Methods to Adjust RF Output Power on Amplifiers: Manual vs Automatic Control

The discussion focuses on methods to achieve variable RF output power control in a self-designed 10-1000 MHz, 100W CW amplifier. Suggested approaches include using a dual gate MOSFET (e.g., BF1100) with Gate 2 voltage control for gain adjustment, RF PIN diodes for higher power handling, or single-ended/push-pull high-power MOSFETs like the PD55008. The Motorola MC1350P gain control IC is also mentioned as a viable option. To implement selectable power levels (25W, 50W, 75W, 100W), integrating a reflectometer circuit is recommended. This circuit uses a ferrite transformer and capacitors to provide DC feedback proportional to forward power, which can be amplified and fed back to the gain control stage for power regulation. However, designing a single amplifier covering the entire 10-1000 MHz range is challenging; typically, multiple amplifiers covering narrower frequency decades are used (e.g., 10-30 MHz, 30-150 MHz, 300-1000 MHz). The physical design of reflectometers varies significantly with frequency, and assistance is offered for designs up to 30 MHz.
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