What is a characteristic of HF communication compared with communications on VHF and higher frequencies?
Why Below about 30 MHz, the ionosphere's F region routinely refracts signals back to Earth, so HF signals can be returned for hundreds or thousands of miles of skip. At VHF and above, signals normally pass through the ionosphere into space, so contacts are mostly line of sight plus a bit of extra range from the radio horizon. That is why worldwide DX is an everyday event on HF but an unusual occurrence on VHF, where it depends on special modes like sporadic E or tropo ducting.
Watch out HF antennas are physically much larger, not smaller, because wavelength grows as frequency drops (a half wave at 7 MHz is about 66 feet). Wide bandwidth modes and low static both favor VHF and up, since HF bands are narrow and noisy with lightning crashes.
Lower frequency bends back, higher frequency punches through: HF skips, VHF goes line of sight.