| • Science | • People | • Locations | • Timeline |
An analog (American English spelling) or analogue (British English spelling) signal is any continuously variable signal. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context, however mechanical, pneumatic, hydraulic, and other systems may also use analog signals.
The word "analog" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and frequency out.
An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge.
Any information may be conveyed by an analog signal, often such a signal is a measured response to changes in physical phenomena, such as sound, lightLight is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. The three basic dimensions of light (and of all electromagnetic radiation, temperatureTemperature is the physical property of a system which underlies the common notions of "hot" and "cold"; the material with the higher temperature is said to be hotter. General description The formal properties of temperature are studied in thermodynamics., positionThe word position can have one of several meanings: 2-dimensional or 3-dimensional location; In finance, a position means entitlement to receive or obligation to deliver an asset or financial instrument, as in "long position" (ownership) and "short positi, or pressurePressure (symbol: p is a measure of force per unit area. where p is the pressure F is the force A is the area Often F is taken to be the of the magnitude of the mean vector force normal to the surface of area A upon which it exerts; the "surface" not nece, and is achieved using a transducerA transducer is a device that converts one type of energy to another, or responds to a physical parameter. A transducer is in its fundamental form a passive component. If the component is electrical then it generally has two electrical terminals. See also.
For example, in an analog sound recording, the variation in pressurePressure (symbol: p is a measure of force per unit area. where p is the pressure F is the force A is the area Often F is taken to be the of the magnitude of the mean vector force normal to the surface of area A upon which it exerts; the "surface" not nece of a sound striking a microphoneA microphone sometimes called a "mic" (pronounced "mike"), is a device that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids and in radio and television broadcasting. creates a corresponding variation in the current passing through it. An increase in the volume of the sound causes the fluctuation of the current to increase while keeping the same rhythm.
The primary disadvantage of analog signalling is that any system has noise—that is, random variations—in it. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically these losses are lessened by shielding, good connections, and several cable types such as coax and twisted pair.
The effects of noiseIn general usage, noise can be considered data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. Noise is still considered information, in the sense of Informa make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well.
Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties altered: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase of the base signal also work.
Analog circuits do not involve quantisation of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end.
Clocks with hands are called analog; those that display digits are called digital. However, many analog clocks are actually digital since the hands do not move in a smooth continuous motion, but in small steps every second or half a second.See digital for a discussion of digital vs. analog.
Sources: Some of an earlier version of this article was originally taken from Federal Standard 1037C in support of MIL-STD-188.