7000-7300 KHz (7.0-7.3 MHz) or 40 m band
The popular 40 m band has clearly defined skip zone during the day. D-layer absorption is not as severe as on the lower bands, so short-distance skip via the E and F layers is possible. During the day, a typical station can cover a radius of approximately 800 km. Ground-wave propagation is not important. At night, reliable worldwide communication via F2 is common on the 40 m band.Atmospheric noise is less troublesome than on 160 and 80 m, and 40 m DX signals are often of sufficient strength to override even high-level summer static. For these reasons, 40 m is the lowest-frequency amateur band considered reliable for DX communication in all seasons. Even during the lowest point in the solar cycle, 40 m may be open for worldwide DX throughout the night.

Source: ARRL Handbook, 1993