HF technology - high frequency with High frequency is the range of radio frequency electromagnetic waves, radio waves, between 3 and 30 MHz. Also known as the decameter band or the decameter wave as wavelengths ranging from 1 to 10 decameters. The frequencies directly below HF are labeled as MF, or medium frequency. Higher frequencies, on the other hand, are known as very high frequency, or VHF.
The HF band is the major part of the shortwave band of frequencies, so communication in these frequencies is often called shortwave radio. Because the radio waves in this band can be reflected back to Earth by layers of the ionosphere in the atmosphere, called "skip", these frequencies can be used for long-distance communication on intercontinental routes. The band is used by international shortwave transmitters (2.310 - 25.820 MHz).
The dominant means of long-distance communication in this band is skywave (skip) propagation, in which radio waves directed at an angle to the sky reflect (actually refract) the return to Earth from layers of ionized atoms in the ionosphere. With this HF method, radio waves can travel beyond the horizon, and can be received on intercontinental routes.
However, the usefulness of this part of the spectrum for such communication varies greatly in a complex combination of factors. Such as sunlight/darkness at the transmitting and receiving site. Transmitter/receiver solar terminator proximity, season, sunspot cycle, solar activity, polar aurora.