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.

Description

Most analog transmissions involve modulations of intensity from a stable, baseline source. In intensity modulation, the intensity of a source's signal output is modulated by an incoming analog baseband signal. A baseband signal is a signal that is in its original form and has not been changed by a modulation technique. This is the case with most analog amplitude techniques and many optical transmission techniques. ^[1]

In some cases, the source may be directly modulated by a signal that is not a baseband signal. In these cases the original electrical signal generally modulates an electrical subcarrier frequency. This is the case with all frequency modulation techniques.^[2]

Phase moduleation techniques, which operate by encoding data using phase shifts, is rarely used in analog transmission, since it is more effective to transmit data using digital techniques.^[3]

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 date to combine an input signal with a carrier signal. Usually, this carrier signal is a specific frequency, and data is transmitted through it's 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.^[4]

Types of analog transmissions

Most analog transmissions fall into one of several catagories. 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. A modem (a portmanteau word constructed from modulator and demodulator) is a device that modulates an analog carrier signal (sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information. ...

Benefits and drawbacks

Analog transmission is still very popular, in particular for shorter distances, due to signifigantly lower costs and complex multiplexing and timing equipment is unnecessary, and in small "short-haul" systems that simply do not need multiplexed digital transmission.^[5]

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 attentuation problems. Furthermore, as digital techniques continue to be refined, analog systems are increasingly becoming legacy equipment.^[5]

Recently, some nations, such as the Netherlands, have completely ceased analog transmissions on certain media, such as television. ^[6], for the purposes of the government saving money. ^[7]

See Also

• Analog signal
• Analog television
• Analog to digital converter
• modulation
• signal

It has been suggested that this article or section be merged into Analog electronics. ... Analog television (or analogue television) encodes television picture and sound information as an analog signal, that is, by varying the amplitude and/or frequencies of the signal. ... This article or section should include material from AD converters In electronics, an analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... Signaling or signal may mean: Look up signal and signaling in Wiktionary, the free dictionary. ...

References

1. ^ Data Communications and Networking By Behrouz A. Forouzan, Sophia Chung Fegan. 2003 McGraw-Hill Professional. ISBN 0072923547
2. ^ Communication Networks: fundamental concepts and key architectures By Alberto Leon-Garcia, Indra Widjaja. 2003 McGraw-Hill Professional. ISBN 007246352X
3. ^ Pulse analog transmission of TV signal. Di Biase, V; Passeri, P; Pietroiusti, R. ALTA FREQ. Vol. 56, no. 4, pp. 195-204. 1987
4. ^ The Froehlich/Kent Encyclopedia of Telecommunications By Allen. Kent, Froehlich E. Froehlich.1991 Marcel Dekker. ISBN 0824729005
5. ^ ^{a b} Telecommunication System Engineering By Roger L. Freeman.2004 John Wiley and Sons. ISBN 0471451339
6. ^ http://www.dslreports.com/shownews/80237
7. ^ http://www.nytimes.com/aponline/technology/AP-Netherlands-TV.html?_r=2&oref=slogin&oref=slogin