.net barcode reader free Introduction to radio broadcasting and communications in Software

Maker Data Matrix in Software Introduction to radio broadcasting and communications

CHAPTER
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RADIO BROADCASTING AND COMMUNICATIONS SEEMS TO HOLD A STRANGE KIND OF
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magical allure that attracts a wide variety of people and holds them for years There is something fascinating about the ability to project yourself over vast intercontinental distances Radio communications have been with us now for the entire twentieth century and into the twenty-first Experiments are on record as early as 1867, and by the turn of the century wireless telegraphy (as radio was called then) sparked the imaginations of countless people across the world Radio communications began in earnest, however, when Guglielmo Marconi successfully demonstrated wireless telegraphy as a commercially viable entity The wireless aspect to radio so radically changed communications that the word is still used to denote radio communications in many countries of the world Marconi made a big leap to international fame on a cold December day in 1903, when he and a team of colleagues successfully demonstrated transatlantic wireless telegraphy Until that time, wireless was a neighborhood or crosstown at best endeavor that was of limited usefulness Of course, ships close to shore, or each other, could summon aid in times of emergency, but the ability to communicate over truly long distances was absent All that changed on that fateful day in Newfoundland when Marconi heard the Morse letter S tickle his ears Wireless telegraphy was pressed into service by shipping companies because it immediately provided an element of safety that was missing in the prewireless days Indeed, a ship that sank, leaving its crew and passengers afloat on a forbidding sea, was alone Any survivors often succumbed to the elements before a chance encounter with a rescue vessel Some early shipping companies advertised that their ships were safer because of wireless aboard It was not until 1909, however, that wireless telegraphy proved its usefulness on the high seas Two ships collided in the foggy Atlantic Ocean and were sinking All passengers and crew members of both ships were in imminent danger of death in the icy waters But radio operator Jack
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2 Introduction to radio broadcasting and communications Binns became the first man in history to send out a maritime distress call There is some debate over which distress call Binns transmitted, but one thing is certain: It was not SOS (today s distress call), because SOS was not adopted until later Binns probably transmitted either CQD or CQE, both of which were recognized in those days before standardization Regardless of which call was sent, however, it was received and relayed from ship to ship, allowing another vessel to come to the aid of the stricken pair of ships All radio prior to about 1916 was carried on via telegraphy (ie, the on-off keying of a radio signal in the Morse code) But in 1916 some more magic happened On a little hill in Arlington, Virginia, on a site that now overlooks the Pentagon and the US Marine Corps base called Henderson Hall, there were (and still are) a pair of two-story brick buildings housing the naval radio station NAA (callsign since reassigned to the VLF station at Cutler, ME) On a night in 1916, radio operators and monitors up and down the Atlantic seaboard from the midwest to the coast and out to sea for hundreds of miles heard something that must have startled them out of their wits, for crackling out of the ether, amidst the whining of Alexanderson alternators and ZZZCHHT of spark-gap transmitters, came a new sound a human voice Engineers and scientists at the Naval Research Laboratory had transmitted the first practical amplitude-modulated (AM) radio signal Earlier attempts, prior to 1910, had been successful as scientific experiments, but they did not use commercially viable equipment Although radio activity in the early years was unregulated and chaotic, today it is quite heavily regulated Order was brought to the bands (don t laugh, ye who tune the shortwaves) that was lacking before Internationally radio is regulated by the International Telecommunications Union (ITU) in Geneva, Switzerland through the treaties arising from World Administrative Radio Conferences (WARC) held every 10 to 15 years In the United States, radio communications are regulated by the Federal Communications Commission (FCC), headquartered in Washington, DC Amateur radio has grown from a few thousand hams prior to World War I to more than 900,000 today, about one-third of them in the United States Amateur operators were ordered off the air during World War I, and almost did not make a comeback after the war There were, by that time, many powerful commercial interests that greedily coveted the frequencies used by amateurs, and they almost succeeded in keeping postwar amateurs off the air But the amateurs won the dispute, at least partially In those days, it was the frequencies with wavelengths longer than 200 m (ie, 20 to 1500 kHz) that were valuable for communications The cynical attitude attributed to the commercial interests regarding amateurs was, put em on 200 meters and below they ll never get out of their backyards there! But there was a surprise in store for those commercial operators, because the wavelengths shorter than 200 m are in the high-frequency region that we now call shortwaves Today, the shortwaves are well-known for their ability to communicate over transcontinental distances, but in 1919 that ability was not suspected I once heard an anecdote from an amateur operator who was there In the summer of 1921 this man owned a large, beautiful wire flattop antenna array for frequencies close to 200 m on his family s farm in southwestern Virginia Using those frequencies he was used to communicating several hundred miles into eastern Ohio and down to the Carolinas But, in September 1921 he went to college to study
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Introduction to radio broadcasting and communications 3 electrical engineering at the University of Virginia in Charlottesville When he returned home for Thanksgiving he noticed that his younger brother had replaced the long flattop array with a short dipole antenna He was furious, but managed through great effort to contain the anger until after dinner Confronting his brother over the incredible sacrilege, he was told that they no longer used 150 to 200 m, but rather were using 40 m instead Everyone knew that 40 m was useless for communications over more than a few blocks, so (undoubtedly fuming) the guy took a turn at the key He sent out a CQ (general call) and was answered by a station with a callsign like 8XX Thinking that the other station was in the 8th US call district (WV, OH, MI) he asked him to relay a message to a college buddy in Cincinnati, OH The other station replied in the affirmative, but suggested that you are in a better position to reach Cincinnati than me, I am FRENCH 8XX (Callsigns in 1921 did not have national prefixes that are used today) The age of international amateur communications had arrived! And with it came a new problem the national identifiers in call signs became necessary (which is why American call signs begin with K, W, or N) During the 1930s, radio communications and broadcasting spread like wildfire as technology and techniques improved World War II became the first war to be fought with extensive electronics Immediately prior to the war, the British developed a new weapon called RADAR (radio detection and ranging; now spelled radar) This tool allowed them to see and be forewarned of German aircraft streaming across the English Channel to strike targets in the United Kingdom The German planes were guided by (then sophisticated) wireless highways in the sky, while British fighters defended the home island by radio vectoring from ground controllers With night fighters equipped with the first centimetric (ie, microwave) radar, the Royal Air Force was able to strike the invaders accurately even at night The first kill occurred one dark, foggy, moonless night when a Beaufighter closed on a spot in the sky where the radar in the belly of the plane said an enemy plane was flying Briefly thinking he saw a form in the fog, the pilot cut loose a burst from his quad mount of 20-mm guns slung in the former bomb bay Nothing Thinking that the new toy had failed, the pilot returned to base only to be told that ground observers had reported that a German Heinkle bomber fell from the overcast sky at the exact spot where the pilot had his ghostly encounter Radio, television, radar, and a wide variety of services, are available today under the general rubric radio communications and broadcasting Homeowners, and other nonprofessionals in radio, can own a receiver system in their backyard that picks up television and radio signals from satellites in geosynchronous orbit 23,000 mi out in space Amateur operators are able to communicate worldwide on low power, and have even launched their own OSCAR satellites Some people had written off the HF radio spectrum in recent years, citing satellite technology as the reason But the no-code license for amateur radio operators, which does not carry HF privileges, has proven to be a stepping stone to higherclass licenses, which do Also, the shortwave broadcasting market received a tremendous boost during the Gulf War When the troops of Operation Desert Shield and Desert Storm were assembling to take back Kuwait from the Iraqis, the sales of shortwave receivers jumped dramatically And, following January 16, 1991, when the forces started pouring across the border into the actual fight, the sales
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4 Introduction to radio broadcasting and communications skyrocketed out of sight One dealer told me that he couldn t keep receivers in stock, and that he had sold out most models That interest seems to have matured into long-term interest on the part of a significant number of listeners and new ham operators The antenna is arguably one of the most important parts of the receiving and/or transmitting station (Fig 1-1) That is what this book is all about
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