DX Technic!

Many Radio Amateurs are hunting DX i.e. stations outside your own continent.

DXing on low bands from 160 to 30 meter, we often have useful help of greyline propagation to boost the chances of making a QSO.

On higher bands we need high solarflux and MUF must have reached the band we wish to use to obtain QSO.

Radio frequencies and their primary mode of propagation
Band Frequency Wavelength Propagation via
ELF Extremely Low Frequency 3–300 Hz 1000-100,000 km
VLF Very Low Frequency 3–30 kHz 100–10 km Guided between the earth and the ionosphere.
LF Low Frequency 30–300kHz 10–1 km Guided between the earth and the D layer of the ionosphere.

Surface waves.

MF Medium Frequency 300–3000kHz 1000–100 m Surface waves.

E, F layer ionospheric refraction at night, when D layer absorption weakens.

HF High Frequency (Short Wave) 3–30 MHz 100–10 m E layer ionospheric refraction.

F1, F2 layer ionospheric refraction.

VHF Very High Frequency 30–300MHz 10–1 m Infrequent E ionospheric (Es) refraction. UncommonlyF2 layer ionospheric refraction during high sunspot activity up to 50 MHz and rarely to 80 MHz. Generally direct wave. Sometimes tropospheric ducting.
UHF Ultra High Frequency 300–3000MHz 100–10 cm Direct wave. Sometimes tropospheric ducting.
SHF Super High Frequency 3–30 GHz 10–1 cm Direct wave.
EHF Extremely High Frequency 30–300GHz 10–1 mm Direct wave limited by absorption.