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The crystal radio receiver (also known as a '''crystal set''') is a very simple kind of Radio Receiver . It needs no Battery or power source except the power received from Radio Waves by a long outdoor wire Antenna . INTRODUCTION 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 from ordinary radios containing active powered amplifiers in many respects. 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:
, ultra-thin Litz Wire Inductor s, and low loss Capacitor s yield performance far beyond that of the original Receivers . HOW IT WORKS (SIMPLE VERSION) A crystal radio receives programs Broadcast from Radio Stations . Radio stations convert Sound into Radio Waves and send out the waves everywhere. Radio waves travel across the crystal radio Antenna all the time. Radio waves make radio wave Electricity flow between the antenna wire and the Ground wire. This electricity is connected to the crystal radio. The crystal radio uses a tuner to Tune the electricity to receive just one station. Then it uses a Crystal Detector to convert this radio wave electricity back to sound electricity. It uses an Earphone to convert the sound electricity to sound you can hear. 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 dot and dash Coded radio signals transmitted by early Amateur Radio experimenters using very powerful Spark-gap Transmitter s. 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 . Around 1906, Researcher s discovered that certain Metallic Mineral s, such as Galena , could be used to detect signals. These devices were called ' Crystal Detectors '. Greenleaf Whittier Pickard on August 30 , 1906 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. Several other Mineral s also performed well as detectors. Another benefit of crystals was that they could Demodulate Amplitude Modulated signals. This mode was used in Radiotelephone s 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 it became a best seller. More than any other system, the design contain therein was responsible for bringing radio to the general public. 1920s and 1930s While there were a number of earlier experiments with radio broadcasts to the general public, some Historian s 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 U.S. 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. Many of them cost more than $2,000 USD (in year 2005 equivalent dollars), and less affluent families could not afford to have one. Newspaper s and Magazine s in many countries urged Reader s interested in radio to acquire one of the inexpensive crystal sets or build their own. To minimize the cost, many of the plans suggested winding the Tuning Coil on an empty cylindrical Oatmeal box. For years afterwards, home Experimenter s used oatmeal boxes as coil forms for homemade radios. Even the crystal itself could be made by mixing powdered Sulfur into molten lead to form the Lead Sulfide "crystal". The crystal radio did not require Batteries , but it did require the user to purchase a commercially made set of Headphone s (or telephone receivers as they were called in those days), since that accessory was not suitable for home construction. Non-electric amplification
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 Aid s 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, young scientist Oleg Losev was experimenting with applying voltage Bias es 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 Diode . After the first experiments, he built regenerative and Superheterodyne receivers, and even transmitters. However, this discovery was not supported by authorities and soon forgotten and no device was produced in mass quantity beyond a few examples for research. This was partly due to the low education and overall ignorance of leadership, and partly due to the Totalitarian nature of the USSR regime. The USSR opposed freedom of information, and registered all radio receivers until 1962 , Typewriter s and Copy Machine s until its demise, and the rule is not formally denounced yet. Crystadine was produced in primitive conditions; it can be made in a rural forge - unlike Vacuum Tube s and modern semiconductor devices. It is an unwanted discovery to the authorities, and was consigned to obscurity. Oleg Losev died 1943 in besieged Leningrad , abandoned and nearly forgotten. 1940s When Allied troops were halted near Anzio, Italy during the spring of 1944, personal Portable Radio s were strictly prohibited, as the Germans had Radio Detecting Equipment that could detect the Local Oscillator signal of Superheterodyne receivers. Some resourceful GIs found that a crude crystal set could be made from a coil made of salvaged wire, a rusty Razor Blade and a Pencil Lead for a Diode . By lightly touching the pencil lead to spots of blue on the blade, or to spots of rust, they formed what is called a point contact Diode and the Rectified signal could be heard on headphones or crystal ear pieces. The idea spread across the Beachhead , to other parts of the War , and to popular Civilian Culture . The sets were dubbed "foxhole receivers" by the Popular Press , and they became part of the Folklore of World War II . In some Nazi occupied countries there were widespread confiscations of radio sets from the civilian population. This led to particularly determined listeners building their own "clandestine receivers" which frequently amounted to little more than a basic crystal set. However anyone doing so risked imprisonment or even death if caught and in most parts of Europe the signals from the BBC (or other allied stations) were not strong enough to be received on such a set. However there were places such as the Channel Islands where it was possible. Later years > While it never regained the popularity and general use that it enjoyed at its beginnings, the Circuit is still used. The Boy Scout s (who emerged as the unofficial custodians of crystal radio lore) kept construction of a set in their program since the 1920s. A large number of prefabricated novelty items and simple kits could be found through the '50s and '60s, and many children with an interest in electronics built one. Building crystal radios was a Craze in the 1920s, and again in the 1950s. Recently, Hobbyist s have started designing and building sophisticated examples of the instruments. As much effort goes into the visual appearance of these sets as well as their performance, and some outstanding examples can be found. Annual crystal radio DX Contest s and building Contest s allow these sets to compete with each other and help form a community of interest in the subject. Attempts at recovering RF carrier power Crystal radio tuned to strong local station can be used just as power source for another amplified power-efficient (more often Regenerative ) receiver for distant stations what can never be heard with plain crystal radio. There is long history of less successful attempts and unverified claims to recover the power in the carrier of the received signal itself. Traditional crystal sets use half-wave ) and bridge amplifiers. CONSTRUCTION AND OPERATION Importance of grounding The long wire type antennas often used with crystal radios are Monopoles . To receive signals from this type of antenna, a Ground reference is needed to provide a place for the antenna signal electricity to flow into and out of. Because crystal radios have no other source of power than the electrical power they receive from the antenna, the grounds for crystal radios must be much better than those used by amplified radios. The importance of this is easy to overlook by those familiar with amplified radios. Amplified radios use energy detectors and as such do not need to take much raw power from the antenna and need little or no physical ground. Crystal radios rely on power detection and need to encourage as much antenna current as possible to flow. This requires effective grounding. How it works (complex version) A ''crystal set'' is the simplest Radio Receiver . There are a variety of circuit designs available. A common design consists of a long-wire Antenna , a Variable Inductor and a Variable Capacitor forming a Tank Circuit to select the desired radio Signal Frequency , and a detector consisting of a Diode Demodulator usually consisting of a sharp wire called a Cat's Whisker pressing against a sensitive point on a Mineral Crystal in a holder. A Semiconducting Mineral Crystal , typically Lead sulphide ( Galena ) or Cadmium Sulphide is fixed inside a Brass Cup and the radio operator finds the loudest signal by touching the cat's whisker to various points on the Surface of the crystal. Alternately, a discrete semiconductor Diode can replace a makeshift cat's whisker diode. The most expensive part can be the length of antenna wire. The detector extracts the Amplitude Modulation from the radio signal by Rectifying it, and provides an Audio output in proportion to the strength of the signal coming from the antenna. The entire set is Passive , requiring no external Power . Because no Electrical Amplification is used, sensitive Earphone s are required (a Crystal Earpiece being the general choice in modern designs). These sets have no way to control the audio Volume . The diode detector loses its detection efficiency for weak signals (that must be rectified) because the forward and reverse conductivity of the diode differs much less than it would differ for the stronger current (see Diode ). There are alternative methods of detection that use transistors but requires several volts of bias from an additional power source. In the simpliest case, the base and emitter of the pnp bipolar transistor are reverse biased and used as a diode. The transistor, connected as a diode can be more effective than ordinary unbiased diodes. SEE ALSO ;, Radio Receiver , Transistor Radio , Demodulator ;People: Alfred Powell Morgan - Author Of Books On Early Electronics ;Lists: List Of Historic Technological Nomenclature ;Other: Wireless Energy Transfer , Energy Efficiency , Numbers Station (related to espionage) NOTES REFERENCES General Information
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