Variable attenuators are a type of radio frequency attenuator that permits the signal level to constantly change. Attenuators are devices that decrease the power of a signal without noticeably distorting its waveform. This protects circuitry from receiving a signal that’s too powerful.

Variable attenuators are used when the signal level needs to be able to change frequently. This is useful when you don't know exactly what the final desired signal range is or when accuracy is not a priority. Attenuators can be thought of as the opposite of signal amplifiers. An amplifier increases signal power (or amplitude) while an attenuator decreases it.

How do variable attenuators work?
The signal level of variable attenuators is altered either manually or remotely.
In manual variable attenuators, the signal level is changed by physically controlling the device, using something like an adjustable screw control.

If they are controlled remotely, a motor or PIN diode uses variable voltage to change the signal.

Types of variable attenuators
Variable attenuators come with PIN diodes or MESFETs (metal–semiconductor field-effect transistors) as resistors to modulate amplitude. They can use either balanced or unbalanced pi-pad or T-pad circuits.

Variable Attenuators