These drivers based on quartz oscillators, produce a fixed RF frequency signal. Drivers can be provided at any frequency from 10 to 3 GHz. All models use crystal controlled oscillators. The RF output can be externally modulated. The settling time varies from 2 ns to 100 ns depending on the fixed frequency and RF power. Usually the driver is coupled internally to a power amplifier; if the output power required is very high then the amplifier will be provided separately, offering RF powers up to 500 W CW.