What is the maximum mean power level for a spurious emission below 30 MHz with respect to the fundamental emission?

Spurious emissions are unwanted signals produced by a transmitter, such as harmonics or parasitic oscillations, which fall outside the intended transmission bandwidth. Because the HF bands (below 30 MHz) propagate globally, strict limits are placed on these emissions to prevent widespread interference to other services. According to FCC regulations, the maximum mean power level for a spurious emission below 30 MHz must be at least 43 dB below the fundamental emission's mean power (often written as -43 dBc). This means the unwanted signals must be attenuated by a factor of roughly 20,000 compared to the main signal. Higher attenuation levels like -63 dB or -73 dB are required for VHF/UHF transmitters (above 30 MHz) or for certain commercial standards, but -43 dB is the correct regulatory threshold for HF amateur stations.