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Recommended: The history of radio
Abstract
This paper will discuss the design of an FM receiver. It will begin with a brief historical backdrop of FM broadcasting and its use in society. It will continue by providing the necessary mathematical background of the modulation process. Furthermore, it will enumerate some of the advantages of FM over other forms of modulation, namely AM.
Finally, the paper will discuss the design of a basic FM receiver as well as introduce some circuits and circuit components which the reader may not be familiar with.
Introduction
Frequency modulation (FM) was invented in 1936 by an American electrical engineer/ inventor named Edwin H. Armstrong. Possessing numerous advantages over the existing
AM broadcasting system, as will be discussed later, in combination with relatively low cost of implementation, resulted in its rapid growth. In the years following World War
Two, there were 600 licensed stations broadcasting in the U.S. By 1980, the number grew to 4000. On another historical note, in 1961 stations began broadcasting in stereo.
The basic receiver design consists of the following components. An antenna is used to convert electro-magnetic waves into electrical oscillations. Amplifiers are used throughout the receiver to boost signal power at radio, baseband and intermediate frequencies. The core of the FM receiver, the discriminator, comes in various circuit forms and is used in detection and demodulation. Basically, its role is to extract the intelligence or message from the carrier wave. Another component, essential in most electronic circuits, is the power supply (DC or AC converted to DC). Finally, a transducer (speaker in the case of Radio) is needed to convert the message signal into its final form (audio, mechanical, etc¡). Other components more specific to FM receivers are mixers combined with local oscillators used for frequency manipulation, limiters to control amplitude, de-emphasis and other filter circuits.
2
Mathematics of FM
Unlike amplitude modulation (AM) where the message or modulating signal, call it m(t), is used to modulate the amplitude of the carrier signal, frequency modulation, as the name implies, uses m(t) to transform the frequency of the carrier. The amplitude of an
FM signal should remain constant during the modulating process; an important property of FM. A general FM signal can be described by the following:1
¦µFM(t) = Acos(¦È...
... middle of paper ...
...n its output proportional to s(t).
Over a short time interval, this variation ¡Ö C(wc-wo)t. Thus, the system continues to loop until the frequency of the VCO output matches or ¡°locks¡± onto the incoming frequency.
The time it takes for the system to ¡°lock¡± is called the acquisition time. Once the frequencies match, s(t) becomes s(t) = AB/s sin(¦Èc-¦Èo)
For an incoming FM signal s(t) = AB/2 sin(¦Èc(t)-¦Èo)
= AB/2 sin (kf ¡Òm(¦Ó)d¦Ó ¨C¦Èo)
Running s(t) through a differentiator results in an AM signal which can be easily demodulated using envelope detection.
Once the signal has been demodulated, it is then passed through a de-emphasis circuit, as mentioned earlier. Typically, it is then amplified one last time before heading to the output transducer.
Conclusion
In conclusion, the modulation/demodulation process for FM signals has proven to be much less straight forward than simple AM modulation. However, FM has considerable advantages and its use in radio, satellite and radar applications make it indispensable.
Many methods of signal and system analysis along with filter and feedback design are employed in the building of an FM receiver, whether it be analog, digital or otherwise.
Private prisons are correctional institutions ran by for-profit corporations. They claim to cost less than prisons ran by the state, while offering the same level of service. In fact, the Corrections Corporation of America, one of the largest for-profit prison corporations, states that their business strategy is to provide quality corrections service while offering a better value to their government partners at the same time making a profit (CCA 2010). However, opponents of private prisons say they do not save states money because of their hidden cost. At any rate, more than a few states have found private prisons to be advantageous. For one reason, many states are facing massive deficits and are l...
Has anyone ever wondered how radio communications changed society during the 1930’s? According to the research done by the Education Foundation, many people believe that the most important development in the radio at that time was entertainment; this is entirely false. In fact, radio communications not only made an impact in the way people received their news, but also brought together a nation that got out of a brutal depression. Together, the nations as one made radio communications the commanding form of media in the 1930’s. As stations and businesses were beginning to establish themselves, companies from across the nation were taking notice in the department of advertisement. This new realm ignited a spark for the nation’s new economy which later boomed and gave rise to an economically and socially powerful country.
... law, government supervisors and to the public through the political system available. (Austin and Coventry, 2001). The private prisons are also answerable to the insurers, investors, competitors and the stockholders. Competition from other competitors therefore acts as a better mechanism for control which is not experienced by public prisons. The problem of funding and allocating space efficiently in the prisons would decrease if there were better markets that sell, buy and rent the prison cells. The private prisons are based in such a way that they have introduced factories behind the bars allowing them to reduce their costs and allowing the inmates to earn some money and pay in their own way and give back to the community where they resided. The public prisons do this to some extent which however cannot match that of the private prisons. (Silverman and Ira, 2001).
Wireless communication across the country was something no one ever imagined. The creating of the commercial radio in 1920, created a feeling of belonging to many citizens of the United States. Starting off as a hobby for amateurs, radio quickly expanded. With the creation of NBC, and emerging radio stars like Ernie Hare and Billy Jones radio, families tuned in on a daily basis. Music was brought to lower income families who couldn’t afford to buy a piano. As well as streaming music, radio provided advertising outlets. Promotions regarding cigarettes, automobiles, and soap
The number of Americans that are in prison has elevated to levels that have never been seen before. Prisons in the US have always been crowded ever since the first prison was invented (Jacobs and Angelos 101). The first prison in the US was the Walnut Street Jail that was built in Philadelphia in 1773, and later closed in the 1830’s due to overcrowding and dirty conditions (Jacobs and Angelos 101). The prison system in modern US history has faced many downfalls due to prison overcrowding. Many private prison owners argue that the more inmates in a prison the more money they could make. In my opinion the argument of making more money from inmates in prisons is completely unconstitutional. If the private prisons are only interested in making
Private prisons in the United States, came about in the early 1980s when the war on drugs resulted in a mass wave of inmates, which led to the lack of the prison system’s ability to hold a vast number of inmates. When the cost became too much for the government to handle, private sectors sought this as an opportunity to expand their businesses through the prison industry. Since the opening of private prisons, the number of prisons and inmates it can hold has grown over the last two decades. With the rising number of inmates, profits have also substantially grown along with the number of investors. But what eventually became a problem amongst the private prison industry was their “cost-saving” strategies, which have been in constant debate ever
Today two of the top broadcasting companies are Clear Channel Communications, Inc. and Infinity Broadcasting Company. Clear Channel’s history begins in 1972 with the birth of the San Antonio Broadcasting Company. Three years later, the first “Clear Channel” radio station, WOAI-AM, was acquired – it had its own nationwide frequency. In the late 1980s, the Company entered the television business and acquired half a dozen television stations. In 1994 it became listed as Clear Channel Communications, Inc Common Stock and owned 43 radio stations and 16 television stations in 32 markets.
Should prisons in the United States be for profit? How do for profit prisons benefit the United States? Would inmates rather be in private or public correctional centers? What kind of affects does this have on taxpayers? What are the pros and cons of profit prisons? These are many of the questions that are brought up when discussing for profit prison systems. There are different perspectives that can be taken when it comes to talking about for profit prisons. This paper will discuss some of the ways that the United States has started to become for profit and why it has happened. Finally, this paper will give an opinion of whether or not for profit prisons should be dominant over public facilities.
The radio grew in popularity and was as successful as it was because it was able to reach all across the nation, helped the American people interpret the Great Depression, and was a universal place of communication and entertainment. Although the first radio-wave theorem was developed in 1864 by James Clerk Maxwell, it was not until the 1920s and 1930s that the device really gained popularity in the U.S. During the Great Depression, families, advertisers, and even politicians used the radio for purposes such as entertainment, news, and a forum to the American people.1
Prisons seem like they are popping up everywhere in the U.S. One of the reason for this is an increase in incarceration. History shows that mass incarceration was a big problem back in the 70’s and 80’s when there was a war on drugs. This led to prisons becoming overcrowded and more prisons had to be built to be able to house all those inmates. For-profit prisons are going to want to see this trend continue. A for-profit prison is where inmates are housed in a correctional institution that is run by government organizations. Private prisons have their benefits such as bringing new ideas to help with the rehabilitation of prisoners. Rehabilitation
At the forefront of the privatized prison debate is retention and rehabilitation. Using the name “corrections” in regards to our prison system has become ironic. Privatization of prisons works against this namesake goal of correction and rehabilitation for those in prison. Instead the goal now of prison is not to protect the public or help those incarcerated but instead to generate capital. Corporations CCA and GEO advertise to its investors the truth of high prison retention in making for great profits. When individuals leave and go back to prison after they get out because they are not capable of handling life outside of the system they have lived in so long
"Short History of Radio A Short History of Radio With an Inside Focus on Mobile Radio." fcc.gov. Version 2003-2004. N.p., n.d. Web. 4 Dec. 2013. .
The history of automobile audio dates back to the early 1900s. George Frost did the earliest car audio experimentation in 1922. The evolution of car radios began in the Transitone Th-1, in 1927. The first FM turner band in cars was introduced in 1952. In 1965 the 8-track player was introduced in Ford vehicles. In the early 1960’s, cassettes were introduced, but didn’t become popular until 1977. The FM band became more popular in the 1980s, and the first car compact disc players were introduced in the 1980s. In the early 2000s XM satellite was introduced to the nation. Car audio has made such an impact on vehicles over the last seven decades. Car audio evolved from the simplest forms to the most complex forms. The model of car audio sound systems varies into each and every model of vehicles.
Radio-wave technology is one of the most important technologies used by man. It has forever changed the United States and the world, and will continue to do so in the future. Radio has been a communications medium, a recreational device, and many other things to us. When British physicist James Clerk Maxwell published his theory of electromagnetic waves in 1873, he probably never could have envisioned the sorts of things that would come of such a principle. His theory mainly had to do with light waves, but fifteen years later, a German physicist named Heinrich Hertz was able to electrically generate MaxwellÕs ÒraysÓ in his lab. The discovery of these amazing properties, the later invention of a working wireless radio, and the resulting technology have been instrumental to AmericaÕs move into the Information Age. The invention of radio is commonly credited to Guglielmo Marconi, who, starting in 1895, developed the first ÒwirelessÓ radio transmitter and receiver. Working at home with no support from his father, but plenty from his mother, Marconi improved upon the experiments and equipment of Hertz and others working on radio transmission. He created a better radio wave detector or cohere and connected it to an early type of antenna. With the help of his brothers and some of the neighborhood boys he was able to send wireless telegraph messages over short distances. By 1899 he had established a wireless communications link between England and France that had the ability to operate under any weather conditions. He had sent trans-Atlantic messages by late 1901, and later won the Nobel prize for physics in 1909. Radio works in a very complicated way, but hereÕs a more simple explanation than youÕll get from most books: Electromagnetic waves of different wavelengths are produced by the transmitter, and modulations within each wavelength are adjusted to carry ÒencodedÓ information. The receiver, tuned to read the frequency the transmitter is sending on, then takes the encoded information (carried within the wave modulations), and translates it back into the sensory input originally transmitted. Many of the men who pioneered radio had designs for it. Marconi saw it as the best communication system and envisioned instant world-wide communication through the air. David Sarnoff ( later the head of RCA and NBC) had a vision of Òa radio receiver in every homeÓ in 1916, although the real potential of radio wasnÕt realized until after World War I.
main advantage of FM broadcasting is of it is static free. But the drawback to