- Analog transmission
Analog transmission is a method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable.
Modes of transmission
Analog transmission can be conveyed in many different fashions:
* twisted-pair or coax cable
* fiber-optic cable
* Via air
* Via water
There are two basic kinds of analog transmission, both based on how they modulate data to combine an input signal with a carrier signal. Usually, this carrier signal is a specific frequency, and data is transmitted through its variations. The two techniqes are amplitude modulation (AM), which varies the amplitude of the carrier signal, and frequency modulation (FM), which modulates the frequency of the carrier.The Froehlich/Kent Encyclopedia of Telecommunications By Allen. Kent, Froehlich E. Froehlich.1991 Marcel Dekker. ISBN 0824729005]
Types of analog transmissions
Most analog transmissions fall into one of several categories. Until recently, most telephony and voice communication was primarily analog in nature, as was most television and radio transmission. Early telecommunication devices utilized analog-to-digital conversion devices called modulator/demodulators, or
modems, to convert analog data to digital data and back.
Benefits and drawbacks
Analog transmission is still very popular, in particular for shorter distances, due to significantly lower costs and complex multiplexing and timing equipment is unnecessary, and in small "short-haul" systems that simply do not need multiplexed digital transmission.Telecommunication System Engineering By Roger L. Freeman.2004 John Wiley and Sons. ISBN 0471451339]
However, in situations where a signal often has high signal-to-noise ratio and can't achieve source linearity, or in long distance, high output systems, analog is unattractive due to attenuation problems. Furthermore, as digital techniques continue to be refined, analog systems are increasingly becoming legacy equipment.
Recently, some nations, such as the Netherlands, have completely ceased analog transmissions on certain media, such as television, [http://www.dslreports.com/shownews/80237 Netherlands Ends Analog Transmission - Goodbye antenna, hello digital... - dslreports.com ] ] for the purposes of the government saving money.http://www.nytimes.com/aponline/technology/AP-Netherlands-TV.html?_r=2&oref=slogin&oref=slogin]
Analog to digital converter
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