What measurement is specified by FCC rules that regulate maximum power?

The FCC specifies maximum amateur radio power limits using Peak Envelope Power (PEP). This measurement must be taken at the output of the transmitter, or at the output of an external RF amplifier if one is being used. Measuring at the transmitter output provides a consistent regulatory standard. It is not measured at the antenna input because feedline losses vary widely between different stations, making it difficult to regulate. PEP is used rather than Root Mean Square (RMS) power because it more accurately reflects the maximum instantaneous power of complex waveforms, such as voice modes (SSB). Limiting the absolute peak power helps prevent harmful interference and equipment overload.