Electrical noise is defined as any undesirable electrical energy that falls within the pass band of the signal. For example in audio recording any unwanted electrical signal that fall within the audio frequency band of o hz to 15khz will interfere with the music and therefore be considered noise. The effect that noise has on an electrical signal. A sin wave without noise same signal except in the presence of noise. The grassy-looking squiggles superimposed on the sine wave are electrical noise, which contains a multitude of frequencies and amplitudes that can interfere with the quality of the signal.
Noise can be divided into general categories ; correlated and uncorrelated . Correlation implies a relationship between the signal and the noise. Therefore correlated noise exists only when a signal is present . Uncorrelated noise on the other hand is present all the time whether there is a signal or not.
Uncorrelated noise is present regardless of whether of there is a signal present or not. Uncorrelated noise can be further subdivided into two general categories: external and internal.
External noise is noise that is generated outside the device or circuit . The three primary sources of external noise are atmospheric, extraterrestrial, and man-made. Atmospheric noise is naturally occurring electrical disturbances that originate within earth s atmosphere. Atmospheric noise is commonly called static electricity and is the familiar sputtering , crackling , and so on often heard from a speaker when there is no signal present. The source of most static electricity is naturally occurring electrical conditions, such as lighting. static electricity is often in the form of impulses that spread energy throughout a wide range of frequency. The magnitude of this energy however is in inversely proportional to its frequency. Consequently at frequencies above 30 Mhz or so , atmospheric noise is relatively insignificant.
Extraterrestrial noise; Extraterrestrial noise consists of electrical signals that originate from outside earth s atmosphere and is therefore sometimes called deep-space noise. Extraterrestrial noise originates from the milky way, other galaxies, and the sun. Extraterrestrial noise is subdivided into two categories: solar and cosmic.
Solar noise is generated directly from the sun s heat. There are two parts to solar noise : quiet condition , when a relatively constant radiation intensity exists, and high intensity , sporadic disturbances caused by sunspot activity and solar flare-ups. The magnitude of the sporadic noise caused by sunspot activity follows a cyclic pattern that repeats every 11 years.
Cosmic noise, sources are continuously distributed throughout the galaxies. because the sources of galactic noise are located much farther away than our sun, their noise intensity is relatively small. Cosmic noise is often called black-body noise and is distributed fairly evenly throughout the sky.
Man-made noise man made noise is simply noise that is produced by mankind . The predominant sources of man made are spark producing mechanisms, such as commutators in electric motors, automobile ignition systems . ac power generating and switching equipment , and fluorescent lights.
Man made noise is impulsive in nature and contains a wide range of frequencies that are propagated through space in the same manner as radio waves. Man made noise is most intense in the more densely populated metropolitan and industrial areas and is therefore sometimes called industrial noise.
Internal noise: Internal noise is electrical interference generated within a device or circuit . There are three primary kinds of internally generated noise; shot transit time and thermal. Short noise is caused by the random arrival of carries at the output element of an electronic device ,such as a diode , field -effect transistor, or bipolar transistor . Short noise was first observed in the anode current of a vacuum-tube amplifier and was described mathematically by W.Schottky in 1918. The current carriers are not moving in a continuous, steady flow as the distance they travel varies because of their random paths of motion. Short noise is randomly varying and is superimposed onto any signal present.
When amplified short noise sounds similar to metal pellets falling on a tin roof . Short noise is sometimes called transistor noise and is additive with thermal noise.Transit-time noise and modification to a stream of carriers as they pass from the input to the output of a device produces an irregular, random variation categorized as transit-time noise . When the time it takes for a carrier to propagate through a device is an appreciable part of the time of one of the signal the noise becomes noticeable. Transit-time noise in transistor is determined by carrier mobility, bias voltage and transistor construction.
Carriers traveling from emitter to collector suffer from emitter time delays, base transit time delays and collector recombination time and propagation time delay . If transmit delays are excessive at high frequencies the device may add more noise than amplification to the signal. Thermal noise thermal noise is associated with the rapid and random movement of electrons within a conductor due to thermal agitation. The English botanist Robert Brown first noted this random movement . Brown first observed evidence for the moving particle nature of matter in pollen grains and later noticed that the same phenomenon occurred with smoke particles.
Thermal noise is present in all electronic components and communications systems. Because thermal noise is uniformly distributed across the entire electromagnetic frequency spectrum , it is often referred to as white noise. Thermal noise is a form of additive noise , meaning that it cannot be eliminated , and it increase in intensity with the number of devices in a circuit and with circuit length.
Therefore thermal noise sets the upper bound on the performance of a communication system.
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