The result is amplification of the signal. A TWT can be made to function as an oscillator by coupling some of the output back into the input. This configuration is called a backward-wave oscillator , because the feedback is applied opposite to the direction of movement of the electrons inside the tube. Such an oscillator can generate up to approximately 0.1 watt of signal power in the microwave range. Some characteristic of the circuit, such as its impedance , is made to vary with time at the power-supply frequency.
Parametric amplifiers are useful because they generate very little internal noise .
This makes it possible to obtain excellent sensitivity in receiving systems, minimizing data-transfer errors. Microwave Power Products produces a specialized line of TWT devices.