Question 6A373

Modulation occurring in an RF stage *before* the final power amplifier is termed **low-level modulation**. In this method, the modulating signal is applied to an earlier, lower-power RF stage, creating a modulated signal that is then amplified by subsequent RF stages, including the final power amplifier. This allows the final amplifier to operate more efficiently, often in a non-linear (e.g., Class C) mode, as it only needs to amplify the already modulated waveform. **High-level modulation** (A) occurs directly *in* the final power amplifier stage itself, typically by varying its power supply voltage or current according to the modulating signal. **Pre-emphasis** (C) is an audio processing technique used in FM to boost higher audio frequencies before transmission, improving the signal-to-noise ratio at the receiver; it's not a location of modulation. **Plate modulation** (D) is a specific type of high-level amplitude modulation where the modulating audio signal is applied to the plate (anode) voltage of the final RF amplifier tube. Since the question specifies a stage *other than* the final power amplifier, "low level" is the correct description.