Noise Generators and Sources Information
Noise generators and sources are used to produce noise outputs for testing radio frequency (RF) equipment. Noise generators are used to test and align many types of transmitters and receivers. They measure frequency, are tunable within certain frequency bands, and are used in a variety of test applications. Noise sources are used to provide known good signals. Noise diodes generate random noise. Like monolithic microwave integrated circuit (MMIC) amplifiers, noise diodes need a biasing structure made of other parts (i.e. resistors, capacitors and inductors) and a DC power supply in order to make noise. These singular semiconductor devices are an “engine” for noise sources and are used mainly for testing, calibration, and system analysis. Applications for noise generators and sources include encryption, dithering, jamming or jamming simulation, and base band signal simulation. Noise sources are also used for calibration references.
There are several form factors for noise generators and sources. Portable or benchtop devices can be moved with relative easy for a variety of uses. They include a case or handle, but are not necessarily hand-operated. Fixed devices are kept in one location and are meant to be used in one place. Coaxial devices are connectorized for transmission lines that carry high-frequency signals. Dual in-line modules do not need to be mounted and are placed in series with a cable. Waveguide components are circular, elliptical or rectangular metal tubes or pipes through which electromagnetic waves are propagated in microwave and RF communications. Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. Some noise generators and sources are PCBs that attach to enclosures or plug directly into computer backplanes.
Noise generators and sources vary in terms of frequency accuracy and frequency range. Frequency accuracy is a measure of how accurately the source frequency can be set. A noise generator's internal clock determines the frequency accuracy, which is usually expressed in decibels (dB). The frequency range is the range of output frequencies that a generator can produce. Amplitude, another signal characteristic, is also specified as a signal characteristic for many noise generators and sources.
User Interface Options
There are several user interface options for noise generators and sources. Some devices do not provide user input or programmability. This “black box” storage style is designed for downloading or processing information elsewhere. Other devices include a central processing unit (CPU) or microcontroller that is either an embedded processor or an external controller. These noise generators and sources may also be controlled by or directly interfaced to a personal computer (PC) or workstation. Generally, this is done for programmability and datalogging.