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.