Part of our Getting On The Air: Modes, Operations, and Making Contacts guide.
Ask a hundred DXers which band they would keep if they could only have one, and a huge number of them will say 20 meters. It is not the flashiest band, and it does not have the extreme highs that 10 meters can produce during a good solar cycle. What it has instead is consistency, and in DXing, consistency wins more often than excitement does.
It is almost always open somewhere
The 14 MHz band sits in a sweet spot in the HF spectrum. It is low enough in frequency that the F2 layer of the ionosphere can refract it back to earth even during periods of low solar activity, but high enough that it supports long, multi hop skip across oceans and continents. On 80 and 40 meters you are mostly limited to your own continent or hemisphere after sunrise. On 10 and 15 meters you need a healthy sunspot number for the band to open at all. 20 meters lives in the middle, and that middle ground is exactly why it works almost every day of the year, through the peaks and valleys of the eleven year solar cycle.
Because the band follows the sun, the paths that open change throughout the day. A station on the east coast of the United States might work Europe in the morning, catch South America and Africa around midday, then swing over to the Pacific and Asia in the afternoon and evening. If you sit at the radio long enough on a Saturday, you can often work all six continents on 20 meters alone without ever changing bands.
Practical antennas, practical power
A quarter wave vertical on 20 meters is only around 16 feet tall. A full size dipole is about 33 feet tip to tip, which fits in most backyards, even folded into an inverted V or bent into an L shape. Compare that to 40 meters, where a dipole stretches to roughly 66 feet, or 80 meters at well over 130 feet, and you can see why so many hams with modest lots end up making 20 meters their primary DX band. It rewards good technique and a decent antenna without demanding a huge property or a legal limit amplifier. Plenty of DXCC totals well past 300 have been built mostly on 20 meters with 100 watts and a wire.
It is where the DX goes to be found
DXpeditions know all of this too, which means 20 meters gets heavy attention from rare entities. When a new one fires up, the pileup usually starts on 20 meters SSB or CW before it spreads to other bands. If your goal is chasing new countries, 20 meters is simply where the action concentrates, both because propagation supports it and because everyone else is looking there as well.
The tradeoffs
None of this means 20 meters is perfect. It gets crowded, especially during contests, and the popular DX window near the bottom of the band can turn into a wall of callers during a big pileup. It also is not immune to solar flares and geomagnetic storms, and on a truly dead day even 20 meters can go quiet. But for the person who wants one band to learn, to build an antenna for, and to count on more days than not, 20 meters remains the safest bet in the HF spectrum, and that is exactly why it has earned its reputation as the king of DX bands.