11 March 2010

Radio crystal sets






The invention: The first primitive radio receivers, crystal sets led
to the development of the modern radio.
The people behind the invention:
H. H. Dunwoody (1842-1933), an American inventor
Sir John A. Fleming (1849-1945), a British scientist-inventor
Heinrich Rudolph Hertz (1857-1894), a German physicist
Guglielmo Marconi (1874-1937), an Italian engineer-inventor
James Clerk Maxwell (1831-1879), a Scottish physicist
Greenleaf W. Pickard (1877-1956), an American inventor
From Morse Code to Music
In the 1860’s, James Clerk Maxwell demonstrated that electricity
and light had electromagnetic and wave properties. The conceptualization
of electromagnetic waves led Maxwell to propose that
such waves, made by an electrical discharge, would eventually be
sent long distances through space and used for communication
purposes. Then, near the end of the nineteenth century, the technology
that produced and transmitted the needed Hertzian (or radio)
waves was devised by Heinrich Rudolph Hertz, Guglielmo Marconi
(inventor of the wireless telegraph), and many others. The resultant
radio broadcasts, however, were limited to the dots and
dashes of the Morse code.


Then, in 1901, H. H. Dunwoody and Greenleaf W. Pickard invented
the crystal set. Crystal sets were the first radio receivers
that made it possible to hear music and the many other types of
now-familiar radio programs. In addition, the simple construction
of the crystal set enabled countless amateur radio enthusiasts
to build “wireless receivers” (the name for early radios) and
to modify them. Although, except as curiosities, crystal sets were
long ago replaced by more effective radios, they are where it all
began.
Crystals, Diodes, Transistors, and Chips
Radio broadcasting works by means of electromagnetic radio
waves, which are low-energy cousins of light waves. All electromagnetic
waves have characteristic vibration frequencies and wavelengths.
This article will deal mostly with long radio waves of frequencies
from 550 to 1,600 kilocycles (kilohertz), which can be seen
on amplitude-modulation (AM) radio dials. Frequency-modulation
(FM), shortwave, and microwave radio transmission use higherenergy
radio frequencies.
The broadcasting of radio programs begins with the conversion
of sound to electrical impulses by means of microphones. Then, radio
transmitters turn the electrical impulses into radio waves that
are broadcast together with higher-energy carrier waves. The combined
waves travel at the speed of light to listeners. Listeners hear
radio programs by using radio receivers that pick up broadcast
waves through antenna wires and reverse the steps used in broadcasting.
This is done by converting those waves to electrical impulses
and then into sound waves. The two main types of radio
broadcasting are AM and FM, which allow the selection (modulation)
of the power (amplitude) or energy (frequency) of the broadcast
waves.
The crystal set radio receiver of Dunwoody and Pickard had
many shortcomings. These led to the major modifications that produced
modern radios. Crystal sets, however, began the radio industry
and fostered its development. Today, it is possible to purchase
somewhat modified forms of crystal sets, as curiosity items. All
crystal sets, original or modern versions, are crudeAMradio receivers
that are composed of four components: an antenna wire, a crystal
detector, a tuning circuit, and a headphone or loudspeaker.
Antenna wires (aerials) pick up radio waves broadcast by external
sources. Originally simple wires, today’s aerials are made to
work better by means of insulation and grounding. The crystal detector
of a crystal set is a mineral crystal that allows radio waves to
be selected (tuned). The original detectors were crystals of a leadsulfur
mineral, galena. Later, other minerals (such as silicon and carborundum)
were also found to work. The tuning circuit is composed
of 80 to 100 turns of insulated wire, wound on a 0.33-inch support. Some surprising supports used in homemade tuning circuits
include cardboard toilet-paper-roll centers and Quaker Oats
cereal boxes. When realism is desired in collector crystal sets, the
coil is usually connected to a wire probe selector called a “cat’s
whisker.” In some such crystal sets, a condenser (capacitor) and additional
components are used to extend the range of tunable signals.
Headphones convert chosen radio signals to sound waves that are
heard by only one listener. If desired, loudspeakers can be used to
enable a roomful of listeners to hear chosen programs.
An interesting characteristic of the crystal set is the fact that its
operation does not require an external power supply. Offsetting
this are its short reception range and a great difficulty in tuning or
maintaining tuned-in radio signals. The short range of these radio
receivers led to, among other things, the use of power supplies
(house current or batteries) in more sophisticated radios. Modern
solutions to tuning problems include using manufactured diode
vacuum tubes to replace crystal detectors, which are a kind of natural
diode. The first manufactured diodes, used in later crystal sets
and other radios, were invented by John Ambrose Fleming, a colleague
of Marconi’s. Other modifications of crystal sets that led to
more sophisticated modern radios include more powerful aerials,
better circuits, and vacuum tubes. Then came miniaturization,
which was made possible by the use of transistors and silicon chips.
Impact
The impact of the invention of crystal sets is almost incalculable,
since they began the modern radio industry. These early radio receivers
enabled countless radio enthusiasts to build radios, to receive radio
messages, and to become interested in developing radio communication
systems. Crystal sets can be viewed as having spawned all
the variant modern radios. These include boom boxes and other portable
radios; navigational radios used in ships and supersonic jet
airplanes; and the shortwave, microwave, and satellite networks
used in the various aspects of modern communication.
The later miniaturization of radios and the development of sophisticated
radio system components (for example, transistors
and silicon chips) set the stage for both television and computers.
Certainly, if one tried to assess the ultimate impact of crystal sets by
simply counting the number of modern radios in the United States,
one would find that few Americans more than ten years old own
fewer than two radios. Typically, one of these is run by house electric
current and the other is a portable set that is carried almost everywhere.

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