RF attenuators are circuits that reduce the power level of a signal by a certain amount (gain) with little or no reflection. They reduce the output signal with respect to the input and measure the power reduction in decibels (dB). There are two basic types of RF attenuators: fixed and variable. Fixed RF attenuators reduce output signal power relative to input signal power by a fixed amount over a specified bandwidth while the input and output impedances are kept close to the nominal level, usually 50 or 75 W. Variable RF attenuators use several different methods to vary attenuation between two values in a specified range. For example, continuously variable devices vary the attenuation in a continuous fashion. By contrast, step attenuators vary the attenuation by only a fixed amount at a time. Programmable attenuators and direct-read attenuators that can be set by an external device such as rotary dial are also available. With digital attenuators, the attenuation can be varied by digital control signals. Because digital signals are discrete in nature, digitally controlled attenuators have a number of finite attenuated states.
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