What frequency range is referred to as HF?

The International Telecommunication Union (ITU) divides the radio frequency spectrum into specific bands by powers of ten. The High Frequency (HF) band is universally defined as spanning from 3 MHz to 30 MHz. Knowing the adjacent bands helps you quickly rule out the distractors on the exam. The range from 30 to 300 MHz is the Very High Frequency (VHF) band, and 300 to 3000 MHz is the Ultra High Frequency (UHF) band. The range from 300 to 3000 kHz (0.3 to 3 MHz) is the Medium Frequency (MF) band, which includes standard AM broadcast radio. A helpful way to remember this is to anchor HF at 3 to 30 MHz, which are the primary bands where 'skip' or ionospheric propagation allows for worldwide amateur radio communication.