Why The ITU divides the radio spectrum into decade-wide bands, and HF (high frequency) runs from 3 MHz to 30 MHz. This is the classic shortwave range that includes ham bands such as 80, 40, 20, 15 and 10 meters, where ionospheric refraction gives worldwide skip. Wavelengths there run from 100 meters down to 10 meters.
Watch out The choice covering 30 to 300 MHz is VHF, 300 to 3000 MHz is UHF, and 300 to 3000 kHz is MF, the band that holds AM broadcast and 160 meters.
Each band is a decade: MF 0.3-3, HF 3-30, VHF 30-300, UHF 300-3000, all in MHz.
10 meters is 28 MHz and 80 meters is 3.5 MHz, both HF. The only range that holds both: 3 to 30 MHz.