160 metres, often known as Top Band, is technically a Medium Frequency (MF) band, the only one licensed to amateurs. It is slightly higher in frequency than the AM broadcast band (540 kHz - 1600 kHz), and behaves similarly. 160 meters is the lowest-frequency band on which amateurs are licensed to operate.
Radio communication on 160 metres is prone to extreme D-layer absorption during the day. This typically limits communication to 75 miles. At night, however, the D-layer weakens and contacts can be mode over thousands of kilometres. Like the HF bands, 160 metres usually supports such long-distance communication through refraction of signals via the F2 layer.