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No project kit is complete without a crystal radio
circuit. Most people in electronics have experimented
with this oldest of all radio circuits. Before the days of
vacuum tubes or transistors, people used crystal
circuit sets to pick up radio signals.
The signals from a crystal radio are weak, so you
must use an earphone to pick up the sounds. Your
earphone will reproduce these sounds well because
it is a ceramic type and requires very little current for
operation.
A good antenna and earth ground connection are
necessary for receiving distant stations, but you can
hear local stations using almost anything as an
antenna. A long piece of wire (like the green wire in
your kit) makes an adequate antenna in most cases.
Earth ground means just that; you connect the wire to
the ground. One easy way to do this is to connect a
wire to a metal cold water pipe. If you can’t do that,
you can drive a metal stake into the ground and
connect the wire to the stake.
Build the circuit according to the wiring sequence to
use your crystal diode radio. Two antenna
connections are provided on the radio circuit in your
kit, but don’t use them both at the same time. Try
each connection and use the one that results in the
best reception. Short antennas, 50 feet or less, work
best on terminal 95. Longer antennas work best on
terminal 97.
The part of the radio circuit that includes the antenna
coil and the tuning capacitor is called the tank circuit.
When a coil and the tuning capacitor are connected
in parallel, the circuit resonates only at one
frequency. So the circuit picks up only the frequency
that causes the tank circuit to resonate. The tuning
capacitor changes its capacitance as you rotate it.
When the capacitance changes, the resonating
frequency for the circuit changes. Thus, you can tune
in various stations by rotating the tuning capacitor.
Without this selectivity, you might hear several
stations mixed together (or only a lot of noise).
The signals received by the tank circuit are high-
frequency RF (radio frequency) signals. At a
broadcast station, sound signals are used to control
the amplitude (strength) of the RF signals - that is,
the height of the RF wave varies as the sound varies.
The diode and the 0.001
μ
F capacitor in this circuit
detect the changes in the RF amplitude and convert
it back to audio signals. This converting of amplitude
modulation into audio signals is called detection or
demodulation.
Notes:
EXPERIMENT #110: CRYSTAL SET RADIO (SIMPLE-DIODE RADIO)
Schematic
Wiring Sequence:
o
6-12-96
o
7-98-126
o
8-11-90-100-EARPHONE
o
89-99-125-EARPHONE
o
95-ANT or (97-ANT)
Содержание EP-130
Страница 11: ... 11 I ENTERTAINMENT CIRCUITS ...
Страница 26: ... 26 II BASIC SEMICONDUCTOR AND COMPONENTS CIRCUITS ...
Страница 36: ... 36 III LED DIGITAL DISPLAY CIRCUITS ...
Страница 41: ... 41 IV A TOUR THROUGH DIGITAL CIRCUITS ...
Страница 49: ... 49 V MORE ADVENTURES WITH DIGITAL CIRCUITS ...
Страница 64: ... 64 VI THE WORLD OF TRANSISTOR TRANSISTOR LOGIC ...
Страница 77: ... 77 VII APPLICATION CIRCUITS BASED ON THE OSCILLATOR ...
Страница 88: ... 88 VIII BASIC OPERATIONAL AMPLIFIER CIRCUITS ...
Страница 116: ... 116 IX MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS ...
Страница 129: ... 129 X COMMUNICATION CIRCUITS ...
Страница 136: ... 136 XI TESTING AND MEASURING CIRCUITS ...