A crystal radio receiver , also called a crystal set , is a very simple radio receiver, popular in the early days of radio. It needs no battery or power source and runs on the power received from radio waves by a long outdoor wire antenna.
Overview
Simple crystal radios are often made with a few hand made parts, like an antenna wire, tuning coil of copper wire, crystal detector and earphones. Because crystal radios are passive radio receivers, they are technically distinct in many respects from ordinary radios containing active powered amplifiers. This is because they must receive and preserve as much electrical power as possible from the antenna and convert it to sound power whereas ordinary radios amplify the weak electrical energy "signal" from the radio wave. Today making and operating crystal radios is a popular hobby for many reasons, including:
- Historical and nostalgic significance
- The astonishing results one can get despite its utter simplicity
- The challenge of receiving weak distant signals without amplification
Crystal radios can be designed to receive almost any radio frequency band, but most are designed for the AM broadcast band. A few receive the 49-meter international short wave band, partly because the radio waves are stronger in those bands. The first crystal sets received wireless telegraphy signals broadcast by spark-gap transmitters at frequencies as low as 20 kHz and below. Although crystal radios are designed to detect AM, they can be made to detect FM broadcasts in the 100 MHz range by a technique called slope detection .
Groups of enthusiasts and a number of web sites are devoted to their construction. Regular contests are held comparing the performance of various designs with each other. Reportedly, modern diodes, ultra-thin litz wire inductors, and low loss capacitors yield performance far beyond that of traditional receiver designs.
How it works
A crystal radio receives audio broadcasts from AM radio stations. At each station sound is used to modulate the amplitude of a radio wave that is fed to a transmitting antenna. The radio waves from many transmitters simultaneously induce electric currents between the receiver antenna wire and ground. The receiver comprises a tuner circuit that selects the radio wavelength of the desired broadcast, followed by the crystal detector (such as a Cat's whisker detector or diode) that converts the radio wave back to the original audio waveform for reproduction typically by earphones.
History
Crystal radio was invented by a long, partly obscure chain of discoveries in the late 1800s that gradually evolved into more and more practical radio receivers in the early 1900s; and constitutes the origin of the field of electronics. The earliest practical use of crystal radio was to receive Morse code radio signals transmitted by early amateur radio experimenters using very powerful spark-gap transmitters. As electronics evolved, the ability to send voice signals by radio caused a technological explosion in the years around 1920 that evolved into today's radio broadcasting industry.
Early years
Early radio telegraphy used spark gap and arc transmitters as well as high-frequency alternators running at radio frequencies. At first a primitive detector called a Branley Coherer was used to indicate the presence (or absence) of a radio signal. However, these lacked the sensitivity to convert weak signals.
In the early 1900s, various researchers discovered that certain mineral cryatals, such as galena, could be used to detect radio signals. In 1901, Sir Jagadish Chandra Bose filed for a US patent for "A Device for Detecting Electrical Disturbances" that mentioned the use of a galena crystal; this was granted in 1904, #755840. However, his work, and the patent, went somewhat unnoticed in the western scientific world, as on August 30 , 1906 , Greenleaf Whittier Pickard filed a patent for a silicon crystal detector, which was granted on November 20 , 1906 . Pickard's detector was revolutionary in that he found that a fine pointed wire known as a "cat's whisker", in delicate contact with a mineral produced the best semiconductor effect. A crystal detector includes a crystal, a special thin wire that contacts the crystal and the stand that holds the components in place. The most common crystal used is a small piece of galena; pyrite was also often used, as it was a more easily adjusted and stable mineral, and quite sufficient for urban signal strengths. Several other minerals also performed well as detectors. Another benefit of crystals was that they could demodulate amplitude modulated signals. This mode was used in radiotelephones and to broadcast voice and music for a public audience. Crystal sets represented an inexpensive and technologically simple method of receiving these signals at a time when the embryonic radio broadcasting industry was beginning to grow.
In 1922 the (then named) U.S. Bureau of Standards released a publication entitled, Construction and Operation of a Simple Homemade Radio Receiving Outfit . This article showed how almost any family having a member handy with simple tools could make a radio and tune in to weather, crop prices, time, news and the opera. This design was significant in bringing radio to the general public. NBS followed that with more selective two-circuit version Construction and Operation of a Two-Circuit Radio Receiving Equipment With Crystal Detector that was published the same year and is still frequently built by enthusiasts today.
1920s and 1930s
In the beginning of the 20th century, radios were only for some people who considered it as a hobby. Radios were not accessible to the public, so they built their own radios by themselves with wires wrapped around baseball bats, boxes to form receivers, the transmitters were made from glass and iron, and the speakers they built were from newspapers wrapped in a cone shape.
Still, some historians consider the Autumn of 1920 to be the beginning of radio broadcasting for entertainment purposes. Pittsburgh, PA, station KDKA, owned by Westinghouse, received its license from the United States Department of Commerce just in time to broadcast the Harding-Cox presidential election returns. In addition to reporting on special events, broadcasts to farmers of crop price reports were an important public service, in the early days of radio.
In 1921, factory-made radios were very expensive. When compared to the dollar value of today, some would have cost around $2,000 USD . Since less affluent families could not afford to own one, newspapers and magazines carried articles on how to build a crystal radio with common household items. To minimize the cost, many of the plans suggested winding the tuning coil on empty pasteboard containers such as oatmeal boxes, which became a common foundation for homemade radios.
Non-electric amplification
- As gas lighting and kerosene lamps were widely used before the adoption of electric power, their flame was used for sound amplification. A ceramic cone with a pinhole on its tip was inserted in the middle of the flame, and an earphone unit was attached to the cone's open bottom and sealed air-tight. This acted like a little pump, modulating the fire by periodically sucking away the combustible mixture at negative half-wave, and injecting it back on positive.
- Air pump amplification was first used in pathephones, where a pump was driven by the same spring motor as a turntable. A needle-sized air pipe was placed near a sound membrane, which acted as an air valve and modulated the air flow, amplifying the sound. This method was easily converted for crystal radio, either in a dedicated device or just by putting a "pumped" pathephone's needle on an earpiece's membrane instead of a gramophone record.
Valveless amplifier
"Carbon amplifier" consisting of a carbon microphone and an electromagnetic earpiece sharing a common membrane and case. This was used in the telephone industry and in hearing aids nearly since the invention of both components and long before vacuum tubes. This could be readily bought or handcrafted from surplus telephone parts for use with a crystal radio. Unlike vacuum tubes, it could run with only a flashlight or car battery and had an almost infinite lifetime.
Cristadyne
In the early 1920s Russia, devastated by civil war, the young scientist Oleg Losev was experimenting with applying voltage biases to various kinds of crystals, with purpose to refine the reception. The result was astonishing - with a zincyte (zinc oxide) crystal he gained amplification. This was negative resistance phenomenon, decades before the tunnel
Crystal Lighting. We can hire or sell you Lighting and P.A. packages ...
Welcome to the Crystal (Lighting) web site. We can hire or sell you the special effects that will dazzle your audience. Through the use of intelligent, disco and theatrical lights ...
Crystal Lighting at LightingShowplace.com
Crystal lighting at the guaranteed lowest prices online. Largest selection of in-stock crystal lights to choose from with free shipping.
Crystal Lighting / Crystal Lights at Oberoi Brothers Lighting
Here at Lights UK we have a wide range of crystal lighting , including crystal chandeliers. Crystal lighting makes excellent decorative lighting. Modern ...
Crystal Lighting
©2002-2009 Crystal Lighting. All rights reserved.
Swarovski and Kolarz Crystal Lighting Systems
UK based suppliers of Swarovski crystal lighting, with contemporary and traditional lighting fixtures available. Also offers crystal panels and fibre optic and LED lighting
Crystal Lighting and Chandelier Crystal Designs Add Style to Any ...
Bring instant sparkle to any room with elegant crystal lighting. Kingdom Lighting USA brings you the finest chandelier crystal styles available.
Crystal Lighting
PDF Cutsheets. IES Data Files. REP List . CRYSTAL LIGHTING CORP. Contact US . CRYSTAL LIGHTING CORP.
Crystal Lighting
Asco Lights Ltd, Leestone Road, Sharston Industrial Estate, Manchester, M22 4RW Tel: 0845 2600 268 Fax: 0845 2600 268 E-mail: sales@ascolights.co.uk
Crystal Lighting | Crystal Chandeliers | Crystal Pendants | Crystal ...
We stock a huge range of Crystal Lighting products and Crystal Lighting fittings, with up to 35% off RRP! Free delivery on all home lighting orders over £100. Light My Home is the ...
Crystal Lighting | victorian reproduction lanterns, crystal ...
Over 70 years experience in period reproduction and contemporary lighting fittings. From Victorian style pendants, lanterns, wall lights and table lamps to stylish crystal ...