🔍 Key Concepts

• Grid-bias modulation in RF (radio frequency) stages and how it affects plate current and power output • Relationship between modulation depth (percentage of modulation) and efficiency in an amplitude-modulated (AM) transmitter stage • What happens to carrier power vs. sideband power at zero modulation and at 100% (complete) modulation

💭 Think About

• Think about what the RF stage is doing when there is no modulation: how much power is being delivered to the load compared to the information being sent? • Consider what happens to useful signal power as modulation increases toward 100%: does efficiency of the stage generally increase, decrease, or stay the same? • How does the design of a grid-bias modulated stage differ from plate-modulated or screen-modulated stages in terms of where the modulation is applied and how that affects efficiency?

✅ Before You Answer

• Review how efficiency is defined: ( \eta = \frac{P_{\text{output, useful}}}{P_{\text{input}}} \times 100% ) and what counts as "useful" in AM • Check what happens to carrier power at zero modulation versus complete modulation in terms of information content • Verify typical behavior of grid-bias modulated stages: does efficiency tend to be highest with no modulation, partial modulation, or near complete modulation?