the end of one connecting wire without the loop in through
Hole D and out again through Hole C.
2.Prepare a bolt by slipping a washer onto it. Then slip the loops of
the following wires onto the bolt:
-the connecting wire
-the nearest earphone wire
-the coil wire
3. Slip on the second washer, and put the bolt into Hole 5.
All this stuff can get confusing. Work slowly and carefully.
You'll get it right!
4. Hold the bolt tightly against the base. With your other hand,
put a nut onto the bolt and screw it on loosely. This is the ground
("earth") connection Check to make sure that all wires are clamped
between the two washers.
5. Thread the second connecting wire in through HoIe B and out
again through llole A. Slip a washer on another bolt. Then slip on
the loops of:
- the other connecting wire
-a diode wire
6. Slip on the second washer and put the bolt through the eye of the
tuqing rod and into Hole 4. Put on a nut and screw it on loosel)z as
before. This is your antenna connection.
7. Put a washer on another bolt, and slip on the loops of:
-the diode wire
-the remaining earphone wire
Put on a second washer. Push the bolt into Hole 3, and screw on the
nut.
r

8. Now tighten all your connections by screwing on the nuts
tightly as possible. Your drawings should look like the ones
Fig 9a & b.
Fig. $a
I*ft side Fig. sb
fright side
llole 5: a connecting wire
an earphone wire
Ilole 1: the tuning rod
Ilole 3: a diode wire
an earphone wire
Hole 4: the eye of the tuning rod
a connecting wire
a diode wire
G. CheckYour Connections and Close Up the Base
1. Check your connections:
Left Side:
Right Side:
llole 2: the straight end of the tuning rod
Remember, all connections have to be made correctly on bare
and securely tightened or the radio will not work.
2. Close the base. Fold the front panel towards the coil and slide the
tabs on each side into the slots near Holes D and B.
H. Sand the Tuning Coil
The tuning ball must make contact with bare wire on the tuning coil.
But your coil wire is still covered with a clear plastic coating. The
entire length of the coil under the rod must have the insulation sanded
off. Here's how to do it:
1. Run the tuning ball back and forth a couple of times so it makes
a light mark along the top of the coil. Then turn the coil tube just a
little so that the mark moves out from under the rod.
earphone urire
earphone wire
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":,'2tr:l:i*

2. Sand gently along the mark until the insulation there is removed.
Then roll the tube back so that the sanded area is under the tuning rod
again.
Remember, if the ball doesn't make contact with bare wire, your
radio won't work.
Your crystal radio is now ready!
I. Listen to the Radio
Take your radio to a cold water faucet. Touch the faucet with a con-
necting wire, and hold the bare end of the other wire in your hand.
(To make it easier, attach the bare part of the f,rst wire to the tap with
a rubber band).
Now put the earphone in your ear. Start moving the tuning ball
slowly until you pick up one or more stations.
The sound will not be loud. A crystal radio does not have the power
that a regular radio has. It lacks an amplifier. But if the reception in
your area is good, you should be able to pick up more than one sta-
tion.
EXPERIMENTS WITH YOUR RADIO
1. Experimenting with Different Antennas
A crystal radio works well only if you have a good antenna (aerial)
to receive the radio waves. The farther you live from a radio station,
the better the antenna must be. A cold water tap makes a good an-
tenna. This is why you attached one of the wires to the water faucet.
You used the faucet as an antenna.
Now try other things. Take the wires offthe faucet. Touch the wire
to different items: a drainpipe, a door, a wall, awater pipe, a metal
window frame, andawooden table. DO NOT TOUCH ELECTRI-
CAL WALL OUTLETS OR LAMP SOCKETS. DO NOT TOUCH
ANYTHING THAT CARRIES ELECTRICITY
Outside you might try metal railings, a tree, a car antenna, a concrete
wall, metal flagpoles. Remember: make sure that when you touch
something with the wire, you hold the other wire in your hand.
Listen each time. Which items make good antennas?
-Try other things around the house. What material gives you
the best results? Wood? Plastic? Glass? Metal?
- What size antenna gives you best results: something big,
something long or something small?

2. Experimenting with Different Grounds
You can improve the reception of your crystal radio even more by
connecting it to a ground (earth)-any piece of metal that leads to the
earth. The ground (earth) for a crystal radio acts just like another
antenna (aerial). A water pipe or a radiator will make a good ground.
As before, remember to hold the bare end of the other wire in your
hand.
Try combining different antennas and grounds. Do you get differ-
ent stations? Try switching the antenna and the ground wires to see
which brings in the louder sound.
3. Identifying Stations
By now you should have tried several different combinations of
antennas (aerials) and grounds (earths). Now choose a good location,
and try to identiff the different stations you can pick up. There are
two ways to do this:
l. Listen until the station announcer identifies the station.
2.Try to get the same station on a regular portable radio.
4. Identifying Stations Using Different Antennas
Try identifying different stations by connecting your radio to differ-
ent antenna combinations. Do you pick up the same stations that you
did before? Are all stations you pick up ones that you can identi$z?
Crystal radios are peculiar devices. Sometimes you may pick up very
distant stations, even broadcasts from another country!
5. Keeping a Record of Stations
You may want to keep a record-called a log-of the different stations
that you hear. In your log you should note the date, the time of day,
the call letters of the station, and the city where the station is located.
You might also want to note what combination of antenna (aerial)
and ground (earth) you were using, and the approximate position of
the tuning ball on the turning coil. Use the scale on the base for easy
identification.
6. Trying the Radio at Night
Listen to your crystal radio several hours after dark. You may find
that you receive different stations, especially ones that are far away.
HOW RADIO WORI(S
By now, you may be interested in knowing something about how
your radio works. Let's start by taking a look at the radio station
where the whole process starts.