Noise

Noise is any unwanted signal added to a wanted signal. These unwanted signals arise from a variety of sources which may be considered in one of two main categories:

• Interference, usually man-made
• Naturally occurring random noise

Interference arises in communication systems from many sources due to crosstalk: 50/60 Hz supplies (causing hum) and harmonics, switched mode power supplies, thyristor circuits, ignition (car spark plugs) motors, etc.

Naturally occurring external noise sources include atmosphere disturbance (e.g. electric storms, lighting, ionospheric effect), and so-called sky noise or cosmic noise.

Thermal noise is electronic noise generated by the thermal agitation of the charge carriers inside an electrical conductor. Thermal noise in a resistor is of a type called white noise, meaning that its power spectral density is nearly constant throughout the frequency spectrum.

PicoScope has a white noise generator to help circuit designers evaluate noise immunity in their designs.