Practical takeaway
Amplifier class describes how much of the signal cycle the active device conducts. That choice controls efficiency, linearity, and which signals can be amplified cleanly.
E7B · Amateur Extra question group
Amplifier Classes & Distortion
Amplifier class describes how much of the signal cycle the active device conducts. That choice controls efficiency, linearity, and which signals can be amplified cleanly.
Amateur Extra exam focus
The explanation below teaches the ideas behind E7B while keeping the important terms recognizable. The Quiz Me button uses the current question-pool wording for this group.
1. Linear classes preserve the envelope
Class A, AB, and B stages can reproduce amplitude-varying signals when properly biased and driven. Class A is highly linear but inefficient; AB is a common compromise for linear RF power amplification.
2. Switching classes trade waveform fidelity for efficiency
Class C and switching amplifiers can be very efficient but do not linearly reproduce an arbitrary amplitude envelope. They are useful with constant-envelope signals or architectures where filtering reconstructs the intended RF waveform.
3. Distortion reveals the nonlinearity
Clipping, crossover distortion, gain compression, and intermodulation create unwanted spectral components. Bias, feedback, drive level, thermal control, and load impedance all affect linearity.
E7B checklist
- Class A is linear but inefficient; AB is a common linear RF compromise.
- Switching/nonlinear classes can offer higher efficiency.
- Amplitude-varying signals require a linear path unless another architecture reconstructs the envelope.
- Nonlinearity produces harmonics and intermodulation products.
Exam scope: NCVEC 2024-2028 Amateur Extra Class (Element 4), effective July 1, 2024 through June 30, 2028, with February 4, 2026 fourth errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool