THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
■ BY LOUIS E. FRENZEL W5LEF
BUILDING A CRYSTAL RADIO
Really? Is This A Sane Thing To Do?
Who in their right mind would want to build a crystal radio (or crystal set as
it is sometimes called)? A crystal radio is the absolutely simplest radio there
is and is, in fact, the very first communications receiver. It derives its name
from the detector or diode used in detecting the radio signal. The original
diode was a piece of crystal called galena. When you made contact with it by
way of a small wire probe, you created a diode in which current would easily
flow through it in one direction and not flow in the other direction. This
crystal acted as a diode that performed rectification. Rectification is the
process of converting AC to DC, and for detection or demodulating AM radio
signals. Today, the crystal is a semiconductor diode made of the
semiconductor material germanium.
With a crystal diode, a tuned circuit, and an
earphone, you can make a radio that receives AM
(amplitude modulation) radio stations. The big question
remains, why do that? In today’s high tech world of
iPhones, satellite TV, MP3 players, and the Internet, why
revert to such an anachronism? Who listens to AM radio
Some good reasons to build a crystal radio are, first,
as a learning experience. If this is your very first electronic
construction project, it is a good one. It uses very few
components and they are very easy to connect. Second, it
■ FIGURE 1. Schematic
of the crystal radio.
is a good educational project. You learn about resonant
circuits, diode rectification, and soldering.
As for who listens to AM radio, you would be
surprised. If you listen to the radio for music, then you
probably listen mostly to FM. But millions still listen to AM
for news, weather, traffic, and general talk radio shows.
You can still hear lots of music on AM, as well. There are
roughly 5,000 AM radio stations around the country in
even the smallest of towns. As old as it is, AM radio is not
going away anytime soon.
I built my first AM radio decades ago. It was, in fact,
my first actual electronic construction project. And it really
worked. I credit that experience to putting me on the path
to a long career in radio and electronics. Recently, I had
the urge to build a crystal radio again. Mainly just to see if
I could and what I could hear. This project was an attempt
to recapture those simpler days of radio and electronics. If
you have never built a crystal radio, you may want to give
it a try.
HOW IT WORKS
Figure 1 shows the schematic diagram of a basic
crystal radio. An inductor or coil (L) is connected to a
variable tuning capacitor (C), and those are connected to
a diode in series with an earphone. An antenna is
connected to one end of the coil and a ground is