Elenco Electronics EP-130 - Crystal Set Radio

-
133
-
The crystal radio is one of the oldest and simplest
radio circuits, which most
p
eo
p
le in electronics have
experimented with. In the days before vacuum tubes
or transistors, people used crystal circuit sets to pick
u
p radio si
g
nals.
Since the crystal radio si
g
nals are very weak, you’ll
u
se a ceram
i
c type earp
h
one to p
i
c
k
up t
h
e soun
d
s
.
These ear
p
hones re
p
roduce these sounds wel
l
because it is and re
q
uires little current
.
N
ecessary
f
or receiving distant stations is a goo
d
a
ntenna and earth
g
round connection is, but you ca
n
hear local stations using almost anything as an
a
ntenna. A lon
g
piece of wire (like the
g
reen wire in
your kit) makes an acceptable antenna in most cases
.
When “earth ground” is re
f
erenced it means just that
;
you connect the wire to the ground. You can eas
y
make an earth
g
round connection by connectin
g
a
wire to a metal cold water pipe. I
f
you can also drive
a
metal stake into the ground and connect the wire t
o
th
e
s
t
a
k
e
.
C
onstruct the circuit accordin
g
to the wirin
g
sequenc
e
to use your crysta
l
di
o
d
e ra
di
o.
Th
e c
i
rcu
i
t
h
as tw
o
a
ntenna connections for either short or long antennas
,
but onl
y
use one at time. Connect short antennas, 5
0
f
eet or less on terminal 95 and longer antennas on
terminal 97. Try out each connection and use the on
e
t
h
at resu
l
ts
i
n t
h
e
b
est recept
i
on.
Tank circuit is the part o
f
the radio circuit that includes
t
h
e antenna co
il
an
d
t
h
e tun
i
ng capac
i
tor
i
s ca
ll
e
d
.
Wh
en a co
il
an
d
t
h
e tun
i
ng capac
i
tor are connecte
d
in parallel, the circuit resonates onl
y
at one
f
requenc
y.
S
o the circuit picks up only the frequency tha
t
g
enerates the tank circuit to resonate. The tunin
g
capac
i
tor a
l
ters
i
ts capac
i
tance as you rotate
i
t.
Wh
e
n
the capacitance changes the resonating
f
requency o
f
t
h
e c
i
rcu
i
t c
h
an
g
es.
Th
us, you can tune
i
n var
i
ou
s
s
tat
i
ons
b
y rotat
i
ng t
h
e tun
i
ng capac
i
tor.
Wi
t
h
out t
his
s
e
l
ect
i
v
i
ty, you m
igh
t
h
ear severa
l
stat
i
ons m
i
xe
d
together
(
or only a lot of noise
).
The tank circuit receives hi
g
h-frequency RF (radio
frequency
)
signals. The broadcast station uses soun
d
s
ignals to control the amplitude (strength) of the RF
s
i
g
nals - that is, the hei
g
ht of the RF wave varies a
s
t
h
e soun
d
var
i
es.
Th
e
di
o
d
e an
d
t
h
e 0.00
1
μ
F
c
apacitor detect the changes in the RF amplitude an
d
c
onvert it back to audio signals. The conversion o
f
a
mp
li
tu
d
e mo
d
u
l
at
i
on s
ig
na
l
i
nto au
di
o s
ig
na
l
i
s ca
ll
e
d
d
etect
i
on or
d
emo
d
u
l
at
i
on.
No
t
es
:
EXPERIMENT #112:
C
RY
S
TAL
S
ET RADI
O
S
chematic
Wiring
S
equence:

6
-
12
-
96

7-
98
-12
6

8
-11-
90
-1
00
-EARPH
O
NE

89
-
99
-12
5
-EARPH
O
NE

95-ANT or (97-ANT)